Guidelines for Managing Wake Wash from High ... - PIANC USA

INTERNATIONAL NAVIGATION ASSOCIATION 

GUIDELINES FOR MANAGING WAKE WASH 

FROM HIGH-SPEED VESSELS 

Report of Working Group 41 

of the 

MARITIME NAVIGATION COMMISSION 

INTERNATIONAL NAVIGATION 

ASSOCIATION 

© COPYRIGHT PIANC 

ASSOCIATION INTERNATIONALE 

DE NAVIGATION 

2003

PIANC has Technical Commissions concerned with inland waterways and ports (InCom), coastal and ocean 

waterways (including ports and harbours) (MarCom), environmental aspects (EnviCom) and sport and pleasure 

navigation (RecCom). 

This Report has been produced by an international Working Group convened by the Maritime Navigation 

Commission (MarCom). Members of the Working Group represent several countries and are acknowledged 

experts in their profession. 

The objective of this report is to provide information and recommendations on good practice. Conformity is not 

obligatory and engineering judgement should be used in its application, especially in special circumstances. 

This report should be seen as an expert guidance and state of the art on this particular subject. PIANC disclaims 

all responsibility in case this report should be presented as an official standard. 


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CONTENT 

Working group members . . . . . . . . . . . . . . . . . . . . . . .4 

Technical expert . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 

1.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 

1.2 Method of undertaking the task . . . . . . . . . . . .5 

1.3 Definition of high-speed vessel . . . . . . . . . . . .5 

2. International experience with high-speed 

vessel wake . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 

3. Wave generation and vessel wake . . . . . . . . . . . . . .6 

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .6 

3.2 Wave generation and wake characteristics . . . .6 

3.2.1 Conventional wake patterns – 

sub-critical wash . . . . . . . . . . . . . . . .6 

3.2.2 Near-critical wash . . . . . . . . . . . . . . .6 

3.2.3 Super-critical wave pattern . . . . . . . . .7 

3.2.4 General mechanisms . . . . . . . . . . . . .8 

3.3 Propagation and transformation 

of high-speed vessel wake . . . . . . . . . . . . . . . .9 

3.3.1 Direction of wave propagation . . . . . .9 

3.3.2 Composition of wash and its frequency 

components . . . . . . . . . . . . . . . . . . .10 

3.3.3 Wave transformation and 

wave decay . . . . . . . . . . . . . . . . . . .10 

3.4 Wake in coastal areas . . . . . . . . . . . . . . . . . .11 

3.4.1 General wave transformation . . . . . .11 

3.4.2 Propagation of vessel wake 

in coastal zone . . . . . . . . . . . . . . . . .11 

3.5 Wake generated by non-steady operation . . . .12 

3.5.1 Acceleration, deceleration, 

and extent of wash . . . . . . . . . . . . . .12 

3.5.2 Change of wake regime with 

constant speed . . . . . . . . . . . . . . . . .12 

3.5.3 Focusing the wash during course 

changes . . . . . . . . . . . . . . . . . . . . . .12 

3.5.4 Impact of bathymetry on 

operational procedures . . . . . . . . . . .13 

3.6 Bernoulli wake and soliton waves . . . . . . . . .13 

3.7 Wake prediction, analysis, and assessment . .13 

3.7.1 Numerical prediction of wake . . . . .13 

3.7.2 Full-scale trials and measurements . .15 

3.7.3 Model scale trials . . . . . . . . . . . . . . .17 

3.7.4 Wake analysis . . . . . . . . . . . . . . . . .17 

3.7.5 Wake assessment . . . . . . . . . . . . . . .17 

4.3 Environmental impact of wake . . . . . . . . . . .20 

4.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . .20 

4.3.2 Potential impacts . . . . . . . . . . . . . . .20 

4.3.3 Differentiating between causes . . . . .22 

4.3.4 Predicting environmental impact . . .22 

5. Managing vessel wake . . . . . . . . . . . . . . . . . . . . . .22 

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . .22 

5.2 Management measures . . . . . . . . . . . . . . . . .23 

5.2.1 Vessel design . . . . . . . . . . . . . . . . . .23 

5.2.2 Operational measures . . . . . . . . . . . .23 

5.2.3 Non-operational measures . . . . . . . .24 

5.3 Route assessment . . . . . . . . . . . . . . . . . . . . .24 

5.3.1 Overview . . . . . . . . . . . . . . . . . . . . .24 

5.3.2 Route characterization . . . . . . . . . . .24 

5.3.3 Impact identification . . . . . . . . . . . .25 

5.3.4 Developing and assessing potential 

management measures . . . . . . . . . . .27 

5.3.5 Monitoring . . . . . . . . . . . . . . . . . . . .28 

6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 

Annex A – Terms of reference . . . . . . . . . . . . . . . . . .32 


4. Impacts associated with vessel wake . . . . . . . . . . .17 

4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .17 

4.2 Safety impacts . . . . . . . . . . . . . . . . . . . . . . . .18 

4.2.1 Safety of people . . . . . . . . . . . . . . . .18 

4.2.2 Safety of vessels . . . . . . . . . . . . . . . .18 

4.2.3 Structural damage . . . . . . . . . . . . . .19 

3 Report of Working Group 41 - MARCOM

WORKING GROUP MEMBERS 

Christian Aage, Technical University of Denmark, 

Denmark 

Adrian Bell (Chair until September 2002), Kirk McClure 

Morton, Northern Ireland, United Kingdom 

Lars Bergdahl, Chalmers University of Technology, 

Sweden 

Alan Blume (Chair), U.S. Coast Guard, United States of 

America 

Ernst Bolt, Ministry of Public Works, Transport and Water 

Management, Netherlands 

Hendrik Eusterbarkey, Federal Waterways and Shipping 

Administration, Germany 

Tetsuya Hiraishi, Port and Harbour Research Institute, 

Ministry of Transport, Japan 

Henrik Kofoed-Hansen, DHI Water & Environment, 

Denmark 

Denis Maly, Port Authority Bruges-Zeebrugge, Belgium 

Martin Single, University of Canterbury, New Zealand 

Jorma Rytkönen, VTT Manufacturing Technology, 

Finland 

Trevor Whittaker, Queen’s University, Northern Ireland, 

United Kingdom 

TECHNICAL EXPERT 

Björn Elsäßer, Queen’s University, Northern Ireland, 

United Kingdom 


Report of Working Group 41 - MARCOM 

4

1. INTRODUCTION 

1.1 SUMMARY 

The intent of this report is to provide an overview of the 

hydrodynamic and physical aspects of high-speed vessel 

wake and to provide guidance for its effective management. 

This guidance does not prescribe a solution. Rather, 

it provides a process that waterway management authorities 

and vessel operators can use to develop an appropriate 

solution for managing high-speed vessel wake. This guidance 

is consistent with the International Maritime 

Organization’s (IMO) High-Speed Craft Code (2000) 

and may be used to support the development of the route 

operational manual required by Regulation 18.2.2 of that 

Code. 

The report does not address other issues associated with 

the operation of high-speed vessels that are within the 

purview of other organisations (e.g., IMO, the 

International Association of Marine Aids to Navigation 

and Lighthouse Authorities (IALA)); nor does it address 

issues related to vessel design since they are beyond the 

expertise of PIANC. 

Although these guidelines were developed in response to 

concern about the potential impacts of high-speed vessel 

wake (see Annex A), they can be used as the basis for 

managing potential impacts of wake generated by any vessel. 

1.2 METHOD OF 

UNDERTAKING THE TASK 

The working group accomplished its task through a series 

of three meetings and correspondence. Members of the 

working group also corresponded with experts in their 

respective countries. 


1.3 DEFINITION 

OF HIGH-SPEED VESSEL 

For the purpose of this report, the term “high-speed vessel” 

includes vessels that meet the definition of a highspeed 

craft in the IMO High-Speed Craft Code (a vessel 

capable of a maximum speed equal to or exceeding 

3.7 ∇ 0.1667 (m/s), where ∇(m 3 ) is the displacement of the 

vessel at the design waterline), or a definition adopted by 

a national maritime authority. 

2. INTERNATIONAL 

EXPERIENCE WITH 

HIGH-SPEED VESSEL WAKE 

Real or perceived safety and environmental impacts associated 

with high-speed vessel wake in confined waters 

have been reported in many locations including Canada 

(Sandwell, 2000), Denmark (Kofoed-Hansen, 1996; 

Danish Maritime Authority, 1997; Kirkegaard et al., 1998; 

Kofoed-Hansen and Mikkelsen, 1997), Great Britain 

(Marine Accident Investigation Branch, 2000), Ireland 

(Maritime and Coastguard Agency, 1998), Sweden (Strom 

and Ziegler, 1998; Allenström et al., 2003), The 

Netherlands (Anonymous, 2000), New Zealand (Croad 

and Parnell, 2002; Kirk and Single, 2000; Parnell, 1996; 

Single and Kirk, 1999), Finland and Estonia (Peltoniemi et 

al., 2002), and the United States (Anonymous, 1999; 

Stumbo et al., 1999). To date, much of the research undertaken 

on high-speed vessel wake wash has appeared only 

as unpublished reports for various authorities and management 

agencies. 

Wake effects on rivers, lakes, and other inland waters 

also can be substantial. For example, see Nanson et al. 

(1994), Gadd (1994), Pickrill (1985), and references 

therein. 

As a result of these reported impacts, vessel operators and 

waterway managers alike have tried a number of different 

approaches for managing high-speed vessel wake. These 

include establishing standards for maximum allowed wave 

heights, maximum allowed wave energy, speed limits, and 

risk assessments. Other measures that have been used 

include the installation of wave-absorbing materials on sea 

walls and other harbour structures as well as efforts to educate 

other waterway users about the potential impacts of 

high-speed vessel wake. Based on the experience to date 

from these different efforts, it is increasingly apparent that 

the effective management of high-speed vessel wake is a 

multi-faceted problem that defies a simple “one size fits 

all” solution. It is also apparent that a means of managing 

high-speed vessel wake wash that addresses legitimate 

concerns related to waterway safety and protection of the 

marine environment, while also not unduly restricting 

their operation, must be identified to realize the full contribution 

of high-speed vessels to the national and global 

marine transportation systems. 


3. WAVE GENERATION AND 

VESSEL WAKE 

3.1 INTRODUCTION 

This section provides a description of the fundamentals of 

wake wave generation by vessels and wave mechanics. It 

contains the basic information necessary to understand the 

effects of wake on the coastline and on other vessels. The 

description primarily deals with the free wave system 

sometimes referred to as Kelvin, Havelock, and Bernoulli 

wave systems and does not discuss near-vessel or bound 

wave system problems. 

3.2 WAVE GENERATION AND 

WAKE CHARACTERISTICS 

3.2.1 Conventional wake 

patterns – sub-critical wash 

© COPYRIGHT 

In 1887, Lord Kelvin described the wave system produced 

by a moving vessel in deep water. This wave pattern is 

confined to a wedge shape known as the Kelvin wedge 

(Fig. 3-1). Within this wedge, which has an apex angle of 

±19.5°, it is possible to distinguish between diverging 

waves, propagating at an angle of θ = 90º to 35º from the 

vessel’s track, and transverse waves, propagating at an 

angle of θ = 35º to 0º from the vessel’s track. Under 

steady conditions, the transverse waves along the vessel’s 

track travel at the same speed as the vessel. 

PIANC 

V 

Fn l = , 

gL 

where V (m/s) is the vessel speed, g (m/s 2 ) is the acceleration 

of gravity, and L (m) is the vessel waterline length. 

The Kelvin wave pattern is strictly correct only for a moving 

point source. The wash of a vessel will be the superposition 

of a number of these patterns from many sources, 

of which the bow and stern wave system will generally be 

dominant. 

When the length Froude number is 0.4 (Fn l = 2π ) in deep 

water, the wavelength of the transverse waves is equal to 

the vessel’s length. The pressure peaks at the bow and 

stern amplify each other while the wave-making resistance, 

which is the net longitudinal force due to the fluid 

pressure of the water acting on the hull, increases significantly 

(Lewis, 1988). This speed is called the hump speed 

and forms a firm barrier for most ‘conventional’ vessels 

(Fig. 3-2). Basically the vessel continuously tries to move 

‘uphill’, which requires more energy. In practice the resistance 

hump speed most often occurs when length Froude 

numbers are between approximately 0.4 and 0.6. Highspeed 

vessels, the subject of these guidelines, are able to 

pass through this ‘hump speed’ in deep water. This 

requires a relatively high ratio of propulsion power to vessel 

displacement. 

Figure 3-2 Resistance of a typical ship hull 

in deep and shallow water 

Figure 3-1 Steady state Kelvin wave pattern 

(Ekman, 1906; Newman, 1977) 

All vessels operating in deep water produce a Kelvin type 

wave pattern. In deep water the wavelength is a function 

of the wave speed. The higher the vessel’s speed, the 

longer the generated waves become. The most important 

parameter for the characterisation of the Kelvin wave pattern 

is the vessel’s speed related to its waterline length 

given in dimensionless terms by the length Froude number 

(Fn l ). The length Froude number is defined as: 

The Kelvin wave pattern is only valid for deep-water 

conditions. Deep water in this context means that the 

vicinity of the bottom does not affect the propagation 

speed of the waves produced. 

3.2.2 Near-critical wash 

In 1908, Havelock investigated the wave pattern generated 

by a single point source in shallow water. He introduced 

the depth Froude number, stating that the characteristics of 

the wave pattern in depth-limited water are a function of 


6

vessel speed and water depth. The depth Froude number 

(Fn h ) is defined as the ratio of the vessel speed to the wave 

propagation speed in shallow water: 

V 

Fn h = , 

gh 

where: V (m/s) is the vessel speed, g (m/s 2 ) is the acceleration 

of gravity, and h (m) is the water depth. The classical 

Kelvin wave pattern will be generated at depth Froude 

numbers under 0.57. The length of the transverse waves, 

which are the longest waves in the pattern, will increase as 

the depth Froude number becomes larger. 

As the depth Froude number approaches 1.0, the vessel’s 

speed becomes equal to the maximum wave propagation 

speed in the given depth of water. This speed is often 

referred to as the critical speed. At this stage, all transverse 

waves are left behind the vessel and a wave builds perpendicular 

to the vessel as shown in Figure 3-3. If the vessel 

stays at critical speed, this wave will extend further from 

the vessel’s track and build in height. All diverging waves 

are found behind this critical wave. The conventional 

Kelvin wave pattern is often referred to as sub-critical. 

Where the water depth starts to change the wave pattern 

significantly (Fn h > 0.85), the range is often referred to as 

the near-critical speed range. 

3.2.3 Super-critical wave pattern 

At higher depth Froude numbers (Fig. 3-4) the transverse 

waves disappear. They simply cannot keep up with the 

vessel since the water depth limits their speed. In water of 

constant depth, the first wave crest in the pattern is straight 

and the crest length is related to the time the vessel has 

been travelling at the particular depth Froude number. The 

following waves have curved crests and troughs and are 

also continuous. 

Figure 3-4 Super-critical wave pattern 

in constant water depth 

The angle of propagation θ for the first wave is determined 

by: 

cos θ = 1 / Fn h . 

Therefore, as the depth Froude number increases, the 

waves bend further backwards and their angle of propagation 

becomes increasingly perpendicular to the vessel’s 

track. For example, whereas at a depth Froude number of 

1.5 the angle of propagation is approximately 48º; at a 

depth Froude number of 2.0 the angle of propagation is 

60°. 

Figure 3-3 Critical wave pattern 

in constant water depth 

At critical speed there is one transverse wave that moves 

with the vessel and dramatically increases the wave-making 

resistance. This is because the energy in the longest 

wave can no longer disperse generating more waves 

behind, as was the case at lower speeds. This is the main 

reason most conventional vessels are not capable of 

exceeding the critical speed. It also needs to be mentioned 

that the critical wave pattern is unsteady and changes with 

time. The shape of the first wave is a function of the distance 

the vessel has been travelling at critical speed. 

The wash generated by a high-speed vessel operating 

above the critical depth Froude number in shallow water 

has some unique peculiarities. A typical wave time trace 

of wash from a high-speed vessel operating in shallow 

coastal waters measured 2700 meters from its track is 

shown in Figure 3-5. The trace has been divided into 

zones according to wave period and grouping. The first 

group, Zone I, comprises the long period super-critical 

wash waves and is peculiar to high-speed vessels operating 

above the critical depth Froude number. The second 

group, Zone II, comprises waves similar in size and height 

to the wash waves produced by conventional vessels of 

comparable displacement and length. Finally there is a 

group of tail waves in Zone III. These are peculiar to highspeed 

vessels with transom sterns. 


Figure 3-5 Typical wave trace of a large high-speed vessel at super-critical depth 

Froude number with wash zones indicated 

© 

The time series was measured at a distance of 2700 meters 

from a catamaran. The average wave periods are 11 seconds 

(s), 5s, and 3s, for Zone I, II and III respectively. 

3.2.4 General mechanisms 

The basic mechanism of wash propagation is discussed in 

the following section. For simplicity, linear wave theory is 

used, though there is an argument to use higher order wave 

theory in very shallow water. 

With regards to the propagation of surface water waves the 

water depth plays a significant role. In deep water the 

wave celerity is a function of the wavelength, but in shallow 

water the water depth limits the wave celerity. Water 

depths of more than half the wavelength can be considered 

as deep water, whereas water depths of less than 1/20 th the 

wavelength is commonly regarded as shallow water. 

COPY- 

RIGHT 

a) b) 

Figure 3-6 a) illustrates the deep-water propagation of 

waves generated by a point source moving from A to B at 

speed V. Waves generated at A would have travelled as 

far as the outer circle if they had propagated at the individual 

wave phase speed (celerity). The fastest and 

longest waves would have moved along the track to B 

while shorter and slower waves would have travelled to 

locations such as C and D. However, in deep water the 

wave energy travels at only one-half the phase speed. As a 

result, the locus of wave energy, and therefore the largest 

wave, moves only as far as the inner circle, to points such 

as B’, C’, and D’. In the meantime, the point source has 

generated new waves along its way to B. The energy from 

these waves propagates outward in progressively smaller 

inner circles. The resulting limit of wave propagation for 

all waves generated as the ship moves from A to B is tangent 

to the inner circle forming the Kelvin wedge. For any 

value of V, this forms an apex angle of ±sin -1 (1/3) = 

±19.5°. 


Figure 3-6 a) Wave rays for sub-critical operation b) Wave rays for super-critical operation at Fn h = 1.3 


8

The visible wave pattern then lies mainly inside and along 

the wedge. As individual waves propagate outward at 

their phase speed and attempt to outrace the wedge, they 

die out and disappear. The largest waves, therefore, form 

along the wedge and wave amplitudes diminish within a 

short distance outside the wedge (Lighthill, 1978; 

Newman, 1977). 

A similar wave ray diagram can be drawn for a shallow 

water wave pattern and a depth Froude number greater 

than 1 with the important difference, however, that in shallow 

water the celerity and speed of energy propagation are 

equal. This is shown in Figure 3-6 b) for a depth Froude 

number of 1.3. There are no waves travelling from A at an 

angle θ of less than 39.7° in this example. All waves radiated 

at A have travelled as far as the outer semicircle. As 

waves in shallow water are non-dispersive, the energy of 

the wave ray A – C has travelled to C. The wave travelling 

in the direction of D is in intermediate water depth. 

Hence, the energy has travelled more than half the distance 

A – D, as this wave is partially dispersive. The wave travelling 

towards F is a deep-water wave, as its wavelength is 

short compared to the water depth and, hence, it is fully 

dispersive. As a result the energy has travelled only half 

the distance to F'. 

3.3 PROPAGATION AND 

TRANSFORMATION OF 

HIGH-SPEED VESSEL WAKE 

The following sections focus on propagation of the free 

wave field generated by a vessel at super-critical speed. 

© COPYRIGHT 

3.3.1 Direction of wave propagation 

The direction of propagation for the leading wave in the 

super-critical wash is only a function of the depth Froude 

number. This was originally proposed by Havelock (1908) 

and proven by various other authors. This relationship is 

plotted in Figure 3-7. 

Whittaker et al. (2000) studied the divergence between the 

first and the following waves and determined that this 

angle is dependent on the depth Froude number. The theoretical 

divergence between the first and second leading 

crest is shown in Figure 3-8. The divergence angle is 

defined as the difference in propagation direction between 

successive waves. Whittaker et al. (2000) has shown that 

this relationship is valid for real wave patterns. At high 

super-critical Froude numbers the waves are more parallel 

than at lower super-critical depth Froude numbers. The 

divergence decreases with perpendicular distance from the 

vessel; the rate of decrease also depends on the water 

depth. In deeper water the change in wave pattern is less 

than with the same distance in shallow water. 

wave direction [°] 


Figure 3-7 Angle of wave propagation 

at outer edge of stationary pattern (sub-critical) 

and leading wave (super-critical) 

Figure 3-8 Divergence of second wave compared to first with varying depth 

Froude number and perpendicular distance from vessel normalised by water depth 


With each successive wave the divergence angle decreases 

at constant perpendicular distance from the vessel’s track. 

Thus, the waves further back in the pattern become 

increasingly parallel to each other. Finally, the pattern 

contains waves whose crests are almost parallel to the vessel's 

track. The slight change in the propagation direction 

of the waves leads to an apparent lengthening of the waves 

farther from the vessel. Hence, the peak-to-peak distance 

of the wave increases with distance from the vessel’s track. 

Waves with a period in excess of 40 seconds have been 

measured 2.7 kilometres from the vessel (MCA, 1998). 

Though the wash measured as a time series often appears 

as a series of sinusoidal waves each with a slightly shorter 

period, the surface elevation is in fact a superposition of an 

infinite number of waves. Using the zero crossing period 

on its own to calculate the wave speed will lead to slightly 

smaller values of wave celerity. Most importantly it has 

to be recognised that the period of the waves in a vessel’s 

wake is not a function of hull design, but rather of vessel 

speed, water depth, and the distance the wave travels from 

the point where it was generated. In contrast, the height of 

the waves in the wake is a function of the hull design. In 

general, for vessels with a similar hull form but different 

lengths, the height of waves generated by the shorter vessel 

will be lower than those generated by the longer vessel. 

The implication is that the period of the waves generated 

by vessels of different lengths operating at the same depth 

Froude number will be the same. However, the waves 

generated by the shorter vessel will be less pronounced 

when compared to the waves generated by the longer vessel 

since they will not be as high. 

3.3.2 Composition of wash and 

its frequency components 

So far these guidelines have only focused on the location 

of crests and troughs in the wave pattern. The wave-making 

resistance, which is a significant part of the total resistance 

of a vessel, corresponds to the energy used to generate 

the wave pattern. This resistance is spread as a continuous 

spectrum over the wave rays radiated from the vessel. 

The distribution of the wave-making resistance is often 

referred to as the free wave spectrum or the amplitude 

function. In deep water this distribution is a function of 

the vessel speed, the hull length and displacement, and the 

hull shape. 

Figure 3-9 a) shows such a distribution for a typical ship 

hull in deep water. There is a different distribution for 

each vessel speed for a given hull, or to be more precise, 

for each length Froude number. In shallow water the distribution 

is a function of the vessel speed, water depth, hull 

length, displacement, and shape. A shallow water distribution 

for the same vessel speed is given in Figure 3-9 b) 

for a depth Froude number of 1.3. Note that there are no 

wave resistance components between θ = 0° and 39.7°, 

and a large amount of energy is concentrated between 

39.7° and 60°. These resistance components form the 

leading waves in the super-critical wave pattern. The area 

underneath these curves is proportional to the wave pattern 

resistance. In this case, the area under both curves is 

almost equal. 

3.3.3 Wave transformation and wave decay 

Havelock (1908) investigated the decay of wave height 

with distance at sub-critical depth Froude numbers. He 

found that the decay of both the transverse and diverging 

waves is proportional to ϖ n , where ϖ is the distance from 

the vessel and n is a constant value. He showed that the 

theoretical decay inside the Kelvin wedge has the exponent 

n = -1/2 and the waves along the outer edge of the 

wedge decay have an exponent of n = -1/3. 

Figure 3-10 Decay of wave amplitude 

as investigated by Havelock 


Figure 3-9 a) Distribution of wave-making resistance over propagation angle (θ) 

b) the resistance is here made dimensionless as resistance coefficient (C w ) 


10

Kofoed-Hansen et al. (1999) suggested a decay rate of 

n = -0.55 based on a best fit through a wide range of wake 

measurements for catamarans operating at super-critical 

speeds. They also stated that a decay rate of n = -1/3 close 

to the vessel (less than 3 vessel lengths) would be more 

appropriate. Whittaker et al. (2001) concluded from a 

series of towing tank tests in shallow water that the decay 

rate could be substantially less. The lowest decay rate 

observed was as low as n = - 0.2. While Havelock compared 

the wave height at a straight ray from the vessel (Fig. 

3-10), the later comparisons are based on the maximum 

wave height found in wave cuts at different distances perpendicular 

from the vessel’s track. 

3.4 WAKE IN COASTAL AREAS 

3.4.1 General wave transformation 

There are a number of processes that can affect the wave 

as it propagates into coastal and shallow water areas. The 

most important are listed as follows: 

• Refraction - the bending of wave fronts and wave height 

reductions as they travel into shallower water 

• Diffraction - the lateral transfer of energy along the 

wave crest 

• Shoaling - the alteration in wave height as waves propagate 

into shallow water 

• Wave-current interaction - the alteration of wave celerity 

and height due to currents 

• Breaking - energy dissipation due to increased wave 

steepness 

• Friction - energy dissipation due to friction on seabed or 

obstacles or due to percolation through a porous seabed 

• Reflection - alteration in wave height due to full or 

partial reflection from structures or seabed 


All these processes are general coastal processes and are 

not discussed in detail as part of these guidelines. For 

more details see Vincent et al. (2002). 

3.4.2 Propagation of vessel wake 

in coastal zone 

The propagation of waves from a vessel to the shore can be 

divided into two processes: 

• Vessel speed - depth Froude number based transformation 

of wake. As described in Section 3.2.3, the first 

wave crest of the supercritical wave pattern is straight in 

constant water depth, and the angle of propagation 

depends only on the ratio of vessel speed to maximum 

wave speed. The following waves transform, and as a 

result the wave period changes with distance from the 

vessel in water of constant depth. 

• Transformation of wake due to change in bathymetry. 

Variations in waterway bathymetry can cause the 

height, propagation direction, and celerity of waves to 

change. These are common coastal processes as listed 

in Section 3.4.1. 

Both the depth Froude number based transformation and 

the bathymetric transformation need to be combined to 

predict the wash. The leading wave can be treated as a 

monochromatic shallow water wave. The following waves 

are a superposition of an infinite number of wave components 

(see Section 3.3.1). Even in shoaling water, the 

waves forming the pattern have different celerities, which 

results in the dispersion of energy from one wave to the 

next further back in the trace. 

Once in the breaker zone the linear wave theory is no 

longer valid. This means that the waves can no longer be 

considered as being sinusoidal. Several wave theories 

have been developed in the past century, which deal with 

shallow water waves like Boussinesq wave theory, or 

higher order wave theory (Demirbilek and Vincent, 2002). 

In some cases the long waves propagating into areas with 

extremely shallow water, e.g., on mud flats or salt 

marshes, can be approximated as solitary waves. 

In some studies the leading group of long-period waves, 

which are often the most critical waves in terms of risk, 

have been treated as waves with a very narrow spectrum 

(Kofoed-Hansen et al., 1996 and 1999; MCA, 1998). The 

correlation between the modelling and some full-scale 

measurements proved to be sufficient for most practical 

problems. 

Wash and wind waves will superimpose causing local 

steepening that can lead to breaking and energy loss. 

Otherwise, they will pass through each other unchanged. 

In general, high-speed wash is very small compared to 

fully developed wind waves. Thus, high-speed wash can 

hardly be detected in wash measurements with the presence 

of pronounced wind waves or swells. Vessel wash 

can, however, still be a problem on the shoreline even 

under storm conditions as the very long period waves are 

still present but masked. No evidence has been found that 

suggests that wind affects the long wave components in 

high-speed wash because the interactive time is too short 

and the steepness is too small. 


3.5 WAKE GENERATED BY 

NON-STEADY OPERATION 

3.5.1 Acceleration, deceleration, 

and extent of wash 

During acceleration in water of constant depth the wave 

pattern and the wave resistance will change. When accelerating 

from sub-critical to super-critical speeds the vessel 

has to pass through a resistance hump at critical speed (see 

Fig. 3-2). While at near-critical or critical speeds, the 

wake generated is more energetic vis-à-vis the wake generated 

at either sub- or super-critical speeds. It is, therefore, 

desirable to pass through the near-critical speed 

range as quickly as possible. The same applies to deceleration, 

where the operator should aim for a quick decrease 

in speed near the critical wake regime. The different wake 

regimes are shown in Figure 3-11. If possible, the operator 

should avoid operation at depth Froude numbers 

between approximately 0.85 and 1.1. 

unacceptable waves were being generated when the vessel 

was abeam of location A and reduced speed immediately, 

it is likely that substantial wash would still propagate to 

location A. 

Figure 3-12 Outer envelope and extent of wash 

3.5.2 Change of wake regime 

with constant speed 

Figure 3-11 Wake regime depending 

on speed and water depth 

When accelerating the vessel will produce a wave pattern 

with a transitional zone. This transitional zone is nonsteady 

and will change its position and area with time. A 

simplified wave pattern generated by a high-speed vessel 

with instantaneous acceleration in constant water depth is 

shown in Figure 3-12. It is assumed the vessel started its 

passage at the left and instantly accelerated to a super-critical 

speed. Three zones can be identified in the graph. An 

object at location A will encounter the full wash waves. 

An object at location B will experience the same leading 

waves as location A; however, with reduced wave heights. 

An object at location C may be subjected to little or no 

wave action from the leading waves. As the vessel continues 

to operate, some waves will continue to travel toward 

locations A, B, and C with the boundary of the wash continuously 

moving outward. Finally, location C will 

encounter the short tail waves (Fig. 3-5, Zone III). The 

implication is that even if the operator recognised that 


© COPY- 

RIGHT PIANC 

12 

Although a high-speed vessel may continue to operate at 

constant speed, the wake regime may change with variation 

of water depth along the vessel’s route. A vessel 

approaching a fairway from deep water may operate at 

sub-critical speeds. Continuation of operation at high 

speeds into shallow water results in the transition to critical 

speed. Depending on the bathymetry the vessel might 

operate for a considerable time at near-critical speeds and 

finally proceed to super-critical speed or decelerate. It is 

extremely important to recognise that the wash progressing 

toward the shoreline may have been caused by operating 

at near-critical depth Froude numbers along an earlier 

part of the passage. 

3.5.3 Focusing the wash during course changes 

When a vessel changes course, the energy density on the 

inside of the turn will be higher than the energy density on 

the outside of the turn. The difference is more pronounced 

for larger course changes than smaller changes as well as 

when the vessel is operating at higher speeds. This is 

because although the energy transferred into the wake is 

equal on both sides of the vessel’s track, it becomes 

focused on the inside of the turn insofar as it is transferred 

into a smaller area. As a result, the waves generated by the 

vessel will also be higher on the inside of the turn than 

those generated when the vessel is operating on a straight 

course. Similarly, the waves on the outside of the turn will 

be lower.

To mitigate the higher energy density and waves on the 

inside of a turn, it may be necessary to increase the radius 

of the turn or to make the change in a number of smaller 

changes with sufficient distance between them to avoid 

creating areas of increased wash concentration. It may 

also be necessary to reduce speed during the change of 

course. Particular care should be taken where the focused 

wash of the inner bend will propagate onto shoaling areas, 

such as banks or headlands, as a further increase in wave 

height can be expected. On the other hand, turns can be 

used to decrease wash heights on the outer bend, if the 

operational area allows such manoeuvres. 

confined water are capable of producing large Bernoulli 

wakes. Figure 3-13 is an example of a Bernoulli wake generated 

by a large container vessel in water approximately 

15 meters deep operating at sub-critical speeds. 

3.5.4 Impact of bathymetry 

on operational procedures 

While the variation of water depth along the passage may 

change the wake regime it also has a significant impact on 

the power requirement of the vessel. As described in 

Section 3.2.2 and illustrated in Figure 3-2, the resistance 

of the vessel increases close to the critical depth Froude 

number. Hence, the vessel needs sufficient propulsion to 

overcome this resistance peak. A vessel approaching shallow 

water might, therefore, proceed at near-critical depth 

Froude number with constantly decreasing speed while 

generating a wake with higher energy compared to supercritical 

operation at the same water depth. This is most 

likely if the vessel’s speed is reduced for some reason, e.g., 

extra drag due to hull fouling, the vessel is loaded higher 

beyond its normal service load, or partial power loss 

(Cain, 2000). 

Sudden bathymetric changes can be used to transition 

quickly from either a sub- or super-critical wake regime to 

the other without prolonged operation at near-critical 

speed. One means of accomplishing this is to construct a 

steep depth contour in the channel as described by 

Feldtmann and Garner (1999). 

3.6 BERNOULLI WAKE 

AND SOLITON WAVES 

The dynamic displacement of water caused by the forward 

movement of a vessel through water results in a velocity 

field around the hull (bound wave field). While this velocity 

field is responsible for the pressure distribution along 

the surface and, hence, the generation of waves, it has little 

effect on the far field propagation and transformation of 

the Kelvin wave pattern (free wave field). However, in a 

confined environment, e.g., fairway, shallow water or 

canal, the flow field can be restricted by the surrounding 

boundaries. This is very distinct in inland canals and is 

directly related to the blockage. 

© COPY- 

RIGHT PIANC 

Theoretically any type of vessel will produce such a displacement 

wave. However, in particular large vessels in 

Figure 3-13: Bernoulli wake and Kelvin wake 

generated by a large container vessel 

A vessel operating close to critical speed (i.e., depth 

Froude number between 0.85 and 1.1) is capable of generating 

a solitary wave, which in fact can be faster than the 

vessel. Both conventional vessels and high-speed vessels 

can produce solitary type waves, which are of very long 

period and can travel several vessel lengths ahead in very 

shallow open water. Large displacement vessels operating 

in shallow water are particularly prone to generating this 

type of wave (Scott-Russell, 1865; Dand et al., 1999; 

Whittaker et al., 2001). 

3.7 WAKE PREDICTION, 

ANALYSIS, AND ASSESSMENT 

3.7.1 Numerical prediction of wake 

A numerical non-linear time-domain model capable of 

calculating vessel-generated waves, wave propagation, 

and wave transformation in non-homogeneous media is 

the ultimate tool for evaluating the potential for vessel 

wake to have adverse safety or environmental impacts. 

Besides predicting the unstationary flow field and the 

associated wave pattern around the vessel hull, the same 

model (preferably) will be able to calculate the dynamics 

of the transient waves in the surf zone including the maximum 

wave height before wave breaking as well as run-up 

on beaches and river banks. Such models do not exist yet; 

however, if they did, they would be far too computationally 

demanding for practical use. 

In recent years, the use of computational fluid dynamic 

(CFD) codes has provided a valuable supplement to more 

classic methods for design and optimisation of vessel 

hulls. Comparisons between results from various CFD 

codes, full-scale measurements, and towing tank tests have 

increased confidence in using these models for prediction 

of wake wash caused by multi-hull vessels at varying 


water depths. A general limitation of these models is that 

they do not permit calculations of the far-field wave pattern. 

Most often, the calculation is limited to an area within 

approximately three to five vessel lengths. 

Furthermore, the codes usually only provide a stationary 

solution of the potential flow field at a constant depth. 

Predicting the impact of the wake for a certain vessel operating 

on a given route requires, in most cases, the solution 

of an unsteady problem in a three-dimensional domain. 

This is, in most cases, not feasible with one particular 

numerical model. Hence, the numerical prediction of the 

wake problem is divided into two different problems: 

• Prediction of the wave field near the vessel. 

• Prediction of the wave transformation and propagation 

in the far field and coastal zone. 

Very few numerical models predict both problems; those 

that have been developed to date are coupled methods 

(Raven, 2000; Kofoed-Hansen et al., 2000). 

3.7.1.1 Prediction of the wave field near the vessel 

The wave field generated by a vessel can be derived by 

numerical methods in several ways. These methods can be 

grouped in principle in two categories: panel codes and 

thin vessel theory models. Because of the inherent limitations 

associated with each type of model, several research 

institutions are working on hybrid models. 

Potential Flow Panel Codes 

These codes use a non-linear free-surface potential flow 

method, where the hull and water surfaces are represented 

by a large number of panels. As the pressure along the hull 

is calculated, sinkage and trim can be predicted. Since the 

boundary conditions are non-linear the problem cannot be 

solved directly. The actual wave surface is derived by 

means of iteration starting with a flat surface and an estimated 

trim and sinkage. Shallow water effects can be 

implemented. However, as in most codes, the grid moves 

with the vessel and only steady state or quasi-steady state 

conditions can be computed. Only panel codes with timestepping 

treatment have the potential of solving fully nonsteady 

conditions. The computational effort is rather large 

and, thus, the computation time can be considerable. Most 

models calculate the wave elevation or free surface profile 

up to a few vessel lengths distance from the vessel. A 

review of the current capabilities of panel codes can be 

found in Raven (2000) and Hughes (2001) as well as more 

detailed literature. 

Thin ship theory code 

This theory, which is often referred to as slender body theory, 

assumes the vessel hull(s) to be slender compared to 

their length. Most theories represent the body of the vessel 

as a series of Kelvin sources along the centreline of the 

hull assuming a linear free surface condition. As such the 

theory is limited to linear wave theory and in particular 

small waves compared to the wavelength. The theory 

behind these programs originates from work carried out by 

Lord Kelvin, Havelock (1908), Mitchell (1898) and 

Eggers et al. (1967). The strength of each of the sources 

is derived from the local slope of the hull at a number of 

water lines. The locations where the local slope is determined 

are often referred to as panels. The underlying 

equations are multiple integrals and are solved directly by 

numerical integration. The code can compute only steady 

state (constant speed) conditions and shallow water problems. 

Some programs include the input of reflective 

boundaries to simulate tank walls and, thus, allow the 

results to be compared with narrow tank experiments. 

Trim and sinkage is usually user defined. More recent 

codes derive the sinkage and trim by means of calculating 

the forces on the hull from the surrounding surface elevation 

through iteration. Difficulties occur with transom 

sterns, as basic thin vessel theory cannot deal with flow 

separation. Adjustments to the code like artificial appendices 

(virtual stern) or the use of potential flow methods 

have helped to improve the predictions significantly. Very 

high length Froude numbers seem to produce numerical 

instabilities with certain codes or the accuracy decreases. 

Thin ship theory still is heavily used and produces good 

results for many vessel wash problems. There is no limitation 

to the distance from the vessel at which a wave elevation 

can be computed. However, some programs can 

only derive entire wave fields and the computation is 

restricted to constant water depth. Other effects like surface 

tension, wave breaking, and seabed shear stress are 

usually neglected. In particular, due to numerical damping 

and other numerical inaccuracies, the error can become 

too large in the far field to be acceptable. 

Most thin ship theory programs can be run on a normal 

desktop computer and results are obtained within seconds. 

A description of current programs can be found in Gadd 

(1999), Molland et al. (2000), Tuck et al. (2001) and 

Doctors (1997) as well as more detailed literature. 


3.7.1.2 Prediction of wave transformation and propagation 

in the far field and coastal zone 

Once the generated waves are no longer influenced by the 

vessel, other coastal engineering tools can be used to compute 

the wash propagation over a variable bathymetry. To 

date only a few successful approaches have been published: 


14

• Kofoed-Hansen et al. (1996, 1999 and 2000) and MCA 

(1998) used a spectral wave model, which describes the 

propagation, growth, and decay of short-period waves 

in near shore areas to predict the wave height contours 

over a variable bathymetry. The model includes the 

effects of refraction and shoaling due to varying depth, 

wave generation due to wind, and energy dissipation 

due to bottom friction and wave breaking. The basic 

equations in the model are derived from the conservation 

equation for the spectral wave action density. 

• The model boundary allows for the variable spectral 

forms and permits the wave conditions to vary along the 

boundary. For wash studies, waves were specified in 

terms of mean wave height, mean wave period, mean 

wave direction as well as parameters for spreading from 

the mean direction. The code also can be modified to 

allow for the input of empirical decay rates derived 

from experiments. A linear refraction-diffraction 

model also has been used to calculate the wave disturbance 

patterns of the time history as the wave propagates 

from the vessel to the shore (MCA, 1998). 

• Raven (2000) suggested a number of analytical techniques 

for calculating wave propagation in the far field, 

where effects from banks or bottom topography can be 

neglected. He also demonstrated the successful coupling 

of a steady state panel code with a space domain 

Boussinesq-type model. A similar approach is discussed 

in Kofoed-Hansen et al. (2000). The principle 

behind the Boussinesq-type models is to eliminate the 

vertical dimension in the flow description without losing 

important effects like the influence of the vertical 

acceleration on the wave propagation. The non-uniform 

distribution of the velocity profile is responsible 

for the frequency dispersion. The idea is to couple the 

two types of models in order to utilise the computational 

cost effectiveness of the two-dimensional Boussinesq 

model where it is possible, and to apply the detailed, 

but time-consuming Navier-Stokes (or Euler/CFD) 

based free surface model only in areas where the flow 

field is three-dimensional. 


To calculate the essential boundary conditions for the 

Boussinesq model, the full three-dimensional velocity 

field and the free surface elevation is required. The free 

surface elevation is not generally sufficient as pointed out 

by Kofoed-Hansen et al. (2000). 

The great advantage of using a Boussinesq-type model is 

the possibility of simulating the wash sequence including 

both Bernoulli and Kelvin wake. The tool has proven to 

be very powerful. However, it still has its restrictions and 

requires further development. 

• Chen and Sharma (1995) investigated the wave generation 

of a slender vessel in a shallow channel at near critical 

speed using a combination of thin-ship theory and 

simplified Boussinesq equations. In particular the periodic 

generation of solitary waves was presented, which 

required the use of a non-steady model. The methods 

produced good results for a shallow channel with variable 

cross section. Jiang (2000) combined the thin-ship 

approximation with an enhanced Boussinesq method 

with improved results, and Jiang et al. (2002) expanded 

the model for a moving ship, accelerating or decelerating, 

in an arbitrary bottom topography, although with 

simplified Boussinesq equations. 

In general there is some agreement that Boussinesq-type 

models will give more realistic results, particularly if the 

phase relationship of the successive waves is modelled 

correctly. More complex wave models based on 

Boussinesq-type equations with a wider applicability in 

terms of wavelengths are currently being developed. 

Together with improved algorithms and faster desktop 

computers these models will be more applicable to a wider 

range of cases. 

Regardless of what type of numerical model is determined 

to be the most appropriate, it is necessary to calibrate it 

against either full- or model-scale experiments and then 

validate its output with field data before it can be used as 

a practical tool for managing wake wash. 

3.7.2 Full-scale trials and measurements 

3.7.2.1 Measurement techniques 

A range of measurement techniques can be used to obtain 

wave elevations generated by a vessel. It is beyond the 

scope of these guidelines to discuss all the techniques in 

detail. An overview of the techniques applied so far is 

given and some of the difficulties and criticisms are discussed. 

The basic types of point measurement techniques 

are listed in Table 3-1. Three different types of techniques 

are listed in Table 3-2 that can be used to map a whole 

wave field. Not all devices are suitable for all locations, 

i.e., near field, far field or shoreline. The basic difficulty 

is accessibility and range as listed in Table 3-1. The equipment 

used to measure the wake should undergo a rigorous 

calibration procedure. It is important that the device is 

capable of measuring long-period waves (over 20 seconds) 

with small amplitude. If possible, validation should be 

undertaken with a different type of equipment, particularly 

for those devices not measuring elevation directly. 


Table 3-1 Single point measurement techniques for ship wave measurements 

Type: Quantity measured: Technique: Requirements: Constrains: Reference: (examples) 

Wave staff Water elevation Capacitance Mounting pole, Shallow water Parnell & Kofoedlogger 

only Hansen (2001) 

Surveying rod Water elevation Optical Accessibility, Very labour Hannon & Varyani 

& camera solid structure intensive (1999) 

Altimetry Distance from Laser, Solid structure Location Kirk McClure Morton 

above surface Ultra-sound, for transducer (1998), Koushan 

Radar et al. (2001) 

Subsurface Water elevation / Echo sound Watertight - 

water depth 

device 

Subsurface Water pressure Piezo transducer Watertight Depth limitation Whittaker (2001), 

device for short waves Stumbo et al. (1999) 

Aqua Particle velocity Acoustic Doppler Watertight device Depth limitation Fissel et al. (2001) 

Doppler 

for short waves 

Wave Acceleration Accelerometer Floating buoy Small signal for Koushan et al. (2001) 

riding Buoy with adequate very long waves 

size/weight 

Table 3-2 Area measurement techniques (3 dimensional) 

Type: Technique: Reference: 

Stereo photogrammetry Optical, two pictures taken at different locations Inui (1962). 

of same area at same time 

LIDAR Fast scanning laser beam across surface Bolt (2001) 

and time delay of reflection measured 

RADAR 

Microwave beam scanning surface 

and time delay of reflection measured 

3.7.2.2 Monitoring and trial procedures 

Full-scale trials can serve two different purposes and as a 

result the necessary procedures for undertaking such 

assessments may differ. 

General vessel performance measurements 

Measurement of the wave generation by the vessel and the 

wave profile at a given distance from the sailing line may 

be carried out. In such cases a steady state wave pattern is 

of interest. These trials are similar to tank tests and, hence, 

are subject to similar procedures. However, it has to be 

recognised that conditions are not as controlled as in a 

towing tank. Apart from the vessel speed over ground, 

course over ground, and continuous recording of the vessel's 

position after constant time intervals, it is recommended 

to record still water trim, overall displacement, 

and operation / control of trim flaps, stabilisers, and foils. 

It has to be ensured that the vessel has been operating at 

constant speed for a distance long enough (in particular 

close to critical speed). The vessel needs to continue for 

sufficient distance with constant speed after passing the 

monitoring location (persistence of wash). It is also desirable 

that the seabed is smooth and constant in water depth 

along the vessel's track unless deep-water trials are carried 

out. The slope of the seabed perpendicular to the vessel’s 

track should be uniform. However, constant water depth 

would be desirable. Preferably trials should be undertaken 

with no or minimal current. In any case a repetition of 


16

at least one trial in opposite directions is recommended for 

repeatability (assuming the vessel is symmetrical). The 

background wave climate, with particular attention to 

other vessels’ wake, wind generated waves and swells, 

needs to be minimal to reduce post-processing of the data. 

Wake assessment of a vessel along its operational route 

It may be necessary to monitor the wake of a vessel along 

a given route for risk assessment or numerical modelling 

purposes. Due to the variability of the operation, several 

passages may need to be monitored to cover different tidal 

stages, variable loading of the vessel or different operational 

procedures. The monitoring might, therefore, be 

undertaken over a period of several days. The length of 

the monitoring window needs to be sufficient to cover the 

full extent of wash (possibly more than 40 minutes). It is 

recommended to start monitoring well before the vessel 

passes the monitoring location. The primary reason is that 

waves could travel ahead of the vessel or the change of 

operation further out causes larger disturbance than the 

nearby passage. Monitoring should be continued after the 

passage of the concerned vessel until no significant waves 

have been measured for a considerable time. It is recommended 

to record at least still water trim, overall displacement, 

and operation of trim flaps, stabilisers, and foils. 

3.7.3 Model scale trials 

Guidelines on tank testing have been published by the 

International Towing Tank Conference and are not discussed 

in detail in these guidelines. Information can be 

obtained through the Naval Architecture Institutions and 

major naval research institutes and departments. Attention 

may be drawn to the effects caused by the narrow tank 

width in shallow water tests, which are discussed in Inui 

(1954). Close to critical speed the towed model is capable 

of producing a number of solitary waves depending on the 

distance towed at such speed Dand et al. (1999). However, 

this has limited practical relevance. The propulsion system 

has also significant effect on the wave generation by the 

vessel as shown by Taatø et al. (1998). It was found that 

the wave amplitude generated by a water jet propelled 

model increased by 10 to 40 percent compared to the wave 

amplitude generated by a towed model. Several research 

groups have used wide shallow water tanks with a tank 

width of up to 10 vessel lengths to establish an unreflected 

free wave pattern behind the vessel. Again the towing 

length needs to be long enough to generate a steady-state 

pattern (persistence of waves). 

(moreover the event is transient and not periodic). Modern 

wavelet analysis might, however, be a good tool for mapping 

both frequency and time information. 

• Signal preparation: For the removal of high frequency 

noise, a filter method of higher order is recommended. 

A more efficient filter technique that does not result in 

a phase lag is to make a fast Fourier transform, cut the 

high frequency noise and make an inverse transform. 

Moving averages may also be used, but are less 

favourable as the signal is not removed but only 

smoothed. Tidal variations or varying offsets may be 

best removed with moving averages or high frequency 

pass filter. 

• Wave cuts in the space domain derived from numerical 

steady state simulations may be converted into the time 

domain. 

• Wave-by-wave analysis: Complying with standard 

engineering procedures the zero-crossing technique 

should be adopted. Thus, the wake can be characterised 

in terms of zero-crossing period and zero-crossing 

wave height. Otherwise a peak-to-peak analysis can be 

used. 

3.7.5 Wake assessment 

The wave generation of the vessel can be assessed using 

the wave-making resistance (denoted using either R w or 

the wave resistance coefficient C w ) as well as the ratio of 

the distribution of resistance R w to the propagation direction 

θ (∆R w /∆θ). 

As the wave trace is transient, the use of significant wave 

height (H 1/3 or H m0 ) and average wave energy (energy per 

unit area) is ambiguous. While significant wave height 

deceptively suggests an average height throughout the 

wash trace, both values depend on the sample length and 

become smaller with large sample lengths for the same 

wash event. In general, using maximum wave height 

(H max ) and relating maximum wave period (T max ) and distribution 

of wave height and period through the entire 

wave trace, e.g., Fig. 3-5, are good measures to characterize 

the wake at a given location for risk assessment purposes. 


4. IMPACTS ASSOCIATED 

WITH VESSEL WAKE 

3.7.4 Wake analysis 

Due to the short period of the event and the large spreading 

of periods, wave data needs to be analysed in the fulltime 

domain on a wave-by-wave basis. Frequency domain 

analysis of super-critical wash using Fourier transforms is 

not recommended due to the low-frequency content of 

super-critical wash relative to the required sampling time 

4.1 OVERVIEW 

The objective of this section is to highlight some of the 

potential safety and environmental impacts associated 

with wake from high-speed vessels. Many of these impacts 

are based on reported incidents that have been attributed to 


Some examples are discussed in Kofoed-Hansen and 

Mikkelsen (1997) and Marine Accident Investigation 

Branch report (2000). Although potential impacts associated 

with wake from high-speed vessels are a legitimate 

concern, it is important to note that many of the impacts 

discussed in this section are not unique to these vessels. 

Wake from other types of vessels can have the same, or 

very similar, impacts. Although every effort has been 

made to identify the most significant impacts, it is possi 

ble that there may be others. 

The potential for wake wash to have an adverse impact on 

safety or the environment is related to the physical characteristics 

of the waterway and adjacent shoreline as well as 

the characteristics of the wake. It is also related to how the 

wake interacts with the people and vessels that use the 

waterway, the structures that are built on, or near the 

waterway, and the near-shore flora and fauna. The implication, 

whether wake will have an adverse impact on safety 

or the environment, is site specific. 

4.2 SAFETY IMPACTS 

Safety impacts associated with wake generally involve: 

• People on or near the shoreline; 

• Vessels underway or moored; or, 

• Structures located in, on, or adjacent to the waterway. 

4.2.1 Safety of people 

Wake characteristics in combination with shoreline features 

and waterway topography can be used to identify 

potential impacts to the safety of people on or near the 

shoreline. In general, impacts involving people on or near 

the shoreline are primarily associated with transverse 

waves generated by vessels operating at or near critical 

speed and the long-period waves that comprise the first 

group of waves generated by vessels operating at supercritical 

speeds. Impacts that can be attributed to these 

waves based on shoreline characteristics are summarised 

in Table 4-1. Some of these impacts may be of more concern 

during certain times of the year, e.g., summer months 

when beaches are being used by bathers, or more pronounced 

during certain environmental conditions, e.g., 

high or low tide or during calm weather, when large waves 

may be unexpected. 

4.2.2 Safety of vessels 

4.2.2.1 Overview 

Just as the characteristics of the wake generated by a vessel 

is related to its physical characteristics (e.g., length, 

beam, draft, displacement), how another vessel will be 

impacted by wake is related to its own physical characteristics 

(Bolt, 2002). How a vessel responds to wake also 

depends on how it is operated when wake is encountered 

and is therefore related to the knowledge and skill of the 

vessel’s operator. Consequently the specific risk to each 

vessel must be assessed individually. This is true regardless 

of the type of vessel that generated the wake. 

However, there are several general observations that can 

be made about wake generated by high-speed vessels or 

other vessels operating at or near critical speeds (MCA, 

2001): 

• All vessels are affected by some part of the near- or 

super-critical wash due to the wide range of wave periods 

(see Fig. 3-5). 

• Small craft are particularly at risk of being swamped, 

broached, or capsized by the steep, near breaking waves 

produced by vessels operating in the near-critical zone. 


Table 4-1 Impacts related to the safety of people based on shoreline characteristics 

(Kofoed-Hansen, 1996; MCA, 1998) 

Shoreline Characteristics Potential Risk Probable Cause 

Shallow sloping beach People may be caught in Rapid inundation of large 

water or knocked down areas from run up of long-period waves 

Moderate / steep People knocked down Plunging and breaking waves 

beaches, boat ramps 

Damage to boats and 

vehicles on ramp 

Shorelines with sea walls People on narrow beaches Rapid inundation of exposed beach 

trapped against sea wall from run up of long-period waves 

Breaking waves that overtop the seawall 


18

• Long period wash waves may cause large vessels to 

yaw and alter course, which in a confined channel can 

increase the risk of grounding, or when passing other 

vessels in close proximity can increase the risk of collision. 

• Maximum pitch motions are expected for most vessels 

when the super-critical wash is encountered as either 

head or following waves. 

• Maximum heave motions are expected for bigger vessels 

when the super-critical wash is encountered as 

beam waves. 

• Wash induced roll can increase the risk of grounding at 

the turn of the bilge of deep draft, wide beam vessels, 

such as container vessels, operating in confined channels 

with small under-keel clearances. 

• Orbital motions of fluid particles in shallow water are 

elliptical rather than circular so that a vessel’s horizontal 

motion is larger than its vertical motion. 

4.2.2.2 Vessels underway 

© COPYRIGHT 

Wake characteristics, in combination with the topography 

of the waterway, can be used to identify potential impacts 

to the safety of vessels. In general, impacts related to the 

safety of vessels are primarily associated with transverse 

waves generated by vessels operating at or near critical 

speed as well as the long-period waves comprising the first 


group of waves and the short-period waves comprising the 

third group of waves generated by vessels operating at 

super-critical speeds. Impacts to vessels that can be attributed 

to these waves are summarised in Table 4-2. Some of 

these impacts may be more pronounced during certain 

environmental conditions (e.g., calm weather, high or low 

tide, or certain times of year when large numbers of small, 

recreational vessels are using a waterway). 

4.2.2.3 Vessels on moorings and in harbours 

The wave pattern reaching moored vessels is usually more 

complicated compared to open water due to the influence 

of coastal structures and the local bathymetry. The angle 

of propagation is due to wave refraction, reflection, and 

diffraction around solid obstacles and, unless the berth is 

open to the incoming waves, these changes need to be considered. 

The wavelength can be shorter due to diffraction, 

which can increase the height at the same time. Potential 

impacts of wake on moored vessels are summarized in 

Table 4-3. 

4.2.3 Structural damage 

The effect of wake on floating structures depends on the 

response characteristics of the object. Consequently the 

risk to each structure must be assessed individually. Of 

particular concern is the possibility that the waves will 

cause excessive movement of floating structures. There is 

also the possibility that the impact of breaking waves may 

undercut pier footings. 

Table 4-2 Impacts related to the safety of vessels (Kofoed-Hansen, 1996; MCA, 1998) 

Waterway Topography Potential Impact Probable Cause 

Open water Small craft may be swamped, Waves generated by vessel operating at 

broached or capsized 

critical speed, or short-period, high-amplitude 

waves in the third set of waves 

Larger vessels may have 

difficulty maintaining course 

Long-period waves can cause 

larger vessels to yaw 

Harbour or estuary Vessels with small under keel Long-period waves result in considerable 

entrances with clearances may ground seiching over large areas with shallow water 

shallow bars 

Small craft may have 

difficulty maintaining course 

Wash generated by vessels operating at 

trans- and super-critical speeds can create an 

oscillating current over bars and shallow banks 

Shallow banks (

Table 4-3 Potential impacts on moored vessels (MCA, 2001) 

Activity Potential Impact Probable Cause 

Moored vessels Excessive movement Transverse waves generated by vessels operating 

(surge, heave and roll) may at or near trans-critical speeds and both 

cause moorings to fail, damage long-period and tail waves generated by vessels 

to vessels as well as docks and operating at super-critical speeds 

piers, vessels to touch bottom 

Vessels with small under keel 

clearance may ground 

Long-period waves result in considerable 

seiching over large areas with shallow water 

Loading / discharging cargo Disruption of cargo operations Long-period waves generated by vessels operating 

that are sensitive to vessel at super-critical speeds 

movement 

Vessels alongside a moored Damage to either or both vessels Transverse waves generated by vessels operating 

vessel (tugs, bunker barges, due to large relative motion due at or near trans-critical speeds and both 

etc.) to different response to waves long-period and tail waves generated by vessels 

operating at super-critical speeds 

4.2.3.1 Historic and archaeological monuments 

The possibility of damage to sites of cultural significance, 

including historic monuments and archaeological sites, on 

the seabed (such as old historical sites and wrecks), and 

the shoreline (forts and other historical sites) is prevalent 

in several countries including Denmark, New Zealand, and 

Sweden. For example, in the archipelago of Göteborg, 

Sweden, many bays are sheltered from large wind waves 

and the tide is minimal. After the introduction of highspeed 

ferries a several-hundred-year-old burial ground for 

sailors close to the sea was threatened by wake erosion. 

Although the erosion was halted in 1997 when the speed 

of the fast ferries was limited, there is evidence suggesting 

that wake from large container ships may be a heavier 

threat (Svensson, 1999). 

4.3 ENVIRONMENTAL 

IMPACT OF WAKE 

© COPY- 

4.3.1 Overview 

All waves, whether generated by the wind or a vessel, can 

have some impact on the marine environment. As indicated 

in Section 4.3.2, there are characteristics of high-speed 

vessel wake that contribute to its higher propensity vis-àvis 

wake from other vessels to impact the marine environment. 

However, for the reasons raised in Section 4.3.4 it 

cannot be assumed a priori that high-speed vessel wake is 

the cause of any adverse impacts to the marine environment 

that might be observed in areas where these vessels 

are operating. Determining the cause of adverse impacts 

RIGHT 


to the marine environment that are observed in a given 

area requires detailed, local studies. 

The severity of any environmental impact caused by wake 

will depend on how the wash regime differs from the natural 

wave climate. It is also dependent on the susceptibility 

of the recipient shores to wave attack. Naturally sheltered 

environments and soft sedimentary shores are more 

likely to be adversely impacted than naturally exposed 

environments with rocky shores. 

The available literature on the ecological impacts of highspeed 

vessel wake is limited insofar as most studies have 

focused on the wash generated by watercraft other than 

high speed vessels, i.e. conventional ferries, boats, and 

personal water craft (jet skis and wave riders). However, 

the studies that have been conducted are useful since they 

highlight potential effects of high-speed vessel wake on 

the marine environment. 

4.3.2 Potential impacts 

4.3.2.1 Physical change 

In general, an increase in wave action, whether from natural 

causes (e.g., storm events) or vessel wake will result 

in higher energy within the coastal system. This increase 

can result in an adjustment to the beach environment 

including beach orientation, erosion, accretion, and 

increasing the envelope of dynamic change in the attainment 

of a new equilibrium to the wave conditions. One 

factor influencing the vulnerability of a shoreline to being 

changed by waves is its morphological state. In general, 

Report of Working Group 

41 - MARCOM 

20

a stable shoreline is less vulnerable to attack than one that 

has been previously disturbed, either because of prior 

storm events or human activity (e.g., shoreline construction 

or sediment removal). The vulnerability of a coastal 

zone to wave attack is also dependent upon its material 

composition and typical particle size. 

The addition of energy to the system from wake can cause 

sediment mobilisation and accelerated weathering of 

rocky shores. The probable wake related causes of these 

impacts are summarised in Table 4-4. 

© COPY- 

Changes to the physical environment, with particular 

emphasis on sediment transport, can cause a variety of different 

environmental impacts. Mobilisation of larger sediments 

can result in rapid changes to biological communities. 

Sedentary organisms may be relocated, crushed, and 

damaged as the rocks and boulders on which they are 

attached are rolled around. Resuspension of finer sediments 

can create an abrasive environment that may damage 

soft-bodied animals and algae and prevent spores from 

settling. When sediments do settle out, they can potentially 

smother benthic organisms and cover fish eggs and 

spawning grounds. Aquatic plants can be physiologically 

RIGHT 

impaired if their surfaces are covered with silt. 

Resuspension of sediments also increases the turbidity of 

the water, and by blocking the light that reaches the bottom 

can have an adverse impact on benthic organisms. 


4.3.2.2 Impacts on flora and fauna 

The flora and fauna that inhabit coastal environments are 

subject to inundation as well as the hydrodynamic forces 

associated with both wind and vessel generated waves. 

Waves are a primary agent of ecological disturbance that 

affect individuals, populations, and communities to varying 

degrees. The potential biological impacts of wake on 

coastal and shoreline habitats, which are summarised in 

Table 4-5, are a consequence of changes to the natural 

physical environment or natural wave climate. Without 

external influences, near-shore and intertidal habitats may 

exist in a state of long-term equilibrium. Although an 

increase in the energy within a coastal system by introducing 

vessel wake can be sufficient to upset the equilibrium 

(Kirk McClure Morton, 2000), it is usually difficult 

to assess changes caused by a changed wave regime due to 

vessel wake. 

Table 4.4 Physical impacts of vessel wake 

(Bell et al., 2000; Kirk McClure Morton, 2000; Single, 2002) 

Potential Impact 

Probable Cause 

Sediment Transport 

Sediment resuspension 

and associated increase 

in turbidity 

Cross-shore and long-shore 

transport of bottom sediment 

and associated accretion 

or erosion 

Weathering of Rocky Shores 

Long-period waves penetrate deeper into the water column than 

shorter-period waves and can disturb bottom sediments farther 

off-shore than would likely occur under normal conditions. 

Large, steep waves similar to storm generated waves can move sediment 

seaward; if they attack the beach at an angle, the material will be transported 

along the shore. Short, steep waves may transport material onto higher 

sections of the beach. Depending on the angle of attack, wake wash 

encountering the shore can result in either cross-shore or long-shore transport 

of sand and other shoreline material. Large, steep waves, similar to those 

generated by storm waves, can move material seaward and form a bar 

in front of the beach. If the waves attack the beach at an angle, 

the material will be moved along the beach. Short, steep waves can move 

material higher up on the beach. High-speed vessel wake wash has been 

observed to result in both accretion and erosion. 

The impact of the incoming wave and the resulting fluctuations in cracks 

can separate layers of rock from the bedrock. Laboratory measurements suggest 

that regular waves, e.g., vessel wake wash, generate higher crack pressures 

than mixed waves, e.g., wind generated waves, of similar magnitude. 

Hence the weathering of rocky shores by the leading waves of the wake 

from high-speed vessels may be larger than the weathering induced 

by comparable natural seas. 


Table 4-5 Biological impacts of vessel wake 

(Danish Maritime Institute, 1997; Bell et al., 2000; Hotchkiss et al., 2002) 

Potential Impact 

Probable Cause 

Fixed and mobile organisms may be dislodged and stranded; 

plants may be broken and or uprooted. Overtime species 

distribution within the intertidal and near shore zone may change; 

some species may be removed 

Smothering of plants, sedimentary animals, and spawning grounds 

Loss of sea grasses 

Altered distribution of species within the intertidal zone 

Localized algal blooms and associated increase in turbidity 

Reduced productivity and loss of bird nesting areas; change in 

feeding behaviour of birds, lower over wintering survival rates 

Reduced productivity of seal rookeries; loss of haul-out areas 

Waves with higher than ambient energy 

due to wake wash breaking on individual 

plants and animals. Sediment mobilisation 

can damage individual organisms as well as 

cause habitat loss. 

Settling out of fine, suspended sediment 

Turbidity from sediment mobilisation can 

reduce the amount of light reaching 

the bottom 

Increased immersion due to regular 

inundation of intertidal zone 

Resuspension of nutrients associated with 

sediment mobilisation 

Beach nesting and shoreline feeding areas 

inundated by run up of long period waves; 

cliff nesting areas inundated by 

breaking waves 

Inundation by breaking waves 

4.3.3 Differentiating between causes 

Although high-speed vessels (e.g., high-speed ferries) 

have been in operation for over ten years, relatively little is 

known about the impact of their wake on the marine environment 

vis-à-vis the wake from other types of vessels. 

This is mainly due to the difficulty of distinguishing 

between impacts that result from different causes including 

normal wind generated waves, storms, high-speed and 

non high-speed vessel wake, and other human activities. 

Making such a distinction is particularly difficult since the 

coastal environment naturally is always undergoing some 

change (Kirk McClure Morton, 2000). 

4.3.4 Predicting environmental impact 

© COPY- 

Even though most coastal areas are always undergoing 

some change, the physical and biological environment of 

a beach or a coastline generally is shaped by the predominant 

wave climate, which is the product of both regular 

wind and storm generated waves as well as vessel wake. 

Hence, if the wave climate changes significantly, it is reasonable 

to expect that the coastline and its physical and 

biological properties will also change, although it is not 

always immediately apparent how the change will become 

Report of Working Group 41 

- MARCOM 

RIGHT 

manifest. The implication is that any effort to assess how 

high-speed vessel wake may impact the marine environment 

will require the comparison of data obtained both 

before and after a particular shoreline is exposed to wake 

from these vessels. It should be noted that in many cases 

the physical impact could be initially large and then 

become more stable; therefore, any assessed impacts 

based on initial trends could possibly result in overestimating 

the impact. Although models can be developed to 

help predict how wake might impact a particular shoreline, 

given the complexity of shoreline systems, model results 

should not be generalized to similar shorelines in other 

areas (Bell et al., 2000). 

5. MANAGING VESSEL WAKE 


5.1 INTRODUCTION 

Concern about the potential safety and environmental 

impact of high-speed vessel wake are causing high-speed 

vessel operators and waterway managers to establish 

either voluntary or mandatory management measures. 

Establishing effective management measures for highspeed 

vessel wake requires an understanding of the causal

elationship between a vessel’s wake and its actual or 

potential impact. As discussed in Sections 3 and 4, establishing 

this causal relationship is a multi-faceted problem 

that requires understanding how wake interacts with other 

vessels, people, structures, and near-shore flora and fauna 

as well as the bottom and shoreline of the waterway. This 

requires knowledge of the physical characteristics of the 

wake generated by the vessel as well as how the wake is 

affected by the physical characteristics of the waterway as 

it propagates away from the vessel’s line of travel and 

shoals to break at the shore. It also requires understanding 

the effect of the management measures that are considered 

on wake generation to ensure that the measures implemented 

will be effective and that they will not result in 

unintended consequences. The implication is that there is 

not a simple, universal solution for managing high-speed 

wake insofar as how wake interacts with the physical environment 

and human activities is site specific. In addition, 

there are differences in the wake generated by different 

hull forms and sizes and operating speeds – differences 

that may permit alternative ways of mitigating the potential 

impact. 

5.2 MANAGEMENT MEASURES 

Mitigation measures can be divided into three categories: 

vessel design, operational measures, and non-operational 

measures. It is likely that the management regime adopted 

for any given route will involve a combination of operational 

and non-operational measures. 

5.2.1 Vessel design 

Insofar as the wake generated by a vessel is directly related 

to its hull form, vessel design is a primary means of 

managing wake. Although it is possible to modify a vessel 

after it is constructed (e.g., increasing its length or 

installing trim tabs or interceptors) to improve the characteristics 

of the wake that is generated, the cost of doing so 

may be prohibitive. Similarly, modifications may be prohibited 

by regulatory requirements or physical constraints. 

Therefore, naval architects should understand the potential 

implications of the wake generated by a given hull design 

for wake management and consider any wash criteria 

related to the intended route including design requirements, 

along with emissions, speed, and other limiting factors. 

There are, however, key features of high-speed vessel 

wake that cannot be reduced or removed by optimising 

the hull form and design ratios. An example is the wave 

period, which generally increases with vessel speed and 

distance from the navigation line and is a particularly 

important parameter in wave impact in shallow water 

areas. 

5.2.2 Operational measures 

Operational measures can be used to reduce both the safety 

and environmental impacts of wake. Because the potential 

impacts of wake are related to the physical characteristics 

of both the vessel and the waterway, operational 

measures are generally related to the route or the vessel’s 

operational profile. Insofar as ferry routes are a function 

of geography, it is usually not possible to reduce potential 

impacts by selecting an alternate route. However, there are 

some changes that might be possible, including 

• Moving a route farther from shore to increase the distance 

between the vessel’s track and the area where 

wake impacts are of concern. 

• Establishing route segments so that changes in water 

depth do not cause the vessel to transition from subcritical 

or super-critical speeds into the critical speed 

range. 

• Relocating where course or speed changes are made to 

avoid focusing wake at a particular location or to avoid 

generating wash associated with the critical speed 

range. 

• Altering the orientation of a route relative to the shoreline 

to change the angle at which the wake encounters 

an area of concern. 

• Modifying the schedule to reduce the potential for 

impacts that may be associated with predicable shoreline 

use or environmental factors (e.g., tide or sustained 

winds from a particular direction). 

Although the characteristics of the wake generated by a 

vessel are a function of the hull form and cannot be altered 

unless the vessel undergoes modifications after it is constructed, 

there are several operational measures related to 

the vessel’s operational profile that can be used to reduce 

the potential impacts of vessel wake. These include 


• Training vessel masters and mates so that they understand 

the relationship between the navigation of the 

vessel and the generation of wake. 

• Ensuring that the navigation of the vessel conforms 

with the courses and speeds established for each leg of 

the route. 

• Ensuring that the vessel is trimmed on each run to minimize 

the wake that is generated. 

• Establishing contingency plans for situations (e.g., loss 

of engine power), or other situations when it may not be 

possible to follow normal operating procedures. 


5.2.3 Non-operational measures 

The intent of non-operational management measures is to 

reduce safety related impacts of wake by lessening the 

potential for people and small craft to interact directly 

with wake. Some non-operational measures include: 

• Posting signs on shore or including notices on navigation 

charts in areas where high-speed vessel wake 

might reasonably be encountered. 

• Engaging in outreach activities to ensure the public is 

aware of the potential impacts associated with wake. 

• Designing new sea walls and quay walls or retro-fitting 

existing ones with wave absorbing materials to reduce 

wave amplification by reflection. And, 

• Coordinating with other operators and harbour authorities 

or owners to identify impacts and means of mitigation. 

Non-operational measures intended to inform the public 

are particularly important in areas where wake from highspeed 

vessels is not actively managed or is a new activity. 

5.3 ROUTE ASSESSMENT 

5.3.1 Overview 

Developing appropriate management measures for highspeed 

vessel wake requires identifying the potential safety 

and environmental impacts the wash may have. This 

requires ensuring that the interrelationship of wake generation, 

transformation, and impact is understood. Since the 

impacts that may occur are the result of a number of factors, 

including wake generation and transformation, the 

physical characteristics of the waterway and its shoreline, 

as well as how the waterway and shoreline are used, this 

interrelationship is route dependent. The route assessment 

is an objective, systematic process for identifying potential 

impacts and for developing management measures that 

may be implemented by vessel operators and waterway 

managers that are appropriate for a particular route. 


A route assessment is intentionally flexible so that it can 

be applied to different waterways and different vessels. It 

is also flexible with regard to the outcome. In other words, 

it does not favour one measure for reducing potential wake 

impacts over any other. Similarly, whereas in some 

instances a single management measure may be sufficient 

to prevent an impact from occurring, there may be other 

cases where a suite of different measures may be needed. 

Another aspect of the model is that it is scaleable so the 

level of effort is appropriate for the safety and environmental 

impacts being considered. The process involves 

four steps: 

1. Characterizing the route. 

2. Identifying the potential impacts and severity of wake. 

3. Developing and assessing potential management measures. 

4. Implementing and monitoring management measures. 

Conducting a route assessment requires an understanding 

of specific vessel and route variables. The information 

needed to conduct the route assessment can be grouped 

into five general areas: 

1. The characteristics of the vessel’s wake in its entire 

operational envelope. 

2. The bathymetry and shoreline topography of the proposed 

route. 

3. Waterway activities along the route. 

4. Shore activities along the route. 

5. Properties of the physical and biological environment 

of the adjacent coastline. 

5.3.2 Route characterization 

Route characterization involves dividing the planned route 

or routes, if alternatives are available, into segments. 

Although there are a number of ways this can be accomplished, 

the most practical approach is to segment the 

route according to where the vessel will be operating at 

sub-critical, near-critical, and super-critical speeds based 

on the ranges of depth Froude numbers described in 

Figure 5-1. In addition, deep-water operation might be 

segmented by ‘conventional low speed’ and ‘high speed 

sub-critical’ speeds (MCA, 1998). Stumbo et al. (2000) 

have observed that in deep water the transition from conventional 

low speed to high speed sub-critical speed 

occurs when vessels have a length Froude number 

between 0.65 and 0.9. Using depth Froude numbers, and 

length Froude numbers when appropriate, to segment the 

route provides a means of conducting a first order assessment 

of potential wake impacts along a planned route. It 

may identify places where some change to the route (e.g., 

a speed or course change), may eliminate or at least significantly 

reduce some of the potential wake impacts. 


24

Figure 5-1 Operational zones for route characterization based on wash regimes 

© 

5.3.3 Impact identification 

Once the route is divided into segments, the type and location 

as well as the likelihood and severity of the potential 

impacts that wake may have on each segment of the route 

must be identified. It is also necessary to identify the 

aspect of wake that may cause the impact and then determine 

whether wake from high-speed vessels is a primary, 

secondary, or tertiary cause of the identified impact. 

5.3.3.1 Identifying potential impacts 

Identifying potential wake impacts requires first ascertaining 

who, (e.g., swimmers or people near the shore), or 

what, (e.g., small-craft underway or moored in marinas, 

near-shore or coastal marine habitats, or waterfront structures) 

may be impacted. It also requires determining the 

locations where wake impacts can reasonably be expected 

to occur. The description of where an impact may occur 

should include some reference to the shoreline (e.g., offshore, 

near-shore, on-shore), as well as a geographic reference 

(e.g., the name of a location or other landmark). 

Although latitude and longitude may be useful for providing 

more precise locations, the use of common names provides 

a means to quickly identify areas where wake may 

have an adverse impact. 

COPY- 

RIGHT 

Identifying potential wake impacts requires understanding 

of how the waterway is used as well as information about 

the characteristics of the waterway’s natural and physical 

environment. There are any number of ways that this can 

be accomplished, including site surveys and meeting with 

representatives of different waterway users, natural 

resource agencies, and land owners. It is likely that the 

level of effort required to identify potential safety and 

environmental impacts will vary between routes and 

between different segments of the same route. Regardless 

of the means and level of effort employed, it is important 

that the result is a complete picture of the type and location 

of the potential safety and environmental impacts that 

wake may have on each segment of the route. 

When identifying potential impacts, it is helpful to establish 

when a particular impact may occur. Determining 

when an impact might occur is needed for determining the 

frequency that high-speed vessel wake might cause a 

potential impact. It also might help to highlight possible 

causal relationships that have to exist for an impact to 

occur (e.g., state of the tide or sustained winds from a 

given direction). Several different timeframes can be used 

when identifying when an impact might occur. Whereas 

some potential impacts might occur multiple times a day, 

others might occur infrequently, for example, those that 

are related to seasonal weather patterns. Establishing the 

timeframe might also help highlight impacts that are not 

exclusively related to wake from high-speed vessels. 


Report of Working Group 41 - MARCOM

Table 5-1 Likelihood and consequence scores 

Likelihood 

Score Description Examples 

5 Very Likely Every passage 

4 Likely Most passages 

3 Quite Possible High tide during passage 

2 Possible During storms or other periodic 

environmental conditions 

1 Unlikely Only during unusual / 

unpredictable circumstances 

Consequence 

Score Description Examples 

5 Very High Unacceptable impact, people may receive 

serious injuries or die, small craft cannot 

navigate safely, waterfront structures cannot 

be occupied / used, marine environment 

disrupted 

4 High 

3 Moderate Noticeable impact, people may be injured, 

moored vessels or waterfront structures may 

be damaged, marine environment likely 

to be damaged 

2 Slight 

1 Minimal No noticeable impact, use of shoreline / 

waterway not interrupted, any damage 

to marine environment is minimal 

© 

5.3.3.2 Wake components 

To develop appropriate management measures it is necessary 

to determine both the component of wake (i.e., wave 

height, wave length, energy, and the magnitude of the 

high-speed vessel’s wake) in terms of characteristic wave 

height/energy, wave period/length and wave direction that 

might be expected to cause each of the potential impacts 

that are identified. In some instances there may be more 

than one component that might be of concern. Failure to 

identify the component, or components, of wake that reasonably 

can be expected to cause a potential impact can 

result in developing management measures that are not 

appropriate. 

5.3.3.3 Likelihood and consequence of potential impacts 

COPY- 

After the potential impacts and the responsible component 

of high-speed vessel wake have been identified, it is necessary 

to assess both the likelihood that a particular impact 

will occur and its potential consequence. Suggested scales 

for assigning likelihood and consequence scores are 

shown in Table 5-1. It is recognized that the descriptions 

and definitions for the different scores are somewhat subjective. 

This is unavoidable since, for the most part, there 

RIGHT 


will be limited site-specific data available upon which to 

base assessment. Therefore, the assessment must be based 

on the best available information and the experience of 

those who are conducting it. 


26 

5.3.3.4 How important is wake 

Once the preceding steps have been completed, a determination 

should be made whether high-speed vessel wake is 

a primary, secondary, or tertiary cause of the potential 

impacts that are identified. Making such a determination 

is necessary to help provide some basis for establishing the 

extent to which a high-speed vessel operator should reasonably 

be expected to be responsible for preventing a 

potential impact from occurring. Making this determination 

will require having an understanding of the impacts 

that may be caused by other vessels as well as those that 

result from natural processes. It will also require an 

understanding of the physical differences of waves generated 

by other vessels as well as those generated by natural 

processes vis-à-vis those generated by high-speed vessels. 

As discussed in Section 4.3.3, it is recognized that it may 

not always be possible to make this determination with a 

high degree of certainty.

5.3.3.5 Priority 

Since it may not be reasonable to develop mitigation measures 

for every potential impact, it is necessary to establish 

a prioritised list of those that are identified. An initial prioritised 

list can be established based on an index number 

(I n ) calculated using the following equation: 

L 

I n = s x C s 

, 

CF s 

where L s is the likelihood score, C s is the consequence 

score and CF s is the causal factor score. CF s values are 

provided in Table 5-2. An example of potential management 

actions based on the index number is provided in 

Table 5-3. 

5.3.4 Developing and assessing potential 

management measures 


© COPYRIGHT 

5.3.4.1 Overview 

The route assessment is the foundation of any measures 

that are developed to managing wake. To be effective, the 

management measures that are employed should reduce 

the identified impact by 

• Focusing on the component of wake that is responsible 

for the potential impact; and 

• 

Ensuring the magnitude of the component that is of 

concern is maintained within acceptable limits. 

In addition, management measures should be appropriate 

for the location where they will be implemented. 

Management measures may be mandated by government 

agency regulations, company operating policies, or both. 

Establishing management measures should involve agencies 

responsible for waterways management, vessel operators, 

and effected stakeholders. 

5.3.4.2 Establishing management measures 

The first step in the process of developing a management 

regime for wake is to determine whether there is adequate 

data available to establish a maximum value or standard 

for the component or components that are of concern that 

Table 5-2 Causal factor scores 

Causal Factor Score (CF s ) 

Description 

1 High-speed vessel wake wash is the primary cause of the impact 

2 High-speed vessel wake wash is a secondary cause of the impact 

3 High-speed vessel wake wash is a tertiary cause of the impact 

Table 5-3 Index numbers and recommended actions (MCA, 1998) 

Index Number (I n ) 

Recommended Action 

1-5 Minimal No mitigation required 

6 – 10 Acceptable No mitigation required. Monitoring is required to ensure controls 

are maintained. 

11 - 15 Moderate Mitigation is required, but the costs of prevention may be taken into 

account. Mitigation measures should be implemented within a defined 

period. Monitoring is also required. Where moderate risk is associated 

with high or very high consequences further assessment may be necessary 

to establish more precisely the likelihood of harm as basis for determining 

the need for mitigation. 

16 - 20 Significant Vessel should not operate on route until risk has been reduced. 

21 -25 Unacceptable Vessel should not operate on route until risk has been reduced. 

If it is not possible to reduce risk even with unlimited resources, 

the vessel should be prohibited from operating on the route. 


cannot be exceeded when measured at a specified location 

(e.g., a minimum water depth or distance from the shoreline). 

The ultimate responsibility for making this determination 

resides with the agencies responsible for waterways 

management. However, vessel operators and effected 

stakeholders should participate in this process. 

Insofar as the route assessment may identify a number of 

different wake related impacts that are of concern, a single 

standard may not be appropriate for the entire route. 

Therefore, to avoid overprotecting some portions of a 

route while not providing enough protection along other 

portions, it will be necessary to establish different standards 

for different portions of a route. This is particularly 

true if the identified impacts are related to different components 

of wake. An advantage of standards is that compliance 

can be verified by measuring the wake. However, 

it is probable that in many areas sufficient data may not be 

available to establish a standard or set of standards. In 

these instances, it is necessary to either establish a value 

based on the best available data for the component of wake 

that is of concern or, if the data cannot support a standard, 

establish general criteria to minimize the potential that 

wake will have an adverse impact on safety or the marine 

environment. 

Many areas where high-speed vessels have been introduced 

have had conventional commercial vessel traffic for 

some time, and the environment is likely to have been 

modified by wakes from those vessels as well as by 

numerous other human activities and natural processes. In 

most cases the wakes of conventional vessels generally 

cause few complaints, presumably due to familiarity over 

time. For such locations the wake from conventional commercial 

vessels may be used as a reference for establishing 

a standard for high-speed vessel wake. 

Despite the fact that wake generated by high-speed vessels 

is substantially different from wash caused by conventional 

ships and ferries, the choice of a standard should reflect 

a connection between these two types of wake. 

Characteristic measures such as wave energy (Stumbo et 

al., 1999), maximum wave height prior to breaking 

(Kofoed-Hansen, 1996; Parnell and Kofoed-Hansen, 

2001), particle velocity at the seabed, and wave run-up on 

the shorelines can be used in a formulation of standard. 

Standards based on this approach have been implemented 

in Denmark, Sweden, New Zealand, and the United States. 


After acceptable standards or criteria have been established, 

the next step is to identify an appropriate suite of 

management measures. It is likely that this suite will 

include both operational and non-operational measures. 

Since the measures that may be employed to comply with 

the established standards and criteria are linked directly to 

the vessel and its operation, vessel operators should have 

the primary responsibility for identifying specific management 

measures. However, it is expected that the management 

measures will be subject to review by the agency 

responsible for waterways management. 

Once potential management measures are identified, new 

likelihood, consequence, and causal factor scores should 

be assigned and the index number recalculated to determine 

whether it is within an acceptable level for the vessel 

to operate on the route in question. 

5.3.5 Monitoring 

A monitoring program should be developed to determine 

whether the management measures that are implemented 

are effective in preventing or reducing impacts associated 

with wake. Although the details of the monitoring program 

are site specific, at a minimum the program should 

provide a means of determining or verifying whether wake 

from high-speed vessels is having adverse impacts on 

safety or the marine environment. In some instances, this 

will require having access to baseline data so that impacts 

that occur over time (e.g., shoreline erosion or habitat 

degradation), can be detected. It may also be necessary for 

the monitoring program to provide data that can be used to 

differentiate between impacts associated with high-speed 

vessel wake and impacts associated with wake from other 

vessels or natural processes. This is particularly important 

for impacts where high-speed vessel wake is considered to 

be a secondary or tertiary factor. 

6. CONCLUSION 

The characteristics of wake from high-speed vessels are 

fundamentally different from the wake generated by ‘conventional’ 

displacement vessels. Although wake from any 

type of vessel can potentially have adverse impacts on 

waterway safety or the marine environment, wake from 

high-speed vessels has received a significant amount of 

attention in countries around the world. In addition to 

concerns about the potential safety and environmental 

impacts of high-speed vessel wake, there is also concern 

that efforts to manage wake might result in the development 

of standards that are inappropriate and which might 

also unduly restrict the operation of these vessels. As a 

result, vessel operators and waterway managers alike have 

tried a number of different approaches for managing highspeed 

vessel wake. 

Based on the experience to date from these different 

efforts, it is apparent that the effective management of 

high-speed vessel wake is a multi-faceted problem that 

defies a simple “one size fits all” solution. It is also apparent 

that a means of managing high-speed vessel wake that 

addresses the legitimate concerns related to waterway 

safety and protection of the marine environment while also 

not unduly restricting their operation must be identified for 

the full benefits of high-speed vessels to be realized. 

Waterway managers and high-speed vessel operators are 

encouraged to follow the guidelines for conducting a route 

assessment and developing management measures that are 

outlined in this report. 


28

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ANNEX A 

TERMS OF REFERENCE 

The introduction of high-speed ferries in the mid-nineties 

has led to wake conditions not known earlier. 

The vessels in question are characterised by a travelling 

speed of 35 to 45 knots. They may be catamaran types but 

can also be single hull vessels. 

According to observations by the general public in 

Denmark, the waves created by the wake are more dangerous 

than the waves created by traditional ferries. They 

are higher and they may appear without warning and suddenly 

rise in shallow waters, then break and cause run-up 

on the coast. Danish newspapers and television news have 

shown dangerous situations for small boats and for 

bathers, and large numbers of complaints and protests 

from coastal house owners and landowners, from fishermen, 

anglers, sailors, rowers, hunters, divers, swimmers/holidaymakers 

were received by the authorities. 

Anxieties were also voiced regarding coastal erosion, subsidence 

of natural stone reefs and disturbance of bird sanctuaries 

and dike safety. 

In 1995 the Danish Maritime Authority commissioned the 

Danish Hydraulic Institute to carry out a technical investigation 

of wake wash from fast ferries. 

This investigation concluded that 

• the new high speed vehicle ferries generate waves, 

which, in coastal and shallow water regions, are considered 

by the general public as being considerably different 

to the waves caused by conventional vessels. 

• this view has been widely confirmed by the measurements 

and calculations which have been made. 

The report also mentions that wake wash problems have 

appeared in Sweden, Ireland, Australia, New Zealand, 

England, Portugal, and U.S.A. In Denmark regulations 

were issued in 1998 concerning the effects of waves from 

high-speed ferries on leisure activities, on the environment 

in general and in particular on erosion and dike safety 

problems. 

• categorize problems met 

• analyse in which ways such problems may be foreseen 

and avoided 

• gather information on regulations established in various 

countries and regions 

• coordinate study with IMO working groups on problems 

in relations to high-speed ferries; 

all in order to set up guidelines for traffic planners, ship 

owners, and relevant public authorities, including waterway 

managers. 


PIANC started in 1995 a working group that deals with 

harbour facilities for high-speed ferries. The task for this 

new working group is therefore limited to high-speed ferries 

in motion. This working group was requested to 

• gather information internationally about experiences 

with high-speed ferries 


32

Guidelines for Managing Wake Wash from High ... - PIANC USA

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