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SHIPBUILDING & EQUIPMENT | PROPULSION & MANOEUVRING TECHNOLOGY
Improving propulsion effi ciency
PROMAS Shipowners today are very aware of the energy effi ciency of their vessels. While fuel
costs are a major aspect of the operating expenses of most ships, the reduction of emissions is
becoming even more crucial. With Promas (Propulsion Manoeuvring System), Rolls-Royce is
offering an innovative system for the increase of propulsion effi ciency.
Jonas Bäckström
Raising propulsive effi ciency by improving
the rudder and propeller
performance, and the interactions
between them, is a valid way of reducing
the fuel consumption and thus the CO 2
emissions.
When Rolls-Royce introduced Promas
(Propulsion Manoeuvring System) after
several years of development to the market
in 2007, it pointed out the signifi cant fuel
savings possible from installing it.
Benefi ts have been recognised, and systems
have been installed both on newbuildings
and retrofi ts for a variety of types of ship.
System description
Promas consists of a full-spade rudder with
a twisted profi le, a bulb integrated with
the rudder facing a hubcap on the propeller,
and propeller blades optimised for
the new hydrodynamic conditions. These
components form a hydrodynamically integrated
system from one single supplier
that improves the overall propulsive effi -
ciency compared with a typical propeller
and rudder combination.
The improvement in effi ciency is achieved
by several components. A twisted rudder
shape adapts the rudder to the rotation
24 Ship & Offshore | 2011 | N o 1
of the propeller slipstream, giving a lower
drag and better recovery of swirl energy
in the slipstream. For low speed manoeuvring,
the cavitation-free steering angle
range is also extended. The rudder bulb
reduces hub vortex losses, and also has a
benefi cial effect on the wake fi eld. This is
enhanced by the hubcap, which acts as a
hydrodynamic fairing cover. A different
design of the propeller blade is also used,
rebalancing the loading pattern on various
regions of the blade. This improves the
propeller effi ciency allowing fuel savings
to be made without increasing propeller
induced noise and vibration. Best results
are achieved on blunt single screw vessels
with a block coeffi cient greater than 0.8
and a design speed in the 14 to 18 knot
range. Effi ciency increase can be as much
as 6% to 9% compared with conventional
solutions. Faster and slenderer single screw
vessels such as car carriers can reach an effi
ciency increase of 2% to 5%. In a welldesigned
twin screw vessel there are less
improvements to be had, but even a gain
of 1% to 3% can represent a substantial
potential for savings. Since the additional
costs of Promas compared to a standard
propeller and rudder are reasonable, in-
stallations on many types of bulk carriers
and product/chemical tankers will have a
pay-back time of less than two years.
With exhaust emissions now in focus, a
reduction in fuel consumption can represent
a useful contribution both to cutting
CO 2 emissions directly and reducing the
amount of other pollutants.
Installations of Promas
The fi rst contract for Promas comprised
two shipsets for 33,500dwt bulk carriers
built in China for Kristian Jebsen. These
were based on a 5.2m propeller diameter.
Since then the range of applications has
widened to RoPax ferries and pure car and
truck carriers currently under construction,
a ferry with an innovative Rolls-Royce propulsion
solution combining Promas with
Azipull azimuth thrusters, and also retrofi
ts for an existing ferry and several cruise
ships.
Azipull, a new Ulstein Aquamaster azimuth
thruster from Rolls-Royce, uses a
pulling propeller ahead of the streamlined
leg and lower gear house, and a simple
gear drive transmission.
Two RoPax ferries for Fjord Line will have
Rolls-Royce propulsion systems, stabilisers