The Performance, Safety and Production Benefits of SPS Structures ...

The elastomer, as a two-part liquid, is injected intoclosed cavities formed by steel plates and perimeter bars(not shown in Figure 2.1) that are welded or glued toboth plates. To obtain a bond strength greater than of 6MPa once cured, the plates are grit blasted and need to beclean, free of contaminants and dry when the elastomer isinjected.A summary of the technology development undertaken todate and future development work is given in AppendixA.There is increasing interest in new constructionapplications. Ship operators are keen to take advantageof the benefits in improved lifetime performance,reduced maintenance and structural simplicity. An SPSdesign of a Rhine river barge is currently undergoingclass approval; and a prototype service barge for BritishWaterways has been completed and is undergoing trialsas part of a major fleet replacement project. SPS is alsogaining wider use in specific components on ships, wheresome of the unique properties such as fire protection andnoise attenuation are exploited.2.2 RECENT APPLICATIONS OF SPSSPS has found many applications in both civil andmarine industries. Recent projects include a replacementhighways bridge in Canada, where SPS was used toreplace a concrete deck, thus allowing the capacity of thebridge to be increased without upgrading the foundationsand substructure.Figure 2.4 Newbuild RoRo Ferry Funnel CasingsFigure 2.2 Indented Bulk Carrier Tank TopIn the marine industry much of the experience to date hasbeen in deck re-instatements of vehicle ferries, offshoresupport vessels and bulk carriers. Figure 2.2 shows thetank top of a bulk carrier that has suffered extremeindentation of the plating due impact from heavy cargoesand grab damage. The tank top plating was repairedusing an SPS Overlay which returned the structure to a“better than new” condition, as shown in figure 2.3.After 6 months’ service the repaired plating has sufferedvirtually no significant indentation under the sameoperating conditions. The tank top remains flat and even,allowing faster unloading and more efficient cleaning ofthe hold, thus speeding up the turn-round time andimproving the readiness for the next cargo.Figure 2.3 SPS Overlay Repair on Bulk Carrier TankTopIn 2003 Flensburger Schiffbau Gesellschaft commencedthe fitting of SPS panels in the funnel casings of a seriesof new ro-ro vessels (Figure 2.4). The SPS panels wereselected over conventional steel because significantspace savings were required to house machinery andequipment in a confined space. They are approved toA60 standard, with no additional insulation; and this inassociation with the elimination of secondary stiffenersmet the requirements for the application. The panels arestiff, easy to erect and significantly flatter than equivalentstiffened steel panels.A potential application for SPS is the “double hulling” ofexisting single hull vessels. A scheme has beendeveloped which uses pre-fabricated SPS panels to formthe inner hull plating. Use of SPS in this applicationhelps maximise cargo carrying capacity by keeping theinternal structure of the inner hull to a minimum. Tominimise the impact of time-out-of-service, IE’s solutioninvolves dropping the large panel sections through slotsmade in the existing deck or outer hull as shown inFigure 2.5.Other newbuild development projects include:• UR S21 compliant hatch covers: IE has developedhatch cover designs for panamax and capesize bulkcarriers. SPS provides an ideal solution to the newrequirements, as it has a high resistance to theincreased pressures and impact loads anticipated bythe new regulations. The simplified structure gives2

hatch covers that are structurally efficient and easyto manufacture.• Lightweight vehicle decks for dedicated vehiclecarriers: IE is working with industry partners todevelop SPS deck structures that are efficient bothstructurally and in use of space.Figure 3.1 Typical Section Through aDouble Hulled VLCCFigure 2.5 Use of SPS Panels to “Double-Hull” existingSingle Hull Tankers• Kawasaki Ship Building Corporation and IE aredeveloping SPS scantlings for the revolutionary SeaArrow bow. This innovative application of SPSwill provide a structure that will resist high impactloads from the sea, but will collapse in a controlledmanner in a collision. This will minimise overalldamage to both vessels and reduce the risk offlooding and loss of cargo.• IE has commissioned a study by StrathclydeUniversity, which investigates the economics ofusing SPS in the production of superstructures. Theinitial results show that labour costs for constructionusing pre-fabricated SPS panels can be reduced byover 50% against a conventional all-steel alternative.3. THE APPLICATION OF SPS TO DOUBLEHULL TANKERS3.1 BACKGROUND TO DOUBLE HULLTANKERSThe tank configuration of double hull tankers is nowfamiliar to the marine industry. Figure 3.1 shows atypical cross section through a double hull VLCC. Theresulting structure is based entirely on conventional shipconstruction concepts, with transverse web frames thatsupport stiffened plate panels for the inner and outerhulls. In the example shown there are approximately 300longitudinal stiffeners, each of which has to pass throughevery transverse web frame and bulkhead leading to15,000 or more intersections over the cargo region alone.The transition from single to double hulled vessels hasbeen driven by the imperatives of safety andenvironmental protection. The paradox is that theresulting ships are more complex than before, with asubstantial increase in the number of fatigue andcorrosion prone details, where risk of initiating structuralfailure can occur. As well as the basic requirement fortankers to have double hulls, there are now additionalregulatory measures stipulating increased survey andmaintenance (including access for inspection) on tankers.It has been argued that similar standards of inspectionand maintenance of single hulled ships would haveresulted in a similar improvement to safety, but at alower cost.In light of recent incidents involving tankers, especiallyolder single hull ships, it is clear that improvements intanker safety are important and urgently required.However, the fact remains that tankers are now morecostly to build and maintain than ever before.3.2 DESIGN ISSUES FOR CONVENTIONALSTEEL DESIGNSFrom the point of view of hull design, the ideal ship:• Has a structure which is sympathetic in terms ofconstruction – simple and easy to build• Requires little through-life maintenance• Suffers little or no corrosion• Has a minimum of breakdown in coatings• Suffers no cracking or other structural problems• Does not unduly vibrateSince the 1960s considerable experience has beenaccumulated in service performance of tanker designswhich have grown in size, often through a process ofextrapolation of structural arrangements.Through the 1970s, ‘80s and ‘90s, advances incomputing technology have enabled naval architects togain a better understanding of dynamic loads from wavesand ship motions, along with the importance of detaildesign, structural alignment and construction quality.Design processes have improved and lessons from3

construction related failures and insufficient maintenancecontinue to be addressed.In the early days of double hull tankers there was littleknowledge on which to draw, other than the experienceof single hulled tankers. Whilst this was extensive, theindustry was unsure how it would extrapolate to doublehulled vessels.and 3.4. Such failures had been experienced on singlehull tankers and much work in the marine industry hasbeen undertaken to understand and avoid such problems.3.2(a)Early Concerns of Double Hulled TankersFollowing the introduction of OPA90, it became clearthat double hulled tankers would supersede single hulldesigns. Concerns were raised about the universaladoption of a standard requiring tankers to be of doublehull construction, many of which centred around theconsequences of an accident involving a double hullvessel, compared to that of a single hull.Figure 3.2 Critical Areas for Fatigue and StructuralFailures on Double Hulled TankersAMSA has recently published a brief summarycomparison of single and double hull tankers (Ref 1),which gives a very clear description of the merits anddisadvantages of double hulled vessels. These includeoil outflow and considerations of hydrostatic balancefollowing collisions and grounding. The difficulties ofsalvaging a double hulled vessel due to flooding and lostbuoyancy following a grounding incident are alsoaddressed. The intact and damaged stability of doublehulled tankers was also questioned, due to concerns overthe raised centre of gravity associated with doublebottom tanks and the greater free surfaces of wide tanks.Other concerns centred around structural issues and werelegitimately raised in light of the experience borne outover the previous 20 to 30 years. Double hulled tankershave a high level of structural complexity, the number ofstructural intersections is almost twice that of anequivalent size single hull ship. Leakages of cargo intothe ballast spaces from cracks in the inner hull structurewere seen as a major risk. Fatigue and corrosion werehighlighted as potential causes of such failures.Fatigue:The well documented service histories of single hulltankers were used to highlight potential areas for fatigueproblems. Figure 3.2 shows the areas that are critical forfatigue on double hulled tankers. These includeconnections of inner hull plating at the upper and lowerintersections of the sloping hopper, connections at thetoes of brackets and stringers and the intersections ofsecondary longitudinal stiffeners with transversemembers.Secondary stiffeners and their associated intersectiondetails are well known sources of structural problems.Depending on their location, geometric configuration andconstruction, a combination of service loads, residualstresses and corrosion can result in coating breakdownand fatigue cracks. This can lead to ongoing propagationand eventual structural failure as shown in Figures 3.3Figure 3.3 Typical Fatigue Crack Found on Side ShellLongitudinal Stiffeners of Single Hull TankersUse of higher tensile steel has also contributed to fatiguefailures. Apart from fatigue lives being reduced by ageneral increase in working stresses associated withreduced scantlings, problems have also been encounteredwith increased residual stresses introduced duringconstruction. These arise in areas such as stiffenerintersections, where a welding sequence has createdresidual stresses that are difficult to “relieve” in HT steel.When using this material, care is required with detaildesign and with construction processes.Figure 3.4 Early Experiences of Fatigue Damage Led toCrack Propagation and Larger Structural Failure4

Corrosion:Undetected corrosion has been a major cause of some ofthe most noteworthy marine disasters. A paper producedby OCIMF (Ref 2) provides a very concise summary ofthe potential problems facing the operators of doublehulled tankers. In particular it highlights the difficultiesof coating, inspecting and maintaining the ballast spaces,which in conventional steel designs are cellular, with acomplex arrangement of internal stiffeners, brackets andassociated structural details. In today’s double hulledtankers it is common practice to provide full coating ofthe ballast tanks, but to coat only the bottoms of cargotanks. A second paper by OCIMF (Ref 3) provides avery clear view of the various sources of corrosionaffecting tankers and their influence on corrosion rates.These include coatings, washing processes, sulphurcontent of cargo, inert gas quality, construction materialsand others.It is clear that control of corrosion plays a major part inthe safe operation and maintenance of a double hulledtanker. Conventional steel designs, with their inherentcomplexity are costly to protect and maintain. This isdue to the large surface areas, difficulty of access andlarge numbers of points for potential initiation of coatingbreakdown.Experience of double hulled tankers to date:To date there is little documented operational experienceon the structural performance of double hulled tankers.Anecdotal evidence suggests that the experience has sofar been satisfactory. Whilst there are cases of minorstructural failures, such as fatigue cracks in stiffenerintersections and inner hull connections with the slopinghopper, these have been found and addressed with nomajor incidents. Regular inspection and maintenanceremains a clear necessity.A paper by Bergesen, produced in 2000 (Ref 4) providesa comprehensive summary of experience in operatingthree double hulled VLCCs. The paper concludes with anumber of measures for protecting both ballast and cargotanks from corrosion. The paper also notes that waveloads on the bow have resulted in local buckling ofinternal structure and hull plating deformation, resultingin a “starved horse” appearance.Today’s double hulled tankers are not known to besuffering from structural failures. However, the effortrequired to design and construct intersections with goodservice performance adds considerably to the productioncost and the problems have not been completelyeliminated.3.3 USE OF SPS IN DOUBLE HULLED TANKERSIntelligent Engineering believes that SPS technology willprovide improved safety through greater resistance toimpact, collisions, fire and explosion. Furthermore, thestructural simplification that SPS provides will givecommercial benefits in terms of reduced costs forproduction, inspection and lifetime maintenance. Byremoving secondary stiffeners from the structure, thehigh risk areas of coating breakdown, acceleratedcorrosion and fatigue cracking are eliminated.3.3(a)Design principles in using SPSUsing SPS in ship structures requires a fresh view ondesign, especially in areas of structural intersections.Basic longitudinal strength is assessed in a similar way tocurrent established methods, using classic navalarchitecture theory and standard hull section propertycalculations. With SPS structures, the continuous innerand outer face plates of the composite sandwich areincluded in the section properties, but the elastomer coreis not included in the calculation. Depending on localstrength requirements, a portion of the steel area, aboutthe neutral axis, may be redistributed to the deck andouter hull to maintain the section modulus whilereducing overall weight.SPS design for local strength involves a new approach.Conventional ship structures are commonly designedusing established ‘empirical’ classification society rules.These do not yet exist for SPS structures, which behaveas true composite materials with isotropic properties.Design assessment rules for sandwich plate shipstructures are being developed by Lloyd’s Register andare expected in draft form in 2005.The scantlings of SPS plating are generally in the rangeof 3 mm to 8 mm for the steel face plates and 20 mm to50 mm for the core thickness. The required scantlingsare a function of the loads and spacing of the supportingframing, and are currently determined by direct designcalculations, using normal stress criteria for yield andshear. Corrosion margins are added to the face plates, asrequired.SPS panels are very stable, since the stiff elastomer coreprevents local buckling effects. Semi-empiricalequations have been developed to determine the in-planeload carrying capacity for any combination of transverseloads. These have been verified using full scale tests andnon-linear finite element analyses. Current designpractice uses finite element analysis to check the in-planeload carrying capacity of SPS panels. This is achievedwith models using solid or layered shell elements toaccount for both material and geometric non-linearity.The maximum transverse framing should be in the rangebetween 3.2 to 4.0 m. SPS plating should have an aspectratio (the ratio of length of the long to short plandimension) between 1.4 and 1.7, to produce an economicplate with the maximum buckling strength. SPS panelsshould be arranged so that the largest dimension isaligned along the length of the ship.5

SPS structures have a high inherent resistance to fatigue.The bond between the elastomer core and the face platesis virtually fatigue insensitive. Joints between SPSpanels and connections of SPS panels to supportingstructure have a good inherent resistance and may bechecked using standard fatigue assessment techniquesalready used in the marine industry.3.3(b) Summary of SPS applications in double hulltankersSPS can replace traditional stiffened plating in the maindeck, inner and outer hull and longitudinal bulkheads ondouble hull tankers, to provide both construction andoperational benefits. Without secondary stiffening, themajority of fatigue and corrosion prone details areadvantageously eliminated; and with suitably optimisedproduction techniques there are many advantages forconstruction in terms of cost and time.At the beginning of this section a list of needs for theideal ship design were suggested. In answer to thesepoints, SPS has unique properties that offer distinctadvantages over conventional designs:• The structural simplification afforded by SPSprovides the opportunity to eliminate secondarystiffeners and their associated connections withprimary structures such as transverse web frames andbulkheads.• In comparison to its all-steel counterpart, thefabrication of an SPS structure has substantially lesslabour input, reduced weld lengths and volumes,reduced surface areas for coating and reduced hullweight.• The sandwich plate dissipates highly localisedbending strains in the plating to the primary structuralframing, thus eliminating hard spots associated withcoating breakdown at stiffener intersections.• The elimination of stiffeners and connectionsremoves a source of high risk for structural failures.The impact resistance of SPS also provides improvedperformance against extreme event loading such aswave impact, slamming, grounding and collisions.• The reduced surface area of internal structures andclutter-free layout enable faster and better coatingapplication. Since paint coatings will be easier toapply and the amount of free edges and cornersgreatly reduced, the reliability of coatings will begreatly enhanced with SPS structures. This is a highcost aspect of ship maintenance, and with a currentcost of up to $35 per square meter for blasting,cleaning and paint application, there are significantlife-time savings to be made.• Inspection and maintenance are greatly reduced inSPS structures. Tank inspection will be faster andmore reliable. With less cluttered structural layouts,tank drainage and cleaning will be faster and moreeffective and will help avoid the build up of silt andmud in ballast tanks.• Permanent deformation of conventional stiffenedpanels is common and often requires steelreplacements and strengthening during a ship’s life.The ability of SPS to absorb damage from waveimpact, grounding and collisions whilst resistingperforation of the hull, will in many cases avoidflooding and enable faster and safer recovery of agrounded ship.• SPS also allows different metals to be used on eitherside of the sandwich. This offers new solutions tochemical tanker designers, by allowing a costeffective means of constructing tanks with stainlesssteel internal surfaces.In addition to hull structures, SPS will find many otherapplications in ships. Inherent properties, such as fireresistance and the attenuation of noise and vibration,mean that SPS will have useful applications in key areassuch as accommodation and machinery spaces. SPS mayalso provide solutions for double-hulling of existingsingle skin ships where the elimination of secondarystiffeners will minimise the impact on access to the innerhull, and hence maximise cargo carrying capacity.4. DESIGN STUDY OF SMALL PRODUCTSTANKER4.1 BACKGROUNDAs part of Intelligent Engineering’s ongoingdevelopment programme, a design study was undertakenfor the cargo tank section of a 14k dwt double-hulledproducts tanker.A conventional steel design for the ship was used as areference point for the SPS design study and the resultsare presented here in summary form. The objective ofthe work was to investigate the feasibility of using SPSconstruction on a double hull tanker and to makecomparisons between the two designs, with a view toassessing and quantifying the benefits of SPSconstruction. Lloyd’s Register’s Rules and ShipRightDirect Calculation Procedures were used as a basis forscantling design.SPS can replace the traditional stiffened plate of the maindeck, inner and outer side shell, double bottom andcentreline longitudinal bulkhead of the tanker to provideboth construction and operational benefits. Withoutsecondary stiffening, the majority of fatigue andcorrosion prone details are advantageously eliminated.The sandwich plate dissipates highly localised bendingstrains in the plating into the primary structural framing,thus eliminating the ‘hard spots’ associated with coatingbreakdown at stiffener intersections.In comparison to its all-steel counterpart, the fabricationof an SPS structure has substantially less labour input,reduced weld lengths and volumes, reduced surface areasfor coating in combination with improved coating6

application, and reduced hull weight. In operation thesmooth surfaces of SPS plating allow for better ballasttank drainage and cleaning The principle dimensions ofthe tanker are listed in Table 4.1.between the main web frames. Figure 4.2 shows askeletal view of the conventional steel mid-section; theinner bottom, inner skin and longitudinal bulkhead areremoved to provide a clear view of the structure.Table 4.1 Principal DimensionsLength overall: 144.0 mLength between perpendiculars: 134.5 mBreadth: 21.50 mDepth: 11.30 mDraft: 7.65 mDeadweight: 14000 tonnesCargo capacity (98%): 16660 m 3Ballast capacity: 6610 m 34.2 DESCRIPTION OF CONVENTIONAL ANDSPS DESIGNDuring the design study both the conventional steel andSPS designs underwent several iterations to optimise thescantlings, following the results of the FE analysescarried out using the ShipRight design assessmentprocedures. The following information is based on thefinal set of scantlings determined.Figure 4.2 Steel Tanker Structural LayoutDuring the design study it was determined that the SPSdesign could use a 3.5m spacing of the web frames. Allsecondary longitudinal stiffeners were eliminated fromthe structure. Double bottom girders have beenintroduced, along with an additional intermediate stringeron the side structure and centreline bulkhead. Theincreased floor spacing along with the additional girdersFigure 4.3 SPS Tanker Structural LayoutFigure 4.1 Sketch of Midship Section(14k dwt Products Tanker)The conventional steel design uses a standardconfiguration with a centreline bulkhead and “J” tankscovering the side structure and double bottom. The tanktop has a small rise of floor to aid tank drainage andstripping. Figure 4.1 shows the layout of the midshipsection, including basic dimensions. The transverseframe spacing is 3m and the longitudinal stiffenerspacing is 675mm. There are no intermediatelongitudinal girders between the centreline bulkhead andthe girders beneath the hopper side knuckle on the innerbottom. In the bilge area, additional webs are providedand stringers help maintain optimum panel sizes for theSPS plating on the external and internal hull plating.Finally, as the secondary stiffeners have been eliminatedand access through the inner bottom is much improved,the height of the double bottom can be reduced by600mm, which has the additional advantage of increasingthe cargo capacity by around 6%. Figure 4.3 shows asimilar skeletal view of the SPS hull section.Table 4.2 Comparison of ScantlingsConventionalStructural Component SteelScantlingsInner Plate14 mmBottom &HopperLongitudinals HP 320x12Outer Plate14 mmBottom Keel Plate 16 mmSPS ScantlingsSPS 7-50-7.5SPS 7-50-77

InnerShellOuterShellCentrelineBulkheadSideSideLongitudinalsLower StrakeMiddle StrakeUpper StrakeLower StrakeMiddle StrakeUpper StrakeStiffenersLower StrakeUpper StrakeHP 280x1214 mm13 mm12 mm15 mm14 mm13 mmHP 220x1015 mm13 mmSPS 6-40-6(5700mm a/b)SPS 5-35-5SPS 6-30-6(5700mm a/b)Main Deck Plate11 mmSPS 6-25-6Longitudinals HP 220x10Transverse Web Frame Spacing 3000mm 3500mmTable 4.3 Summary of Hull Girder Section PropertiesHull Girder Section Modulus, m 3Location Conventional SteelScantlingsSPS ScantlingsKeel 7.720 6.376Tank Top 12.734 10.352Main Deck 5.255 4.534Table 4.2 lists the basic scantlings of both designs andprovides a comparison of the two different structures andTable 4.3 gives a summary of hull girder sectionproperties.4.3 DESIGN ASSESSMENT SUMMARYFE analysis of the mid-section was carried out usingLR’s ShipRight direct calculation procedures, using FEmodels as shown in Figure 4.4. An example set of thetank design pressures used in the FE analysis is given inTable 4.4.StructuralComponentTable 4.4 Example Tank Design PressuresPressure(kPa)Tank Top 95OuterBottomInner SideShellOuter SideShell949394Main Deck 24LongitudinalBulkhead95CommentPressure at centreline assuming tank at98% capacity and relatively heavy cargo(specific gravity = 1.0)Pressure equal to draft (T) plus 0.5 timespassing wave height (h w)LR Direct Calculation Guidance Notes h w= 4.6x10 -2 L e -0.0044L = 3.42 mNote: Part 4, Chapter 9, Section 4, Table9.4.1 lists a design head for outer bottomh T2 = T + 0.5C w > 1.2T (T = 7.65 m,C w = 7.71x10 -2 L e -0.0044L = 5.74 m, 1.2T =9.18m)Pressure at centreline, assuming tank at98% capacity and relatively heavy cargo(specific gravity = 1.0)Pressure at baseline equal to outer bottomPressure reduces to h w at load waterline(LWL) and to zero at h w above LWL draftLR Part 3, Chapter 3, Section 5, Table3.5.1, h 2 = L/56Pressure at base of bulkhead equal to tanktop pressurePressure reduces to zero at the main deckThe hull section modulus at the main deck, keel and tanktop for the steel and SPS designs are listed in Table 4.3.The SPS deck and keel section moduli are 4.8% and7.5% less than the all-steel design. In comparison to theall-steel design the balance of material (ratio of deck tokeel moduli) about the neutral axis is improved in theSPS ship. The primary bending stresses have not beenevaluated since, at the time of the design study, the stillwater bending moments for the ship were not available.The results of the FE analysis were assessed against thestress criteria listed in Table 4.5 The stress comparisonof the two designs is summarised in Table 4.6Table 4.5 Double Hull Tanker - Allowable StressCriteriaStructuralMemberApplied LoadingStressComponentMaximumAllowable Stress,MPaGradeGeneralAHull girder loadsσ 175 / k L 175Hull Girder (still water & wavecombined)τ 110 / k L 110Local loads and hullgirder loadsσ 216 / k 216Local loads σ e 177 / k 177Local loadsPlating 1(in line with hull σ x 108 / k 108girder stress)Local loads(transverse to hull σ y 147 / k 147girder stress)Longitudinal Local loads σ 100 / k 100Stiffeners Local loads τ 83 / k 831. Primary structure plating including inner and outer hull andlongitudinal bulkheadsNotes: • σ e = von Mises equivalent stress• σ = bending stress• τ = average shear stress over depth of web plate• For LR Grade A steel: k = 1.0, k L = 1.0Table 4.6 Analysis Stress Results – Local Pressure LoadsStructuralMemberStressQuantityAllowableStressCriteriaStress, MPaAll-SteelScantlingsSPSσ x 108 88 106Tank Top Plating σ y 147 128 118σ e 177 113 110Tank Top Stiffs σ x 100 87 -Outer BottomPlatingOuter BottomStiffenersInner Side ShellPlatingOuter Side ShellPlatingσ x 108 89 102σ y 147 124 119σ e 177 115 111σ x 100 103 -σ x 108 136 * 86σ y 147 84 112σ e 177 123 102σ x 108 86 88σ y 147 59 91σ e 177 78 848

Main Deck σ x 108 - 104Plating σ y 147 - 31σ x 108 - 109Longitudinalσ y 147 - 138Bulkhead Platingσ e 177 - 131Note: * local peak stress at the location of plate thickness change,anticipated that an extension of thicker lower plate by 200 mmremoves high stress.4.4 QUANTITY COMPARISONSFollowing the design study, a comparison of the twooptimised designs was made. A 15m length of the midsectionwas used and the comparisons for weight, surfacearea and other important parameters are summarised inTables 4.7 and 4.8.StructureTable 4.7 Weight ComparisonWeight, tonnesConventionalSteelScantlingsSPSScantlingsDifferencetonnes %Double Bottom 133.4 116.8 -16.6 -12.4Side Shell 102.1 109.9 +7.8 +7.6Longitudinal24.0 22.4 -1.6 -6.6BulkheadMain Deck 50.3 52.0 +1.7 +3.4Totals 309.8 301.1 8.7 -2.8Table 4.8 Other Comparisons Between Conventional andSPS DesignsStructureWeight, tonnesConventionalSteelScantlingsSPSScantlingsDifferenceDelta %Painted SurfaceArea, m 2 6280 5025 1255 -20# StiffenerIntersections310 10 310 -97Weld Volume,cm 3 215000 93000 122000 -574.5 CONCLUSIONS AND FURTHER WORKThe design study verifies that SPS technology can beapplied to a double hull tanker and assessed successfullyagainst industry-standard assessment procedures. Thestudy demonstrates that SPS offers a number of benefitsto the design of double hull tankers:• The weight of the SPS design is slightly less than theconventional steel design. The weight comparisonincludes the mass of elastomer core.• The elimination of secondary stiffeners provides a20% reduction in internal surface area and representsa major saving in terms of paint volume, ease andquality of application.• The weld volume reduction of 50% is achievedthrough the elimination of stiffeners and theassociated intersections with transverse primarystructure. This represents significant savings inproduction time and cost.• The SPS design has an uncluttered internalarrangement of structure and can accommodate areduced double bottom height of up to 600mmwithout compromising access for inspection. Thisprovides a potential for an additional 6% of cargocarrying capacity.• Inspection and maintenance are greatly enhanced forthe SPS design, with easier access, faster inspectionand significantly fewer locations with potential forcoating breakdown and structural failure.There is further work to be completed. The designassessment needs to include a more complete review oflongitudinal strength and verification by a classificationsociety. There is yet more scope for optimisation of theSPS structure and further gains in structural efficiencyare expected.5. PRODUCTION METHODOLOGIESThe design study summarised in Section 4 above showsthat SPS structures can be designed with weight savingsand strength equivalence to conventional ship structures.Production of SPS panels involves some key processeswhich are unique to SPS technology.• The internal surfaces of the steel cavities needpreparation to achieve the required surface roughnessof at least 60 microns and a surface cleanliness of SA2 ½. The preparation uses standard steel fabricationpractices and is best achieved using steel grit orcorundum, which have suitably hard particles and anangular profile.• The internal cavities must be clean and dry prior toinjection. They must also be airtight in order toprevent elastomer leakages during injection.• SPS panels are restrained during injection and curing.This ensures that the face plates remain flat. On aproduction line this may be achieved using simpleportable frames which can be clamped at the edges.• The injection process usually takes around 8 to 12minutes. At this stage the temperature of the panelsshould be no less than 20°C.To realise the maximum commercial benefit of SPStechnology, successful integration of SPS into theproduction lines of shipyards is essential. Workcontinues with yards in Europe, Asia and N. America toimplement SPS into shipyard construction processes.Currently there are two main options for production ofSPS structures:• Use of pre-fabricated SPS panels delivered to theproduction line• Integration of SPS panel fabrication within theproduction lineIn the first option SPS panels are pre-fabricated to thedesigner’s specification and dimensions, away from theproduction line. This option allows for SPS panels to be9

pre-fabricated at a single site for distribution to manydifferent locations. The advantages of this method is thata specialised facility using fast, modern productiontechniques can produce panels with varying designparameters, rapidly and in great numbers. Theeconomies of scale of such plant mean that theproduction costs are very low for each unit area ofstructure. This methodology is well suited to the casewhere small ship yards require SPS components to beincluded in a new vessel, or specialist fabricatorsbuilding accommodation blocks, hatch covers and othership components for delivery as complete blocks tolarger ship yards.In the second option larger areas of SPS structure arefabricated and injected with polymer as an integratedprocess on the production line. A typical ship productionfacility would use a process similar to the following:• Steel plates are cleaned and prepared as required andbrought to the production line where they are joinedusing automated welding to create large panels.• The large panels are moved along the line to a pointwhere secondary stiffeners are introduced, positionedand welded to the plating. Although automatedwelding techniques are employed, this process can bevery lengthy due to the sheer number of secondarystiffeners and the amount of welding to be deposited.• Once the secondary stiffeners are attached, primarystructures (e.g. floors, webs, girders and stringers)which have already been prepared with openings andcut-outs for the secondary stiffeners are introduced tothe production line. These are attached to the largeplate panel using automated welding, but in additionthe intersections of the primary and secondarystructure need to be carefully welded in a sequencewhich minimises the risk of distortions and residualstresses. This is a very time consuming part of theproduction process and one where great attention toquality is required. Not only do the intersectionscreate difficult areas for automated welding to beused, but lugs and collars can add complexity andtime to the process.• Once the primary structure is added, the panelsbecome 3D sub-assemblies which can then be erectedand assembled into larger blocks ready for erectinginto the main ship structure.In integrating SPS into a production line similar to theabove, the process will be modified as follows.• Steel plates are cleaned and prepared as required andbrought to the production line where they are joinedusing automated welding to create large panels thatwill form either the inner or outer SPS face plate.• The inner SPS face plate is moved along the line tothe point where primary structures (e.g. floors, webs,girders and stringers) which have already beenprepared with access openings and cut-outs fordrainage, are introduced to the production line. Nosecondary stiffeners are required, eliminating manymetres of welding and the complexity ofintersections.• The outer SPS face plate is moved along the line tothe point where the perimeter bars are welded to theedges of the plate and SPS spacers are added toprovide the necessary control over the core depth.Once this process is complete, the inner SPS faceplate (complete with primary structure) is placed overthe outer SPS face plate and welded to the perimeterbars to form an air-tight cavity ready for theelastomer injection.• The complete panel is moved along the line to the“injection bay” where the panel is injected withelastomer resin. Care is needed at this point tocontrol the temperature of the panel during the curingstage of the elastomer and also to restrain the panelsas described above.The above are only outline descriptions of the processesand do not enter into detail, but the important point isthat the SPS production process eliminates the timeconsuming step of introducing the secondary stiffenersand the associated intersections with primary structure.Initial estimates have indicated that the amount of timespent in attaching secondary stiffeners may be as high asdouble that required to complete the steps involving SPScavity forming and elastomer injection. This can save upto 8 hours elapsed time in the production of a singlepanel sub-assembly.6. INSPECTION AND MAINTENANCEThe simplified structures made possible with SPStechnology offer benefits for inspection and maintenance.The ballast tanks of conventional double hull tankershave significant internal structure, often with manythousands of intersections.A principal concern for double hull tankers is theapplication, inspection and maintenance of coatings inthe ballast tanks. In the 14k products tanker exampleoutlined in Section 3, the reduced surface area of coatingrepresents approximately 20% of the ballast tank internalarea. The elimination of secondary stiffeners also meansthe elimination of edges and corners where coating breakdown is initiated.Inspection of inner hull spaces is very time consuming,due to the cellular nature of the space and the necessityof inspecting the intersections. This often requiresclimbing over each longitudinal stiffener and having toinspect under flanges using torches. Where coatingbreakdown is found, it is necessary to note the location;and remedial action can be laborious, time consumingand expensive. SPS structures are inherently less costlyto apply original coatings, less susceptible to coatingbreakdown and easier to inspect and re-coat.10

Repair of damaged SPS panels is a four-step processrequiring cutting and removal of the damaged steel plate,routing of elastomer, installation of a new steel plate andinjection of elastomer. The procedure to repair adamaged SPS section is illustrated in Figure 6.1.Top Steel FaceBacking BarsSteps 3 and 4: SPS ReinstatementOnce the repair cavity is dry and cleared of any debris,backing bars are tack welded in place. The replacementplate is welded in place with a square butt weld. Newelastomer is injected into the repair cavity and theinjection port and vent holes are sealed. The newlyinjected elastomer bonds to the existing elastomer.ElastomerTop Steel FaceElastomerTop Steel FaceElastomerSquare Groove ButtBottom SteelFaceBottom SteelFaceTop Steel FaceVenting PortInjection PortBottom SteelFace7. CONCLUSIONSThis paper gives an overview of SPS technology and itspotential application to double hull tankers. A designstudy undertaken by Intelligent Engineering is used todemonstrate the viability of using SPS for the hullstructure of a small products tanker.SPS technology is finding a wide application in both thecivil and marine industries. The number of marineapplications is growing and new construction projectsinclude components such as decks and machinerycasings, as well as complete hulls for inland waterwaysvessels. SPS technology has a number of clear benefitsto offer the marine industry:Enhanced Safety and Environmental Protection• The energy absorption characteristics provideexcellent resistance to impact from collisions andgrounding. This is of particular relevance to doublehulled tankers, since the risk of hull perforation andsubsequent flooding is greatly reduced, aiding fastand safe recovery of ships.• Fire protection to A60 standard and above can beachieved with SPS panels. In many cases noadditional fire insulation is required.• SPS also provides resistance to blast and ballistics,enabling protection of key areas of the ship fromaccidental damage and from deliberate attack fromterrorism or piracy.Figure 6.1 SPS Repair ProcedureStep 1: Cut Steel Face platesThe damaged SPS steel facing plate is cold cut, hydro cutor back gouged to free it from the adjacent undamagedplate. The damaged plate is removed by applyingsufficient heat to soften the elastomer to allow it to befreed. The cutting methods may be cold cutting withsteel or carbide disks, air-carbon-arc gouging, or highpressure jet with a water/abrasive mixture.Step 2: Elastomer Removal from Damaged SectionThe elastomer is routed, ground or hydro-blasted to aminimum of 30mm from the cut edge. The methods forrouting/gouging may be hand-held power tools (routersand angle grinders) or high pressure water jet equipment.Reduced Costs• SPS enables the design of simpler structures and theelimination of secondary stiffeners and associatedconnection details.• The elimination of stiffeners can remove severalkilometres of welding and many thousands of squaremetres of internal surface area. Economies aretherefore available in construction and tank coating.• With efficient pre-fabrication of SPS panels (eitherthrough separate production of panels, or throughintegration of SPS structures to the production line),cost reductions are achievable.• Inspection and maintenance costs are reduced. SPSstructures are faster and simpler to inspect, and havefar fewer high risk locations for coating breakdown,corrosion and fatigue cracking.Improved Space Utilisation and Crew Comfort• SPS enables simpler structures. The lack of stiffenersimproves access and space utilisation.11

• The ability to provide fire protection with noadditional insulation helps minimise the impact oninternal spaces, especially in accommodation areas.• The noise and vibration attenuation properties of SPSoffer the ability to manage structure borne noise andimprove comfort for passengers and crew.8. REFERENCES1. AMSA, ‘Comparison of Single and Double HullTankers’, www.amsa.gov.au, 2001.2. OCIMF, ‘Double Hull Tankers – Are They TheAnswer?’ Oil Companies International MarineForum, 2003.3. OCIMF, ‘Factors Influencing Accelerated Corrosionof Cargo Oil Tanks’, Oil Companies InternationalMarine Forum, 1997.4. Tanker Structure Cooperative Forum (Bergesen),‘Experience With DH Tankers – An Owner’sViewpoint’, Shipbuilder’s Meeting in Tokyo October2000.9. AUTHORS’ BIOGRAPHYMartin Brooking is the Engineering Design Director forIntelligent Engineering Ltd. Previously EuropeanMarine Business Manager at Lloyd’s Register, heoriginally trained as a ship surveyor and gainedexperience in both field surveying and plan approval oftankers. He has also worked in the Offshore Industry asa Consultant Engineer with WS Atkins Ltd and DNV-Veritec Ltd, where he gained particular experience inanalysing and solving fatigue problems on ships andoffshore structures.Stephen Kennedy, PhD (Alberta), P.Eng, TechnicalDirector and co-founder of Intelligent EngineeringLimited, is the inventor of the Sandwich Plate System.(SPS) on which he holds many patents. Previously aProfessor at Carleton University, Ottawa ON, hespecialized in the design and behaviour of steel structuresincluding buildings, bridges and ships. He is widelypublished and has carried out research for TransportCanada, the Canadian Coast Guard and the United StatesCoast Guard, the latter dealing with the inelasticbehaviour of icebreaker hulls. He focuses his attention onthe development of, obtaining regulatory approval forand licensing of SPS Technology.12

APPENDIXSPS TECHNOLOGY DEVELOPMENTMATERIAL CHARACTERISATIONThe polyurethane elastomer core is an engineered plasticthat has been developed by Elastogran GmbH inaccordance with Intelligent Engineering’s materialcharacterisation specification for the anticipated extremesof the full range of operating temperatures between -45ºCand +100ºC. Mechanical properties of the elastomer,including density, tensile strength (as illustrated in FigureA.1(a)), compressive strength, shear modulus andPoisson’s ratio were verified in accordance with theappropriate ASTM or DIN standards and are summarisedin Table A.1.Mechanical PropertiesThermal PropertiesTable A.1 Characteristic Elastomer Material PropertiesTest ResultsDensityρ e = 1150 kg/m 3Tensile BehaviourProperty -80 o C -60 o C -40 o C -20 o C 23 o C 60 o C 80 o CE (MPa) 3859 2924 1765 1164 874 436 248σ y(MPa)38.9 29.5 28.4 23.0 16.1 8.1 6.2ε u (%) 7.2 11.1 13.2 15.1 32.1 43.1 47.4Compressive BehaviourProperty -80 o C -60 o C -40 o C -20 o C 23 o C 60 o C 80 o CE (MPa) 3878 2813 1347 1166 765 501 336σ y(MPa)52.1 33.5 30.9 21.4 18.0 10.2 7.9Shear Modulus (Torsion Pendulum Test)Property-80 o C-60 o C -40 o C -20 o C 23 o C 60 o C 80 o CG(MPa)1386 955 559 429 285 180 135Poisson Ratioν = 0.36Thermal Expansion CoefficientProperty -30 o C -10 o C 10 o C 30 50 o C 70 o Co Cα (x10 -6 m/m·oC) 96.1 120.1 133.6 148 162.5 184.7.7Specific HeatProperty -20 o C 23 o C 60 o C 80 o Cc (J/kg·oC)1217 1414 1588 1687Thermal Conductivityk = 0.1774 W/m² o C (R-value/mm thickness = 0.032 o F·ft 2·h/Btu)STRUCTURAL BEHAVIOUR AND PERFORMANCEClassification rules commonly specify minimum plateslenderness parameters to preclude local failures becausesuch failures prevent the flexural and compressionmembers (stiffened steel plates, girders, transverses)from reaching their maximum strength. For the SPSsystem, in a parallel manner, a minimum bond strengthand a modulus of elasticity of the core material arerequired to preclude local failures and to limit sheardeformations in the core that reduce this strength. Thesevalues have been determined analytically and verified bytests.Bond at the interface between the core and face plates isrequired for composite action under normal operatingloads, which may include dynamic loading events likewave action or impact loads (grab or heavy cargo) thatoccur frequently; and must be maintained for the fullrange of normal operating temperatures. More than onethousand tests have been conducted in shear and directtension (direction of load transfer across the interface) onbond strength test specimens, as illustrated in FigureA.1(b), with a variety of surface preparations (primedsurface, commercial bonding agents, surface roughness,casting conditions, elastomer properties, ambienttemperatures, base metals, and on samples subject toadvanced corrosion, seawater and chemicals to determinethe bond strength for anticipated fabrication andoperating conditions. Based on the results of these tests,specifications for surface preparation and design valueshave been established.The characteristic flexural and compressive strength ofSPS plates was established by tests as illustrated inFigures A.1(c) and (e). Compression tests includedstocky columns, which gives cross sectional compressivestrength (no buckling) and more slender columns thatfailed by either inelastic or elastic global buckling. Thetests verify that SPS plates with a core modulus ofelasticity greater than the minimum specified can obtainthe flexural (plastic moment capacity) or compressivestrength without local buckling, de-lamination of the faceplates or any other local failure modes generallyassociated with laminates. Analytical predictions ofstrength calculated from commercially available finiteelement programs, verified against the test results, werein close correspondence with mean test-to-predictedratios of 0.98 and 1.05 and coefficients of variation lessthan 5% for flexure and compression respectively.Additional full-scale ultimate (proof) load tests, like thelashing pot test shown in Figure A.1(d), are conducted asrequired.The same finite element programs are being used forparametric model studies to develop design equations forClassification Rules for determining the scantlings forSPS ships and SPS ship components. IntelligentEngineering is currently working with Lloyd’s Registeron developing a set of rules and regulations for sandwichplate ship structures. Until these rules are available, SPSships can be designed and assessed by direct designcalculations, which establish equivalency to comparativesteel ships. Intelligent Engineering has receivedapprovals from major ship classification societies for theuse of SPS in new builds and the rehabilitation of shipswith over 26,000 m² of SPS decks, hulls, tank tops,bulkheads, bow fingers and funnel casings in service on30 projects.13

Stress, MPa9080706050403020100-80 o C-60 o C-40 o C-20 o C23 o C60 o C80 o C0 100000 200000 300000 400000 500000Strain, µε(a) elastomer tension coupon test(b) bond strength(c) flexural strength(d) lashing pot pull-out test(e) compressive strengthFigure A.1 Global and Local Strength(a) fatigue resistance of a block connection(b) salt water and chemical resistanceDisplacement, mm8steel6420-2-4-6SPS-80 500 1000 1500Time, ms(c) inherent vibration damping provided byvisco-elastic coreStand-off distance, m450400350300250200150100500steel platebimetallic SPSSPS0 15 30 45 60 75Angle, θ(d) ballistic resistanceFigure A.2 Improved Resistance14

Other performance characteristics that have beenestablished and quantified include:• Fatigue resistance (S-N curves) of the interface bondand welded connection details specifically developedto join prefabricated SPS plates (refer to FigureA.2(a)).• Salt water and chemical resistance of the elastomercore should it become exposed during the life of thestructure. Figure A.2(b) shows test samples fromone of four test series where sets of 30mm elastomercubes were completely immersed in typical chemicalspecies.• Vibration damping and structural borne noisetransmission Figure A.2(c) illustrates typicaldisplacement attenuation curves for SPS and steelplates subject to a single pulse. The inset pictureillustrates a standard vibration characterisation testconducted at BASF laboratories in Ludwigshafen.• Ballistic resistance limits for stiffened steel and SPSplates (all-steel and bi-metal) subject to standard7.62mm rounds are illustrated in Figure A.2(d). Thesetests were conducted by QINETIQ (formally DERA).FIRE RESISTANCE AND ENGINEERINGSPS has exceptional resistance to fire. It is an extremelyeffective barrier to heat, flame, smoke and toxic gases. Itwill contain a fire and prevent it spreading to adjacentcompartments, greatly limiting the growth of a firethroughout a structure. This has been demonstrated byan extensive series of full-scale deck panel and bulkheadtests, conducted in accordance with IMO (SOLAS)standards at independent fire laboratories. The MaritimeCoastguard Agency (MCA) co-developed the fire safetytest programme and has witnessed SPS fire tests. FigureA.3(a) shows the standard SOLAS stiffened steel deckpanel without structural fire protection. The plate isseverely distorted and the maximum surface temperatureincrease on the unexposed surface is +713ºC. The surfacetemperature on SPS plate with structural fire protection,shown in Figure A.3(b), is +3ºC. The correspondingtemperature on an insulated steel plate was +192ºC.(b) SPS 8-40-8 deck plateFigure A.3 Safety of Life at Sea – Enhanced FireResistanceThe steel face plates present a fully non-combustiblebarrier to a fire that may occur from either side and theelastomer core provides an extremely effective insulatoragainst heat from fires. If an SPS panel is directlyexposed to fire for an extended period then the elastomercore acts as sacrificial layer on the fire side (ablation)and gases from the elastomer surface vent into the fireside through temperature controlled pressure releasevalves. Only the exposed elastomer surface layer isaffected, the remaining elastomer and the elastomer-steelbonded surface on the unexposed surface are unaffected.SPS can provide greater insulation than conventionalarrangements. After the standard 60-minute fire test(945ºC at one hour), the average temperature increase onthe unexposed surface of a SPS 4-25-4 plate withoutstructural fire protection was 96ºC. The correspondingincrease for a SPS 8-40-8 plate was 24ºC. For an A-60barrier, SOLAS requires this increase to be no greaterthan 140ºC. With SPS plates the unexposed surfaceremains cooler longer, extending containment of the fire,and allowing more time for people to escape and firefighters to fight the fire. Based on the experimentalevidence and fire engineering analyses conducted withthe University of Strathclyde, the MCA has submitted thefollowing information papers to the IMO on theperformance and behaviour of SPS when subjected tofire loads.• Equivalence of a New Composite Structural Materialto Steel in Maritime Structures SPS (Sandwich PlateSystem), Maritime Safety Committee 74 th session,2001• Fire Equivalence of SOLAS Chapter II-2 for theSandwich Plate System (SPS), Sub-committee onFire Protection 47 th session, 2002(a) stiffened steel plate15

(a) corner impact test, punctured steel plate(b) corner impact test, SPS plate - no rupture(c) deformed shape of large-scale stiffened steelicebreaker hull test specimen(d) deformed shape of large-scale SPS double hullproduct oil tanker test specimensteelSPS plate(e) stiffened steel hull- terrorist bomb(f) blast test specimensFigure A.4 Environmental and Asset Protection – Impact and Blast Resistance16

Lloyd’s Register, together with the University ofStrathclyde, are conducting a series of Fire EngineeringAnalyses for a number of SPS designs in accordancewith recently introduced IMO guidelines (SOLASChapter II-2 Regulation 17). Based on the analysis of theDFDS Tor Line funnel casing constructed withprefabricated SPS plates, Lloyd’s Register presented thefollowing conclusion in the submission, which wassubmitted to the Danish Maritime Authority and is nowapproved.“From review of the extensive research and developmentand the fire engineering analysis carried out byIntelligent Engineering Limited and StrathclydeUniversity, some of which is reproduced in this report, itis concluded that for its intended use, SPS meets all therelevant safety objectives and functional requirements ofthe revised SOLAS Chapter II-2 and should beconsidered as at least equivalent to a conventionalinsulated stiffened steel plate of A-60 fire rating.”ENERGY ABSORPTIONTo increase its energy absorption capacity, a structuremust be simplified and designed to allow localizedprogressive plastic membrane action in the hull or sideshell plating to occur. Simplification is achieved byeliminating stiffeners and by introducing a plate structurewith equivalent in-plane buckling capacity and stiffnessto the stiffened plate, and flexural capacity to sustaintransverse loads. This is uniquely achieved with the SPSplate section. Furthermore, the ductile core eliminateshard spots over primary supports and providescontinuous support to the face plates, dissipatinglocalized bending strains. The net effect is an increase tothe puncture resistance and blast resistance. A furtherbenefit is that the polyurethane elastomer provides aneffective crack arrest layer. In the case of double hullproduct oil tankers, the inner cargo tank lining can beeffectively isolated from cracks that propagate from tears(sheared plating which may eventually occur under highenergy impacts) in the outer hull through the framingmembers into the inner hull, thus preventing oil outflow.Figures A.4(a) and (b) graphically illustrate the localimpact resistance of a stiffened steel plate and a SPSplate when subjected to a corner shaped impactor,simulating the impacts of ship hulls with floating semisubmergedcontainers or dead heads or grazing offwharfs or from grabs for tank tops in bulk carriers. Theimpactor was mounted on a pendulum swing with a massof 2 tonnes that was raised two metres and released. Theimpactor struck the plate at approximately 20 km/hr.The stiffeners of the steel plate were buckled where theyframed into transverses and the plating was holed orpunctured. The impacted faceplate of the SPS plate wasplastically deformed in the shape of the impactor andembedded into the elastomer core in the shape, but notpenetrated.Figure A.4(c) shows a plastically deformed stiffenedsteel plate icebreaker hull section. At the load points thehull plating was bent sharply (hard spot withconcentrated bending strains) and ruptured. FigureA.4(d) shows the outer hull of a 40,000 dwt SPS productoil tanker loaded with four 500T actuators. The hullplates, and longitudinal and transverse girders, weredesigned for both normal operating loads and tomaximize the energy absorption capacity for extremeloads events. The hull plating developed plasticmembrane action between longitudinal girders, whichextended into adjacent cells as the longitudinal buckled.Rupture of the outer SPS plating did not occur as theelastomer core effectively distributed the load anddissipated the bending strains.Figures A.4(e) and (f) show a stiffened steel hull sectionthat was subject to a terrorist bomb attack and twostructurally equivalent plates that were subjected tounderwater blast loads. In both cases the steel platesshear, tear and open. Not only is the hull ruptured butalso a significant portion of the blast energy wastransmitted to the structure or contents behind the hullplate causing secondary damage. The SPS plateeffectively contained the blast load through plasticmembrane action.The use of SPS plates coupled with the appropriateenergy absorption design philosophy improves the crashworthiness of the hull structure (maximizes the totalenergy absorption of the structure), provides a decreasedrisk of environmental pollution and asset protection.LATEST DEVELOPMENT PROGRAMMEIn addition to the programmes described above, IEcontinues to develop SPS technology. The objectives ofthe development are to improve understanding of thecharacteristics and capabilities of the technology, todevelop design methodologies and to test the suitabilityfor new applications.Among the latest developments are:• Ongoing classification approvals for specificapplications: These have been achieved with sixmajor classification societies.• General material type approval for the elastomercore: This has been granted by DNV and similarapprovals are being pursued with the others societies.• A programme to establish a set of ship designverification rules: Lloyd’s Register is developing aset of rules and procedures for design assessment ofship structures using steel composite construction.This will enable designers to work towards anestablished standard for strength.• Investigation and full scale testing of SPSperformance in ship collisions and grounding: Thiswork will compare the performance of SPS and all-17

steel ship structures for resistance to impact andperforation.• Ongoing blast and ballistics trials: There isincreasing interest from the marine industry for bothblast protection in offshore structures and theprotection of ships’ accommodation spaces and otherkey areas against piracy and terrorist activities.• Ongoing fire testing for specific applications. Anobjective of IE is to achieve general acceptance ofSPS as a fire protection barrier.18