ABS - Bulk Carrier -Safer and Stronger Vessels

ourM I S S I O N

quality & environmentalP O L I C Y

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Bulk Carrier Solutions: Safer and Stronger Vessels 1

Executive Summary

Bulk carrier safety initiatives have received a new sense of urgency, accompanied with a greatersense of liability in the marine industry. The relationship of bulk carrier age to total loss of a vessel cannot be ignored, but other operational considerations also play an important role inmaintaining the structural integrity.

Statistically, for conventional bulk carriers, those vessels with more than 20 years of operationhave a greater total loss probability, in addition to a greater loss of life probability. Capesize (more than 80k dwt) and handysize (10 to 40k dwt) vessels account for the majority of losses at sea. This is a concern as 51 percent of the handysize fleet is 20 years old or greater. There aremany operational considerations contributing to the loss of a vessel that must be addressed forthe next generation of bulk carriers.

ABS SafeHull is the starting point for an ABS approved design. Application of the principlesfound in ABS SafeHull provide the cornerstone to a structurally sound vessel. Additionally, theABS SafeShip program follows a vessel from inception through its service life. This informationmanagement system allows owners the best method for maintaining their vessels. For furtherdesign verification, several analytical tools exist to address unique considerations for the largerbulk carrier designs.

Design alternatives to the conventional single sided vessels have been proven in the market tobring added strength, including the double hull or double side skin design. Bulk carriers withdouble sides are more durable ships bringing added benefits for safety and operations.

ABS is a classification society of choice for bulk carriers. With practical experience andunmatched technical capability, ABS offers shipowners and shipbuilders of these vessels the most comprehensive classification services available.

Table of Contents

INTRODUCTION .....................................................................................................................3

ABS STRONG POSITION .......................................................................................................4

MARKET SHARE..............................................................................................................................................4

RECENT ACTIVITY - DOUBLE SIDE SKIN BULK CARRIERS ...................................................................................4

BULK CARRIER LOSSES.........................................................................................................5

OPERATIONAL CONSIDERATIONS ........................................................................................8

HOLD SIDE FRAME PROBLEMS .........................................................................................................................8

Fatigue ..........................................................................................................................................................8

Corrosion ......................................................................................................................................................9

Damage.......................................................................................................................................................10

GREEN WATER.............................................................................................................................................11

SPONTANEOUS COMBUSTION .........................................................................................................................11

IMPROVING BULK CARRIER SAFETY..................................................................................12

APPLICATION OF ABS SAFESHIP ....................................................................................................................12

APPLICATION OF ABS SAFEHULL...................................................................................................................12

Bulk Carrier Designs ..................................................................................................................................13

Side Frames ................................................................................................................................................13

Cross Deck Structures .................................................................................................................................14

Corrugated Transverse Bulkheads...............................................................................................................14

TAIL SHAFT BEARING PERFORMANCE .............................................................................................................15

PERMANENT ACCESS FOR SURVEY ..................................................................................................................15

DESIGN ALTERNATIVES ......................................................................................................16

DOUBLE SIDE SKIN BULK CARRIERS ...............................................................................................................16

PARAMETRIC STUDY: DOUBLE SIDE SKIN BULK CARRIERS.................................................................................17

Longitudinal Framing .................................................................................................................................18

Transverse Framing ....................................................................................................................................18

Double Side Space.......................................................................................................................................18

Ship Configurations ....................................................................................................................................18

Operating Costs ..........................................................................................................................................20

HYCON BULK CARRIERS................................................................................................................................21

APPENDIX 1

DOUBLE SIDE SKIN BULK CARRIERS TO ABS CLASS.........................................................................................22

APPENDIX 2

WEIGHING THE OPTIONS ..............................................................................................................................24

2 Bulk Carrier Solutions: Safer and Stronger Vessels


Introduction

In selecting the most appropriate classification society for a new construction project, the clientshould consider the following:

ABS strong position in bulk carrier classification comes from years of experience, backed byadvanced technical programs that address the needs of the industry, including shipowners andshipbuilders. ABS stands out as a technology leader committed to continual research and thedevelopment of appropriate Rules and Regulations governing the design parameters and vessellife.

ABS surveyors experience is further enhanced by a commitment to technology and the analyticalprograms offered by the engineering department. By responding to clients needs through aworldwide network of offices, clients receive the necessary attention to ensure project success.

ABS has programs already in place and personnel with the needed experience to aid in the designand construction of the next generation of bulk carriers. ABS currently has projects for both thelatest Dunkerque-max bulk carriers and double side skin (DSS) bulk carriers. ABS has the tech-nology and practical experience necessary to meet the design challenges posed by these vessels.

Classification with ABS Includes: The most authoritative and appropriate Rules for

the classification of bulk carriers. Design review to verify the design complies with

the ABS Rule requirements. Surveys during construction to assure compliance

with classification requirements, as given in theRules and on the ABS approved plans, and atten-dance on board during official sea trials.

Governmental authorizations to issue certificatesand/or conduct surveys pertaining to the Load Line,MARPOL, SOLAS, tonnage conventions, and ISMCode.

Acceptance by the ABS Classification Committeeand award of the appropriate notation.

Performance of periodic surveys to assure that thevessel is maintained to class standards.

The Benefits of Classing with ABS Include: Knowledge that the vessel is appropriate for the intended service. Backing of years of relevant knowledge and experience. Single source for all technical needs. Indication of due diligence of owner/operator. Compliance with governmental requirements. Indication of performance of proper maintenance. Assurance of protection of capital investment.

Based on extensive and varied experience, ABS provides comprehensive classification services fulfilling client needs for any bulk carrier project, whether single or double sided.

ABS Strong Position

Market Share At the beginning of 2002, the ABS bulk carrier fleet had 13 percent market share of existing vessels and 17 percent of vessels on order.1 ABS is well-equipped with proven experience and

the technical tools necessary to meet todays market demand and provide for future projectsuccess.

The ABS fleet at year-end 2001, contained 737 bulk carriers, aggregating 22.8m gt. Recent contracts include the construction of new DSS bulk carriers of 51,000 dwt in China.

By year-end 2001, ABS had a total of 65 bulk carriers aggregating 2.3m gt on its orderbook from owners worldwide. Experienced operatorsrecognize ABS technical excellence and chooseABS for their classification needs.

Currently there are over 5,800 vessels in the dry bulk carrier fleet. Of these vessels, some 119 (2 percent) are DSS bulk carriers.2

Recent Activity - Double Side Skin Bulk CarriersABS partnered with two different owners on the construction of DSS bulk carriers in 1996. TopGlory and Hong Kong Ming Wah Shipping Company partnered with Oshima Shipyard in Japanfor their handymax bulk carriers. DSS bulk carriers are also being built to ABS Class in Chinaand Taiwan.

In January 1997, Oshima Shipyard in Japan delivered the 48,000 dwt Pacific Scorpio to HongKong Ming Wah Shipping Company. This vessel was the last in the series of six vessels. TheScorpio marked a double milestone for the bulk shipping industry: completion of the first signifi-cant order by a major shipowner for double sided bulk carriers, and also a first for the SafeHull-built bulk carriers.

The order was originally placed with the convictionthat such a vessel would provide simplified mainte-nance and operation, increased efficiency in loadingand unloading, and enhanced structural safety.Additionally, these vessels are expected to pay back the increased steel and construction costs in less than half their service life.

These vessels represent a step forward in longevity and safety and represent cumulative benefits for theirowners.

____________________________1 Source: LLP Seaway, gt based2 Source: LLP Seaway, Jan 2002



Bulk Carrier Losses

Tragic losses from bulk carrier casualties led many in the marine industry, including ABS, toinvestigate what design modifications could be made to promote bulk carrier safety and deter further losses. Bulk carriers are built to transport various dry cargoes. The most common aregrain, iron ore and coal. In the 1960s there were various problems associated with the transporta-tion of grain that were addressed after a series of accidents involving these types of vessels.Requirements for the safe carriage of iron ore and other high-density cargoes were enhanced in1997 with the introduction of structural survivability criteria and continue to be under scrutinytoday.

Primary barriers to resist flooding of a single skin side (SSS) bulk carrier vessel include: Hatch covers and foredeck fittings Side shell plating with attached supporting side frames

Once the foremost hold floods, a ship will likely suffer a total loss and by some estimates, the number one cargo hold floodingaccounts for about 40 percent of casualties for bulkcarriers. Three areas of the hull structure havebeen identified as main areas of concernfrom past casualties. These are the:

Hold frames and brackets Corrugated bulkhead Cross deck structure

Over the time period 1982 to2001, hull damage leading tosinking of conventional bulk carriers accounts for some 72 reportedlosses. During the same time period, there was one record-ed DSS bulk carrier lost.

Cracked or damaged side shell is the leading cause of bulk carrier losses. This data has been substantiated by a study conducted for the International Maritime Organization (IMO) and submitted to the Maritime Safety Committee (MSC) by the United Kingdom in March 2002. This study confirmed that for any size bulk carrier, side shell damage dominates recorded losses.By comparison, there are much fewer losses attributable to hatch cover failure.

This chart illus-trates the area ofthe initiating eventfor a recorded incident leading tototal loss. Side shell damage canhave a dramaticand sometimesunseen effect onthe structuralsoundness of abulk carrier.

This chart gives theprobability for eachtype of initiating event,across the various vessel types. Here itdepicts that the largerbulk carriers, capesizeand panamax, have ahigher likelihood ofloss.


These charts depict that side shell failures are the most likely reason for loss and are more likelyto occur to the panamax and capesize bulk carriers that are more than 20 years old.


Age is a contributingfactor in the loss ofbulk carriers.Statistically, bulk carriers 20 years andolder exhibit a greaterchance of total loss than their youngercounterparts. Intercargonotes that the actualnumber of ships andlives lost has fluctuatedeach year, while theaverage age profile oflost bulk carriers hasremained at around 20 years.3

Many operational factors con-tribute to the structural sound-ness of a vessel. These issuesmust be addressed to ensure thatsafe operation is maintained andcasualties are reduced.

____________________________3 Bulk Carrier Casualty Report, 2001 and the Previous Ten Years (1992-2001), Intercargo


Operational Considerations

For the safe operation of a bulk carrier there are many facets that must be identified and considered. The majority of structural problems associated with bulk carriers arise with the sideshell. Other issues to address include the effects of green water on deck.

Hold Side Frame ProblemsFor conventional bulk carriers, the cargo hold sideframes and brackets can be considered the weakest link in the structure of the vessel. These elements aresubject to fatigue, corrosion, and mechanical damageduring loading and unloading.

The International Association of Classification Societies(IACS) first responded to these problems in 1993 whenit introduced the Enhanced Survey Program (ESP), inan attempt to identify and correct degradation throughcorrosion, fatigue, and hard wear and tear. Casualtystudies in the mid-1990s also focused on the foremostcargo hold.

FatigueBulk carriers are susceptible to many modes of cyclic forces that combine with other forces acting upon the vessels structure. Over time these cyclic stresses, can seriously weaken the vessels structural capacity. Three areas on a bulk carrier that are especially prone to fatigue are the hold side frames, the side longitudinals in the upper and lower wing tanks, and the toes of the hatch coaming termination brackets.

Cyclic wave pressure acts upon the side framesof the vessel in a constant cycle of loading andunloading forces. For bulk carriers carrying high density cargo, such as iron ore, the sideframes do not have an internal pressure to coun-teract the external forces and the side shell is forced inward by the unbalanced forces.This can result in a weakening of the side frame.Conversely, internal pressures created by lowerdensity cargo impose loads in the opposite direction when a wave trough is encountered.This occurs when the cargo fills the cargo holdsand pushes out on the side frame structure. This pressure can also fluctuate and react withthe motions of the vessel.

Additional fatigue loads on the side frames arise from hull girder shear forces. Bulk carriers withcargo loaded in an alternate hold pattern experience high levels of still water shear forces as theweight of the holds loaded with the cargo are pushing down and the buoyant forces are pushingup the empty holds. These upward and downward acting still water forces combine with theshear forces that fluctuate with the wave motions to impose fluctuating stresses on the sideframes.


Similarly, the longitudinal framing of the upper and lower wing tanks is subjected to fluctuatingstresses due to the external wave action as well as the internal pressure from the ballast tanks.These longitudinals are alsosubjected to the fluctuatinglongitudinal hull girderstresses imposed by the passing wave along the length of the vessel. The toes of the hatch coaming termination brackets are subjected to the fluctuatinglongitudinal hull girderstresses as well as the torsional wave induced stresses imposed by wavesencountered at oblique wave headings.

CorrosionCertain products, including coal, phosphates and raw sulfur, transported by bulk carriers can rapidly corrode the hold sideframes and promote fractures. For a capesize bulk carrier carryingcoal and iron ore it has been recorded that a hull web frame, withan original thickness of 10 mm can corrode to only 3 to 5 mmalong the bottom portion of the hold in a short period. Additionally,the hold frame does not corrode evenly along the vertical length ofthe frame.

POSITION AREA OF PITTING CORROSION WEB THICKNESS

Upper Few 10 mm

Upper >50 percent 7 9 mm

Middle >100 percent 5 8 mm

Bottom 100 percent 3 5 mm

*due to carriage of coal and iron ore

The corrosive nature of coal is due to its sulfur content. This occursas condensation in the cargo hold of the vessel reacts with coal to produce a diluted solution of sulfuric acid, which over time corrodes supporting structures and frames.

Corrosion increases the structures susceptibility to fatigue andbuckling, and lessens the structural integrity of the vessel, as theweb thickness is not sufficient to support the heavy cargo beingtransported. As a result, the frame can detach from the side shell.


DamageSide shell problems are prevalent in all sizes of bulk carriers, although there is a higher occur-rence for the larger panamax and capesize bulk carriers.

For high-density cargoes the speed of loading may cause damage to the ships structure. Any timethe vessel is loaded in an asymmetrical manner, in relation to the central axis, the ship will twist.This will create other stresses within the hull structure.These stresses can have a damaging effect on the hull,even in still water conditions.

It is known that the dense nature of iron ore, about 3 tonsper cubic meter, generates large stresses on a ships struc-ture. Loading this cargo must be carefully controlled tonot exceed allowable stresses. The risk associated withimproper cargo loading can be greatly magnified once thevessel encounters the dynamic forces due to wave action.

Additionally, careless maneuvering of equipment used byterminals can cause accidental damage to bulk carrierstransporting grains, ore and coal. Loading and unloadingpractices have a very real effect upon the vessels opera-tional life span that can ultimately lead to damage or lossof the side shell plating. The practice of dislodging cargofrom side shell frames with jackhammers, removing orewith multi-ton claws, or loading minerals at high rateswithout considering the physical effect on the ship arecommon occurrences. Certain types of bulk cargoesrequire bulldozers to move cargo during unloading, with inevitable damage to frames, bulkheads and plating.

Additionally, the concentrated weight distribution oflower profile cargoes require special attention. Scrapmetal, for example, must be handled carefully to prevent damage to the bottom plating of the hold. Steel coils, if not properly secured, with their largeweight concentration may shift during voyage and damage the hull.

Photo credit: International Dry Bulk Terminals Contact Group (DBTG)


These ocurences may cause unseen damage that ismanifested over the operational life of the vessel. Thiscan include structural cracks and detached side shellframes.

This damage to the vessel hull only accentuates thefatigue and corrosion affects. Side shell deficienciesaccount for the majority of the bulk carrier losses. Theloss of the side shell plating may result in the total lossof the vessel.

Green WaterThe flooding of spaces below the main deck due tohatch cover or securing device failure, or failure ofother deck fittings, has been linked to green waterloads. Failures have been attributed both to directimpact loads of an impinging wave, and to impact byloose gear, deck equipment or fittings that have brokenaway from their foundations and then been carried bygreen water.

Design options to provide increased reserve buoyancyabove the main deck and added bow protection againstgreen sea loads are currently being analyzed to reducethe occurrence and effects of green water on deck.Based on the formal investigation report on the loss of the Derbyshire, new model tests and extreme valuepredictions for severe wave conditions have been carried out and are being used to reassess strength

requirements for hatch covers and foredeck fittings.

Preliminary assessment of these model test results indicate that current IACS unified strengthrequirements for hatch covers are adequate for ships in the intact condition, but that furtherassessment and refinement may be in order to account for greater forward green water loads ifthe foremost cargo hold or forepeak spaces were to flood. Work is also proceeding within IACS to evaluate the capacity of foredeck fittings and equipment attachments at the deck to resist thelateral loads of boarding green seas.

Spontaneous CombustionAdditional problems arise in the transportation of coal, which may emit combustible methanegas. Spontaneous combustion may also occur in certain types of coal that are self-heating. Evenwith the transportation of fishmeal there is a need for special consideration as it too can sponta-neously combust.


Improving Bulk Carrier Safety

ABS programs to improve bulk carrier safety not only monitor the vessel through its entire lifecycle, but also identify the loads that act upon the vessel and the verify the design against corro-sion and fatigue. Additionally, ABS has programs available to evaluate the other aspects of vessel operation.

Intercargo also reports that recent rules seem to be having a positive effect.4 Changes that willallow for permanent survey access are a further effort to improve the safe operation of bulk carriers.

Application of ABS SafeShipThe ABS SafeShip program starts in the design office with theapplication of the proven power of ABS SafeHull, recognized as the most rational, dynamically based system available for evaluating the design of a bulk carrier.

As the vessel takes shape in the shipyard, construction conforms to the superior requirements of the ABS SafeHullConstruction Monitoring Program.

On delivery, a structural database is created utilizing ABSSafeNet Hull Maintenance. Specified as-built drawings areentered into the ABS SafeNet Vessel Drawings system, pro-viding life-cycle storage and easy updating of this crucialinformation.

In service, the unique technical and commercial capabilities of theABS SafeNet Hull Maintenance, Maintenance & Repair, and SurveyStatus modules are used to manage the structural and mechanical condition of the vessel.

Significant cost savings flow from improved performance, less down time, greater operating efficiencies and reduced exposure to risk.

Free enrollment in the ABS SafeShip program is open to all new and existing vessels designed to meet ABS SafeHull criteria.

Application of ABS SafeHullABS SafeHull is ideal for identifying the loads and failure modes that need to be considered for abulk carrier. The ABS SafeHull System was conceived as a complete technical resource compris-ing criteria based on design and structural evaluation, as well as a comprehensive suite of soft-ware applications programs, technical support services, and related technical documentation andguidance.

The SafeHull criteria has been developed, based on extensive research and analysis, with a viewto improving the performance of problematic structural areas in bulk carrier designs. Other criti-cal areas, such as the supporting structures in the upper wing tanks and forebody structures,have also been addressed in the criteria.

____________________________4 Bulk Carrier Casualty Report, 2001 and the Previous Ten Years (1992-2001), Intercargo


This system is divided into two parts. During the design process, or Phase A, the general arrange-ment passes through a refining process beginning with an automated generation of the HullConfiguration. Next, calculations determining the dynamic loads assess the reaction of thedesigned vessel against specific criteria. This is followed by a determination of the structuralcomponents, compliance with strength criteria and fatigue assessment.

Evaluation of the design is the next step in the process. Commonly referred to as Phase B, thisstage generates a Finite Element Model (FEM) that again runs through a calculation of dynamicloads. Following 3-D Global Finite Element Analysis, the design runs through an assessment ofFailure Modes to confirm its structural integrity. This process verifies a design with a lifetimeperformance able to withstand all relevant failure modes.

For bulk carriers, torsional strength of the hull is of concern due to large hatch openings.Attention is also given to the effects of loading two adjacent holds known as block loading, as well as the strength of ballast holds. These conditions are explicitly covered in the load casesfor structural analysis.

Bulk Carrier DesignsTypical bulk carrier designs represent a compromise between operational demands and structuralrequirements. Consequently, the margins of safety of different structural components are not uni-form. Of main concern are the lack of structural redundancy and inadequate support in the trans-verse direction. In addition, the rigid double bottom structure and large upper wing tanks aremuch stiffer than the side frames and cross deck structure.

Side FramesSide frames are one of the weakest links in a bulk carrier structure. These vertical frames on theside shell connect two highly rigid structures, the double bottom/lower wing tank and upperwing tank. Side frames in dry cargo holds experience maximum stresses when alternate holds areloaded with high-density cargo and the ship is fully loaded. The low cargo profile causes sideframes in these holds to experience greater flexure due to the large external pressures that are notcounteracted by internal cargo pressures. The flexing is further magnified by the rotation of therigid lower wing tank caused by the large downward force of the high-density cargo acting on

SafeHull Design Cycle


the double bottom. All these effects contribute to reduc-ing the fatigue life of the connecting brackets of the sideframes, sometimes causing their detachment from theside shell.

Cross Deck StructuresIn the past, minimal attention was paid to the strengthof cross deck structures, because they were not consid-ered significant to the strength of the hull girder.Because of frequent occurrences of buckling in theseareas, more attention is now directed to the design ofcross deck structures. Three kinds of buckling problemscan occur in these structures. First, in the case of blockloading (a load condition in which two adjacent holds are loaded with heavy cargo), large trans-verse bending (sagging) can occur in the transverse bulkhead, causing high compressive forcesand stresses in the cross deck structures.

The static and dynamic external pressures further magnify the compressive stress. A secondbuckling problem occurs in oblique wave conditions, where wave-induced torsion creates shearing forces in the longitudinal direction of the cross deck, which can result in shear bucklingof the cross deck plating. Thirdly, lateral bending in the cross deck from shearing forces canresult in buckling of the hatch corners. The buckling problems become more pronounced inwide bulk carriers with large cargo holds, since wave-induced torsion is a function of the breadthof the ship.

Corrugated Transverse BulkheadsCorrugated transverse bulkheads, especially those in dry cargo holds, are also considered criticalin a bulk carrier structure. Prior to 1997, the SOLAS Convention assumed that watertight trans-verse bulkheads were able to prevent progressive flooding if the hold was accidentally flooded.Nominal hydrostatic loads, which do not necessarily represent the actual dynamic loads in adamaged condition, were applied. The 1997 amendments to SOLAS recognized that the collapseof corrugated bulkheads after side structure failure, and subsequent progressive flooding, mightbe one of the primary causes for bulk carrier losses.

This weakness was identified by ABS in 1994 during the development of SafeHull criteria forbulk carriers, when evaluating the effects of loads in a simulated flooded condition, with estimat-ed equilibrium waterline and static and dynamic loads (including sloshing) of sea water in theflooded hold. IACS Unified Requirements now address this known weakness.

The strength formulation for corrugated bulkheads was developed based on the results of a seriesof 3-D finite element analyses of corrugated bulkheads. The vertical bending moment acting onthe transverse bulkhead is a function of torsional rigidity of the upper and lower stools, the stiff-ness of the double bottom structures, and the loading in the hold.

The ultimate strength of corrugated bulkheads is examined to prevent catastrophic failure in theevent of accidental hold flooding. The criteria also address in an explicit manner other criticalareas, such as:

fore-end strengthening against slamming: transverse webs in the upper and lower wing tanks, in way of the ballast hold; double bottom structures for alternate hold loading conditions; transition zones between the fore peak and Number 1 cargo hold; and operational wear and tear, primarily of inner bottom plate and side frame connections.


Tail Shaft Bearing PerformanceFor the larger bulk carriers driven by high-powered diesel engines there is the potential for tail

shaft bearing problems if careful attention is not paid tothe propulsion shafting alignment during the design andconstruction of the vessel. The issue is of particularimportance in the design of bulk carriers where theextremely high bhp of the engine results in very stiff,large diameter shafting.

The ABS SHAFT software can be used to analyze shaftalignment and evaluate tail shaft bearing conditionusing deflection data derived from the finite elementmodeling of the hull structure.

ABS SHAFT takes into account hull flexibility as well as permitting the evaluation of the condition of the tail shaft bearing. This program is intended for the

design/evaluation stage of the vessels life, but it can also be used to trouble-shoot existing installations.

Permanent Access for SurveySOLAS Regulation has been drafted requiring ballast tanks and cargo holds of bulk carriersgreater than 20,000 gt, constructed on or after 1 January 2005 to be provided with a permanentmeans of access to enable, throughout the life of a ship, overall and close-up inspections andthickness measurements of the ships structures to be carried out by the flag Administration andships personnel. The means of access are to be described in a Ship Structure Access Manualapproved by the Administration, an updated copy of which is to be kept on board.

Of particular importance are the following means of permanent access: Vertical access to a minimum of 25 percent of the total number of hold frames port and

starboard equally distributed throughout the hold including at each end in way of trans-verse bulkheads, with no less that three means of vertical access fitted port and starboard.

Three means of access fitted at both ends of sides of the cross deck and in the vicinity ofthe centerline. Each access is to be accessible from the cargo hold or directly from the maindeck. Alternatively, if the height of the overhead structure of the cross deck is less than16m, a movable means of access (e.g., hydraulic arms with a stable base or wire lift plat-form) may beaccepted.

One longitudinal,continuous access isto be provided forthe full length ofeach top side andbottom hoppertank, if 6m inheight, fitted adja-cent to side shellwith vertical accessladders to the maindeck access.Portable laddersmay be used forsuch tanks with aheight less than 6m.

Source: IACS document, IMO DE 45, March 2002


Design Alternatives

Tragic losses from bulk carrier casualties led many in the marine industry, including ABS, toinvestigate what design modifications could be made to reduce the risk of further losses. Doubleside skin bulk carriers, and modifications thereon, are being built to counteract some of the problems associated with single side bulk carriers.

Double Side Skin Bulk CarriersThe double hull principle is not new to the marine industry. Tankers are being built with a dou-ble hull to reduce the risk of oil spills after collisions and grounding. For bulk carriers, the moti-vation is to protect the primary structural members against cargo-related corrosion and mechani-cal damage, as well as providing a barrier against extensive flooding due to low-impact side shelldamage.

To date there has not been a reported loss of a purpose built DSS bulk carrier with a size greaterthan 20k dwt. One DSS vessel of 20k dwt was lost at sea after 23 years of operation. On average,a DSS bulk carrier is scrapped after 27 years of service.

DSS bulk carriers have improved structuralintegrity by:

Eliminating exposed, damage-pronetransverse framing and their endattachment

Protecting against cargo-related corrosion and mechanical damage

Allowing better quality surface prepa-ration and coating application bothinitially and carrying out repairs

Creating much stiffer side structureseffectively eliminating the flexing orfatiguing of side frame structures inconventional designs

With the addition of a double side, improvements are made to the operation of bulk carriers. Thetime required for cargo discharge is decreased. For coal, on average, this translates to 10 percenthigher daily discharge rate when compared to ships with conventional hold configuration.

Because of thesmooth hold sides,the damage per tonof cargo dischargedcan be six timeslower than the aver-age in conventionalbulk carriers. DSSsmooth holds alsosave time and costsin hold cleaning andprotect the cargoagainst external tem-perature variations.

SideFrames

DoubleHull

SideShell


Significant savingsand economic advan-tages can be realizedthrough an increasein structural strength.The DSS design notonly eliminatesexposed damage-prone side frames,but also reduces therisk of hold floodingand possible sinking;especially for smallersize bulk carrierswith fewer compart-ments. On the otherhand, if the doubleside space were usedas a ballast tank itwould require closerattention.

The construction costdifferential for a DSSbulk carrier is nomi-nal, and higher resalevalues may be real-ized. Additionally, theoperational advan-tages translate into

economic advantages as the speed of cargo discharge has been improved, time and cost is savedin hold cleaning, and less down time is required for repairs.

Parametric Study: Double Side Skin Bulk CarriersIn 1999 ABS conducted a study to determine the structural design and operating costs of DSS bulk carrier designs. The study focused on the:

Selection of the most suitable width of the DSS structure Identification of the type of DSS framing system Determination of the newly formed side space (ballast vs. void) Scantlings/steel weight of DSS vs. SSS comparison based on SafeHull requirements Construction cost of DSS Estimation of annual operating cost

In determining the ideal width of the double side space, ABS used current IMO regulations on access openings 600x600 (horizontal) and 600x800 (vertical). The space should providesufficient width for safe access and inspection. The ABS Rules and SOLAS mandate that 1000mmbe the minimum width; however, the ABS study increased the width to 1400 mm for capesizeand handymax, and 1200 mm for panamax to provide adequate space for inspection and mainte-nance, as well as provide the space needed for adequately sized structural frame members.Additionally, the type of double hull framing could be either longitudinal or transverse. In eithercase, the horizontal stringers and vertical webs in the double side space are required for strengthand safe access.


Longitudinal FramingLongitudinal framing in bulk carriers poses additional design concerns that result in increasedfatigue. In the longitudinal framing in the double side space system, the horizontal stringer hasno impact on longitudinal framing scantlings. The web framing in the double side space could be every third or sixth frame spacing, and fatigue would be a factor in wider frame spacing. In a longitudinal framing system, side pressure is transmitted to the vertical web or the transversebulkhead. Additionally side pressure loads can cause high shear forces in the webs. Careful consideration needs to be made for this high shear force.

Transverse FramingTransverse framing is preferred for a variety of reasons. One advantage is that the web frame loca-tion is flexible. Additionally, greater buckling strength is found in the side shell plating as it issubject to large vertical direction compressive loads. The web frames support the local scantlingrequirement, and the side pressure loads go directly to the upper and lower hopper tanks elimi-nating the high shear problem encountered by the longitudinal system. The ABS study considersa transverse framing system.

Double Side SpaceFor the DSS bulk carrier there is an additional consideration of the space created by the design. Ifit is used as ballast space it will require high quality internal coating. There is an added cost formaintenance, and the double side spaces cannot replace the designated ballast cargo, owing tovolume and strength considersations. However, if it is left as a void space there is no need for ahigh quality internal coating. The ABS study considers it as a void space.

Ship ConfigurationsThe ABS study compares DSS and SSS for three typical sizes of bulk carriers: capesize, panamaxand handymax. These ships were selected to establish a baseline reference in each of theserespective size ranges against which DSS bulk carriers of identical deadweight, cubic capacity andspeed would be compared with SSS bulk carriers.

Typical Ship Size of Single Side Bulk CarriersSHIP TYPE SIZE (DWT) L.B.P. (M) BREADTH (M) DEPTH (M) DESIGN DRAFT (M)

Capesize 150,000 264.00 45.00 23.20 16.90

Panamax 60,000 212.00 32.24 17.80 12.40

Handymax 45,000 180.00 32.00 15.80 10.50

To provide the DSS ships with a cubic capacity equal to that of the single side equivalent, thedepth of the DSS ships were increased to compensate for the loss of cargo capacity due to thedouble sides. The depths of the capesize, panamax and handymax double sided ships wereincreased by 0.6m, 0.7m and 1.11, respectively. The length and breadth remained the same.


Although larger vessels are now the norm in bulk carrier new construction, the steel weightincrease and economic findings can be used as indicators in understanding the differencebetween single sided and double sided bulk carriers.

Comparing a typical SSS and DSS capesize vessel, there is a weight increase in the cargo block of 419 tons for the DSS bulk carrier. This can be broken down into the various sections in the table below.

REGION DSS WEIGHT TONS SSS WEIGHT TONS DIFFERENCE TONS

Longitudinal Members 8,834 8,585 249

Web Frames 1,831 1,640 191

Trans. Hold Frames 590 634 -44

W. T. BHD 1,416 1,452 -36

D. T. BHD 588 550 38

Hatch Coamings 170 170 0

Cross Deck 360 360 0

Bilge Keel 10 10 0

Phase B Increase 283 262 21

TOTAL 14,082 13,663 419

*For a capesize vessel of 150,000 dwt

TOTAL STRUCTURAL WEIGHT OF EACH SHIP (TONS) DIFFERENCE (TONS)

Double Hull Single Side

Cargo Block Weight 14,082 13,663 + 419

Total Weight 17,377 16,893 + 484

*For a capesize vessel of 150,000 dwt


By adding the steel necessary beyond the cargo block region, the total structural weight differ-ence of a typical DSS capesize bulk carrier would be 484 tons.

The addition of this steel also adds to the construction costs.

TOTAL STEEL DIFFERENCE CONSTRUCTION WEIGHT (tons) COST DIFFERENCE

SSS capesize 16,893

DSS capesize 17,377 484 $484,000

*Note: the construction cost is based on $1000 per ton steel (average between Japan and Korea)

Operating CostsIn the study, it was determined that the operating cost difference is small. Although there will besome revenue loss due to port draft restrictions requiring the carriage of less cargo.

ANNUAL COST DIFFERENTIALCONVENTIONAL VS. DSS DESIGN

Capesize Panamax Handymax

Port Charges $10,000 $13,200 $11,800

Canal Tolls $1,300 $8,600 $11,500

Fuel Cost $6,700 $4,700 $5,100

# of total voyages (9) (13) (11)

days at sea (297) (264) (301)

days at port (35) (72) (48)

Cargo Hold Maintenance -$22,300 -$10,400 -$5,600

Cargo Hold Cleaning -$22,500 -$18,000 -$12,000

H & M Insurance Cost $11,400 $8,900 $5,800

P & I Insurance Cost $5,700 $3,700 $4,900

TOTAL ANNUAL COST DIFFERENTIAL -$9,700 $10,700 $21,500

(-) Cost savings for DSS design in 1997 USD


The operating cost savings for a capesize DSS bulk carrier adds up to a total of $194,000 (USD)over a 20-year period.

Capesize Cost Differential

Initial Cost Differential = $484,000

Operating Difference = -$194,000

(-$9,700 per year for 20 years)

Total Cost Differential = $290,000

COST DIFFERENTIAL

Net Present Value (@ 6 %) = $373,000

*Note: 1997 USD value

Overall, a DSS bulk carrier offers added structural strength and operational advantages over theconventional SSS bulk carrier, which may eventually translate into economic benefits. The off-hire risk of DSS bulk carriers is reduced with better maintenance and efficient operation, result-ing in better availability. Repair and maintenance costs can be reduced due to the smooth-sideinner hull and protected structural members located in the double side compartment spaces.Owners of DSS bulk carriers can also expect a better resale value for vessels that have had theappropriate repairs and fewer damages.

Hycon Bulk CarriersHybrid Configuration (Hycon) Bulk Carriers are being built with double sides in the fore andaftermost holds in a shipyard in Japan. The concept of the Hycon Bulk Carrier evolved with theincreased structural integrity demands from IACS in 1999 that addressed flooding of holds of SSS construction.

The weight of the extra steel used for the inner skin in the fore and afts holds is offset as no extrasteel is needed for the deck. Additionally, protection has been added where the wave action is themost severe.

The structural safety of the hybrid design brings structural stiffness by reducing flexing andfatigue from wave loads at the fore end of the side structure. This double side also reduces therisk of hold flooding should the side structure fail.


Appendix 1

Double Side Skin Bulk Carriers to ABS Class

ABS Classification Activity sample of DSS Bulk Carriers built 1995 to 2002.

Oshima Shipyard - JapanPacific Acadian, Pacific Dolphin, PacificEmerald, Pacific Mercury, Pacific Primate,Pacific Scorpio48,400 dwtOwner - Hong Kong Ming WahBuilt: 1995 to 1997 to SafeHull standards

CSBC Shipyard - TaiwanChina Steel Trader, China Steel Investor154,600 dwtOwner - China Steel ExpressBuilt: 1997 to SafeHull standards

Oshima Shipyard - JapanTop Sugar, Top Pioneer, Top Progress, Top Explore, Top Reliance29,600 dwtOwner - Top GloryBuilt: 1998 to 1999 to SafeHull standards

Pacific Dolphin

China Steel Trader

Top Progress


Oshima Shipyard - JapanTop Leader, Top Knight, Top Beauty, Top Vigour73,600 dwtOwner - Top GloryBuilt: 1999 to SafeHull standards

New Century (formerly Jing Jiang) Shipyard - ChinaClipper Galaxy51,000 dwtOwner - Galaxy Shipping Built: 2002 to SafeHull standards

Top Leader


Appendix 2

Weighing the OptionsThere are pros and cons to be considered for an informed decision to be made regarding DSS andSSS bulk carriers.

Pros: Pros: Safer in structure Commercially competitive Flexible in operation

Cons: Cons: Loss of grain capacity Vulnerable to side structure

(for handymax vessels) failure Effect of regulations yet to be

evaluated

Pros: Pros: High corrosion resistance, only Easy blasting, re-coating and

when double hull is left void renewing of side structure if necessary

Cons: Cons: Extensive corrosion is envisioned Hold frames are exposed to

if the hull space were used for cargoes with high ballast corrosion rates

Pros: Pros: Improved resistance against low Hold structure and hull girder are

energy collision resulting in holds strengthened against one hold flooding flooding, and easily maintained

Cons: If side shell integrity were

breached, one hold flooding may lead to a progressive flooding and loss of the ship

Pros: Pros: Hold side structure is protected Hold frames are easily accessible

from possible mechanical for repairsdamage

Cons: Cons: Repair work of DSS structure Hold frames are vulnerable to

may require hot work in confined mechanical damage duringspace both outer/inner hull unloading

Perception

Corrosion

Floodingresulting fromdamage toside structure

MechanicalDamage

DSS Bulk Carriers SSS Bulk Carriers


Pros: Pros: Access to DSS spaces will be Hold structure and hull girder

facilitated using the hull are strengthened against onestructure in the absence of hold flooding and easily ballast maintained

Cons: Cons: Maintenance work could be Special means of access is

more challenging due to DSS necessary (permanent meansspaces being confined of access is not feasible)

Pros: Pros: Small difference as long as the Lighter than the same size for

strengthening for hold flooding DSS BCsis exempted in SOLAS XII

Cons: Heavier than the same size of

SSS BCs such effect may become larger of smaller BC

InspectionandMaintenance

Steel Weight

DSS Bulk Carriers SSS Bulk Carriers

Produced byABS Marketing Development & Communications

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TX 2097 05/02 4000

ABS - Bulk Carrier -Safer and Stronger Vessels

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