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THE ROLE OF MATERIALS IN SHIP DESIGN AND OPERATION

Wade G. Babcock, AMPTIAC Quarterly Editor-in-ChiefThe Advanced Materials and Processes Technology Information Analysis Center

Rome, NY

Ernest J. CzyrycaSurvivability, Structures, and Materials DirectorateCarderock Division, Naval Surface Warfare Center

West Bethesda, MD

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INTRODUCTION

A sport fisherman on a quiet lake or river chooses a shallow draft, flatbottom boat. A deep sea fishing charter chooses a larger, vee-bottom ves-sel with lots of power. A cargo company chooses a long, square cross sec-tion, boxy vessel. Some vessels are welded steel while others are wood andstill others are made of glass or carbon fiber reinforced polymers. All ofthese boats share the same basic principles of keeping their operators orcargo dry, enabling them to cross a body of water, and accomplishing acertain task. But the differences in structure, speed, agility, sea-keeping,and overall abilities are enormous.

It is obvious that the mission of an aircraft carrier is different fromthat of a cruiser. But why would a fisherman choose a shallow-draft, flatbottom boat to go bass fishing in? These questions are factors the design-er must consider when building a new ship, and there are many more.

In this issue’s MaterialEASE, we seek to provide a look at some of themost pressing considerations ship designers face when choosing materi-als for current and future Navy ships. While there is no way we can tack-le all the issues unique to shipbuilding, what we seek to do here is pres-ent at least the “first tier” of considerations pertaining to materials thatany ship designer will have to address. The information is compiled heresuch that the lay person can gain a basic appreciation for some of themost important materials issues in shipbuilding.

Not only are there multiple grades of steel used throughout modernships, but one can see from the articles in this special issue that there areefforts underway to change the fundamental materials and structures ofcombatants. The next 30 years may see the most dramatic shift in ship-building technology since steel replaced wood.

First, take a look at modern ships. Since World War II, welded steel(so-called monolithic) hulls have almost completely replaced riveted steelhulls for all ships greater than 100 feet long. All of these structures are fab-ricated with a network of longitudinal and lateral “T”-shaped structuralmembers covered with plate to form the hull shape. All joints are weldedtogether and the grades of steel used typically fall into one of three cate-gories: moderate yield strengths of 35 to 50 ksi, higher yield strengths ofaround 80 ksi, and the highest yield strengths of 100 ksi or more.

In the United States, high yield strength Navy steels of 80 and 100 ksiwere specified in the 1950s with compositions separate from those of general industrial steels. These “HY” series steels had to meet significanttoughness and weldability requirements, especially at cold temperatures,

and were used in nuclear submarine pressure hulls and critical areas ofsurface ships for ballistic protection and as “crack arrestors.” Theserequirements were driven by the catastrophic failures incurred in the firstwelded ships built from steels common in riveted construction. HY-80and HY-100 have recently been augmented with even newer industrialHSLA (high strength, low alloy) grades which will meet the strength,toughness and weldability requirements, but should be significantly lessexpensive. (For more information on HSLA steels, please see the article byCzyryca, et. al. in this issue.)

Any of the steels used in Navy ships must adhere to certain criteriademanded by the Navy and shipbuilders. There are fundamental weld-ability, toughness, and forming characteristics for metals which must bemet in the construction phase. Then there are additional parameterswhich dictate the ship’s eventual performance, such as weight, shockloads, vibration, fracture toughness in environmental extremes, and fireperformance. Since these two phases of a ship’s lifetime are governed bydifferent needs in terms of material performance, we have chosen todivide this report along these lines. Neither operation of the ship nor con-struction can be examined independently however, so care should betaken to consider each in the context of the other. The first section willcover the main materials issues of concern during the construction phaseof a modern ship. The second section will discuss the most importantmaterials considerations during the operation of the vessel.

Most Navy ship hulls are constructed of steel, except for a few specialpurpose vessels which have either fiberglass or wood hulls. (These areused specifically for tasks where reduced magnetic signature is critical,such as mine clearing.) Many ships have structures above the waterline(called “topside”) fabricated of aluminum and more recently some useglass reinforced polymer (GRP) composites. Most of the discussion in thisreport will be in relation to steel, except where noted on topics whereother materials have been applied.

SECTION 1: MATERIAL ISSUES RELATING TO CONSTRUCTION OF NAVY SHIPS

It should be noted again that any material parameters considered during the construction phase will impact operational characteristicsdownstream. For instance, the time and procedures required to weld astructure together are major cost points during a ship’s construction.

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There is significant pressure to reduce these costs, therefore the weld-ability of a metal is critical. However, if welds are not done carefullythey are literally a breeding ground for flaws and will thus criticallyimpact the service performance of the vessel in operation.

Strength

Overall size of any structure is often a function of the strength of its com-ponent materials. In the case of ships, high strength steels with yieldsstresses ranging from 30 to 130ksi are typically used. In general, most ofa ship’s structure is made from 50 or 80ksi yield stress steel, with criticalareas making use of stronger grades as needed. Less dense alloys of aluminum may be used for topside structures, and recently compositesare regularly finding their way onto ships also (mostly for topside structures – less commonly for hulls.) The current ultimate load carry-ing abilities (tensile and compressive) of reasonably cost effective GRPcomposites limit all-composite hulls to about 200 feet in length.

A more complicated facet of the overall strength issue is the abilityof a structure to do its intended job. For instance, if a designer calls for 0.5 inch thick plate with a yield stress of 50 ksi, it might seem appro-priate that a thinner, 80 ksi plate could be substituted. Ship structures(and most other large structures for that matter) are never that simple.Plate steel is welded into monolithic structures with interconnecting I- and T-cross-section beams. Hull or deck plating is then welded intoplace creating “grillage” structure. Thinner plate (even with higheryield stress) will behave differently, often buckling much sooner thanthicker plate. For this reason, careful attention is paid to buckling modesof overall structures and thicker plate is often required even when itsspecific strength is well overmatched to the task.

Similarly, the overall length of a vessel determines its loading characteristics. In a shorter vessel (up to ~150 feet), its structural com-ponents must perform well in bending and be stiff. For a hull greaterthan 200 feet in length, the ultimate tensile and compressive behaviorof its components takes over. While composites can be made withextremely high strength capabilities, the cost of their component materials and fabrication grows rapidly (especially as more exoticcomponents are chosen). Steel structure can be fabricated to handleboth loading scenarios (stiffness and ultimate strength, based onlength) at a much more affordable cost.

Weldability

An immense amount of welding is required to build a steel ship.Thousands of piece parts are cut and assembled, requiring miles of weldsat the joints. Many of these joints require multiple passes to complete. Byfar, welding is the most labor intensive portion of constructing a ship.Welds in a ship structure are also very critical to its overall strength, durability, and toughness. Even small defects in weldments can create theinitiation point for considerably larger cracks and eventual failures.

Because of the massive amount of welding required, and its impor-tance to the structural integrity of the vessel, careful welding processesare stringently adhered to. While HSLA steels require diligent attention todetail and procedure during welding, the HY-series steels require evenmore weld preparation and post treatments. One of the reasons for thepush to replace HY-series steels with HSLA grades in the 1990’s, was thereduction in labor required for welding. In general, any steel grade meet-ing the strength, toughness, and other requirements, but which is sim-pler to weld with a lower predisposition to weld flaws, is desirable. Thecost of alloying steels to increase weldability must be balanced againstthe added cost of welding labor associated with a less weldable grade.

Toughness

In addition to strength and weldability, toughness is one of the mostsalient attributes of metallic structures. In shipbuilding, toughness is acritical feature of the structure and its component materials (both plateand weld metals), as they must be able to deform plastically to someextent, and tolerate cracks and flaws while maintaining overall structur-al integrity. This is obviously complicated by the fact that Navy ships mustbe capable of operating in every ocean environment, from the frozen arc-tic to the steamy tropics.

Steels, however, have a ductile-to-brittle transition in toughness astemperature decreases. It is a function of temperature, loading rate, andmicrostructure of the steel. Below a temperature specific to each steelgrade, the material will have little resistance to catastrophic crackgrowth. In the transition regime, the combination of dynamic loadingand cracks or defects in areas of stress concentration, may result inunimpeded, rapid crack propagation through the material.

For shipbuilding steels, it is imperative to select grades with a lowtoughness transition temperature (below the expected operational tem-perature range). For the higher strength steels used by the Navy, alloyingand processing methods are used to produce grades with very low tough-ness transition temperatures, but again, this can increase cost and reduceavailability of the grade.

Marine Corrosion

Ocean-going ships are intended for use in one of the most corrosive envi-ronments on the planet, and as such, corrosion is considered carefully inthe design phase of any vessel. There are various materials options,design strategies, coating, and cathodic protection technologies availableto the designer and shipbuilder.

Painting a ship is probably the Navy tradition with the strongestlove/hate relationship. The process is necessary to protect the vessel fromthe sea’s corrosive effects, yet it is a never ending task that eats up signif-icant labor resources and time. There is rarely a moment in a ship’s serv-ice life when something aboard is not being painted. And these paints arenot the kind of materials you find at a hardware store: there are many

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different formulations, each specifically engineered to perform criticaltasks around the ship. Many also require very rigorous surface prepara-tion and curing processes which place additional drains on manpower.

From the designer’s perspective, the ship must be built in such a wayas to reduce corrosion (limiting entrapped areas where water can collectand stand for instance) and also allow for the significant corrosion pre-ventative processes that will go on for the duration of the ship’s life.Structural elements must allow for periodic and sometimes often recoat-ing, and some elements must allow for replacement if they are particu-larly susceptible.

There have been efforts to replace corrosion-prone steels with othermetals like aluminum or titanium. These alternative metals offer a lowerdensity (which can reduce weight) and some corrosion resistance, butthey present their own unique problems which are beyond the scope ofthis article. In short, marine grade aluminum (5000-series) is the onlynon-ferrous, corrosion resistant metal that has seen widespread use inNavy ships as topside structure over the past 30 years. This is mainlybecause of the availability and relatively low cost of marine aluminum,a consequence of commercial crew boat and high-speed ferry construc-tion using well-understood fabrication and welding processes.

Formability

Ship hull forms and grillage structures require component steel orcomposites to be formed into a multitude of complex shapes. The considerable amount of welding required to fabricate steel structuresalso imparts a significant amount of residual stress and often unwant-ed deformation in the finished structure. This combination of initialforming requirements coupled with post-assembly straightening ofdeformed plate, requires that the steels chosen for ship construction be amenable to a wide range of forming procedures. The labor associ-ated with these forming procedures must be balanced with the cost of alloying or preprocessing of steel plate to increase formability. In addition, formability of the grade impacts toughness, weldability,and strength.

Composites offer the ability to be formed into much more complexmonolithic shapes, but are not as amenable to assembly of multiplesubsections. Transferring structural loads and accommodating thermalexpansion mismatch is not a trivial endeavor in large structures. In fact,joining technology (including composite-to-composite and composite-to-steel) is currently one of the most limiting (and potentially the mostpromising) area of development. All of thesefactors must be balanced carefully in theselection process.

Availability

About 40-50% of the steel used by DOD isconsumed in Navy ship fabrication. The HY-series steels were specific to Navy applications, forcing manufacturers to

divert production from common grades and increasing the lead timerequired for production. When combined with their unique alloyingrequirements, these factors make HY steels considerably more expensivethan more common industrial grades. Some recent efforts to utilizeindustrial-standard HSLA steel grades have helped to increase the effec-tive amount of steel available, as well as lower the cost of procurement.

Affordability

Currently and for the foreseeable future, one of the most pressing factorsin materials selection for Navy ships is affordability. With labor costscontinually rising and often outpacing the increased cost of raw materi-als, the balance between these must carefully accommodate and antici-pate how materials decisions impact construction labor expense. Thelong-term costs of maintenance and readiness must also be factored in.Choosing the cheapest material in the construction phase cannot be aconsidered a success if the decision requires a significant increase inconstruction labor and/or creates a maintenance nightmare during the30 to 50 year expected lifetime of the platform.

Traditional steels and newer composite materials each offer specificadvantages. As compared to composite materials, steels are less expen-sive to purchase, relatively less expensive to fabricate, and potentiallymore expensive to maintain. When considering the cost of building aship from steel, one must always factor in the long term cost of repeat-ed painting and corrosion mitigation. Composites cost more to fabricate,but offer the promise of lowered maintenance cost through their corro-sion resistance. There are however, questions as to the long-term main-tenance of composite joining technologies, environmental attack caus-ing delamination (as simple as water infiltration), and perhaps moreas-yet-undiscovered issues.

SECTION 2: MATERIAL ISSUES RELATING TO OPERATION OF NAVY SHIPS

Once a vessel enters the fleet, many of the materials selection decisionsmade years before during design continue to impact its day-to-dayoperation.

Weight

In design of air and space craft, weight is the driving force for almost allmaterials and structural decisions. Wherever weight can be reduced, ittypically is, no matter what the cost. Lower weight translates to greater

speed, range, and payload capacity, as well as agenerally reduced cost of operation in the form offuel requirements.

While not quite as critical as air and spacecraft, weight reduction in ships is very impor-tant. The same economies of increased payload,speed, and range translate, as well as a reduc-tion in fuel requirements. There are additionalbenefits to reducing topside weight of ship

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structure, such as increasing the sea-keeping ability of the ship viaimproved stability of the platform in a seaway. (Reduced mass higherup on the ship keeps the center of gravity low and reduces rollmoments.) While the overall weight of a ship is determined predomi-nantly by decisions made in the design phase, they have the greatestimpact on service performance, including the growth margin criticalfor added or improved capabilities over the life of the ship. Therefore wehave chosen to include the discussion in our Operation section.

Many ships currently in use have aluminum topside structures.While these structures employ modern high-strength alloys, the fabrica-tion methods and design are still very traditional, utilizing conventionalwelded grillage construction. Composites have also been used veryrecently for some limited topside structures, such as mast enclosures andcompartments. (For more information on composites aboard ships, seethe article by Potter in this issue.)

Most recent research efforts to reduce weight on ships have focused onusing higher yield stress steels to replace those with lower yield stresses.This enables the use of thinner plate, and thus reduces weight. One can-not replace all structural plate with thinner material however, as bucklinginstability becomes an ever increasing issue. Much research and experi-mentation has gone into studying how ship structure performs with thin-ner, higher yield stress steel and this work will no-doubt continue.

Other innovations such as the advanced double hull (ADH) seek toreplace conventional construction with new techniques which reduce theoverall number of metal piece parts needed. (For more information onthe ADH concept, please see the article by Beach, et. al. in this issue.)Composites have been used on hulls shorter than 200 feet long with greatsuccess. The raw material and labor cost to build composite hulls is stilltoo high for applications without a specific requirement (such as reducedsignature) for composite materials.

Fracture Toughness

As discussed earlier, fracture toughness is a critical property required inthe steels and weld metals of warship hull structure. Structural compo-nents’ ability to withstand the day-to-day rigors associated with thermalextremes, impacts from piers and other boats, maintenance procedures,sea conditions, and other “normal” events is important. These, however,are not the most important conditions that impact readiness. Naval vessels are also subject to shock loading from hostile weapon effects, suchas air and underwater explosive devices and projectiles require protectionmeasures against shock, blast, and penetration.

Steels used in ships are formulated and processed to have a greaterability to withstand fracture and a greater flaw tolerance under shockconditions than more common structural grades. This allows them towithstand high intensity loading and remain ductile, sustaining damage without rupture or fracture. Similarly, the welding processes are carefully engineered to produce very clean and uniform welds that

are also very tough and flaw tolerant. The qualification of Navy steelsinvolves a progression of fracture toughness testing from small impacttests to large scale, full thickness explosion tests. These tests demonstratethe capability of the welded system to sustain gross deformation, in thepresence of cracks and low temperature, without fracture. The specifica-tions for both base metals (plate, forgings, castings, etc.) and welds contain toughness test requirements to assure their ability to resist fracture and tolerate flaws.

Marine Corrosion

Someone once said that from the moment steel comes from the mill, it isconstantly trying to get back to the earth in the form of rust. This is espe-cially true of Navy steels, which are expected to do their job in one of themost corrosive naturally occurring environments. Salt water and seaspray cover every surface of an ocean-going vessel and are constantlyattacking its structure. Not only the structural components, but every sys-tem aboard the vessel is being chemically corroded. Galvanic corrosion(produced by the differences in electronic potential between componentmetals aboard a ship electrically connected via the ship’s structure andionically conductive seawater) is also a critical concern. In addition, theship itself generates combustion products (in turbine and diesel poweredvessels, as well as ancillary combustion engine-powered systems on othervessels) which are high in corrosive compounds of sulfur and some acids.Upper structures of the vessel are subject to these airborne pollutants.

There are multiple ways of combating corrosive elements. As men-tioned in the first section, there are various materials options, designstrategies, cathodic protection, and coating technologies available to thedesigner and shipbuilder. Once the vessel is in service, combating corro-sion becomes a major maintenance requirement.

Coatings are used to protect the steel hull (or other substrates) fromattack by salt water and other water- and airborne corrosive com-pounds. They require a significant amount of care during applicationand frequent reapplication to maintain their protection. From simplyscraping, sanding, or grinding a small area, to significant removal,surface preparation, and reapplication of a coating to a large area,coating maintenance is a never-ending process. Once there is a discon-tinuity in the coating, corrosive attack is mitigated by cathodic protec-tion, either by sacrificial anodes or by impressed current systems. Thesacrificial anodes are typically blocks of zinc alloy, electrically coupledwith the steel hull and which preferentially corrode, protecting theexposed steel. The anodes are positioned about the hull of the ship andreplaced periodically as they deteriorate. Impressed current systems usepermanent anodes on the hull and generate a potential field to coun-teract the corrosion potential of exposed steel.

Galvanic corrosion (caused when, steel is be connected to materialsof higher corrosion resistance), is mitigated by utilizing coatings orinsulators to help reduce the electrolytic connection enabled by the

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seawater, and by sacrificial anodes. (There typically is a concentration ofanodes in the stern, where the bronze propeller, galvanically connectedto the hull via the shaft, would otherwise cause accelerated corrosion ofany unprotected steel.)

Biological Attack

In addition to corrosion protection, the hull coating below the waterlinemust posess anti-fouling properties to maintain hydrodynamic perform-ance and fuel efficiency. The most commonly used coatings prevent orslow the attachment of marine organisms by containing compoundstoxic to the animals, thus preventing them from attaching in the firstplace. Another method is to apply a coating whose chemistry or surfacemorphology hinders the creatures’ attachment, thus allowing them to besloughed off by water flow once the vessel gets underway.

Fire

Fire is probably one of the most dangerous events that can threaten thesafety of a ship and its crew. Shipboard fires must be fought with fire-fighting systems available on the ship. The crew must fight and defeatthe fire if the vessel is to survive. Crew training in fire-fighting and dam-age control are critical to ship survival.

Structural steels are vulnerable to annealing and softening withexposure to fire-generated heat, thus allowing structures to collapse.Shipboard composites can be a fuel source for fires, thus exacerbatingan already serious situation. In both cases, active and passive fire insu-lation systems are used to keep structural members protected from heatand flame for a certain period of time – presumably long enough to geta fire under control. For composites, great careis taken to select component materials withhigher levels of fire resistance.

An additional fire concern is the produc-tion of smoke and toxic gases from burningmaterials. Ships contain many flammable andnon-flammable compounds (liquids like fuel,oil, greases, paint, etc.; solids like furnishings,electronics, composite structures, metals, etc.)which when exposed to either heat or flamecan burn, volatilize, or smolder. The smokeand gases generated are of just as much con-cern as the fire itself. First and foremost, they hinder the ability of crewto get near a fire’s source to extinguish it. Secondly, they can pose a sig-nificant threat to large portions of the vessel even if the fire itself is smalland easily controllable.

Naval vessels, given their intention to go into harm’s way, aredesigned with materials and structures that meet higher standards of fireresistance and control. Additionally, active fire suppression systems areoften incorporated into combatants. All of these factors are balancedagainst affordability, but given that fire is one of the most dangerousthreats to a surface combatant, more resources are usually allocated tothis area.

Signature

Ships are very difficult to hide on the open water. A ship’s main defenseagainst detection is to reduce the amount of electromagnetic, acoustic, orthermal radiation it emits or reflects. In order to do this, ship designersare employing any number of technologies to absorb and deflect enemyradar, reduce thermal and acoustic emission, and in general increase thestealth characteristics of surface combatants.

As mentioned elsewhere, composite structures are being used on thetopside of ships to reduce weight. They also offer the capability of inte-grating absorbing and reflecting materials into topside structures. Bybuilding composite shrouding around the very reflective metal masts oncurrent ships, the electromagnetic signature of a ship can be dramatical-ly reduced. Future vessels will use predominantly composite topsidestructures to further reduce signatures.

Composite hull forms and new steel double-hull technologies offerthe promise of reduced thermal and acoustic signatures. Composites caninsulate the internal components from the water, while double hulldesigns allow for flooded compartments which can act as thermal andacoustic barriers. Composite and double hull technologies are alsoallowing more design freedom to create lower-profile, critically-shapedhull forms which further reduce all types of signatures, includingreduced wake.

Wave Loading

The structural demands of a Navy ship, and indeed any ship, are char-acterized by one particular load condition that most other structures willrarely see. Ships are subjected to a constant low-frequency, high-cycle

fatigue stress induced by wave motion. This isdue to ships not being rigid beams; they are infact a structural beam uniformly supported byhydrostatic pressure along its bottom surface.As the ship moves through water whose surfaceis not flat, often the ends are supported morethan the middle (or vice-versa), creating arepetitive bending moment in the structure.There are also repetitive lateral forces exertedon the structure which create other bendingmoments. While these moments are accountedfor in design, the component materials still

acquire damage over the service life of the vessel. The fatigue strength ofa welded steel structure does not increase relative to the strength of thesteel. Therefore, the use of higher strength steels requires detailed designagainst fatigue cracking over the life of the ship. Fatigue testing of struc-tural joints and computational techniques are employed in modern shipdesign to characterize the fatigue life of the structure.

Vibration

Vibration is a constant companion to any ship. There are hundreds of pieces of equipment aboard a vessel chugging away at their individ-ual tasks, each one imparting its own characteristic vibration mecha-

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nism into the vessel’s structure. While most large equipment is built on vibration-isolating spring mounts, none of these systems is perfectand always some vibratory load is transferred to the substructure. Evenwhen large equipment is well isolated, its acoustic noise induces vibra-tional loading into surrounding structure.

Vibration can induce fatigue, fretting, and other forms of degradation into structural materials. It also produces detectable noise transmitted through the water and interferes with a ships’ own sonarsystem effectiveness. Constant small movements cause surfaces to wear, and tiny amounts of elastic deformation may induce fatigue-likefailures over time. Since vibration cannot be eliminated, material andstructure decisions must take these degradation mechanisms into account.

Hull Damage

Ships are always susceptible to hull rupture from collision with fixedobjects (rocks, piers, sea walls, etc) and other vessels. Navy ships alsoface the possibility of having explosives detonated close by (hull whip-ping and blast loading) or being impacted by projectiles and fragments.Material choices are critical in reducing these threats, or at least reduc-ing the amount of damage. Unlike merchant vessels, Navy ships areexpected to maintain a high level of performance even when damaged.Therefore component materials’ ability to not only limit damage butalso be quickly repairable is paramount.

Hull survivability is part of the structural design of warships. Grillageis analyzed and built such as to limit the amount of damage caused by perceived threats. New designs such as double hulls (and some composite structures) have additional, built-in resistance to hull rupture.

Materials with high fracture toughness are obviously prime choicesto limit damage propagation. Specific materials are often used in criti-cal areas of the hull. The hull structure must be fracture resistant underhigh intensity loading at temperatures as low as -40 °F.

CONCLUSION

Materials play a key role in many aspects of the construction and operation of modern ships. For construction of Navy vessels, there aremany standard and traditional procedures that determine most of these aspects. While steel is by far the most common, economical construction material, there is significant interest in aluminum,

titanium, stainless steels, and composites for future, high-speed ships.The Navy is aggressively pursuing improved structures and novel construction methods that could serve to dramatically revolutionizefuture vessels. They will have significantly different hull forms, be fabricated increasingly by automated methods, and will utilize evenmore light-weight metal, hybrid, and composite structures than we currently envision.

The Navy is evolving its combatant fleet with the introduction of newmaterials and new construction methodologies. We have provided inthese pages a brief look at the most pressing issues ship designers consider when choosing materials. Future vessels will utilize new materials to enable capabilities that far outpace their current sisters, justas the armored steel, steam turbine powered battleships of the early 20thcentury were revolutionary technological leaps ahead of their wooden,wind-powered predecessors.

REFERENCES

American Society of Naval Engineers, www.navalengineers.org.

C.R. Crowe, and D.F. Hasson, Materials Trends in Marine Construction.United States Naval Academy, Division of Engineering and Weapons,Annapolis, MD (1990)

E.J. Czyryca, Advances in High-Strength Steel Plate Technology forNaval Hull Construction. Naval Surface Warfare Center, CarderockDivision, Metals and Welding Department, Annapolis, MD

Federation of American Scientists, www.fas.org

T.C. Gillmer, Modern Ship Design, 2nd Edition. Naval Institute Press,Annapolis, MD (1977)

National Shipbuilding Research Program, Advanced ShipbuildingEnterprise, www.nsrp.org

Ship and Submarine Materials Block, Navy Exploratory DevelopmentProgram FY1991 Block Plan. Naval Surface Warfare Center, CarderockDivision (Formerly David Taylor Research Center), Bethesda, MD (1990)

Carbon and Alloy Steels, ASM Specialty Handbook, Steels for Ships andOffshore Structures. J.R. Davis editor, ASM International, Materials Park,OH (1996) pp. 669