The present state of affairs with respect to plastics in shipbuilding in Japan. Part 1

INTERNATIONAL SHIP STRUCTURES

CONGRESS

Part

I

THE PRESENT STATE OF AFFAIRS WITH

RESPECT

TO PLASTICS IN SHIPBUILDING IN JAPAN

REPORT

BY PROF. DR. MASAO YOSHIKI

Part II

THE USE OF PLASTIC MATERIALS IN SHIP

STRUCTURES

REPORT SR 63/10 OF LLOYDS REGISTER OF SHIPPING BY J. B. DAVIES B.Sc.

Prof.Dr. M.Yoshiki and Mr. J.B.Davies were requested

iDy the Chairman to prepair reviews with respect to

the use of plastic materials in ship structures. The layer part of the contents of these reports was incorporated in the report of the Netherlands Panel. However it was deemed useful to distribute also the

original reports to the delegates of the Second International Ship Structures Congress

Printed by the Printing Office of the Department of Mechanical Engineering,

Part I CONTENTS by M.Yoshiki. I, II. III. Introduction Basic Research Primary Construction Page ft 1 2

IV. Secondary Construction 't 3

V. Outfit, Finish and Others 4

VI. Fabrication and Inspection Standard 't 4

VII. Conclusion 4

References

t

4

Part II by J.B. Davies.

I. Introduction Page 9

II. Present State of Affairs 't 15

III. Developments 25

IV. Research in Connection with

Plastics in Shipbuilding f' 26

V. Conclusions and Recommendations

References t,

28

The present paper reviews the present state of applications of plastics in Japanese shipbuilding industry with main emphasis on the development and researches of plastics. Plastics materials being used in

shipbuilding are classified as follows:

Primary construction (e.g. hull, deck house)

Plastics for shipbuilding

Structural plastics

Secondary construction

(e.g. ventilator, tank, propeller) Non-structural plastics (tertiary)

(e.g. door, pipe, deck finish, paints)

Fibreglass reinforced plastics began to be introduced into Japan about 1954, and in the period of 1955 to 1958, some sporadic attempts were made to use this type of plastics for manufacture of boats, life-boats, or outfits at different places. But on account of imperfect development of materials and inferior technique of fabrication, many difficulties were found. in the application of plastics to shipbuilding and these efforts petered out. For a drastic advance in the application of plastics to ship-building, the necessity is being keenly felt for organization of a more

comprehensive research program with the pooled efforts of individual producers of basic materials, plastics fabricators and users.

Systematic developmental researches on structural plastics (mainly, fibreglass reinforced plastics, to be hereinafter abbreviated as PEP) are concentrated in the 51 'th Research Committee of the Shipbuilding Research Association of Japan (to be hereinafter abbreviated as SR-Sl) on one hand and in the Reinforced Plastics Association and the Boating Association of Japan (to be hereinafter abbreviated as SP-Committee). The SR-51 devotes

their efforts chiefly to the basic researches related to the applications to superstructures, and secondly and tertially applications (including common plastics) (1960-1962), while the SP-Committee devotes their efforts to application of plastics to secondary construction of mine sweepers and manufacture of racing motor boats with FRP (1961-1962). Now there is

ripening movement to make a merger of these two and establish a permanent research and development organization in 1963.

II. BASIC RESEARCH

11.1 Mechanical Strength

The SR-51 /i/ conducted comparative tests on cloth-phenol, hard polyvinyl chloride (PVC), and FRP (epoxide resin, phenol resin, polyester resin) for fatigue strength (rotary bending, plate bending), weathering strength (half to one year outdoor exposure, and weather meter), sea water

immerdion strength (one to three months), temperature characteristic (tensile strength) etc. Meanwhile, the overnment Mechanical Laboratory and the Tokyo Chemical Industrial Research Institute carried out chiefly experimental studies on the mechanical properties of FRP, for instance, the effect of dynamic properties of FRP /2/,

/3/

(fatigue, creep, stress concentration), pre-loading and stresses on its weathering strength. /4/

-2-To investigate the overall properties of FRP as basic materials for boats, the Boat Materials Committee and the Basic Materials Committee

/5/

were formed under the SP-Committee (1960). In line with the conceptions presented in the Marine Design Manual of the Owens-Corning Fibreglass

Corporation USA, these committees investigated the qualities of domestic-produced FRP, clarified the characteristics of seven grades of FRP coni-bined with various fibreglasses (equivalent to Ml - M5, M7, M8 ander the Marine Design Manual) found out various elastic constants and strengths

and made a statistical study.

On the other hand, a four-year long investigation /6/ of FRP Dlates has been conducted on the long-time weatherproofness (outdoor exposure), waterproofness (fresh water and _3.5% sea water) anti-corrosiveness to

chemicals (gasoline, 3o% sulphuric acid, _io% caustic soda). 11.2 Structural Strength

SR-51 /i/,

/7/

studied on the fabrication, static strength and fatigue strength of bonded joints (lap joints of FRP, epoxy, phenol, PVC); welded joints (PVC, polyethylene); and bolted joints.

Strength test of stiffened FRP plate and FRP sandwich construction were conducted by SR-51

/7/

(bending of stiffened FRP plate; bending and

compression of FRP honeycomb, FRP foam sandwich plate), by SP- tank

committee

/a/

(hydraulic pressure test of stiffened FRP plate as tank member for wooden mine sweepers), SP-B class runabout committee

/io/

(stiffened FRP plate as bottom plate for racing motorboats, and by SR-51

/7/

(bending

and hydraulic strength of the panel with which the stiffeners cross at right angles).

11.3

Characteristics as outfit

SR-51

/7/

carried out investigations on the heat-insurating

charac-teristic as panel (FRP single board, FRP honeycomb Sandwiched Board), on the acoustic characteristic

(Pvc

honeycomb, FRP honeycomb, FRP single

board, stiffened FRP plate,), on the ventilating duct characteristic (PVC), on the technique of piping outfit (PVC, application to hot water system, method of joining, manner of supporting), etc.

The Plastics Research Committee of Japan Welding Engineering Society has conducted studies on the welding, bonding and testing of plastics, and now is drawing up a draft engineering standard.

III. PRIMARY CONSTRUCTION 111.1 Boat Hull

In Japan, the production of FRP-made pleasure motorboats is expanding steadily, the figure for 1962 being estimated at 1400 (converted to 14 feet). Several plants specialize in this line of production, the sizes of the

boats produced ranging from 8 to 21 feet. Every year a boat show is held to announce the year's new styles. Thus, pleasure boats in Japan are now

established as a commercial item.

Meanwhile, researches for manufacture of racing motorboats (including runabouts and hydroplanes) with FRP in the interest of longer life and

better performance as compared with the wooden boats were undertaken by SP-Committee

/io/,

/ii/, and after various basic tests and prototypes of a 3

meter runabout and a 2.5 meter hydroplane have been perfected with slightly smaller weight than the wooden ones; equal performance but with nearly twice the strength of the latter. Fig. 1 shows the construction of 3 meter

boat Association are pushing developmental researches for ocean-racing motorboat

(7

meter, 200 np) which can negociate the waves on the open sea.

Another project worthy of note is the manufacture of yachts for 1964 Tokyo Olympic Games /12/ (Fin and Flying Dutchman). Meanwhile, there are some examples of plastic boats for practical purposes, such as the lavergathering boat, already commercialized, which is highly being appreciated for its light weight; life-boat which are being vigorously studied; and small fishing boats which are now being planned.

2 Superstructure

SR-51 /13/ has been responsible for the study of replacing the wooden wheelhouse of the patrol boat "Haruchidori" (44.80 in x 6.80 m x 3.55 m) with FRP. The wheelhouse, 3.75 in long x 3.60 m wide x 2.1 m high, was built

of 6.5 min thick FRP, with hat section stiffeners inserted at 700 mm inter-vals; and the panel deflection was designed not more than 1/50 of span and

the stiffener deflection not more than i/ioo of span. There are five

building blocks and the joints were executed with metal fixtures of aluminium alloy between ceiling and side wall and in mat-in connection between side wall and side wall. FRP-made outfits included two watertight doors, two side

Light boxes, two signal flag stands and one searchlight stand. The finished weight turned out equal to 54% of a steel one or 65% of a wooden one. Very

little vibration was felt in the trial run. Fig. 2 shows the construction of this wheelhouse.

Other examples of application to superstructures included the compass house /14/ (3 in x 3 in x 2.4 m) of a 45.000-ton tanker, and the

super-structure of a wooden pleasure boat /14/; both were of sandwich construc-tion with FRP and PVC-foam plastics. In the latter case the reducconstruc-tion of weight as compared with a wooden structure amounted to about 3 tons (or 6% of displacement tonnage) and the speed increased even about io% over the expectation. Fig. 3 shows the construction of this superstructure.

SECONDARY CONSTRUCTION

The fairwater (covering of seachest) of the mine detector of a medium mine sweeper (46 in x 8.4 m x 3.9 m wooden lightweight-constructed), which

has been traditionally fabricated of stainless steel, is now made of FRP /5/. The dimensions are 2.7 m x 1.2 m wide x 0.5 m deep; whereas the thickness was 4 mm and the weight 110 kg in the case of stainless steel, it becomes 8 mm and 50 kg in the case of FRP. The tentative product has been submitted to a ball dropping impact test with satisfactory results of

collision resistance as compared with stainless steel and plywood. Also basic researches /a/ have been carried out to use FRP for fabrication of the fresh water tank and the fuel tank (about 7 in3) of a medium mine sweeper.

Part of the bridge of a submarine (2 m x 1.5 m x 1 m) has been con-structed of PRP. /16/

Manufacture with FRP of the distilled water tank (350 1, pressure 1.2 kg/cm2) for marine battery was tried. /17/

Developmental studies for using plastics for fabrication of propellers for small boats and fishing boats have been conducted; /18/ the materials are nylon

6,

fibreglass reinforced nylon, polyacetal, polycarbonate, and ABS, and the injection mold method was adopted. In the case of propellers

for medium vessels, propellers of diameters 0.95 in and 1.5 m were tenta-tively produced by FR? hand layup and are now under test on real vessels.

OUTFIT, FINISH AND OTHERS

SR-51 designed a plastic model room in one of the cabins (2.6 m x 3.2 m) in the trade fair ship "Sakura-maru; and applications of various plastics to the outfit are still being investigated (long range test for strength, fabrication, heat insulation, sound-insulation, vibration, etc.). In the said model room all the outfit items from the fixtures including the wall, ceiling, floor, entrance door, window frames; the furnitures including the beds, wardrobes, desks, shelves, book-cases, toilet cabinets, sofas, rotating chairs to the equipment including the windows, wash basins, water taps, air ducts and grills, the illuminating fixtures; the drapery and the curtain rods were made of plastics.

The observations in time of manufacture and during the voyage showed that the bed, desk, sofas etc. were warped; plastic fixture of windows developed a slackness in the screwed portion and sprung a leak. Meanwhile, the edge strength of plastic-made equipment was found insufficient. There was no other particular trouble. But some items showed no weight reduction through application of plastics (for example, bed, sofa and other items calling for rigidity); others yielded to metal ones. This suggests that there is certain limitation to the applicability of plastics for these items.

Recently built (April, 1963) sightseeing ships of Seto Inland Sea, "Sumire-maru" and Kohaku-maru" (77.00 m x 12.80 m x6.00 m, 2700GT.) made the best use of above mentioned researches, and their inboard ceilings, carpets, floorings, inboared paints, polyglass doors, various kinds of decolating panels, fittings and furnitures of crew space (paper honeycomb) etc. were vastly replaced by plastics.

FABRICATION AND INSPECTION STANDARD

SP-Committee /5/ has formulated the standards for plastics fabrication and inspection procedures of the fairwater and tanks of mine sweepers.

CONCLUSION

Development of new plastics materials fr shipbuilding in Japan has nearly reached a saturation point and their scope of applications has also been nearly settled. With considerable amount of data accumulated, the

next step will be to analyze them and establish the standards for designing, fabrication, testing and inspection.

REFERENCES

/i/ The Shipbuilding Research Association of Japan; Report of The 5lth Research Committee (1960) /2/ S. Shimamura; Reinforced Plastics 8.1 (1962)

//

S. Shimamura; Reinforced Plastics 8.6 (1963)

/4/ H. Maki and S. Shimamura; Reinforced Plastics 8.6 (1963) /5/ Boat Material Committee; Reinforced Plastics 7.4-5 (1961)

Basic Material Committee; Reinforced Plastics 9.2 (1963)

(W&S 5331/1)

/6/

K. Tabei; Reinforced Plastics

6.3 (1962)

/7/ The Shipbuilding Research Association of Japan; Report of The Slth Research Committee

₍₁₉₆₁₎

/s/

Tank Committee; Reinforced Plastics

7.3 (1961)

/9/

I. Hishida; Reinforced Plastics

7.4-5 (1961)

/io/

Boat Plastics Committee (B Class Runabout), Report

₍₁₉₆₁₎

/ii/ Boat Plastics Committee (B Class Hydroplane), Report

₍₁₉₆₂₎

/12/

T. Toda; Reinforced Plastics

9.4 (1963)

/13/

Y. Tokunaga; Engineering Materials

ii.6 (1963)

/14/ M. Makino; Plastics (Japan) 14.2

₍₁₉₆₃₎

/is/

Fairwater Committee; Reinforced Plastics

5.6 (1960)

/16/ S. Shimamoto; Jour. Soc. Naval Architects in Kansai, Japan

_{99 (1960)}

/17/

S. Shimamoto; Jour. Soc. Naval Architects in Kansai, Japan

102 (1961)

/ia/

A. Yazaki; Reinforced Plastics

7.4-5

(1961)

STA M? J(CT1ON rAiNco Al PL'y WOOD & 574 .Itt,. 4fftcI -t .flVQfl. -ABET h Ilv $r4A./ J(Cr,A.' il »sS S\SSS '_ s '_'-_. b. -.

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1.

3M

RACING- RUNABOUT fl_,1 /SO'D4' LCN(I BHE'. cuP ALE p, Í. tJA .LLAL Hui. L

--SSC - 5C 7CC -r::: T 400C -5060 9Oi2d4

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-i

JL 6S(C5+C)

50

3O.754 l2O9O4J ÇTI (90)

-

7S

- ---40-

,

(54)

Fig. 2, Patrol Boat HARUCHILXJRI" Wheel house

1. Upper bridge deck, 2. Centerline section, 3. Bridge deck

'..Lap joint '1D" part, 5. Hattype stiffner

6..

Upper part connection L' 7. Lower part connection "B" 8. Stiffner at corner "C"

I;

1T'

Iiu4

+ 3ph li A 2O p*O*NAPI* r r i I

NAft COME C lION

1 0 1 2 31

ROOF- VANL ROOF PAPEL SEcTIeN

9 A 20-.t 20-¶

fi

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---.=.;,-;-.-.

j-132 44 1 poi'rtç-rp. ruTry _SCPtw hi top -lT rn , A x20 FlST cLAc LotiW6e FtPo

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Excursion Ship "RIKtJCHU MARU NO. i

"

/

(W&S 5331/1) alTi

I. INTRODUCTION

The purpose of this review is to give those members of the Congress who may be unfamiliar with these materials, an introduction to plastic materials with particular reference to those useful in shipbuilding and an

indication as to the extent to which they are, and may be, used in ship construction.

Survey of Plastic Materials

The term plastics normally refers to materials that can be shaped under the influence of pressure and heat, or more accurately, to synthetic organic and inorganic macro-molecular materials. These materials are found neither as crystals nor as a pure liquid but in a state between the two, being built up of long and complex molecules by polymerization.

These materials are an extremely wide range that fall roughly into the following groups, depending on their molecular structure.

Thermoplastics are those comprising straight and branched chain molecules that are entirely dependent for cohesion on the molecular

bond, or intermolecular forces. They are softened by heating and set again on cooling without undergoing chemical change; this physical change is reversible and they will revert to their original state on the application of further heat.

Thermosetting plastics are those in which further chemical reaction permits a degree of cross linking that results in a three-dimensional network. They are increasingly infusible on heating and undergo this reaction, known as polymerization, which is not reversible. This reaction is characterised by three stages, viz. 'A' stage when the resin is still liquid, 'B' stage (after heating) when the resin is a thermoplastic solid and 'C' stage (after further heating) when the resin is fully cured and has become an infusible solid.

The structural arrangement within each group can vary sufficiently to produce a marked effect on the physical properties. Some linear

materials can contain areas of crystallinity, the extent of which affects the strength, rigidity and softening point. Cross-linking in the three dimensional structure also increases strength and rigidity although in this case the temperature effect is less pronounced within the working range.

An important effect of the structural arrangement is the visco-elastic behaviour of the materials under load. Under short term loading, plastics exhibit elastic properties, but by virtue of the dependance on inter-molecular forces, the sustained load will result in a degree of viscous flow. They are therefore essentially time-dependent, and for this reason are seldom used for important load bearing members unless rein-forced by strong inorganic fibres. The members are also temperature sensi-tive, particularly the thermoplastics group, due to the effect of tempera-ture reducing the inter-molecular forces.

The most important types are summarised in the accompanying tables,ç but it should be realised that these tables are incomplete and are included for comparison only. For the convenience of a compact review, the types of plastics are classified in Table i

Thermoplastics

The dependance of the straight and branched chain polymers on the molecular bond accounts for their relatively low strength and sensitivity to time and temperature. Their principal characteristic is the readiness to soften and flow with increasing temperature by virtue of the weakening of the intermolecular forces. Thus, they are easily formed and are

TABLE

I

-SIThIMARY OF PLASTIC MATERIALS

Group

Definition

General Characteristics

Thermoplastics Thermosetting moulding materials Reinforced plastics Laminated plastics Expanded plastics Casting resins Coating resins Adhesives Silicones

Straight and branched linear chain organic polymers. Powders that yield cross-linked polymers during the moulding process and which normally contain fillers for specific purposes. Cross-linked polymers reinforced with inorganic fibres. High pressure compression moulded fibrous sheets reinforced resins cross-linked during laminating process. Synthetic inflated macromolecular materials. Liquid resins for casting at atmospheric pressures. Synthetic high-polymers of all kinds suitable for protective coatings. Various synthetic polymers suitable for use as adhesives. _{Semi-inorganic synthetic polymers of various molecular weight.}

TABLE II

-S1ThIMARY OF THERMOPLASTICS

Group

Name

Acrylics Vinyls Fluorines Styrenes Polypropylene Amides Cellulose Polycarbonate

The properties of thermosetting moulding materials can be controlled by the use of certain fillers to give a range of hard infusible materials with varying electrical and chemical properties for specific purposes. For compression and transfer mouldings the phenolics are most popular on

account of their relatively low cost and versatility. The epoxy and polyester resins are later developments, the former possessing excellent bonding properties.

Reinforced plastics are a relatively new group of materials which have grown rapidly in recent years. These materials may be formed at low as

well as high pressures and are characterized by their light weight

corrosion resistance and good mechanical properties. The reinforcement is usually glass, but asbestos, cotton, sisal, jute and other synthetic fibres may be used. Polyester resins are mostly used with epoxide resins where higher performance is a requirement. Acrylics, silicones, nylons and other resins are occasionally used for specific requirements.

Laminated plastics comprise fibrous sheet based materials bonded under pressure at elevated temperatures with thermosetting resins that cross-link during the laminating process. The finished laminates are rigid and strong with the mechanical properties depending on the base material. Phenolic resins are generally used but epoxide, melamine and silicones are used for specific purposes.

The thermosetting resins are listed in Table _3. Expanded Plastics

12

-conducive to a wide variety of economic processing techniques. Although normally unsuitable for structural purposes, they possess excellent

electrical properties and chemical resistance.

The mechanical properties can be controlled by either:

i) modifying the molecular structure to vary the arrangement of side

branches,

varying the degree of crystallinity, or by the careful use of plasticisers.

The most useful of the thermoplastics are the polythenes and vinyls. With polythene the degree of crystallinity, and therefore density, can be

controlled and the material is produced in varying density grades. The high density grades have superior mechanical properties, are harder, more

brittle and better resistant to temperature. The vinyls include p.v.c.

which is normally rigid but can be modified by the addition of plasticisers. It has excellent abrasion resistance and is conducive to reinforcement to give useful mechanical strength.

The mechanical properties of the styrene group can be obtained by modifying the molecular structure. Polystyrenes are both versatile and

transparent, and among the most easily moulded thermoplastic. Polypropylene is another useful material and has a range of properties slightly superior to most thermoplastics.

A summary of the thermoplastic materials is shown in Table 2. Thermosetting Plastics.

The controlled inflation of synthetic macro-molecules has permitted the development of a range of cellular material of exceptionally low density. Their characteristic structure is conducive to efficient thermal insulation, in which respect they compare favourably with any available alternative. The closed, uni-cellular types are more cross-linked than the open cell types, with the result that they are more rigid and also more resistant to heat transmission. The materials are finding increasing use

TABLE III

-SUMMARY OF THERMOSETTING PLASTICS

Resin

General Description

Usual Fillers

Phenolic Urea Melamine Alkyd Polyester Allyl Epoxy Silicones

Phenol-formaldehyde. Furfuralaldehydeiphenol resins Urea formaldehyde Melamine formaldehyde Unsaturated polymerisable alkyd type resins, Esterification of polyhydric alcohols and polybasic acids. Diallyl Phthalate Condensation linear polymers with epoxide groups from epichiorohydrin and polyhydric compounds. Semi-inorganic polymersorga- nopolysiloxanes.

Woodflour, cotton, flock, paper, fabric, asbestos, mica, silica. Alpha cellulose, cellulose. Cellulose, asbestos, mineral fabric, glass fibre,

flock.

TABLE Ill

- TYPICAL PROPERTIES OF EXPANDED PLASTICS

Type

Nature

Specfic Gravity

Thermal Conductivity Btu/ft2/°F/in/hr

Polyurethane Rigid 0.008 to 0.40 0.2 to 0.25 (Iso cyanate) Flexible 0.24 to 0.63 0.2 to 0.3 Polystryrene Rigid 0.016 to 0.32 0.28 Polyvinylchloride Rigid 0.03 to 0.08 0.23 to 0.31 (p.v.c ) ixib1e 0.06 to 0.16

-Cellulose acetate (c.c.a. )

Rigid 0.064 to 0.11 0.30 to 0.31 Phenol formaldehyde Rigid 0.048 to 0.16 0.20 to 0.28 Silicones Rigid 3.5 0.28 Semi-rigid

Casting resins comprise a family of liquid resins that can be

polymerized with the aid of catalysts and accelerators in open moulds and subsequently oven cured to form hard infusible materials. The properties, which can be controlled to some extent by additives and fillers, are dependent on the moulding condition, cycle and cuie.

The main resins are allyl, epoxy, phenolic, polyester and polycarbonate. The phenolic grades have rather poor chemical resistance and are not

recommended for high temperatures, whereas the epoxides, which offer the best all round characteristics, maintain excellent electrical properties over a wide range of temperature.

Coating Resins and Adhesives

High polymers offer a very wide range of coating materials for various purposes, many being specially developed for specific requirements. The selection is a matter of whether the ultimate requirement is protective, against chemical or wear, or decorative. Similarly, there are many polymers forming the basis of an extremely wide range of adhesives for bonding

almost every combination of materials in present day use.

One of the most important of this group is the epoxicle group which are proving excellent, both as coating and adhesive materials.

Silicones

Silicones include the range of semi-organic polymers known as organopolysiloxanes. The type of organic group and the degree of cross linkage determines the physical form which can be fluid (waxes, polishes and lubricants), resins or elastomeric (silicone rubbers). They have

excellent electrigal properties through temperatures ranging from sub-zero to just above 300 C.

II. PRESENT STATE OF AFFAIRS

11.1 General

as the cores in structural panels faced with reinforced plastic laminates. The low density and thermal conductivity of the various types are shown in Table

_4.

Casting Resins

Plastic materials being used in shipbuilding are classified as shown below, and it is proposed only to elaborate on those materials used for structural plastics.

Plastics in Shipbuilding

Structural Plastics Non-Structural Plastics

I I

(Section 11.5) Primary Construction Secondary Construction

(Section 11.3) (Section

_11.4)

Of the many various types of plastic used in ship construction, reinforced plastics are showing the greatest promise as a structural

16

-most suitable material when, as is commonly the case, strength and stiff-ness are the over-riding considerations. The only plastic materials which

compete seriously in this respect are those with fibrous reinforcement, viz, reinforced plastics. These have a strength/weight advantage over steel, but they suffer a disadvantage in performance/cost ratio which only special circumstances can offset.

Properties which normally matter for structural application are lightness, strength, stiffness and dimensional stability, also resistance to weathering, chemical attack, heat and fire.

As the initial cost of a reinforced plastic component is usually much higher than that of the conventional material and design, this material is only being used where any of the above properties outbalance

the extra initial cost over the service life of the structure. However, in the case of an item in series production, the costs are often more

favourable from deductions due to the production rate and the large numbers involved. The main considerations appear to be lightness, durability and ease of maintenance.

11.2 Properties of Plastics used in Shipbuilding

The main thermosetting resins used in reinforced plastic laminates are polyester, epoxy and phenolic. The first two are by far the most important as both can be moulded at room temperature and pressure, and therefore do not recjuire any expensive tooling. Epoxy has superior proper-ties to polyester, but has the disadvantage of a much higher cost and is not so easily handled due to toxic and dermatitic risks.

Polyester resins have the great advantage that they cure through an additional polymerisation reaction and do not evolve volatile by-products in the process. They can therefore be moulded at low pressure, such as contact pressure when the pressure is only sufficient to keep the

moulding in the mould. Their development made it possible to mould shapes of almost unlimited size at an economic price, which previously had been impossible.

When used alone, however, polyester resins are not strong nor tough, but in combination with certain reinforcing materials, mainly some form of glass fibre, they exhibit properties which make them suitable as structural materials of considerable load-bearing capacity. This is by far the most important application of polyester resin.

The resins are cured by means of a suitable catalyst and accelerator at temperatures from 20'C and higher, with or without ressure. A general purpose resin has good hea resistance up to 120 - 140 C while improved resistance up to 180 - 200 C can be obtained with a tri-allyl cyanurate modified polyester. The material is generally unaffected by dilute acids, but is attacked by certain concentrated acids, strong alkalis and some weak alkali solutions. Also there is no effect from organic solvents such as xylene or petroleum but it is attacked by ketones, esters and

chlorinated solvents.

The usual type of polyester used in ship structures is a genera: purpose resin with good mechanical properties, low water absorption and a reasonable degree of heat distortion. In addition, there are other resins formulated for a specific requirement such as heat, fire or chemical resistance. These specific types are generally more expensive and have lower mechanical properties than the general purpose type.

Epoxy resins are used for the production of reinforced plastics, surface coatings, adhesives and for casting purposes. They are of impor-tance for their improved properties, chemical resisimpor-tance and exceptional adhesion, particularly to metals. They are used in a similar manner to polyesters, being cured by means of a hardening agent, with or without heat or pressure. The resulting solid is dimensionally stable, tough and

resistance to heat distortion and, above all, is chemically inert. By the use of various hardeners, fillers, diluents and resinous modifiers, the handling characteristics and selected properties of the resin can be varied over a wide range. Diluents are used to regulate the viscosity and improve the wetting ability of the adhesive and laminating formulations. Resinous modifiers are used to improve flexibility, impact strength and thermal shock resistance. Fillers may be metallic or non-metallic and are added to lower the coefficient of thermal expansion, increase thermal conductivity, alter surface hardness, improve adhesive properties and other flow characteristics. Each application must first be carefully studied so that the optimum materials may be used for a specific job.

The structures are invariably made of laminates using glass fibre in one form or another, and by the contact method at room temperature and pressure. Other reinforcements are used, such as asbestos fibres, but only when a specific property is the prime requirement. The most widely used type are small chopped strands, or fibres, either in the form of mats or sprayed as in the depositor technique. This type is a general purpose reinforcement which can be easily moulded and is useful for providing bulk

to a laminate. Glass cloths of many weaves are available, but these are infrequently used in contact moulding and then only for specialised.

applications. Roving cloths, however, are an exception to this an as they drape well on curved moulds, they are often used to form stiffening

members or on the face of the moulding to give a strong abrasion-resistant surface layer.

There are several methods of moulding reinforced plastics and the selection of a particular method is mainly dependent on the size of the unit, production rate, total production and the costs involved. The contact process, either hand lay-up or spray deposited, is by far the most widely used. Typical figures of pressures involved and glass content achieved are shown in the following table, based on polyester with glass mat reinforcement.

The above processes are listed in order of working pressure and hence order of tooling up costs. The percentage glass content of the

laminate increases according to the pressure, and consequently gives higher strength figures.

The mechanical properties of the laminate are mainly dependent on: Type of resin.

Modification to the resin system by additives.

Glass content and orientation of the reinforcement. Moulding Process Moulding Pressure

p.s.i. Glass Content Contact 0 ₂₇ Vacuum Bag 14 37 Pressure Bag

20 - 50

42 Autoclave

50 -

100 47 Matched Die

50 - 170

50

TABLE V

-TYPICAL STRENGTH PROPERTIES OF RESIN CASTINGS

TABLE VI

-TYPICAL PROPERTIES OF G.R.P. LAMINATES (POLYESTER)

Resin s.g. Tensile 1,000p.s.i. Flexural 1,000p.s.i. Compressive 1,000p.s.i. Polyester 1.22 6 -9 10 - 20 13 - 30 Epoxy 1.20

8-12

16-21

15-22

Phenolic 1.30 5 -9 8 - 15 7 - 15 Reinforcement % Glass Content s.g.

Thickness per ply.

ins.

Tensile Strength p.s.i.

Flexural Strength p.s.i.

Flexural Modulus Mat - 2 ozs. 30 1.42 .055 14,000 21,500

O95 x

io6

Woven Rovings - 26 ozs.

50 1.64 .037 33,000 27,100 1.81 Cloth - 10 ozs. 46 1.60 .016 24,100 31,100 1.96 x o6

Typical properties of the resins and laminates are shown in Tables

5 and

6.

The main advantages of G.R.P. materials in ship construction can be slimmaris?d as follows:

Material can be formed with or without heat and pressure. Good physical properties with good strength/weight ratio. Impervious to corrosion, rotting and marine atmospheres. Not subject to attack by borers and reasonably resistant to marine growth.

(y) Reduced maintenance and easy to repair.

11.3

Plastics in Primary Constructions

11.3.1

Boat Hulls

The production of G.R.P. pleasure boats is expanding steadily in nearly all producing countries. At each major Boat Show the percentage of plastic boats on display is increasing at the expense of wood and steel craft. The most significant increase over the past few years has been in the number of hulls in the 20 to 40 ft. range, although there has not been any great increase in number of craft in the higher ranges nor in the length of the largest hull. More high quality sailing yachts and inter-national racing craft are being moulded in G.R.P. One of the latest moves in the yacht racing field was the recent decision of the International Yacht Racing Union to investigate the Rules for

5.5

metre rating yachts to permit their construction in G.R.P.

The largest hull known to have been moulded to date is a 77 ft. pilot vessel built in Holland, using the 'Airex' sandwich construction. This

system consists of a p.v.c. core with G.R.P. face laminates and has been used on several craft built in Holland, Sweden and Italy, one of the most notable hulls being a 47 ft. landing craft for the Dutch Navy. Other notable craft are the 67 ft. Halmatic motor yacht, moulded in 1960 and

the ₅₇ ft. motor minesweeper which was built of honeycomb sandwich construction for the U.S. Navy in

1958.

Considerable interest is being shown in the use of G.R.P. for

fishing boats in many countries including U.S.A., Canada, Japan and South Africa.

In

this latter country, the material is thought to be particularly

suitable for their waters and craft of up to 80 ft. are being built and developed. Established fleets of gillnetters, about 26 ft. in length, are already operating with the Pacific North West Fishing Fleets in U.S.A.

While definite figures are not available for the production of ships' lifeboats, it appears that the largest proportion are now being built of G.R.P. The construction is generally single skin but some craft

are built of the '.kirex' sandwich construction. Boats of up to 36 ft. in length are in service, while designs are being prepared for larger craft up to ₃₉ ft. in length carrying 150 persons and about 17 tons in weight. An interesting development in this field is the tanker lifeboat which is basically a conventional hull with a totally enclosed canopy to afford the crew protection while sailing away from a burning tanker. Several boaLbuilders are putting forward G.R.P. hulls with canopies of G.R.P. or plastic reinforced asbestos as a solution to this problem.

It may be noted here that there appaers to be no record of G.R.P. lifeboats of any significant size in service, or being built, for any of the shore-based lifesaving authorities.

20

-11.3.2

Superstructures

Both sandwich and single skin with stiffeners have been used for plastic deckhouses. A wheelhouse (12 ft. x 12 ft.) fitted on a Japanese patrol boat showed a saving in weight of 46% and _35% over a similar

design in steel and wood respectively. In this particular design, a panel deflection of i/so of the span and a stiffener deflection of i/ioo of the span were worked to. Several trawlers with plastic wheelhouses are now in service in Arctic waters and will be subject to regular examination. Deckhouses have been fitted on various river craft, including Russian hydrofoils and the Denny hovercraft, and also to M.T.B»s and other small

craft in Britain and Norway.

Several proposals have been forwarded for wheelhouses in large tankers, but some have not materialised, although a compass house (io ft. x 10 ft.) has been fitted on a 45,000 ton tanker built in Japan.

11.4

Plastics in Secondary Constructions

The following are brief details of various applications of the

materials in secondary construction members, either as the complete member or a part thereof.

Fuel and water can be carried in built-in or separate tanks of

G-.R.P. Tanks of up to 250 ou. ft. capacity have, so far, been constructed. The material is not affected by any of the normal fuel oils nor is the water affected by the material, provided the necessary care is taken with the design and construction of the tanks. Similar tanks and associated piping, also in G.R.P., have been used for the carriage of wine.

Various 'fair waters' have been built of G.R.P. for covering under-water detecting gear in warships and also propeller cones in merchant

ships. These covers are very much lighter and simpler structures against what would be a fairly expensive fabrication in metal.

Several firms have produced plastic propellers, usually of nylon

6,

which have been in service for several years. Development studies have been carried out in Japan on propellers for small boats and fishing craft. These propellers have been injection moulded in nylon

6,

glass reinforced nylon, polyacetal, polycarbonate and A.B.S. materials. Propellers up to

5 ft. in diameter, moulded in G.R.P. by the hand lay-up process, are at present undergoing service tests. Considerable work has been done in Italy on the isovitrification of propellers where, after sand blasting, several layers of glass reinforcement and resin are applied over the blade

surface and each layer is post cured at elevated temperatures. Other coatings which have been tried are polyesters, polythene, vinyl, phenol and polyamides.

A resin coating reinforced with glass fibre is proving highly

satisfactory as a protection against corrosion of both old and new exposed tailshafts. Both epoxy and polyester resins have been used, and the

operation cf resin coating and winding on of the glass tape may be carried out on a lathe in the shop or done by hand at the ship. Coatings of

neoprene bonded onto the shaft with a rubber based cement are also used but are more expensive than the previous method.

Laminated plastic underwater bushes on rudder stocks, pintles and shafts are becoming commonplace. The usual type is fabric based phenolic with a few of nylon. These bearings are quite successfull if provided with

sufficient water grooves and the clearance is adequate, particularly with the nylon bearings which swell when immersed in water.

It is common practice now to internally fill a rudder with poly-urethane, foamed in situ, as a precaution against internal corrosicn and also to reduce the risk of fracturing the sideplating due to vibration.

reduce maìntenance. Ducts of this material are proving useful where chemical fumes have to be exhausted, such as from storage battery com-partments. The ventilator heads are also very much lighter and more

easily handled than the steel designs.

Various epoxy resin repair kits are available for the repair of steel structure and machinery components. These kits contain an epoxy resin cement for fairing and filling corrosion pits and similar damage

as well as glass reinforcement for "bandaging-up" fractured structure. 11.5 Plastics in Non-Structural Items

The more important of the many uses of the various plastics in items of outfitting, eguipment, auxiliaries, and finishing reuirement.s are given below.

The use of laminated plastics and vinyl sheetings as decorative wall coverings on accomodation space bulkheads is still increasing. The reduced maintenance and resistance to damage are important factors as well as

decorative.considerations. The laminated plastics are normally melamine and phenolic facing laminates with a bulkhead core of plywood, chipboard, asbestos, etc. Some shipyards are producing their own board by laminating skins of G.R.P. on to a suitable core. Hollow structural panels in

laminated phenolic are available for divisional cabin bulkheads. The resistance of these materials to fire is often a major consideration as their use may be subject to the fire regulations of the various government authorities.

Apart from the normal plastic cabin fittings which have been in use for many years, more recent developments are the use of thermoplastic strips for joinerwork trim purposes, handrails, etc. and the dip coating, generally p.v.c., of small metal fittings for cabin, galley and pantry use. Also the use of G.R.P. for window and port surrounds and for shower units. These shower units are produced as complete units with all the necessary fittings and only requiring connection to the piping systems. Apart from a significant weight saving, particularly in passenger ships, the maintenance on these units is much less and much easier.

P.V.C. is the most common plastic material used in the cabin soft furnishings. Polyether foam is also used in mattresses and in the various cushionings.

In the insulation of accomodation, provision and cargo chambers, the most important materials remain glass fibre, mineral wools and cork. The

expanded plastics are more expensive and their use is normally confined to where they can be easier applied than the traditional materials. The foams are available in slabs and blocks of varying densities, and in the

case of certain polyurethanes, they are two part liquids which will foam in situ. The types available are polyurethane, polystyrene, polyvinyl and expanded rubber. Often the refrigerated spaces are lined with melamine laminated sheets or G.R.P. coated plywoods.

G.R.P. and expanded plastics are used in the construction of insulated doors and plugs for refrigerated chambers. The resulting structures are exceedingly light, strong and resistant to moisture as well as of low thermal transmission. Class II deckhouse doors and cabin doors have also been made in G.R.P., generally of a sandwich construction.

Although plastic sun awnings have been in service for quite a number of years, they have been laminated plastics, usually of the phenol formal-dehyde type. The use of G.R.P. corrugated sheeting has expanded enormously on land and is now finding a marine use in permanent sun awnings; although it is cheaper, it is not as strong as the older materials. Corrugated vinyl sheeting is similarly being used.

22

-G.R.P. has been used. for various boxes and protection covers for deck gear, such as lifebelts, batteries, boat petrol, boat winches, etc. Also for funnel cowls and companies' crests on funnels and sterns.

Several designs for cargo hatch covers for sea-going ships have been prepared, but there is no record of any cover of a considerable size having been moulded. Such covers would have to comply with the require-ments of the various authorities and be subject to extensive testing.

These tests may include the performance of the loaded cover under fire. Oil tanker hatch covers would be subject to similar testing and one design, which has undergoae such tests and several years service experience, has been approved by some classification societies.

Cargo hatch covers of a non-load bearing type are fitted on river barges and also some small hatch covers, such as to fish holds and rope stores, have been produced in G.R.P.

One of the first applications of reinforced plastics was the

swimming pool, which is much lighter add. less expensive in initial cost and maintenance than the traditional tiled pool. With the advent of the crew's portable pool in tankers, p.v.c. sheeting can be conveniently used and this should withstand the frequent dismantling and re-assembly.

Neoprene deck coverings are proving satisfactory as weather deck and internal deck compositions and as underlays in accomodation spaces. Their use as a weather deck covering shows considerable reduction in weight and they are slightly less expensive than wood. Decorative vinyl and neoprene rubber sheetings and tiles are showing little progress against the traditional linoleum.

Turning to life saving equipment, such as rigid liferafts, containers for inflatable rafts and lifebuoys are also made of G.R.P. Increasing

use is being made of vinyls for lifejackets replacing some of the traditional materials as buoyancy. In boats, the buoyancy is normally fitted as solid blocks, or foamed in situ in the case of certain polyu-rethanes. Polystyrene blocks, where exposed to oil and water, are

generally sealed in a layer of G.R.P.

Hatch tarpaulins of polyester fibre or nylon proofed with

P.V.C.

are becoming more common. The new types are claimed to be lighter and

easier to handle, stronger, and require less maintenance than the initially cheaper flax canvas variety.

Ropes of polythene and polypropylene have recently been added to the more common synthetic fibres of nylon and polyester fibre. Their strength

is less than that of the older materials but they are linter;

polypropylene has the added advantage that it will float. The synthetic fibres, although initially much more expensive than hemp or manila, are

used. when easier handling characteristics under both wet .nd cold conditions, lighter weight, durability and strength are deciding requirements. The

elasticity of the fibres, although useful for certain purposes, is too great for other tasks and manufacturers are studying meanE of reducing this stretch.

The use of the various plastics in paints and tank coatings has increased enormously. Vinyl based paints are used on the hull and produce an excellent surface with high resistance to corrosion and fouling.

Epoxy resin based paints are highly successful on topsides and decks and have reduced maintenance considerably. It is in the coating of cargo oil tanks in the tanker that the greatest expansion has been made, both epoxy and zinc silicate paints are being extensively used as a means of

corrosion control. The recent reduction in scantlings of oil tanks allowed by some classification societies if the tanker is fitted with an approved

system of corrosion control has, of course, been partly responsible for the very great interest in this field. Deep tanks for the carriage of vegetable oil have also been coated with epoxy resin. Other plastic based paints are the vinyl based emulsions for accomodation work and the new

Regarding plastic piping, as these materials are generally heat sensitive and very susceptible to fire damage, many classification societies will not accept plastic pipes for ships' services essential to safety. They may, however, allow their use for less essential services where suitably protected. from damage and for cold water services and systems in the accomodation spaces. The most suitable for this latter use are the thermoplastics comprising certain p.v.c., polythene and A.B.S. materials. Glass reinforced epoxy and polyester pipes have limited use due to the above restrictions, and they also are more difficult to work and require to be 'tailor-made'. Some large bore steel piping, such as for circulating sea water, has been lined with G.R.P. as protection against corrosion.

Neoprene and p.v.c. have been used as bi-metallic jointing material. Plastic materials have long been in use in the electrical industry and do not need any further comment here.

11.6 Rules, Specifications, Codes and Technical Requirements 11.6.1 Workshops

As the satisfactory processing of G.R.P. by the contact process is sensitive to its environment, most authorities require plastic structures to be moulded in an approved works under controlled. conditions of tem-perature and humidity. No authorities have yet published their works requirements, but the main points with which Lloyd's Register of Shipping are concerned in the approval of building premises are the condition of the building and its capability of maintaining controlled temperature and humidity conditions within acceptable limits. Adequate ventilation has to be provided and the necessary precautions taken against dust, draughts, and U.V. radiation. The arrangements for the storage, handling and use of the resin and glass materials are also subject to critical examination. This classification society has possibly carried. the examination and approval of works conditions to a greater degree than any other body and has published a list showing over seventy firms throughout the world which

they have approved to date.

A sub-committee of the British Ministry of Supply investigating the problem of resin cure, found that good conditions are essential if the material is to fully cure and develop its maximum mechanical properties.

11.6.2 Construction of the Ship

There are, to date, no published structural requirements for plastic ships and fishing vessels. Lloyd's Register of Shipping published in 1961, their Provisional Rules for the Construction of Plastic Yachts, which although dealing specifically with yachts, can be used as guidance for commercial craft. The same Society has recently prepared Proposed Rules for

_5.5

Metre Rating Yachts on behalf of the I.Y.R.U.

The above mentioned Rules for Yachts require the hull structure to be moulded in an approved works and constructed of approved materials in

accordance with approved drawings.

The scantlings of the hull, framing, deck, bulkheads and all major items are given. These scantlings are quoted in ounces per square foot of chopped strand mat, but can be readily converted for laminates of other

con-structions on the basis of equivalent strength to the values given. No test coupons are required, the various tests being carried out on off-cuts from the various laminates.

-

24

-11.6.5

Lifeboats and Lifesaving Equipment

The undernoted national authorities are known to have published rules relating to the construction, testing and approval procedure for G.R.P. lifeboats.

Polish Register of Shipping

Deutsche See-Berafsgenossenschaft United States Coast Guard

United Kingdom Ministry of Transport Registro Italiano.

All these requirements are very similar and call for lifeboats to be built in an approved works under controlled conditions. Details of the materials and the moulding process have to be submitted for approval, as well as the design and construction drawings. The lifeboats are to be

built under survey and the moulder has to employ a rigid inspection system. The lifeboats are generally ttype' approved for series production and the prototype boat of a design is subject to various strength tests, such as deflection, drop, impact and hook tests. Production lifeboats from a series may require to be similarly tested at pre-determined intervals. Sample test coupon laminates similar to the hull construction are made and subjected to various tests.

11.7 Durability of Plastics

Plastic boats were early in service with the various navies and it is after over ten years intensive testing and evaluation that the United States Navy and the British Admiralty have come out in favour of the plastic boat against its wood or metal counterpart. These approvals have specifically referred to the smaller craft below ₅₅ ft. as the larger craft are much more recent. They have found that the boats need less maintenance, are less susceptible to damage, and if damaged are easier to repair.

The United States Coast Guard recently examined one of their early plastic 40 ft. hulls which had been in continuous service since early

1952. Since 1958

the craft has been operating out of the Houston Ship

Canal where the waters are highly corrosive due to refineries waste. The hull was thoroughly examined on the ship and found to be in a sound

condition. Several panels were cut from the hull and no undue degradation of the material was found, confirming the fact that the material will stand up to hard usage in a marine environment. The maintenance of this craft was lower than that of the similar steel boat.

Many of the early material failures in boats and other items have been due to lack of knowledge on resin formulations and inadequate attention to workshop conditions. Later failures are attributed more to faulty or bad design, rather than failure in the material itself.

The reliability of the material is also shown by the United States Navy experience with submarine fairwaters which have been subjected to very severe and rigorous service over the past two years, during which time the structures have been practically maintenance free.

11.8 Fire Resistance of Plastics

All ordinary polyesters burn and will go on supporting combustion with the removal of the source of ignition. The laminate does not melt or flow as would thermoplastic materials, the resin burns away leaving the glass reinforcement limp, and unsupported. Resins can be formulated to improve the fire retarding properties, which unfortunately are often

obtained at the expense of the strength and weathering properties. There are several methods of obtaining these properties.

One of the earliest methods was to add antimony oxide and chlorinated paraffins to the resin system, which could be done by the moulder or, as is becoming more common, by the manufacturer.

Other methods are the use of resins where the fire retarding properties are chemically built-in during formulation of the resin. A group of these latter resins is based on H.E.T. Acid in which the fire retarding properties are achieved without affecting the other properties to the same extent as the other methods. These resins are, of course, much more expensive than the normal general purpose

polyester.

The va:'.ious authorities generally state which methods can be used to obtain the fire retarding properties. Their requirements are not necessarily the same for the same product as in the case of lifeboats, for example, the lJnìted. States Coast Guard do not allow additives which are permitted by the British Ministry of Transport.

III DEVELOPIVNTS 111.1 General

The shipyard, shipowner, availability of plastic materials and the availability of the traditional materials are some of the factors determining the degree to which plastic materials are

to be used. The amount of these materials being used varies greatly from ship to ship and it is on the large passenger liners that one sees the most applications. There are no marked signs of a rapid deve-lopment in this field, and it is thought that in the immediate future, the trend will be a growth in the present uses of the material, rather than development on further uses.

111.2 Increase in Size of Plastic Hulls

As previously mentioned in Section 11.3.1., over the last few years there has been no significant increase in the length of the

largest plastic hull, but rather an increase in the average length due to the greater number of craft between 20 and 40 ft. Although 130 ft. has been suggested as the economic limit in the size of G.R.P. hulls and Lloyd's Register of Shipping Plastic Yacht Rules are for yachts up to 120 ft., it is thought that it will be several years yet before craft of this size are constructed.

It is interesting to note that the 77 ft. hull referred to in

Section 11.3.1 . is a pilot vessel, as development in this work launch

field was expected to be much quicker. Perhaps the marine authorities, viz, pilot, police, customs, fire and harbour service etc., are becoming more interested in the material, now that it has been proved. However,

some authorities, such as the London Metropolitan Police, have been using plastic hulls for several years and are replacing their wood

boats with plastic craft. The most significant advance will possibly be in bhe size and number of fishing vessels, where the relatively high

initial costs could be absorbed by the considerable numbers which may be built.

26

-111.3 Superstructures and Deckhouses

Increasing use of the material may be made in the superstructures of small high-speed craft, small passenger vessels, hydrofoils and other craft where top weight is at a premium. From a reduced maintenance aspect, a standardised deckhouse may be adopted in trawlers, tugs and tankers. These deckhouses could be assembled from standard sections and presented

to the hull as a complete unit incorporating as much of the internal structure and fitting out as possible.

111.4 Miscellaneous Developments

With the increase in specialisation of ships for particular

cargoes, such as chemicals, gas, etc., a possible use of G.R.P./.Plastics may be in the construction of the cargo tanks.

Much work is being done in the fabrication of large tanks and pressire vessels in these materials for the chemical industry and they can easily be

adapted for shipboard use. The filauent winding techniques now being commercially developed may reduce the costs of the tanks and their associated piping to a more economic level.

This same filament winding technique may be used for the manufacture of tubular structures such as masts, cargo booms and large bore piping.

The saving in weight due to replacing the steel cargo hatch covers with a plastic design should show a considerable increase in deadweight and ease in cover handling. However, two main problems will require to be solved, one of restricting deflection under load and the other, of the effect of fire. The first may be achieved by use of high tensile glass reinforcements but the second may require a high quality fire

retarding resin or some other surface coating, both of which may retard the development due to economics.

A recent interesting development is the production of thin gauge steel sheeting with a plastic coating. This plastic coating, usually a plastcised vinyl, is a decorative finish and is applied to the plate just after it has been rolled. This sheeting should have several suitable shipboard applications.

IV. RESEARCH IN CONNECTION WITH PLASTICS IN SHIPBUILDING. IV.1 Testing Methods

Little work is being carried out in this field in the United Kingdom, most of the work being for the aircraft, engineering and building applications. The testing is carried out using ISO standards where possible, otherwise B.S.S., A.S.T.M. and D.I.N. specifications may be used.

A suitable test for the assessment of cure is urgently needed, as is the provision of suitable inspection equipment for carrying out this test and determination of laminate thickness from one side only. IV.2 Materials Research

The resin companies are continuing to work towards better heat and chemical resistance as well as improving the batch to batch uniformity of the materials.

Many glass companies are at present working to improve the

wetting out and higher mechanical properties. The glass reinforcements are also becoming increasingly more uniform. The demand for a reinforcement for corrosion applications is giving stimulus to new types and forms of

asbestos reinforcement that are being developed by asbestos companies in the U.S.A.

Some work that is currently being done by the British Plastics Industry is

Improvement of general purpDo type polyesters.

Improvemci:vt; ; fire retarding polyesters.

Assessment of resin cure. Effect of additives.

Improvement and development of glass fibre finishes. Relative merits of E and A glasses.

Ef1:e.; ; of glass to resin ratio.

Development of new synthetic fibres for improving sirface resistance. IV.3 Structural Research

IV.3.l Properties of Structures as a Fimction of Properties of Materials Projects at present being carried out by the United States Navy on the design of G.R.P. laminates include design and construction features developed as a result of past experience in the use of this material. Amon These projects are:

L

Research and development leading to completion of a Plastic Design Manual.

Research and development of plastic laminates, including a light weight G.R.P. material for surface ship deckhouse structure.

Hydrostatic testing of plastic deckhouse bulkheads and deck plating. Structural research in the United Kingdom, apart from odd workshop tests, has been confined to the examination of plastic craft during service. A test programme is at present being run to determine useful combinations of mat and unidirectional roving fabrics and find suitable design strength and stiffness values as well as the operator variation.

Apart from the American work mentioned above, some basic research work could be done on:

Economical design of framing and stiffening members. Strength of' matting-in connections, glass to glass, and glass to wood.

Effect of time on the bonding of polyester.

IV.3.2

Complex Structures : Combinations of Various Plastics and

Combinatio.r o' Plastics with Non-Plastic Materials.

Considerable work has been done on sandwich panels as can be seen from the extent of Mr. Abrahamsen's bibliography in his Review to the First Congress. In view of the low stiffness of G.R,P. it is thought that the combination of .R.P. and steel should be subject to examination and study. Considerable interest is being shown and development work being carried out in the combination of thermoplastics and G.R.P. for use in the chemical industry. This material is intended for tanks, pressure vessels and pipicg in which the excellent chemical resistance of the thermoplastic, generally, p.v.c., is combined with the high strength of the G.RÒP.

Further work could be carried out in the bonding, bolting and riveting of G.R.P. to the formaT shipbailding materials.

28

-V CONCLUSIONS AND RECOMMENDATIONS

The reinforced plastics industry is now well established and with the growing use of G.R.P. as a structural material, it is considered that advantage coid be gained by the adoption of standard specificatins and test procedures. Without this standardisation much of the information from testing will be of a limited value. The adoption of standard material specification should ensure some measure of quality control.

As G.R.P. is environment sensitive, the adoption of common standards for workshop conditions would also be advantageous.

The British Plastics Federation Repí Jo. 46, published in 1962, is of interest as it reveals some significant gaps in the existing knowledge of the long-term properties of reinforced plastics. It recommends th9

division of basic and applied research and the degree of priority to give to each aspect, and also gives a suggested method of recording experimental data.

REFERENCES

The following are some of the more important references on the general use of plastics in shipbuildirg, and this list should be used in

conjunction with the references given in Mr. Abrahamsen's Review to the First Congress. There are, of course, many other references to specific uses of the material given in the various technical journals.

/1/ Stagl, F.M.,: Current Status of Fiberglass Reinforced Plastics in Marine Applications. In : 17th Annual Meeting of the Reinforced Plastics Division of S.P.I., Chicago, 1962.

/2/ Wert, J.,: Plastic Superstructures in Ships. In : 3rd.

International Reinforced Plastics Conference, British Plastics Federation, London, 1962.

/3/ de Does, J.Ch.,: Some Possible Uses of G.R.P. in Shipbuilding Appendix. In : Report from Working Committee on G.R.P.,

October, 1962.

/4/ de Does, J.Ch., and Wimmers, H.J.,: On the Study of the Design and Construction of G.R.P. Ships. : Paper to the 57th Meeting of

the Schiffbautechnischen Gesellscflaft e.v., November 1962. /5/ Busenaker, O., and. Taal, L.,: Development and Building of

Plastic Boats for the Royal Netherlands Navy.: Schiff und Hafen No. 4, April 1961.

/6/ Engelbrecht, B., Some Fundamental Considerations in Respect of the Use of G.R.P. in Small Boat Building : Schiffbautechnik, March 1963.

/7/

The Development of Reinforced Plastic Boats in Great Britian 1951 - 1961 : Ship & Boatbuilder, Annual Review 1962.

/8/ Plastics Make Progress in Boatbuilding : British Plastics, December, 1962.

/9/

Gibbs & Cox, : Marine Survey Manual for Fiberglass Reinforced Plastics, New York, 1962.