• Nie Znaleziono Wyników

Proceedings of the 9th Symposium Yacht Architecture '86The 8th International HISWA Symposium about Yacht-Design, Yacht-Building and Sailboards, The Netherlands, 14-14 March 1986

N/A
N/A
Protected

Academic year: 2021

Share "Proceedings of the 9th Symposium Yacht Architecture '86The 8th International HISWA Symposium about Yacht-Design, Yacht-Building and Sailboards, The Netherlands, 14-14 March 1986"

Copied!
188
0
0

Pełen tekst

(1)

5YNIP05686101

ARLH

The 9th International Hiswa-symposium about

yacht-designjacht-building and sailboards

organised by Hiswa and

Waterkampioen- magazine

13114 maart

AC

TECHNISCHE UNIVERSITEITLaboratorium voor Scheepshydromechanica MakeMeg 2 - 2628 CD DELFT

(2)

Under the auspices of:

Weesperstraat

93,

1018 VN Amsterdam, The Netherlands and

Waterkampicen Magazine, Postbus 93200,

2509 BA Den Hag, The Netherlands

Production: Eelco Piena/Waterkampioen

Publisher: Koninklijke Nederlandse Toeristenbond AMIB,

Postbus 93200,

2509

BA Den Haag, The Netherlands

(3)

SHIPMATE:::

MIJN MAT

De RS 6100 Navtex

ontvanger vertelt

mij geruisloos in welk

humeur de

weer-goden zijn!

Niets is zo veranderlijk als het humeur van de weer-goden. Daarom is het, vooral met het oog op de

vei-ligheid, erg belangrijk voor de beroeps- en plezier-vaart am vooraf te weten, wat het weer gaat doen.

Shipmate, de Deense specialist in het vervaardigen

van navigatie- en kommunikatie-apparatuur, heeft zodoende een uiterst kompakte en eenvoudig te bedienen navigatie-telex ontvanger ontwikkeld, de

RS 6100 Navtex ontvanger (goedgekeurd door de

PTT).

Binnen het bereik (200-400 mijI) van een groot

aan-tal wereldwijd verspreide zenders, ontvangt de RS

6100 dag en nacht o.a. navigatie- en weerberichten,

stormwaarschuwingen, en informatie over

red-dingakties.

Alle informatie bewaart hij 72 uur in zijn geheugen

(batterijgeheugen 5 jaar).

Door het handige "klikvast systeem D'" van Ship-mate, kan deze kleinste Navtex ontvanger altijd op

een praktische pleats worden gemonteerd.

De RS 6100 is ook als printer aan te sluiten op

andere navigatieapparatuur.

U zoekt ook een Navtex-ontvanger? Dan raad ik u

aan; bel Holland Nautic in Apeldoorn. Dat is de

importeur van Shipmate die u nog veel meer vertelt

over de unieke eigenschappen van de RS 6100.

Een veilig gevoel

24 maanden garantie

Koers op kwaiiteit, koers op

holland nauticzl.

kantoor en showroom. Kayersdijk 175, 7332 AS APELDOORN, Tel. 055-412122

2

Voor kleine tot grote en zeer grate jachten Voor reparatie en nieuw werk

Voor particulier en werf

levert Klaver:

SCHILDERS

SPUITERS

POLYESTER:

LAKKER

i

PLAMUEUR7EN

Onze mensen zijn gedegen vaklieden en kunnen uw jacht efficient van de meest fraaie afwerking

voorzien.

(Oak te bevragen voor bijvoorbeeld plamuurwerk

alleen.)

Onze bedrijven (met spuithallen) zijn

gevestigd te:

ELBURG VOLENDAM VOLLENHOVE

-ZWARTSLUIS.

Met onze speciale containermagazijnen en werkplaatsen zijn wij mobiel door geheel Europa.

WAARMERK VOOR KWALITEIT

(meer dan 80 jaar)

Centraal kantoor

en meldadres:

K LAV ER BV

Productieweg 1

8325 EZ VOLLENHOVE

Tel.05274-3100*

Telex:

42838 KLVER

0.a. behandeld: 2 Flyers, Philips I nnovater en vele andere nationaal en internationaal bekende motor- en zeiljachten (ook klassiek).

(4)

March 13 and 14 1986

International Congress Centre RAI

Amsterdam

9TH INTERNATIONAL SYMPOSIUM

ON DEVELOPMENTS OF INTEREST IN

YACHTDES1GN, YACHTBUILDING AND

SAILBOARDS

LIST CF PAPERS

Gary W. Mull, Naval architect (USA)

THE ABS STRENGTH REUIREMENTS FOR YACHTS Page 5

A. Coquit, Amtec (Belgium)

ADVANCED MATERIALS FOR YACHT CCNSTRUCTICN Page 31

Ir. J.A. Keuning and A. Versluis,

Technological University Delft (The Netherlands)

SAIL DESIGN ND PANEL CALCULATION Page 71

G. Dijkstra, Ccean Sailing Development Holland H. v.d. Linde, Mal-quip (The Netherlands)

SAIL-HANDLING SYSTEMS FOR THE LARGER CRUISING YACHTS Page 99

Jon Bannenberg, Designer (UK)

INTERIOR DESIGN CF CRUISING YACHTS Page 141

Ir. J.P. Klaase Bos and Chuck Stahl Gaastra Sails (The Netherlands)

SAILBCARDSAIL DESIGN FOR MAXIMUM SPEED Page 143

Prof. A. Cardo, University of Trieste (Italy) MANAGING THE COMPUTER AIDED DESIGN OF SMALL

HIGH-SPEED CRAFT AN

SAILING YChTS

Page 165

G. Dijkstra, Prof. ir. J. Gerritsma, ir. J.A. Keuning,

A. Konijnendijk, D. Koopmans, Jac. de Ridder and C. van Tongeren

SAFETY OF SEAGOING SAIL YACHTS (PaneldiscusLdon) Page 183

(5)

Edited by a committee under the chairmanship of Prof. ir. J. Gerritsma of the Ship-hydromechanics Laboratory of the Tech-nical University Delft

Members of the committee: ir. J.A. Keuning, D. Konpmans, F. van Beuningen, W. de Vries Lentsch, E.S. Piena, H. Martens and G. Vis.

INTRODUCTICN

This symposium is organized under the auspices of HIZA, the National Association of Watersportindustries in the Netherlands in cooperation with the Dutch boatingmagazineaterkampioent. The 9th symposium concerns subjects which are of interest to the yachtdesigner, the yachtbuilder, the technically interested yachtsman and surfer.

The first day is dedicated to the technical developments in yacht-design and yachtbuilding. The second day is dedicated to a panel discussion on the subject SAFI:TY OF SEAGOING.SAILYACHTS.

Members of the panel are leading Dutch experts in the field of

yachtde sign.

The technical level of the papers has always been a matter of

concern: not too popular, but also not too technical or scientific. It is important that the main points of the lectures can be understood by a larger group than the exclusive experts.

The aim of the HISA-Symposia is to offer a possibility to exchange knowledge and to stimulate the discussion on the various aspects of the design, the building and the use of yachts and sailboards.

(6)

THE ABS STRENGTH REQUIREKENTS FOR YACHTS

by

Gary W. Mull

ABSTRACT

The paper will present a brief review and analysis of yacht structures developed from traditional classification societies' scantling rules. The development of the American Bureau of

Shipping

Guide for Building

and Classing Offshore Racing Yachts will be traced

to

provide a better

understanding of the methodology used to produce the Guide in order to provide designers and builders with a more straightforward engineering

approach

to

the development of a yacht structure.

The basic scantlings of a 9.14 metre (30 foot) sailing yacht will be developed using the ABS Guide for Building and Classing Offshore Racing Yachts scantlings in order

to

provide a comparison of weight,

strength, and weight distribution. Finally, comments and criticisms

from designers and builders who have used the ABS method as well as

other classification societies' scantling methods will be discussed.

(7)

From time immemorial, the question of haw to build things strong

enough to do their jobs has been a major concern to mankind. Over the

centuries, structures have become more and more efficient as we have learned to more accurately assess loads and as materials and our

knowledge of how to use them have become more sophisticated. Crawling

out of caves and progressing through huts made of animal skins to today's giant skyscrapers, man has shown his inherent desire and

constantly improving ability to control his environment rather than be controlled by it. From foot through ox and horse to tcday's

supersonic Concorde and NASA's space shuttles, man's search for more

convenient and faster transportation dhows no hint of stopping. As

each new mode of transportation has developed, so, too, have the structures and materials developed to keep apace.

Today, in a perverse turn

of

logic so characteristic of man, we

find

enormous energy, exotic materials, sophisticated construction

techniques, and highly-detailed engineering analyses, all focused on one of the oldest and least effective modes of transportation known

-sailing. The fact that sailing more than makes

up

for any supposed

inefficiency in beauty, grace, and pleasure is more than ample

justification of these efforts.

In the early days of sail, as in other arenas of development,

structures were developed purely through trial and error. Little

(8)

properties of the materials used, and no information at all could

be

provided an what sort of loads and stresses a vessel might

be

called

upon to resist. Wbrking with wood and observing the structural

techniques of the Creator in the Skeletons of fish, animals, and men, early vessels emulated the framing system of backbone and ribs and quite literally used skins of animals for skins of the first vessels.

Through the 1600's and early 1700's, although commerce and war made

tremendous demands on the development of dependable ship structures,

trial and error was still the only satisfactory engineering tool used to develop scantlings. In those days, in fact, the mere ability to

calculate displacement was considered an achievement. Stability and

other more sophisticated calculations were still rather mysterious.

Actual structural calculations involving an accurate assessment of design loads; analysis of stresses, and the utilization of materials based on those stresses and the mechanical properties of the materials wasn't even a well-defined dream.

Shipbuilders seldan worked from drawings, but instead developed the

shape and the structure of their vessels

by eye

and from experience. Designers or naval architects as separate fram builders were

non-existent. The builders of those days were meticulous men Whose lives

and fortunes depended upon their creations. In order to augment and

codify their experience, they kept detailed records of their vessels

and how they were built. It was only natural for each builder to

develop his own ideas of overall proportions of the vessels, and to

(9)

try to work out sane sort of guide to the proportions of the

structures. Since displacement was usually, beyond their ability to

calculate, and since length, beam, and depth were very straightforward to measure, these early builders developed overall rules of proportion

to help them design their creations. Beam/length ratios, beam/depth

ratios, etc, were the earliest rules of thunib written down and used

systematical ly for the design of vessels and structures.

Each builder, in trying to develop the scantlings for a new vessel,

would look back through his records of previously built boats and usually use the same thickness of planking, frame spacing, and size of frames, etc, used an the nearest sized previously built boat in his

repertoire. Sanetimes a boat would be a bit longer than any he had

built before, so he would probably make the planking a bit thicker. Sanetimes the boats were a bit beamier or a bit deeper than any Shown in his records, and as a consequence he would adjust beans or frames, etc, accordingly, based on experience, "best guess approximations",

and a certain amount of garnble depending upon the mood. These were

the earliest scantling rules', and though they were totally lacking in conventional engineering, they were fairly, dependable as long as the

builder knew what he was doing, kept good records, and was willing to

take a chance now and again to test the limits. In addition, since

each of these scantling rules were specific to the individual builder,

(10)

workmanship, etc, were all monitored personally and automatically

canpensated for by the individual builder's scantling rule.

Over the years, as transoceanic commerce developed, vessel

underwriters began to realize that, relying upon each individual

builder's methods of determining Ship scantlings exposed them to risks

Whidh they were unable to accurately quantify. Yesterday, as today,

insurers were willing to insure vessels and cargo, but only if they had reliable assurances that the risks were small and predictable.

There may have been an earlier scantling society, but surely the

grande dame must be Lloyd's Register of Shipping. Fbunded in 1760,

Lloyd's Register grew out of the needs of

Lloyd's

of London. Gathering

information

fiuLt

hundreds of builders and vessels,

Lloyd's

developed a

scantling rule based essentially on all of the individual builders'

scantling rules extant at the time. Partially, because of its close

association initially with

Lloyd's

of London, and partially, because of the dbvious necessity for incorporating the margins, errors, and worst

cases of the existing rules,

Lloyd's

Register of Shipping's scantling

rules were quite conservative.

During the intervening years, other scantling societies came into being and began producing their own scantling rules.

Oftentimes these

scantling rules were plagiarized in Whole or or in part fran Lloyd's

rules. In other instances, they would

(11)

building practices and prejudices of the particular country. In every instance, however, it is important to note that the growth of these scantling rules began and derived fram an assessment of current

practice as determined

fit

existing vessels and discussions with

builders. Planking thickness was almost always a function of length.

Frame sizes and spacing were usually a function of hull depth

riLt

gunwale to keel rabbet, etc. As a consequence, an extremely light

displacenmatboat and an extremely heavy displacement boat, if both of the same length, would usually be required to have the same planking

thickness. Aboat with very high freeboard and a shallow underbody and one with very low freeboard and a deep underbody would usually be

required to have the same framing. Basic factors such as

displacement, speed, wave impact, etc, were ignored due to a lack of knowledge or agreement as to how to include them.

As sailing yacht design became a bit more scientific, and as it became more apparent that attention to structural details paid dividends an the race course, it became dbvious that the heavy scantlings of

commercial vessels were not really suitable, and a nuMber of builders began to develop their own scantling rules based an a more complex

point of view. The two best known are Nevins' Rules, based on

displacement, and Herreshoffs Rules, which are based on displacement and a number of other factors derived from various proportions of the hull. Each give lighter individual scantlings but depend heavily on a

high level of craftsmanship and quality of materials. Again, however,

(12)

1.0-since these rules were initially "builder specific", these factors of workmanship and materials were dealt with inherently.

Even with Nevins' and Herreshoffs rules, we are still dealing with the product of the builder's recordkeeping for his own boats and

trying to find basic proportions to size the individual structural

oarrponents. There is still no calculation of load or stress and material specifications are no more scientific than the hopeful phrase, "all wood to be clear grained and free of knots, checks, and other defects."

Reviewing the above, it is interesting to note that Chapman's

"Architectura Navalis Mercaturia" published in Stockholm in 1768 and

the later 'Treatise an Shipbuilding" pOblished in 1775 and finally translated

into

English in 1813 stood for many years as the only really thorough technical work in the field of naval architecture and

ship's scantlings.

Reviewing most of the scantling rules written for the construction of

yachts, a few singular features are very striking: First, virtually

all of the scantling rules for yachts have their genesis in the reliance an existing boatbuilding practice in the form of the

tabulated recordkeeping noted above and, as a canseglence, are based

on very simple factors of length, depth, team, and occasionally

displacement. Thus, their ability to deal with a broad range of

(13)

-displacement/length ratios, beam/length ratios, etc, is not nearly as

flexible or accurate as might be desired.

Secondly, virtually all of these rules are written with the idea

in

mind that just about any design Lunt a 50 metre three masted

world-girdling schooner complete with bowsprit and clipper bow down to a

little 6 metre family daysailer can be handled fairly easily.

Implicitly, this carries with it the requirement that an enormous

range of sizes and types of boatyards with the concurrent variations

in materials and workmandhip be enccmpassed by these rules. Of

course, all of the scantling societies require that vessels classed

under their regulations be constructed

in

approved yards and that they be built under the supervision or inspection of properly qualified

inspectors associated with the scantling ;society.

Thirdly, most of the well-known scantling societies go to considerable effort in their regulations to detail material specifications,

thicknesses, tolerances, etc, and many have particularly cumplex formulae Whidh are used to determine the mechanical properties and

thicknesses of fibreglass laminates wilidh the particular society would

accept in scantling calculations. Similarly, very careful note is

taken of the difference between Engliah and metric units as they

apply to thicknesses and widths, and careful compensation is required,

often resulting

in

corrections an the order of a few hundredths of an

inch

or tenths of a millimetre. It is quite common for all of the

(14)

-scantling societies to utilize mechanical properties, particularly for

frp laminates, which are well below carefully-documented test

properties. In addition, particularly in the case of frp laminates,

it is quite often the case that, if a higher grade composite laminate is used, only a fraction of the improvement over a basic polyester

Chopped strand laminate is allowed in the calculations. In addition,

a careful

study

of the various societies' regulations shows that, in

places Where reasonably straightforward engineering formulae are used or could be used, such as the calculation of bolt sizes for ballast keels which could certainly'be analyzed quite straightforwardly as a

simple prdblem in statics, one finds really-huge safety factors buried

in the regulations. It is not at all mammon to see safety factors

of 4 and 5, and When these are taken in conjunction with mechanical properties that are substantially belaw the true engineering

properties of the materials, this results in structures which are heavier, mcre complex, and far more costly than they really-need to be. Mile it goes without saying that vessels which go to sea must be

safe enough to bring their crews home again, one wonders Where the line should be drawn between conservative design and poor design and construction hidden beneath enormous safety factors.

When one considers the overall sdheme of most scantling societies' regulations, one is struck with the attention to minutae such as a few tenths of a millimetre here and there sharing the same pages with

safety factors of 3, 4, and 5. Why go to the trouble of

(15)

-differentiating between 12 and 12.5 mrn plate thickness (a little over

4 percent) When the entire design is based on using a safety factor of

300 or 400 percent?

The single characteristic found lacking in nearly all of the modern scantling rules is the concept of basing the required structure on a given set of structural loads. In the past, this wasn't terribly

surprising, since the loads and the resultant stresses on a vessel's hull are considerably-more complex than, say, the loads and stresses

of a bridge. The principle reason for the design of bridges having

been based an known loads for quite same time is

simply

that the loads

are extremely easy to calculate. day, however, While the loads and

stresses of a vessel's structure maybe extremely difficult to

calculate f um first principles, the technique of regression analysis now enables us to calculate these loads and stresses very accurately from performance of known boats, particularly ones Which have

sustained documented

failures-Early in 1977, the Offshore Pacing Council, the international body which administers ocean racing throughout the world, began to consider

the possibility of a scantling rule for use on boats developed under

its rating rule, the International Offshore Rule. Ake Lindquist, a

Council member, began work an the basic framework of that scantling

rule. The International Technical Committee, the technical

subccumittee of the CRC, was chaired at that time by Mt. Olin

(16)

-Stephens, Who discussed the idea of this new scantling rule with

representatives of several of the major scantling societies around the

world. The American Bureau of Shipping alone indicated a strong

interest in cooperating with the ORC in developing a new and practical scantling rule for the construction of offshore ocean racing yachts.

Asmall group within the ITC consisting of Olin Stephens as Chairman, Ake Lindquist, Hans Steffensen, and myself began work on the project. The earliest work, by Ake Lindquist, formed a solid foundation for our

initial efforts. Mt. Rbbert Curry, head of the Research and

Development division of the New York ABS office, worked with us from the beginning and made available to us all of the resources of the R&D department there.

Whereas most scantling societies have predicated scantling sizes on

same function of L, early in the 1970's ABS began Shifting over to a

determination of the scantlings based on design

heads.

One may argue that other scantling societies basing their scantling sizes on some function of length is simply using that function of length as a

surrogate for design head. However, this simplistic view, as

mentioned earlier, prevents these rules from taking more accurately

into account variations in beam/length and displacement/length ratios.

The ABS method, which takes into account total moulded hull depth as

well as immersed depth, gives much more flexibility in accounting for

(17)

One noticeable difference between the ABS Scantling Guide for Offshore Racing Yachts and other ABS rules is that previous ABS rules have had the design heads for the various structural members noted as part of

the individual formulae for the various members. However, with the

Scantling Guide, it was decided to produce a series of design heads

L.Exnt the outset. These allow the designer to draw for himself a

"pressure map" (see Fig. 1) Where isobars of equal pressure can be

plotted

on a drawing of the hull, allowing the designer to carefully tailor his structure, including interior arrangements, etc, to meet

the structural loads as effectively as possible without additional non-load carrying structure. Table 7.1, "Design Heads for Plating",

and Table 8.1, "Design Heads for Internals", furnish the designer with

a very, very clear picture of the loads his designed structure must

meet. Of all of the features of the ABS Scantling Guide, this concept

of producing a clear and logical structural model fran which the designer can develop his structure has produced far and away the most

favorable comments from the broadest spectrum of users. The clear

relationship between the structure required by the Rule and the

stresses the structure is being called upon to meet is an Obvious and tremendous advance over the more familiar requirements of other rules which base Shell thickness or sectional properties of stiffeners on a

single factor, such as length or displacement. It certainly seems

more in keeping with modern boatbuilding materials with known mechanical properties to be able to derive a structure from basic

engineering principles rather than the "coOkboce methods of yesterday.

(18)

Of course, the design heads shown in Tables 7.1 and 8.1 are only as useful as their accuracy in accurately predicting real design loads.

For this, we have relied heavily on ,a nuMber of sources of

information. Initially, in the development of the ABS Guide, the ITC

and ABS both requested from designers and builders worldwide any and all well-documented information possible regarding current design and building practice, and particularly documented experience regarding

known structural failures. Working fram a very large nuMber of

reports of structural failures, together with documentation regarding

the design and building of those boats along with tremendous

cooperation fram designers and builders all over the world, we began to piece together, using an analytical approach similar to that

reported in my 1981 HIS WA paper, "Strength Requirements for Sailing

Yachts", relationships of length and immersed depth which most

accurately fitted our data. We Bound that, to a very close tolerance,

the design heads could be described by the sum of a length factor, an

immersed depth factor, and a oonStimat. Partially, because most sailing

yachts, even though they occupy a wide range of relationships between

length, beam, depth, and displacement, they still, because they must

go to sea and sail, stay within a narrow enough spectrum of these

variations that these factors of length and depth quite accurately

describe in engineering terms what we found to be true from an

examination of practical first-hand data.

(19)

produced by the formulae in Tables 7.1 and 8.1, it became obvious and

logical to utilize standard engineering solutions for the development

of the scantlings of the shell and stiffeners. Standard formulae for

stress and deflection of rectangular panels under uniform load are used to derive the required thickness for shell plating. For those interested, a more thorough treatment is given by R. J. Roark and W. Young in their book, "Formulas for Stress and Strain", 3rd edition,

page 203, McGraw Hill Book Company, New York. In addition, it will be

seen that the design pressures vary along the length of the hull.

This ooncept was suggested

by

the well-known Heller-jasper paper, "On

the Structural Design of Planing Craft", by S. P. Heller and N. H.

Jasper, Transactions of the Royal Institution of Naval architects,

1960. Having to do with impact pressures on planing vessels, this

paper nevertheless allowed us to derive a similar "impact" map for

sailboat hulls which more closely matched the information and data we had available. Sailboats are obviously subject to slamming pressures, and in damage reports we found that impact-damaged areas were easily described using the Heller-jasper concept, but with the area of maximum impact moved further forward to more accurately reflect the

sailing characteristics of the heeled sailboat hull in a seaway.

Since our confidetce in the design loads is quite high, we can be

equally confident that somewhat less conservative allowable stresses

can be used in the calculation of the final structure. Additionally,

since most of today's ocean racing yachts utilize much more

(20)

sophisticated materials than in previous years, ABS makes use of allowable design stresses for shell and stiffeners as detailed in

Tables 7.2 and 8.2. This is particularly useful in frp construction,

as it allows the designer and builder to use known tested laminate properties rather than be forced to attempt to approximate design

laminate properties

ficin basic

laminate properties on same broad

approximation WhiCh has its genesis in grams of chopped strand mat

reinforcement per square metre. While many scantling societies have

made attempts to provide methods for designers and builders to use more sophisticated laminates, this is usually only with a more complicated and expensive review and approval system on the part of the society, and even then societies ordinarily only allow 90 percent or so of the tested laminate properties to be used in the

calculations.

Whereas it may be reasonable for old fashioned and less sophisticated designs and construction methods to

be

assessed on the basis of ounces

of reinforcement per square metre, it is unquestionable more in keeping with modern engineering practice to utilize actual material properties wherever possible.

It is also interesting to note that, since many of the other scantling

societies describe laminates an the basis of ounces of reinforcement

per square metre, they also describe laminates in terms of

(21)

dealing with ordinary E-glass and polyester resin

grp

laminates,

specifying the reinforcement content by weight percentage is perfectly

reasonable. However, When discussing more cumplex "high tech"

composite laminates, it is the more common practice, at least in the United States, for fabricators of composite parts, be they aerospace or automotive, to describe laminates on the basis of fibre

reinforcement content by volume. In this manner, the varying

densities of an ever wider growing range of reinforcements is more accurately and logically dealt with.

In the appendix are contained standard calculations done by my office for a very normal 9.14 metre sloop which is currently under production as the FREEDOM 30 by Freedom Yachts (Tillotson-Pearson, Inc.). NO particular attempt has been made to optimize these calculations for weight or longitudinal gyradius, and, as a consequence, frame spacing, beam spacing, etc, has been maintained at the nominal for clarity.

The Second Edition of the American Bureau of Shipping's Guide for Building and Classing OffShore Racing Yachts contains nunErous minor revisions to the original "Little Blue Bode, including a significant one regarding sandwidh construction and the treatment of core sheer

stress. This bcbk is currently at the printers and should be

(22)

American Bureau of Shipping Guide for Building and Classing

Offshore Racing Yachts, 2nd Edition, 1986 (45 Eisenhower Drive,

Paramus, NJ 07652).

G. MUll, "Strength Requirements for Sailing Yachts", HISWA Symposium

Yacht Architecture, 1981.

S. R. Heller and N. H. Jasper, HOn the Structural Design of Planing

Craft", Transactions of the Royal Institution of Naval

-Architecture, 1960.

R. Roark and W. /bung, uFbrmulas for Stress and Strain", 5th

Edition, McGraw-Hill Bock Cdmpany, 1975.

S. Timoshenko, "Strength of Materials, Part I and Part II", Van

.)

Nbstrand Company, 1942.

The Aluminum Association, "Engineering Data for Aluminum

Structures", USA.

Kaiser Aluminum, "Aluminum Boats", 2nd Edition, Kaiser Aluminum

and Chemical Sales, 1978.

Owens 0ot-fling Corporation, "Design Properties of Marine Grade

(23)

V.. Aro /5171,

.

( AeP 1---4164'a A r.

.

.AL MIVIS4014 M I DAT.

aiikWe.4.1o, ,4,..i: O,er flu/

ME-4Of 066 ---G.:0,0a, -.OW, 41.4, X/ ,r-/4,4,,,.., ro. tr. 5. 06 e'e.,,,,verz ,er ,74.-574./e-.4.2,V ,I,L,"? ... - ... ....1, .0 T.. 10.0000.n 00 111.1. .. 0.0.0., 10.. ....**41,0, .... 00.6 .1004.0n 1000 1..0.00.. 10.01... 00.0 00. 40.0. . a00.0.-...1,100.1.0. a 000....1.0.11. 01111.1.112 .. GARY W. MULL .VAL A.RCHITICTS 1... 111.V10 CAW/WM. 04010 _LI_ w -1--.... ...MS, I -1--...r,,, ael OC A 1....A.1.4.0...,,

_.--if

4.77T mew, rd '---, WM 111 .1 I' a, Dm, we /.5, -/, Jonw. 0 _r_

t._...___,.

I ,,,,...f . ...,-,,, , . . I . k 1 4 4 k .

---* ----11EL B6

- 2,4.--___. _

-MI

________,k6 orp.

r_--.

IIII My NM

Se ...-skorz...1, <=444c , AL SI- ' ea. ii At / .1 ....,6 ' Att h. fig ' JP M ft

e-e'

cr-f1,1/ .4.16.9e, - ---rP'e 7-74,- /2,177X/G-f s. .4,...G.4 91," -4f .v.,,0 97- fs-- , .V. /37 51 ..,=4--941 ___,,' ...V,,f,11__ //",,Ps-.4,...,..e. 5,-...,, - /01-"

4ñ-9-( '/7

..,.. ,..',2 -. 1 %

Ii

p..." ,e, ix!...9.1.,9 ..,,,,,, . ! .0. 2,. _.___,L-.I.C1 -.

,..'

%i hi -4 *4 .4 a

t

N ,11.4., ' s ft.-.;-*4

--.

..

.,,...

-

..kfaz--ii L

'4 k 41 !,1

i

a a ve, *

Figure 1.

(24)

Changes to Guide For Building and Classing Offshore Racing Yachts, 1981

Plating Location Desian Head

a Shell below d + 0.15m, (d + 0.5 ft),

where d + 0.15m, (d + 0.5 ft) is

measured vertically from the

underside of canoe hull at its lowest

point.

At forward end of LOA

At 0.05Ln aft of fore end of

Ln

At 0.35Ln aft of fore end of

Ln

At aft end of LOA

b Shell above d + 0.15m, (d + 0.5 ft),

where d + 0.15m, (d + 0.5 ft) is measured vertically from the

underside of canoe hull at its lowest point.

Notes

Shell design heads between locations given above are to be

obtained by interpolation.

f2, = local freeboard at

location being considered; it is the distance, above 8, of location being considered.

d draft as defined in 2.7

Only Valid Until Second Edition of Guide is Published

Fig 2

_

l3-c Deck

Main weather deck, cockpit and

0.04L + 1.83m cabin house front

0.04L + 6.0 ft

Cabin house top, sides and end

d Bulkheads

Watertight or structural

Tank boundary bhd

Table 7.3

Design Heads for Plating,

0.80h 1.20h 1.20h 0.70h 1.913m 6.5 ft

distance to main weather deck at centerline, not

less than 1.52m (5.0 ft.) distance to top of tank overflow, not less than 1.52m (5.0 ft.)

At forward end of LoA

0.70 (h-d-ft)

At 0.05Ln aft of fore end of Ln

1.08 (h-d-fit)

At 0.35Ln aft of fore end of

LWL 1.08 (h-d-ft)

At aft end of LOA 0.63

(h-d-ft)

Basic head; h =

3.0d

+ 0.14L + 1.62m

(25)

Notes:

For aluminum, the minimum ultimate tensile strength is for the welded

condition.

For aluminum, the minimum yield strength is for the unwelded condition

at 0.2% offset.

For cold-molded wood laminate the modulus of rupture is to be 22% of the values give in Table 4.). Special consideration will be given

to

the design stress where the modulus of rupture for cold-molded wood laminate is determined by sample testing. In such cases the modulus of elasticity is also to be determined and the required thickness is

also to comply with 7.3.1, equation b.

Changes to Guide For Building and Classing Offshore

Racing Yachts, 1981

Plating

Table 7.2

Cold-molded Wood Wood Carvel Design Stress rya

Steel and Aluminum Reinforced Plastic

Single-skin Laminate Construction

I-a

Shell and Deck 0.60 075 minimum ultimate 0.5 074 minimum

0.5 074 Modulus of 0.4 Modulus

rt

Watertight Bhd

Tensile strength'

0.75 minimum yield strength2

flexural strength 0.5 074 minimum flexural strength Rupture" 0.5 074 Modulus of Rupture" of Rupture 0.4 Modulus of Rupture

Tank Bhd 0.75 minimum yield strength2 0.5 074 minimum

flexural strength

0.5 074 Modulus of Rupture"

0.4 Modulus of Rupture

(26)

Changes to Guide For Building and Classing Offshore Racing Yachts, 1981

Internal

a Shell

Frames, longitudinals, stringers,

girders, transverse webs and floors

b Main Weather Deck, Cockpit, Cabin

House Top, Front, Sides and End

Beams, longitudinals, transverse webs and girders

c Bulkhead

Table 8.1a

Design Heads for Internals

Stiffeners

Design head given in Table 7.1

See Table 8.1b for values of F

Only Valid Until Secondedition of Guide is

Published Figure 4

Design Head

F x design head for the shell

plating given in Table 7.1 for the mid-length location of the internal

F x design head for the deck, cabin house or cockpit plating given in Table 7.1

(27)

Interpolate botvaen tabular values

Figure 5

Changes to Guide For Building and Classing Offshore Racing Yachts, 1981

Shell Internals 0.25 0.28 0.32 0.36 0.42 0.49 0.57 0.67 0.77 0.86 0.94 1.00 1.00 Table 8.1b

P for Design Head for Internals

Main Weather Deck? Cockpit and Cabin House Internals .

64 Metric Units - 0.254 < last Units 1 - 0.833 1> 1.93. 1. > 6.33 ft. 0.33 0.2540 < I < 1.93 0.633 ft. < I < 6.33 ft. 1.102 - 0.41 Metric Unit 1.102 - 0.1221 lest Units 0.254s < 0.833 ft. 1.0 0.0542L + 0.559 ft 1-1 1.0 and greater! 0.90 0.80 3 0.70 0.60 0.50 a. a 0.40 0.30 0.20 0.10 0.05 0 or negative; 0.0542L + 1.833 > 0.054L + 0.813. > 0.054L + 2.666 ft. 0.2540 0.833 ft.

(28)

Internal Stiffenins Member

neer, Deck beam, deck longitudinal transverse frame, shell longitudinal web frame, floor or stringer

Changes to Guide For Building and Classing Offshore Racing Yachts, 1981

Steel and Aluminum,

0.5 mimimum ultimate tensile strength

Table 8.2

Design Stress oa for Internals

Reinforced Plastic Single-skin

0.5 04 minimum ultimate tensile strength

Non-laminated Wood' Laminated Wood

2,'

Stiffening Member Stiffening Member

0.375 033 modulus 0.42 0:345 modulus'

of rupture of rupture

Prase 8.5 minimum ultinate 8.4 minimum ultimate 0.33 modules 0:345 medu3es2

tensile strength tensile strength ef rupture ef rupture

Beam 05 minimum ultimate 8.4 minimum ultinate 0.33 nadolus 0:345 medulus2 tensile strength tensile strength ef rupture ef rupture

W.T. Bhd stiffener 0.5 minimum ultimate 0.5 8.4 minimum ultimate 0.375 0:33 modulus 0.42 0:345 modulus' tensile strength tensile strength of rupture of rupture

Tk Bhd stiffener 0.32 mimimum ultimate 0.32 0:26 minimum ultimate 0.375 0:33 modulus 0.42 0:34S modulus' tensile strength tensile strength of rupture of rupture

Notes

For aluminum the minimum ultimate strength is for the as-welded condition.

To be considered a laminated frame, the grain is to follow the shape of the member. Design stresses given are for construction with the grain parallel to the direction of the bending stress. For cold-molded wood laminate the design stress to the

plating is to be given as in Table 7.2.

(29)

. ..

7.r.04.0151D-s

... t r-

fre.A4s

Ser-t-4:

LZ

At_ 444.4

.. .. . ....

L

A4-1 2.2. T

4_ (.1

';*$ ... 2Cca. HaZA-. -FRA len 11..34.1 -6,0G I - TC.. z..

dlg*"

1'14

.

657E3

ZL/c.").

.1314G

1 5

Figure!

A.B.S. - Base Scantling Study (ALTJNLENUM)

a411

14439

ia6

GARY W. MULL

NAVAL ARCHITECTS

DESIGN NO. TITLE

PAGE _i_OF

1 / By

r

DATE

(30)

GARY W. MULL

NAVAL ARCHITECTS

TITLE A7'" 'E-717

(ii ra.t)

By

ED

ChAN).

-71:Fda

:

777-77-7--t -

-LZ

325

" Z. K A_7_LE Ent- .1;;LEC-X 14".

cft

z. I

:7S3

= SG.15

/v,A.

EL =

7C'234.1 4.Er=t 1 A. I

Figure'

7.

A.B.S.

Base Scantling Study

(GRP)

- t DESIGN NO. PAGE DATE

a-V-Fov,...)-An

LZ.CstO

-21714

1-Te

root:s:t

'DEC, 4c. E.EA S

..

z.17-

2_,AG

tC..4 .00

(31)

ADVANCED MATERIALS FOR YACHT CONSTRUCTION

-+++++++++++++++++++++++++++++++++++++++++

by A. COCQUYT

AMTEC N.V.

)

Summary

The lecture deals with different available composite

materials and how they are used in yacht construction.

Pro-perties and advantages as well as disadvantages of these

ma-terials are discussed and confronted with those of other

commonly used yacht materials.

Different structure techniques, namely sandwich and

single-skin technique, are also discussed and compared.

Finally a short discussion on structural research,

illustrated by some examples, is given.

(32)

CONTENTS

Introduction.

Growing use of F.R.P. materials in yacht

con-struction.

Used materials and their properties.

Single-skin versus sandwich.

Structural research

:

necessary?

Final remarks.

(33)

3

Introduction

There's no field into which advanced composite materials have

been more rapidly and readily expanded or accepted than the field

of high-performance yacht-building.

This consequently has had an enormous impact on the yards using

this materials. In the early stage the only problem was to use G.R.P.

or steel. Nowadays however F.R.P. itself has diversificated so

greatly that a one-line approach would make a yard run aground

immediately.

To construct reliable high-performance yachts material properties

have to be known quite exactly. It must be noted that figures,

provided for by industry, must be handled with caution and that,

in certain circumstances, it can be usefull to run a series of

material tests.

In view of the still developing materials, construction techniques

have to be updated continuously. This makes it almost

necessary

for a yard to run an intensive research program if it wants to

re-main state of the art.

Growing use of F.R.P.-materials in yacht construction

When we look at the many excellent characteristics that F.R.P.

materials have to offer it's only normal that their

use as a

con-struction material is still increasing. High strength

to weight

ratio, ease of maintenance and repair, durability and resistance

to the marine environment, toughness, non-magnetic and dielectric

properties and low thermal conductivity are some of the many

ad-vantages of the use of F.R.P. materials. The most important

reason

however for their growing application is that

they are far more

flexible both to design and to process than conventional metals.

As for design the orientation of fiber reinforcement

can be chosen

so to suit specific structural requirements, making the

structure

lighter and more efficient. As for the production process on the

other hand, many costly secondary assembly processes are eliminated.

(e.g. welding or riveting).

In the early stage however, i.e. after W.W. II the use of F.R.P.

was very limited. Their advantages were poorly distinguished, mainly

for the following reasons

:

(34)

-

3 ti

4

technical knowledge of the material was very limited

FRP-builders still didn't think in terms of composites. They only

applied rules of steel construction to F.R.P. construction. No

need to say that this lead to erroneous structural concepts.

poor quality products, as made by many low

skilled manufacturers

made vanish the already low confidence regarding these new

materials.

last but not least the conservative thinking of many steel

builders

obstructed greatly the growth of the F.R.P.-shipbuilding industry.

As for this latest argument however, opposite reasoning can also

be

considered. By rejecting the use of F.R.P.-materials, altough several

reports (see for example [1]) clearly pointed out the

advantages of

their application even for superstructures in large ships, steel

builders promoted the separation of a new totally independent

F.R.P.-shipbuilding industry. This industry started building yachts that

were completely made out of G.R.P.

Indeed, in the early stage, some disastrous

decisions were taken

but, as a matter of fact, this separation lead to the high-tech

composite building yards as we know them today.

1

To understand more the astonishing aspect of

this development

a comparison with aviation

industry is uttermost revealing.

Manu-facturers in this area approached the F.R.P. business

in a totally

different way. They started using this new materials

in very small

quantities, thus giving F.R.P. a chance to develop

inside the big

aviation industry.

Today also approach of aviation industry to the

F.R.P.-business

is still different from that of yacht industry.

There's no discussion

that today, anyone who should want to build a

Boeing 747 completely

out of F.R.P.-materials would be

advised to go to a psychiatrist

as soon as possible.

(35)

5

3. Used materials and their properties

Before going into detail on the properties of the different

types of resins and fiber reinforcements used in yacht construction,

a comparison between F.R.P. and other commonly used yacht materials

is interesting to be made.

The decision on which material to use for a yacht seldom involves

an objective analysis. No "straight-line" reasoning can be expected

if one knows that both customer and designer are prejudiced and

prefer certain materials or production systems

;

that each

manufac-turer proves his material to be the best one by overwhelming the

decision makers with non realistic figures and that last but not

least most yards are capable to work with only one type of material.

In the following however we will try to make an objective

compa-rison between different construction materials. Figures that are

mentioned in the different tables should only be considered relative

to each other unless dimensions are mentioned as well. Data are

taken from references

[2]

and

N.

Table 1 lists the acquisition cost comparison for the different

materials. Exact calculation of this quantity can be found in

Dj.

As for the ownership cost statistical data on F.R.P.-craft

are very

scarce. However, several yachts in fiberglass have proven to have

a durability that is higher than the average value for other

ma-terials. With regard to maintenance requirements and

case of repair

F.R.P. offer fundamental advantages. Except for a periodic

inspec-tion no maintenance is required and repair

can be done by low skilled

or even unskilled workers using ordinary hand tools.

Tables 2 and 3 are a summary of the engineering properties of

the most common boatbuilding materials. Table 4 is in

a way deducted

from tables 2 and 3

(see

rq)

and gives a structure comparison.

In this table, for F.R.P., the properties of fiberglass are taken

and applied to a single-skin structure. A

complete discussion of

this figures is beyond the

scope of this lecture but following

things can be marked. On the basis of

strength and stiffness alone,

F.R.P.-materials do not have a clear advantage

particularly when

it is noted that their elongation to fracture is much lower than

(36)

6

appear when their high modulus and high strength per unit weight

are considered, thus meaning considerable weight saving is possible

for structural components.

This high strength to weight ratio, combined with a high

stabili-ty in the marine environment and high durabilistabili-ty under service

conditions makes F.R.P. an excellent tool for boat construction.

However, one has to remain realistic. Figure 1 for example [1] gives

the construction cost for a large GRP cargo vessel compared with

that for a steel one. Although the same reference mentions possible

cost and weight savings when G.R.P. is applied to certain

super-structures of large ships, it is clear that a much more promising

area is the area of small ships and certainly the area of the

high performance yachts. Several disadvantages as there are high

material cost, low resistance to major impact, lower Young-modulus

exist but probably the most dangerous point is that F.R.P. materials

have to be fabricated on the yard. If this process is not optimised,

many, if not all, advantages will vanish.

We will now have a closer look at the properties of the different

F.R.P.-materials used for yacht construction. Data are from ref.

C2]

and

[4 .

Resin systems

Unsaturated alkylstyrene type polyesters have found wide use

in marine applications. Since a few years however more and more

vinyl ester resins and epoxy resins are used, especially when it

comes to high-performance applications. Table 5

lists typical

properties of the three systems used.

Polyester resins offer a greater flexibility with regard to

handling and curing characteristics and are less costly than the

other resin types. Variation of resin/hardener ratio and of the

curing cycle from optimum values however will influence final

mechanical properties of the cured resin.

The curing cycle for polyester as well as vinyl ester

resins

is started by adding a catalyst/accelerator. In marine

applications

these types of resin are only used for hand lay-up processes.

First

the resin is catalyzed and then applied with layers of

(mostly)

fiberglass cloth to a mold using a roller. When needed,

thixotropic

agents may be added to minimize resin run-off.

(37)

Epoxy resins on the other hand are required when superior

mechanical or physical properties are needed. Whereas polyester

resins can be cured at room temperature with no significant loss

of mechanical properties, for epoxy resins however, it is highly

advised to apply the recommended heat cycle as close as possible.

This curing cycle is started by adding what is called a curing

agent.

As for epoxy as a matrix material the most common processing

method used for yacht construction is hand lay-up. Some yards

however are starting to use the more advanced prepreg-technique.

Prepreg stands for preimpregnated fibers, indicating that

fabrica-tion occurs in two distinct stages. The first stage is the producfabrica-tion

of a sheet or tape of fibers impregnated with resin that is partially

cured to produce a flexible aggregate with excellent alignment of

the fibers in unidirectional layers and an exactly known and

control-lable fiber-resin ratio. The second stage is to stack up different

layers of prepreg on a mould, consolidate it by pressure or

vacuum

and heat it up to achieve the final cure.

A comparison between the three resin systems leads to the

follo-wing conclusions. Epoxy resins offer excellent adhesion qualities.

Those of vinyl ester resins are much worse and those of polyester

are rather poor. When it comes to weight saving there's no way

but to go for epoxy resins. Epoxy resins also offer the best

mechanical properties i.e. higher tensile strength and higher

tensile modulus. Also concerning elongation to break, shrinkage

on

curing, fatigue, durability in a marine environment,

epoxy resins

offer outstanding properties in comparison with the

other resin

systems. When it comes to cost however epoxy resins are almost

twice as expensive as polyester

or vinyl ester systems. When the

total price of the resin is of second importance in

comparison

with the other costs, as is the case for a high-performance yacht,

epoxy certainly is the best choice.

Fiber reinforcements and composites

Dealing quite exclusively with

performance oriented yachts,

only fiber-epoxy composites will

be considered when laminate

properties are mentioned. Those properties will only be looked at

in a very general way. Reason for this is that there's a mass of

7

(38)

-8

different materials and data available so that by only presenting

a few of them one can grossly misrepresent the case.

At the present time borosilicate type "E" glass fibers are used

for most yachts. In the area of high- performance yachts however

there is high interest in higher modulus fibers, such as graphite,

boron or aramid (Kevlar). Those fibers offer superior mechanical

properties combined with even less weight (Table 6). Boron is almost

solely applied in aerospace structures and will therefore not be

considered further.

Two types of fiberglass are used as reinforcement materials,

namely E-glass and R-glass. Typical properties of both are shown

in table 7. The R-type obviously has better mechanical characteristic

than the E-type. The cost however is five times as high which is the

reason that in 90% of the cases, E-glass is used.

Two types of aramid fibers were developed by Dupont de Nemours

of which almost only the Kevlar 49 type is being used in marine

applications. Kevlar 49 offers a higher tensile strength and impact

strength than other fibers. It can be used in structures that have

to be light, strong and stiff as well as in highly stressed

struc-tures.

Carbon fibers were originally developed for application in

aerospace structures. Since a few years however their use

in

high-performance yachts is firmly growing. Reason for this is their

extremely high modulus and strength per unit weight, combined

with

excellent fatigue and vibration characteristics. Carbon fibers

therefore are mostly used as stiffeners in hulls or masts. Only

when extreme priority is given to high performance and low

weight,

carbon fiber composites are used as a hull material.

Tables 8 and 9 list several physical and mechanical

properties

of the different fiber-epoxy composites used in yacht

construction.

It can be noted that E-glass must not be used where high tension

is expected. A more critical aspect for yachts however

is the

hull stiffness. It is here that carbon fiber

composites come in as

stiffeners in bulkheads, framing and hull. When it comes to

compres-sion it can be seen that kevlar has rather poor properties and

therefore must not be used in places where large compression

values

are expected

!

As already mentioned kevlar possesses excellent

(39)

P-impact characteristics. Carbon on the other hand has rather poor

impact resistance and should therefore not be used without kevlar

reinforcement in places near the bow where high slamming pressures

may occur,

Fiber-fabrics are available in several varieties as there are

chopped strand mats (only for glass fibers), rovings, woven rovings

and UD's (unidirectional fibers). More information on weaving

techniques can be found in specialized literature. It be noted

that there are a variety of weave patterns each to meet specific

design or construction needs. For high-performance yachts only

woven rovings and UD's are used.

Special woven forms are the so-called hybrid fabrics. They are

a combination of different types of fibers, thus at the same time

lowering cost and improving properties. For example a carbon-kevlar

hybrid, to get the high carbon-stiffness and at the same time the

excellent kevlar-resistance to impact. Some properties of a typical

hybrid composite are shown in table 10.

Finally, a relative cost comparison is shown in figure 2. A

standard fabric of 200 g/m2 is considered. The indicated values

are selfexplaining

4. Single-skin versus Sandwich

First the sandwich-technique will be described briefly, followed

by a comparison with the single-skin method

on processing and

building techniques.

To make things clear however a few notes on single skin have to

be made. Single skin construction is quite similar

to conventional

wood or metal construction. A single thickness of F.R.P.

laminate

is used which is supported by frames to reduce panel sizes and to

provide overall rigidity to the hull. This type of construction is

considered the most simple to fabricate.

The purpose of a sandwich construction is to increase the

rigidi-ty of a panel by increasing its thickness with

relatively little

increase in weight. The principle of this is clearly shown in

figures 3 and 4. Two skins

are used, separated by a thick,

light-weight core that is bonded to the facings by an adhesive. When

(40)

10

loaded, one skin will act in compression, the other one in tension.

The core resists the compression and transverse shear loads while

the adhesive must be capable of transmitting high axial and shear

loadings from the facings to the core.

As for the facing materials, ther's no substantial difference

with the materials already described in the foregoing section so

that they will not be discussed here.

There are mainly three types of core materials used for yacht

sandwich construction, namely wood, foam and honey-comb.

Represen-tative mechanical properties are listed in tables 11 and 12.

Rela-tive cost is shown in figure 5.

For wooden cores mostly endgrain balsa is used. It has very

good mechanical properties but also a rather high density which

obviously is a disadvantage. Also the high resin absorption

during

curing process is a problem that has to be looked at. Even so,

the ease of use and excellent durability of the end product,

combined

with high compressive strength and modulus has led to sharply

increased usage, especially for large hulls when high strength

is

needed. Since cast of balsa is increasing sharply too,

this may

be-come a problem for future applications.

Foam is being widely used as a structural core. Several

types

of foam exist as there are polystyrene, polyvinyl chloride

(PVC),

polyurethane and acrylic foams. For each type a broad range

of

densities is available. The very low cost polystyrene

foams

now-adays are being used almost only for

surfboards. They have a low

density, are very easy to shape but their mechanical properties

are rather low. As a matter

of fact they are not applied for

high-performance structures. The same conclusion

holds for the polyurethan,

foams. In spite of their good mechanical properties,

problems with

existing urethane structures concerning resin-foam

bond have

resul-ted in a firmly decreasing use of the polyurethane

foams.

The acrylic foams have a high strength

and stiffness to weight

ratio and, to a certain extent, they are even

temperature resistant.

They are rather hard to use when it comes to

curved surfaces. This

is probably the reason why the PVC foams are used more. They combine

good mechanical characteristics with good processing characteristics.

(41)

11.

New developments have led to high-temperature PVC foams that, as

a result, can be used with prepreg facings.

For high tech applications, foam and wood have been largely

re-placed by the more efficient high density (aramid) honeycombs.

This is a logical evolution if one looks at the specific needs for

a core material and compares them with the excellent properties

that honeycombs have to offer. They have a very high compression

strength, a very high transverse shear strength and, above all,

they are very light. The two most known types of honeycomb are the

aluminium honeycomb and the aramid paper honeycomb. Almost

only

the aramid one is being used for yacht construction, the aluminium

one being much to sensitive to the marine environment. The most

important disadvantage of the aramid "Nomex" honeycomb core is its

price, being as three times as expensive as the other core materials.

On the other hand it is extremely tough and damage resistant

; it

possesses a unique ability to survive overloads in local areas

wit-hout permanent damage.

It is obvious that the best characteristics are offered by the

honeycomb cores, resulting in an increasing use for high performance

yachts. Balsa and foam cores however posses also very good mechanical

properties at a considerably lower price

!

A discussion of the different adhesive materials is far beyond

the scope of this lecture. It be noted though that, when using

honeycomb cores, only adhesives with excellent mechanical properties

may be taken into account, core-skin contact area being

very small.

To end this section, an elementary comparison between single

skin and sandwich technique on processing and building

methods may

be made. As for processing methods there's no substantial difference

between the two techniques except for, in the

case of sandwich

technique, temperature and pressure are required to get a perfect

skin to core bond. Different ways of providing this pressure are

possible, for example vacuum bagging or autoclave molding.

Hand lay-up techniques are still widely used as a processing

method for yacht construction (see figure 6).

For advanced

applica-tions however it is highly advised to employ bag molding methods

as there are vacuum bag, pressure bag and autoclave molding (see

(42)

densi-12

fications of the lay-ups, resulting in practice in increased

inter-laminar bonds, diminutions of voids and removal of excess resin.

Bag molding methods are combined with "wet" lay-up techniques

as well as with prepreg techniques, the latter ones

undoubtedly

leading to superior results, (see figure 8). As already mentioned

the use of prepregs results in an excellent alignment of the

fibers

in unidirectional layers and in an exactly known and controllable

fiber-resin ratio.

As for building methods on the other hand there are several

differences between the single-skin and the sandwich technique.

Single-skin hulls are generally laid up in a female mold.

Since the

outer surface takes on the quality of the mold

surface, further

finishing is unnecessary. In a secondary bonding operation, frames,

foundations and decking are installed.

Sandwich skin hulls on the contrary are often

laid up over a

male plug. Two different procedures exist. In the

so-called

no-mold process first the core material is tacked to a

lattice

con-struction

; then the outer skin

is laid up and cured ; hull and

lattice construction are seperated and the hull is turned over,

and finally the inner skin is laid up and cured.

In the second

procedure, first the inner skin is laid up over the mold

and cured

;

the core is adhered to the inner skin and

finally the outer skin

is laid up on the core material. Both procedures

require

conside-rable work to achieve a smooth outer surface.

Much has been said on whether sandwich or

single-skin technique

gives best results. Single skin is generally cheeper

and all the

laminate is in the outside skin of the hull, where

it can resist

the local impact abuse encountered in

service. It probably is

the most simple type of construction to

fabricate, certainly in the

case of sailyachts when relatively little framing is needed.

Con-struction of sandwich panels is generally more

difficult because

of the steps necessary to ensure a good bond between the skins and

core. But, for equal stiffness, a sandwich panel will be both

lighter and less space-consuming because no framing is needed.

(43)

13

It is my opinion however that none of both techniques is the best

one. They both have their own advantages and disadvantages and it

is therefore dangerous to maintain a one-sided reasoning on this

point, as almost all yards do. For each case again one has to

consider whether sandwich or single-skin technique should be used

!

5. Structural research

:

necessary ?

This question should not be answered but positive. The only

reason to pose this question is that many manufacturers have

answered this question negative in the past and they still do in

the present:

It has to be stressed though that many aspects of composite

materials are unsufficiently known or investigated. When we look

at 1t from the point of view of a ship-design, things are becoming

even more complicated.

When designing a ship, three basic things have to be considered

or computed

design loadings

selection of construction material

structural analysis

As for the design loadings, until now very conservative rules have

been applied. Only recently some research projects

on this topic

have been launched.

The selection of a construction material is another

very

difficult point. Exact data on material properties

are nonexistent

and it is highly advised to run several series of material

tests

if one wants to know the characteristics of the material that's

used.

For a long period, structural analysis in ship-building

was

identical to application of rules for steel construction. This

of course resulted in structural misconceptions.

Since a few years

however, calculations are done with finite element

methods

resul-ting in much more accurate

structures. Only as an example, figures

9, 10 and 11 show some finite element results on sandwich structures,

done by Amtec engineering

on NISA.

Conclusion can be short but clear

:

structural research

(44)

S. Final remarks

The foregoing sections have clearly pointed out the many

advantages that are inherent to advanced composite materials. If

one is able to work with F.R.P. materials in a proper way, one is

also able to realize structures with unequalled characteristics.

When this is combined with a certain amount of, let's say

"realistic", common sense and if several yards want to keep up

extremely intensive research programs, in the near future "think

composites" will certainly become a reality for yacht construction

industry.

-.

(45)

References

Report SSC-224

"Feasibility study of glass reinforced plastic cargo ship"

George Lubin

"Handbook of composites"

Van Nostrand Reinhold company

University of Michigan

Cellege of Engineering - report 121

"Small craft engineering structures"

Drek Hull

"An introduction to composite materials"

Cambridge press

Hexcel report TSB 124

"The basics on bonded sandwich construction"

1981 Revision

Cytaty

Powiązane dokumenty

Zajmując je, a zwłaszcza zasiedlając, człowiek przez obrzędowe p o­ wtórzenie kosmogonii przeistacza symbolicznie daną okolicę w

W tym samym roku, 17 lipca, odbyło się walne zebranie konstytucyjne Towa­ rzystwa Naukowego w Toruniu, którego Janina Przybyłowa została członkiem.. dyrektorem

W szczególnie trudnym okresie organizowania się tego szkolnictwa należał do ludzi wszechstronnie czynnych.. Poza pracą dydak­ tyczną w szkole przygotowywał specjalne komentarze

Parts of Iraq in recent years have been exposed to a dry climate owing to lack of rainfall and drought caused by low water levels in the rivers Tigris, Euphrates, and Shatt

„Funeralia” gromadzą około 120-150 uczestników, przedstawicieli nie tylko dwóch głównych dziedzin - archeologii i antropologii. Coraz częściej pojawiają

The optical measurement techniques used are: stereoscopic Particle Image Velocimetry (for investigating the flow field behind the propeller till the end of the wing), mono

Jest to wkład w rozwijającą się naukę, która jest nie­ zmiernie w ażną dla współczesnego człowieka - dotkniętego i zagrożonego to­ talnym skażeniem.. W

Studium historyczno-socjologiczne na przykładzie Bartoszyc, Warszawa 2000 (mps pracy doktorskiej — Archiwum Uniwer­