Assignment of mechanics engineering
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This document discusses the design of a sailing cruiser. It begins with an introduction that provides background on the history of yacht design and construction materials. It then outlines the main sections that will be covered, including the hull, mast and rigging, and appendages. For the hull section, it discusses the various loadings a sailing yacht is subjected to, including hydrostatic, hydrodynamic, sailing loads from the rigging, and impact loads. It notes that determining the design loads is challenging due to the many different loads and asymmetrical nature of the loads when the yacht is heeled.
![2. Materials Selection Criteria and Production Methods
The traditional material for spars (masts, booms and spinnaker poles) was wood; different types of
wood were used: Sitka spruce, Douglas fir and Oregon pine. The construction procedure was very
complex, especiallyin the case of high masts, when it becomes necessary to assemble and work many
parts. This activity is still in progress in some shipyards specialized in the restoration of classic sailing
yachts.As an example,fora 25 meters yacht, up to 4 groups of planks in length times 10 in breadth are
necessary to re - build the mast. During the 1960’s wood was eclipsed by aluminum due to its greater
durability, higher specific properties and lower cost. Aluminum alloys, generally 6000 series, are
commonly utilized, with magnesium and selenium that give to the material high mechanic
characteristics and good resistance to corrosion in the marine environment. For short, economical
masts, 6063 alloy is used, 6061 type for high quality masts and 6082 type, which is the most expensive
one, for racing yacht masts.
Aluminum alloys adopted for sailing yacht spars.
Aluminum
alloy
σ0.2% [MPa] σu [MPa] εu HB E [MPa]
AA 6063 150 195 12% 80 69000
AA 6061 235 255 8% 80 69000
AA 6082 255 305 10% 90 69000
Mast profilesare obtainedbyextrusioninawide varietyof sectionshapes,withlongitudinalinertiaJyy
much greaterthanthe transverse one Jxx.Some of them, asanexample,are listedbelow .
Oval sections, used for small-medium size cruising yachts without particular performance
requirements.The ratiobetweenthe two diameters is about 1.5 while the ratio JYY/JXX ranges
between 1.8 and 1.9.
Bulletsections(or“D”sections) are employedforhighefficiencyrigs.The ratiobetweenthe two
diameters is about 1.6÷1.9 and the JYY /JXX ratio for these types ranges from 2.5 up to 3.
Open sections are used when a mainsail reefing system is to be set up. The ratio between the
two diameters is about 1.8÷2.0 while the JYY /JXX ratio ranges between 2.5 and 2.8.
The most part of aluminummastshave constant section along its length; in the case of big and/or high
performance yachts it is a common practice to reinforce the mast base and to taper the top. The first
action is performed by bolting aluminum strips inside the fore and aft part of the section to increase
longitudinalinertia;the more effective alternative consistsinintroducingasleeve insidethe mastand to
bolt or rivet them together. The same method is employed to create masts longer than 18 meters
jointingtwoprofiles.Inthiscase a couplingprofile isintroducedinthe mastfortwo - three diameters in
lengthand the two parts are bolted together. The top of the mast is tapered cutting a strip of material
from the side of the profile of increasing width. Then the two edges are welded together obtaining a
decreasing section towards the masthead. This simple procedure allows a reduction in weight and
makes the top of the mast more flexible.](https://image.slidesharecdn.com/assignmentofmechanicsengineering-191201033434/85/Assignment-of-mechanics-engineering-16-320.jpg)
Assignment of mechanics engineering
- 1. Assignment of Mechanics Engineering Assignment No: 01 (One) Submitted To Mr. Dr. Umer Manzoor Email: umar.ceet@pu.edu.pk Associate Professor, PU Lahore, Punjab Department of Metallurgy and Material Engineering Submitted By Abdul Rehman 18-MME-S2-315 Email:arsplay200@gmail.com
- 2. Topic Design of a Sailing Cruiser Different Parts of the Cruiser Selection of Material Properties
- 3. To Mr. Dr Umer Manzoor Email: umar.ceet@pu.edu.pk Department of Metallurgy and Material Engineering Course: Mechanics Engineering The University of the Punjab Lahore From Abdul Rehman (18-MME-S2-315) Email: arsplay200@gmail.com As you said in the class I analyzed the model and have prepared my assignment on basis of that. It may also contain same mistakes and I could overlook some imported point. I tried my best to prepare this assignment. Therefore, I shall be highly grateful if your overlook consider these mistakes and accept my Assignment. Signatures …………………………………….
- 4. Acknowledgment First of all I would like to thanks to ALLAH all mighty that HE courage me to complete this Assignment. I would like to thank all of other helping hands who were with me to make this Assignment possible. I also would like to thanks our honorable course instructor Mr. Dr. Umer Manzoor, of Mechanics Engineering, Department of Metallurgy and Material Engineering in the University of the Punjab to giving me the opportunity to prepare this assignment. I also would like to Especial thanks to INTERNATIONAL SHIP AND OFFSHORE STRUCTURES CONGRESS to help to complete Assignment.
- 5. Table of Contact INTRODUCTION DESIGN, SELECTION OF MATERIAL AND PROPERTIES Hulls Loadings and Methods of Assessment Structural Responses and Methods Rules and Design Standards Materials Selection Criteria Mast and Rigging Arrangement Materials Selection Criteria and Production Methods Loadings Rules and Design Standards Appendages Arrangements Material Selection Criteria PARTS REFERENCES
- 6. Introduction The history of yachts goes back a long way. The first appearances were in the 1600’s when wealthy Dutch merchants built and sailed small and relatively fast boats called “jacht” especially for pleasure. The real buildinganduse of yachtssprungintolife atthe endof the 1800’s. In the contextof the present report we will restrict our self to the period starting a little before the Second World War up to the present day. Originally “jachts” were built in wood and in construction quite similar to what was customaryin the normal shipbuildingof thattime.The hull was single (massive) planking connected to closelyspacedwoodenframes.The frames were connected to wooden floors and those to the bottom planking. In the earlydaysmany yachtsstill hadflator slightlycurvedbottoms.Atthe upperside the frameswere connectedtothe deck beams on which the deck planking was laid. Longitudinal stringers were mostly absent. Later when yachts got keels the construction changed. The sections became rather more V shapedaskingfordifferentconstructiontechniques.The stembeam, the keel beamand the stern beam were introduced,whichfunctionedalsoaslongitudinalstiffeners,towhichthe frames were connected, whichinturn were connectedbythe floors.The difficultiesandweaknesses in the available connecting techniquesof thattime howeverposedaseriouslimitonthe achievable overall strength and in more in particularthe overall rigidity of the yacht hull structure. All wooden construction was only to return in yacht buildingafterthe 1970’s, whennew andseriousbondingtechniquesbecameavailable,suchasthe epoxy resins, together with new wood laminating techniques. So in the 1930’s the new “composite” constructiontechnique came intoforce,inwhich the keel, stem, stern, frames, beams and floors were all constructedinsteel (andboltedorriveted,laterweldedtogether) towhichthe still wooden hull and deck planking was connected. This was a big improvement but still rather heavy. Still later the completelysteel hull came intoplayinwhichnow inthe composite dconstructionalso the wooden hull plankingandlateralsothe woodendeckplankingwasreplacedby steel and all were riveted or welded together. This yields a sound and stiff construction for the hull. Thisconstructiontechnique,usingeithersteelor aluminum,laststilltodayandismostly favored for the biggeryachtsor for yachts withhighdemandson resistance against external local loads, such as yachts designed for use on long ocean voyages or in the arctic regions. After the 1950’s the new construction material “glassreinforcedpolyester”saw the lightinyacht building.Firstitenabledseries production of yachts bringing the ownership to a wider public. Then the introduction of the more general “fiber reinforced resin” materials and construction techniques brought a complete revolution in the construction of yachts. First the material was used in constructions quite similar to the traditional constructioninwood:i.e.withframes,girders,floors,beamsandthe lot.Commonpractice was also the use of solid and rather thick laminates to overcome the lack of stiffness of the new material. It took some time forthe industryto realize the full potential of the new material andtogrow to more adapted and mature construction techniques. Monolith hull and deck constructions were introduced with integrated stiffeners.
- 7. To be followedshortlybythe very light weight and very stiff sandwich construction technique using a low density foam or wood as core material and very thin inner and outer laminates only. For 15 years nowalsothe use of veryhighqualityfiberswithastonishing mechanical properties, such as aramid and in particular carbon fiber, has revolutionized the construction of high performance yachts again and enormous gains in overall weight, strength and stiffness have been achieved. These are all fields in whichthe yacht buildingindustrybecame the frontrunner,andmanydevelopmentsoriginatedfromthe yacht building industry experiments. The yacht building industry also became the one which was confrontedwiththe associatedproblemsandchallengesfirst.A similardevelopmentcanbe notedinthe evolutionof the rig.Inthe earlyday’swoodas constructionmaterial wasthe norm. Dimensions and the layout of the yacht rig were restricted by the available lengths of wood till adequate connecting techniques (gluing) became available. Still the wooden mast was rather voluminous and therefore heavy. All of this had a serious negative effect on the performance of a sailing boat. In the 1930’s aluminum alloys became available as construction material for masts became available and this introducedthe possibilitiesfor much lighter and slender masts. Also the stiffness of the mast could be improvedaswell asthe quantityand the layout of the rigging. From the 1980’s onwards the composite mast was introduced. Originallytheywere constructedinthe more traditional material glassfiber reinforced polyesters such as in the so called Freedom rig. For over 25 years now carbon fiber and epoxy resin have been introduced for mast construction. In combination with very high tech production techniques this has enabledarevolutioninmastweight,stiffnessandperformance Alsomastsandrigshave been produced like the DynaRig,thatwouldnothave beenpossible inanyother material. This is the first time that this subject of yacht design has been broached in an ISSC forum. Consequently, a slightly wider search of literature and background references has been made with regard to hull structure, masts and rigging and appendages and keels. It has also been necessary in some areas to elaborate on the topics and themesina fundamental manner.Thisexaminationof literature hasbeenbackedup with consultations with leading industrial houses in design and construction of yachts and rigging. HULLS 1. Loadings and Methods of Assessment Determiningthe designloadsforthe hull isadifficultproblem.There are manydifferentloadsthatmust be properly accounted for. Similar to ships, the hull is subject to hydrostatic pressure along with dynamicloadsdue to waves,slamming,groundingandcollisions.Unlike ships,sailingyachthullsare also subject to sailing loads due to the sails and rigging. The mast(s) is in compression and the stays and shrouds are in tension, leading to large longitudinal and transverse bending moments on the hul l.
- 8. Complicatingthe loadingandstressdistributionisthe factthatsailingyachtscan have up to 60% of their weight concentrated at the keel attachment point which is often near the base of the mast; for IACC boatsthe ballastratiois over 80%. In addition the loading is often asymmetrical due to the heel of the yacht and the sailsbeingtoone side.The loadsexperiencedbyasailingyacht are illustrated in Figure 1. Yachts can also be subjecttolarge loadswhile being put into and removed from the water. Boats up to approximately 10m in length are often put on trailers where the hull is supported by a few rollers as point loads. Larger yachts are put into and removed from the water using travel-lifts and slings that normallysupportthe hull inonlytwoplaces.The loadsfromtrailers(if appropriate) andtravel-lift slings dependonlyonthe weightof the hull andare easilypredicted.Theymustbe checked during the design stage and for some yachtscouldbe the critical designloadforthe hull scantlings. Sailing yachts are also subjectedtoimpact loadings arising from a large range of possible impact events, from collisions with othercraft or floatingdebrisandgroundingtoeverydaydockingbumpsandobjectsdroppedontodecks or inside the hull. Impact damage may of course be dangerousbecause abreach may lead immediately to the loss of the vessel, but also because less severe damage may significantly weaken the vessel’s structure. Further, damage may grow with cyclic loadings leading to a catastrophic failure under normal loading. The hydrostaticloadsincalmwater are easilydetermined,buttypicallytheyare notthe critical designloads. The real challenge is in predicting the hydrodynamic and rigging loads on the hull due to sailing, particularlyinextreme conditions.Riggingloadsare discussedinSection4and hence will not be further mentionedinthissection.Designhydrodynamicloadswill be the mainfocus of this section. There are a limitednumberof studiesintopredicting analytically the loads on sailing yacht hulls. Recently, various
- 9. nonlinearmethodshave beendevelopedtopredictthe designloadsforshipsoperatingina seaway. For example,the ISSCcommittee report(2000) on “Extreme Hull GirderLoading”reportsonnonlineartime- domaincodesthatcan determine the nonlinearloadingonaship.Anoverview of nonlinearmethodsfor a ship at forward speed is given by Beck and Reed (2001). Alford and Troesch (2008) present a method to create a wave amplitude time history with a specified extreme wave height that can be used in a nonlinear, time-domain ship motions code. A great deal of research has also gone into predicting pressure loading due to water impact that may have direct application to the analytic prediction of loading on yacht hulls. Korobkin (2004) gives an overview of various water impact models that have beendeveloped.Mostwaterimpacttheoriesare fora constantvelocity,vertical entry.Sailingyachtsare often heeled and the theories must be modified for asymmetric sections. Judge et al. (2003) present results for wedges entering the water at oblique angles. Since water impact happens on an extremely short time scale and the pressure peak is localized near the spray root line and travels very fast across a given panel, the elastic response of the local hull structure becomes important (see for example Faltinsen, 2000). Ideally, the plating and stiffeners in areas susceptible to slamming would be designed using hydro elastic analysis that takes into account both the hydrodynamics and structural dynamics of the problem. An alternative approach to predicting the dynamic pressure loadings due to water impact and attempting to apply these directly to a hull structural model is to use the concept of an equivalent uniformstatic(oreffective) pressure.Thesecorrespondtothe pressureswhich,if appliedto a particular structural componentin a static manner, will result in the same maximum deformation and maximum stress as produced by the actual dynamic loading (Allen and Jones, 1978). Such an approach is also common for high speed motor vessels. Obtaining such an equivalent uniform static pressure using experimental dataforanarray of pressure transducersoveramodel,orfull-scale,hull is difficult due to the non-uniformdistributionof pressure over the hull following a slam and the very short time period associatedwith the event. Realistically, many designs are undertaken using static analysis with such a slammingdesignpressure andreductionfactorstoaccount for location, panel size, structural dynamics and type of boat. The slamming design pressure typically depends on the size and speed of the yacht. Joubert(1982) analysed7 actual yachtfailuresorlarge plasticdeformationsthatoccurredwhenbeating to windwardingale force winds.Usingaknowledge of the hull structure, Joubert was able to hind cast the slamming loads that would be necessary to cause the damage. Using four different analysis techniques(lineartheory,membrane stresses,plasticdeformationanalysis,andplasticlimittheorywith large deformations)he foundwidelydiffering pressure predictions. Joubert’s final conclusion was that although the data is sparse the bottom panel loads on 40 foot length yachts beating in a gale may involve slamming pressures as great as 80 psi. Attempts have been made to use model scale experimental datatoobtainthe average loadona representativepanel areaof the hull bottominvolved in a slam impact. Such an average load may be obtained through the use of ‘slam patches’. These are panels, representative in area of a full-scale hull panel, of high stiffness cut out of a hull model and attached to a load cell via a rigid strut. The load cell then records the average external pressure load actingon the panel.Sucha technique,firstusedformotorvessels(Purcell etal,1988), was appliedtoan Open 60’ yacht by Manganelli et al (2003). Through extensive experimentation they found equivalent
- 10. slammingdesignpressures for the yacht travelling in waves in both upright and heeled conditions. An analytical methoddevelopedforcomparisontothe experimentaldataincluding hydro elastic structural effects indicates good agreement. No comparisons to pressures predicted (or used) by Classification Society rules are presented. Otherresearchspecificallydirectedtowards the predictionof sailingyachtloadsmaybe found in Boote et al.(1985) whoexaminedafinite element model and a classical longitudinal strength approach to an aluminum12m yachtin calmwater. They also discuss full scale trials, although little data is presented. Ward (1985) analyzed the dynamic stresses in a beam due to a slamming like pressure peak travelling across the beam.Thissimplifiedproblemhasdirectapplicationtothe impactforcesonthe bow sections of a yacht sailing to windward. Ward finds similar tends as used in the ABS empirical impact reduction factors. An extensive hydro elastic analysis of a WOR 60 yacht was conducted by Lauran and Temarel (1999). Usinga combinationof finite elementanalysisforthe structure and linear potential flow theory for the hydrodynamicloads,theyfoundthat the largest stresses were in the vicinity of the hull to keel joint area. The effects of heel and rigging loads were included in the analysis. 2. Structural Responses and Methods Loading results in structural deformation and material stress and for marine applications the most critical can be groupedas global bendingortorsion,panel flexure andjoints.Asdiscussed in the section on hull material selection the most common materials used today are composites and the method to analyse the stresses in a composite structures are critical to the accuracy of failure prediction. The reasonfor these becomingthe mostcritical relate tothe ability to tailor laminate performance and the inherent weakness of the matrix as an adhesive. Numerous analysis techniques, ranging from simple empirical "rules-of-thumb",toclassificationsocietyrules,andtoadvancednumerical modelling through finite elementanalysis(FEA) are used.The selectionof the appropriate method largely depends on the design complexity and owner's requirements and budget. With the increasing power of the personal computerand the wider availability of sophisticated analysis software, more small craft designers are acquiringandapplyingadvancedmethods. Traditional Classification Society rules and codes for sailing craft, reflecting common practice, used isotropic beam and plate equations combined with empirical factors to resolve the loads in to the structure (Curry, 1989). Analysis was strictly linear and material ‘knock down’ factors based on fatigue and other uncertainties were combined to produce minimum required scantlings (see Figure 2). Due to the small size of most sailing yachts the primary analysis focused on plate and framing analysis in response to hydrostatic pressure loading. As this analysis usually resulted in relatively large scantlings, global hull girder bending due to waves was largely ignored. Rig loads, particularly forestay and backstay loading, combined with the keel loading could produce sufficientglobal hullgirderbending to cause deck buckling and was included in shallow depth racing yachts. With regards to America’s Cup Class yachts, which have a narrow hull, heavy ballast and tall sail plan,the bendingmomentislarge and the load in the mishap region may be over 100kNm. The bendingmomentisthenthe dominantloadindeterminingsuitablehull scantlings(Figure 3).Composite
- 11. materials were treated as isotropic with a single modulus and the strength determined from testing (Gibbs and Cox, 1960). Whenthe laminatesinclude significantunidirectional laminates, or are unbalanced or asymmetric the blendedplate theorydoesnotproduce acceptable results as the isotropic plate analysis cannot predict an accurate strain field. In this case loads have to be resolved in to forces and moments that may be directlyanalyzedusinglaminatedplate theory.Due tothe complexityinvolvedin resolving these forces and moments two approaches may commonly be followed. In the first case a “worst case” loading location is found and the laminate developed. Typically this would be in the slamming area on the centerline.Thislaminate would then be applied to the entire hull, or would be tapered slightly above the normal heeledwaterline. Localized reinforcements would be applied for point loads such as chain platesandthe mast and keel foundations. The second approach uses classical orthotropic plate theory as traditionally applied to large vessel plate and beam calculations. To maximize laminate tailoring, however,aresolutionof all the loadingisrequired. The current method practiced is through the use of global hull finite element analysis (FEA). Predominantly used only in the domain of high performance vessels, its use has been documented from dinghies (Riber, 1993) to small (Miller, 2000) and large cruising (Miller, 2003) and racing yachts (Hamilton and Patterson, 1992). An example for an America’s Cup Classyachtis showninFigure 4. Typical FEA of hull structuresuseslinearanalysis,howeverinplaces where large deformationsornon-Hookeanmaterial propertiesare possible,then geometric or material non-linear analysis must be used. Typical examples include snap-through buckling and thick core materials, respectively. A finite element analysis with shell elements, which is currently the most commonlyused,doesnotworkwell forestimatingthe core strengthof sandwich panels accurately. For dynamic response to events such as slamming especially, confirmation through physical testing is necessary.Inthe DNV rules,the testmethodisprovidedinorderto predict the slamming impact speed of sandwich panels (Lake, Eaglen, Janes. and Battley, 2007).
- 12. Example of finite element analysis for an America's Cup Class yacht Composites are susceptible to out of plane damage due to impact loadings (Abrate, 1998) and such damage may be especiallydangeroussince itwill probablybe mostly internal delaminating and remain undetected. Impact response is dependent on many impact and material parameters (Sutherland and GuedesSoares,2003), and the impact behavior of GRP is complex (internal delaminating, fiber failure, perforation,membrane,bending&sheareffects,indentationetc) (SutherlandandGuedesSoares, 2006, 2007) it is very difficult to define exactly what we mean by impact behavior or even which type of impactbehavioris‘good’.Firstly,whichimpacteventshouldwe consider?The response will varygreatly depending on which impact event we are considering. For example, one material/structural arrangementcouldwell excel foraslow,head-oncollisionwithadock side, but be very fragile to a fast, oblique impactwithasmall,sharpfloatingobject.The response torepeatedwaterimpactmaywell be a completelydifferentcase again,andspecifictestshave beendeveloped to simulate this (Choqueuse et al. 1999, Downs-Honey et al 2006). Secondly, should the material/structural arrangement absorb the impact energy, or be resistant to penetration, or be resistant to impact damage? These are often mutuallyexclusive.Forexample,aKevlarbullet-proof material (which is designed to absorb the impact
- 13. energyof a projectile bysufferingterminal damage inaone-timecatastrophicevent) wouldveryquickly become structurally useless if used to construct a yacht deck (which is constantly subjected to minor impacts such as heavy foot-falls and equipment drops). Figure 5 shows how impact loads can be included in a multi-hull FE model (Casari et al 2008). 3. Rules and Design Standards The traditional approachto designing ayacht hull structure is to use a classification society’s rules such as Lloyd’s Register (LR) or the American Bureau of Shipping (ABS). The International Standards Organization (ISO) isdevelopinganewstandard (12215) that is mandatory for all boats less than 24m in lengthwhich will be sold in the European Union (mandated through CE directives). The importance of the European market to most yacht builders means that the ISO standards are becoming a universal standard. These are a complete set of rules inherent to motor and sailing yachts. The ISO standards philosophy,similartoClassificationSocietiessemi-empirical rules,consistsindifferentiating motor from sailingyachtsinthe designloadscalculationandstructuresinherenttothe vessels.Larsson and Eliasson (2007) discussthe ISO rules so far as they have been developed. In essence, the scantling rules define different pressure loads to be applied to various parts of the structure such as the bottom, topsides, deck,cabinsides,etc.The different parts of the hull are further subdivided as necessary. For instance, the highest pressure loads are associated with the forebody bottom where slamming damage is most likelytooccur.It shouldbe notedthatthe designpressuresshouldonlybe usedwith the scantling rules for which they were developed because the two are a compatible pair. Typically, a base pressure (or head) isdefinedthatdependsonthe size of the yacht.The base pressure isthenmodified by correction factors to arrive at the design pressure for a given plating location. The correction factors depend on such factors as location of the panel, whether or not the panel will be subject to slamming pressures, and the size andaspect ratioof the panel.The designpressuresare thenputintoformulae includingthe design stresses to arrive at the required minimum panel thicknesses. Once the plating thickness are determined, the stiffener sizes and bulkhead sizes can be determined based on the associated panel loadings and stiffener spacing’s. The scantling determination of structural components is performed with a unique procedure for motor and sailing yachts, independently from the construction material. The rules also specify design loads for the determination of keel and rudder scantl ings as well as hatches, ports, doors, etc. 4. Materials Selection Criteria The primary criterion for hull material selection for the pleasure boat industry is reducing cost. Thus wovenrovingormat E-glassfibersiniso- or-ortho-polyester resins are the most common combination. Improved properties are achieved through higher strength and modulus fibers such as aramid and carbon. Similarly, increased fatigue resistance, higher shear strengths and reduced osmotic blistering properties are possible with epoxy and vinyl ester resins. When sandwich materials are chosen balsa
- 14. woodor PVCcores are usuallyemployed.The alternativemetallic materials are marine-grade steel and aluminum alloys. Wood is still used in niche markets, often in combination with cold-molded construction techniques. The main advantages and disadvantages of each material (except wood) are summarized in Table Material Advantages Disadvantages FRP Composites Lightweight. Easy to mould complex shapes Cheap, more so for series production. Ability to tailor properties. No painting (when gel-coated) or fairing (female moulds). Low wastage. No rot or corrosion. Low maintenance. Easy to repair. Non-magnetic. Low energy material. Little plastic deformation to fail (for impact energy absorption). Low fire resistance, toxic fumes. Production working environment. Fatigue issues in high-stressed applications. Skilled labor source required for quality assurance. Aluminium Lightweight. Easy to work. Non- magnetic. High plastic deformationtofailure relativeto FRP (for impact energy absorption). Expensive. Welding distortion. Costly to paint. Less readily available. Requires heat insulation. Galvanic coupling. Fatigue. Can melt at temperatures seen in fires. Steel Cheap. Simple to fabricate. Easy to repair. Fire resistant. High plastic deformation to failure relative to FRP and aluminum (for impact energy absorption). Heavy. Hard to shape. Welding distortion. Requires heat insulation. Corrosion. Galvanic coupling. MAST AND RIGGING 1. The Arrangement Mast andriggingrepresent for sailing boats the structural system which support the forces developed by sails and control their optimum shape and trim; the boom mainly controls the attack angle of the mainsail and itis subjectedtolower loads. Masts and booms are defined as “spars”, stays and shrouds formwhat isknownas “standingrigging”,thatisthe category of equipmentwhichholdsthe sails, while the term “running rigging” groups other equipments (halyards, sheets) which have the function of continuouslyadaptingthe sail configurationtothe changingwindconditions.Excessive rigdeformation, allowedbyanon-sufficientsystemstiffness,hasthe negative effect of changing the expected pressure distribution on the sails, decreasing the propulsive efficiency of the boat. On the other hand a certain amount of flexibility is necessary to allow the mast to be bended in order to allow the sail to have a proper shape relatively to the sailing condition. As a consequence, mast and rigging should have “reasonablyresistant”section.Because the mastisthe leadingedge of the mainsail, a large section has
- 15. the effectof creatinga highpressure areabehindthe mast,neutralizingasignificantportionof the main sail,thusreducingthe total propulsiveforce androtatingit athwart ship. In addition, the rig system has a very high centre of gravity and an increase of its weight has negative effects on stability and on the capability of the boat to “stand” the wind. This can be counterbalanced only by increasing the keel weight,and so the total displacement of the boat. Excluding unstated masts which are predominantly usedon vesselsunder10 meters,sailingyachtsparsare sustainedbyathree-dimensionalriggingsystem made up by shrouds in the transverse plan of the boat and stays in the longitudinal one. Stays and shrouds are connected to the boat in correspondence of proper reinforced hull points. Common locationsforheadstayand backstay are the bow and the stern,while shroudsare securedathwartshi ps the mast by chain plates. Both shrouds and stays are connected to the top of the mast in case of a masthead rig, and below the masthead in a fractional rig. Diagonal shrouds are connected near the spreader roots and, in Oder to avoid higher compressive loads, angles below 10-12° are not recommended.In the longitudinal plane space availability allows the stay angle to open up to 30° and more while,inthe transverse plane,maximumshroudanglesare limitedbythe reducedhull breadth.To avoid long unsupported spans that may cause buckling phenomena, masts are then fitted with spreaders, in a number to keep the shroud angle over 10°; the highest spars can have up to 6 spreader levels. Shrouds can be continuous or discontinuous; the continuous solution consists of full-length shrouds, with constant section, from the mast attachment point down to the chain plates. The discontinuoussolutionconsistsinseparate spansfromtwosetsof spreaders connected at the spreader endwithmechaniclinks.Inthe longitudinal plane aft of the mast, the mainsail requires unconstrained space so that it becomesdifficulttosetsupportpointsforthe mast at intermediateheights.The waythe mast is supported depends on the type of rig: in a masthead sloop the mast is sustained by a forward head stay and an aft backstay, while in a fractional sloop the mast is sustained by a forestay and, aft backstay attached to the top of the mast and by running backstays attached in correspondence of the forestay. In the cutter configuration the mast has an additional support ahead, a baby stay and, optionally,runningbackstaysafter.The presence or not of running backstays depends on the nature of the yacht: in a cruise yacht it is preferable to avoid the runners in order to make the boat easier to be handled,whilstitisnecessarytosetthemon a racing yachtin orderto bettertrimthe mast and achieve bestperformances.Forall the consideredconfigurationsspreaderscan be set in line with the mast axis or aft swept in order to give ad additional support in the longitudinal plane. Aft sweep of spreaders greater than 15° often negates the need for runners. The type of arrangement heavily influences the performances of the boat and the strength of the mast as well. So it is very important to consider adequately the proper configuration in view of a verification of spars and rigging. Masts can be either deck-steppedorkeel stepped.Decksteppedmastsare usedinboatswhichneed to be trailed or to pass beneathlowbridgesonchannels, because mastscaneasilybe raisedwithoutneeding a crane. For large sailingyachtskeel stepped mast is preferable, mainly for its higher resistance with regard to bending, compression and buckling. This is due to the higher efficiency of the lower end constraint and to the contribution of the through-deck passage, which can be considered an additional constraint. On the otherhand the mast belowdeckrepresentsaconsiderable encumbrance for cabin layout and it heavily influences the interior layout.
- 16. 2. Materials Selection Criteria and Production Methods The traditional material for spars (masts, booms and spinnaker poles) was wood; different types of wood were used: Sitka spruce, Douglas fir and Oregon pine. The construction procedure was very complex, especiallyin the case of high masts, when it becomes necessary to assemble and work many parts. This activity is still in progress in some shipyards specialized in the restoration of classic sailing yachts.As an example,fora 25 meters yacht, up to 4 groups of planks in length times 10 in breadth are necessary to re - build the mast. During the 1960’s wood was eclipsed by aluminum due to its greater durability, higher specific properties and lower cost. Aluminum alloys, generally 6000 series, are commonly utilized, with magnesium and selenium that give to the material high mechanic characteristics and good resistance to corrosion in the marine environment. For short, economical masts, 6063 alloy is used, 6061 type for high quality masts and 6082 type, which is the most expensive one, for racing yacht masts. Aluminum alloys adopted for sailing yacht spars. Aluminum alloy σ0.2% [MPa] σu [MPa] εu HB E [MPa] AA 6063 150 195 12% 80 69000 AA 6061 235 255 8% 80 69000 AA 6082 255 305 10% 90 69000 Mast profilesare obtainedbyextrusioninawide varietyof sectionshapes,withlongitudinalinertiaJyy much greaterthanthe transverse one Jxx.Some of them, asanexample,are listedbelow . Oval sections, used for small-medium size cruising yachts without particular performance requirements.The ratiobetweenthe two diameters is about 1.5 while the ratio JYY/JXX ranges between 1.8 and 1.9. Bulletsections(or“D”sections) are employedforhighefficiencyrigs.The ratiobetweenthe two diameters is about 1.6÷1.9 and the JYY /JXX ratio for these types ranges from 2.5 up to 3. Open sections are used when a mainsail reefing system is to be set up. The ratio between the two diameters is about 1.8÷2.0 while the JYY /JXX ratio ranges between 2.5 and 2.8. The most part of aluminummastshave constant section along its length; in the case of big and/or high performance yachts it is a common practice to reinforce the mast base and to taper the top. The first action is performed by bolting aluminum strips inside the fore and aft part of the section to increase longitudinalinertia;the more effective alternative consistsinintroducingasleeve insidethe mastand to bolt or rivet them together. The same method is employed to create masts longer than 18 meters jointingtwoprofiles.Inthiscase a couplingprofile isintroducedinthe mastfortwo - three diameters in lengthand the two parts are bolted together. The top of the mast is tapered cutting a strip of material from the side of the profile of increasing width. Then the two edges are welded together obtaining a decreasing section towards the masthead. This simple procedure allows a reduction in weight and makes the top of the mast more flexible.
- 17. Aluminium mast section shapes: oval, bullet, rectangular and open Carbon masts began to be used in the early 1980's, initially in racing dinghies, and then the America's Cup andAdmiralsCupyachts. In two decades since their first use carbon fibers’ are not as widely used as one mightthink;infact theyare onlyconsideredwhen weight is critical and are therefore limited to racing yachts or performance oriented cruising yachts. This is an area which has evolved greatly in recent years, as innovative materials and designs have been explored. Monolithic and sandwich structureshave beenused.Dimensioningof composite mastsiscomplexand requires analysis of global and local buckling, aerodynamic considerations and evaluation of the strength reduction due to many attachmentsandgeometrical variations.Highmoduluscarbonfibers’includingM55 and Pitchhave been used but the most popular choices are intermediate modulus fibers’ such as M46 for racing yachts or standard modulus fibers’ such as T300 for cruising yachts. Software now exists to assist in material selectionlike,as an example, SIMSPAR code (Pallu, 2008). Carbon masts consist of mainly longitudinal unidirectional fibers’ (over 80%) with some at ±45° and 90°, in an epoxy resin matrix. Most composite masts are manufactured in two half shells with the primary shell reinforced with local buildups at hardware attachmentpoints.Preimpregnatedfibersare laidupbyhand in a female mould and cured at 120°C in an oven or autoclave. The two parts are then bonded together. An alternative fabrication process involving braiding of fibers’ around a mandrel produces a single part mast. A large number of finishing operations are then required, including machining of holes to fix the mainsail track, rigging attachments and spreader features. Note that the two part masts must also require detail attachment work in addition to the work involved in the bonding of the two sections. Therefore acarbon mast can be builtwithincreasedstrengthinthe directionof the principal loads. For optimum sail shape the bend of the mast is very important, as the bend, along with other factors, directly contributes to the sail’s draft depth. As the vessel becomes overpowered greater mast bend flattensthe sail,andsince a carbon mast can be manufactured with precisely controlled orientation of fibers’ it is possible to create a mast which has the correct bending characteristics. Additionally the inherently easier shape tailoring of a laminated structure provides for optimized aerodynamic or structural shapingthroughoutthe length.Thisisan important advance in technology, complement this withnewsail technologyandtheyformasuperioraerodynamicshape thatcouldever be achieved with an aluminummastandpolyestersails.A review of carbonmastsconstruction is presented in Hall, 2002.
- 18. A top example of this technology is represented by the mast of Mirabella V, the largest sloop of the world. Her carbon epoxy mast is 100 meters long, with five sets of spreaders, a section of 1600 mm in the longitudinal plane and a maximum thickness at the step of 40 mm. Two pieces carbon mast 3. Loadings It should be underlined that, in the last decade, significant progress has been made in the field of aerodynamic and hydrodynamic load analysis, thanks to some prestigious international competition such as the America’s Cup and Admiral’s Cup. Many problems related to the forces generated by sails have beenfacedbydevelopingpowerfulnumerical softwareable totake intoaccounta large number of geometricandphysical variables.Neverthelesssome problemsremainlike,asanexample,the behavior of rigging under wind gust, the dynamic loading on the mast caused by the boat movements in rough sea and the pretensioning loads induced by initial rigging trim. These aspectsare currentlyunderinvestigationbut,upto now,itisdifficulttohave reliable results. The consequence of these, and other, uncertainties is that the range of safety coefficients becomes very wide andit isverydifficulttochoose the correctone.Toomuch severe loads will result in very safe but low performances rigging, too much optimistic loads will result in good performances but unreliable rigging.The correct choice should individuate a compromise able to obtain a good rigging system with “reasonablygoodperformances”and“reasonablysafe configuration”.Thischoice doesnotdependonly on technical aspectsbutalsoonthe skill of the crew: it is obvious that the safety level of a racing yacht cannot be the same of a cruise one. A review of methods used for the calculation of mast and rigging designloadsispresentedinthe following,coveringthe development from the very old empirical ones, up to present numerical methodologies. The loads applied to the mast are mainly due to the forces developed by sails, by pretensioning loads and by the hydraulic jack used to raise the mast.
- 19. An approximate evaluation can be performed on the basis of a uniform pressure distribution as a function of weather conditions and wind speed (Marchaj, 1979). A more rigorous approach, although roughlysimplified,consistsinconsidering the equilibrium between hydrodynamic forces acting on the hull andthe aerodynamicforcesdevelopedbythe sails.The amountof the propulsive effect generated by sails depends on a number of factors such as: the area and geometry of sails, the apparent wind velocityandthe angle of incidence of sails.The resultantof sailsforcesFT can be decomposed into lift L (normal to the apparent wind direction) and drag D (opposite to the apparent wind direction) and expressed in terms of non-dimensional coefficients CL and CD. Lift and drag can be measured in the windtunnel duringexperimental tests on scale models and reported in polar diagrams as a function of the angle of incidence α. The total force FT can also be decomposed into two other components: the drivingforce FRin the directionof the boat'scourse and the heelingforce FHperpendiculartothe boat's course; also in this case non-dimensional coefficients CR and CH are defined. To compute the loadexertedbysailsonthe mast itis thennecessarytoknow the coefficientsCL and CD or CR and CH; a great deal of experimental data on sails has been collected by researchers in wind tunnel tests and some of them are available in literature, such as those published by Marchaj (1962, 1964) or the data collection gathered on board Bay Bea yacht (Kerwin et. al., 1974). The sail forces FR and FH can also be determined by considering the hydrostatic properties of the hull in heeled conditions.The heelingmomentMHcausedby the actionof the windonsailsisbalancedbythe righting moment MR rising when the boat heels. The righting moment for an angle of heel θ is equal to Δ×GZθ where Δ isthe displacementof the yachtandGZθ the rightingarm.The side force FH can be determined as follows: Fh= 𝛥𝐺𝑍𝜑 𝐻 Where h isthe vertical distance betweensails’centre of effort (aerodynamic) and hull centre of lateral resistance (hydrodynamic). From the cross curves of the hull it is possible to know exactly the force necessary to heel the yacht of an angle θ; this will be the transverse force developed by the sails in a quasi-staticcondition.Assuming proper sail coefficients at the design heel angle θ, the apparent wind velocity and the driving force FR can be determined. The starting point for the designer is then to determine the maximum heel angle θ to be assumed for the calculation. For little and medium size sailboatsthe referenceheelangle formastandriggingscantlingistypically30°. In the case of big sailing yachts this could be too large and might lead to excessive mast section dimensions; thus a maximum heel of 20-25° isoftenassumed.Once the drivingandheelingforcesFRandFH have beencalculatedand subdivided between mainsail and foresail, the next problem to solve is how those forces should be applied on mast and rigging. In a simplified approach it can be assumed that the mainsail transmits to the mast a distributedloadalongitslength.The simplest wayto apply this load is by a triangular shape. Takingintoaccount that the pressure on the upper part of the sail is greater, owing to the higher wind velocity,atrapezoidal distribution(Figure13b) would be more suitable. According to lifting line theory the pressure follows an elliptical distribution because of the vortex rising at the upper and lower sail bounds (Figure 13c). The actual pressure distribution will vary dynamically depending on aspect ratio, twistand sheettension.Forapplicationtoafinite element model, this type of distribution can be well
- 20. approximated by a step distribution as shown in Figure 13d. Such a distribution of the load is conservative towards the bending moment on the mast because the centre of application of the resulting force is higher than other ones. (a) (b) (c) Distribution of mainsail load on mast: (a) triangular; (b) trapezoidal; (c) elliptical 4. Rules and DesignStandards FewdedicatedRulesexistforsailingyachtrigsA specificsectionwascontainedinthe old version of Dot Norske Veritas Rules for construction and certification of vessels less than 15 meters (DNV, 1983). A similarsectionispresentedin1993 BureauVeritasRulesforthe classification of yachts (BV, 1993). Both of them presented a quite complete set of formulas to calculate the minimum cross section inertia of mast panels. Unstayed and stayed masts up to two orders of spreaders are considered together with other components like spreaders, booms and running riggings. Some additional information are contained in the new version of DNV Rules for vessels less than 15 meters (NBS, 1990. In the new BV Rules(BV,2006) the riggingloadsare consideredasglobal loads inducing vertical bending moments on the hull girder;onlyloadson chain plates are provided. The Germanischer Lloyds faced the problem in depth by a dedicated series of rules for tall ship rigs (GL, 1997), large modern yacht rigs (GL, 2002) and carbon strand and PBO cable rigging (GL, 2008). While GL (1997) refers to old style sailing ships with traditional rigs,GL(2002) containsa full setof rulestocalculate sail forcesdistributionon modern yacht standing rigging. Design formulas for shrouds, spreaders and Wang are provided as well. Further the developing ISO Standards contain some paragraphs about rigging loads (ISO, 2005) though, at this moment, the rules seem to be not yet in their definitive version.
- 21. APPENDAGES 1. Arrangements: As far as the arrangements of the appendages, i.e. keel and rudder, are concerned a considerable developmenthastakenplace over the past fifty years or so. At first in the wooden construction period the long and integrated keels with the rudder hung at the aft end were the fashion. The layout was partiallydictatedbythe possibilitiesandrestrictionsimposedbythe available materialsand methods of construction at that time. The ballastweightwas connected to the fore ward bottom part of the keel and usually constructed of leador cast iron.The keel wasanintegral partof the hull andthus fairedin the hull over a considerable part and was more or less a peaked vertical extension of the hull. A trend that came from the older designs which started to use more and more V shaped sections in the hull to generate side force so it was in a way a further development of the hull shape evolution at that time. The keel was not consideredasa wing.The rudderwasmore or lessaflapat the aftend of the keel andowed a large part of its effectiveness from a considerable force (lift) carry over on the keel just in front of it. After the transition to steel hulls the shape remained the same for a considerable period of time. 2. Material Selection Criteria In general it should be mentioned that any rule, if applicable, does not allow the use of materials for ballastwitha higherspecificweightdensitythen lead. So in a way the choice is limited. When the keel was an integral part of the hull the material of choice was the same as for the hull, i.e. wood and only the ballast part of the keel was fabricated from either lead or cast iron. In the transition from wood to newer hull construction materials for yachts, such as steel, aluminum alloy and (glass) fiber reinforced polyester, also new construction material for the appendages were used.Insteel andaluminumalloyhullsthe keelswere often made also of the same material as the hull and the ballastwaspouredinfromthe outside afterfinishing of the hull. This implied that usually lead was used. In more modern hulls from these metals still the keels are made from the same materials, welded to and being integral part of the hull. Even when the keel is not faired into the hull over a considerable of its length as with the wooden hulls The choice of materials for the keels, both when the keel is a separate appendage and when it is structurally independent, is influenced by a number of considerations: i.e.: The structural requirements of the separate fin, Its connection to the hull The specific weight density of the materials used The cost involved.
- 22. Two materialsdominatethe field: Lead.Lead has the higherspecificweightdensity of the materials allowed. It comes close to 11 tonsper cubicmeterdepending onitspurity,butisquite expensive.In particular because some 4% of itsweight has to be added as antimony to the pure lead to give it more strength. Typical application of this choice is in the more performance orientated designs. also the health and environmental precautions, which have to be taken during melting and pouring, contribute to the cost Cast iron. Cast iron has a specific weight density of around 7.8 tons per cubic meter but is structurallysoundonitsown.It ismuch cheaper,bothinacquisitionandin manufacturing. Also castingis muchmore common practice and less of a hazard. Typical application of the cast iron keel istherefore inthe cheaperseriesproductionboatmarketthoughitoftenleadstocorrosion problems. The main considerations for the material choice for the rudder are: Weight Strength and Stiffness PARTS: Parts of a Boat from the Side Boats come inmany stylesandshapes,butthe namesof the differentpartsremainconsistent.Every boat operatorshouldknowthe followingtermsanddefinitions. Bow: Front of a vessel Stern: Rear of a vessel Propeller: Rotates and powers a boat forward or backward Starboard: Right side of a vessel Port: Left side of a vessel Hull: Body of a vessel
- 23. Gunwale: Upper edge of vessel's side (generally pronounced gunnel) Cleat: Metal fitting on which a rope can be fastened Navigation lights include all-round white light and red and green sidelights Parts of a Boat from the Front Beam: Maximumwidthof a vessel Freeboard:Distance fromwaterto lowestpointof the boatwhere watercouldcome on board Draft: Depthof waterneededtofloata vessel Keel:Main centerline(backbone) of avessel orthe extensionof hull thatincreasesstabilityinthe water REFERENCE: Alford, L., Troesch, A.W. (2008), “Using Non-Uniform Phase Distributions to Predict Extreme Occurrencesof a StochasticProcess”,underreviewforthe Journal of Engineering Mathematics. Beck, R.F. and Reed, A.M. (2001), “Modern Computational Methods for Ships in a Seaway”, Transactions of the Society of Naval Architects and Marine Engineers, vol. 109, pp 1 – 52. Bureau Veritas (2006), “Rules for the Classification and Certification of Yachts”, Paris, France. Boote D., Morozzo, C. (2005), “The combined use of wood and composites in pleasure yacht construction” (in italian), Proceedings of the Symposium on “Wooden yachts today”, Genova, Faculty of Architecture. Boote D., Ruggiero V., Sironi N., Vallicelli A., Finzi B. (1985), “Stress analysis for light alloy 12m yacht structures. Comparison between a transverse and a longitudinal structure”, S.N.A.M.E., Seventh Chesapeake Sailing Yacht Symposium, Annapolis, USA, pp59-80. Claughton, A., Shenoi, R.A., Wellicome, J.F. (ed) (1998) “Sailing Yacht Design Claughton,A.,Shenoi,R.A.,Wellicome,J.F.(ed.) (1998) “SailingYacht Design - Theory”, Addison Wesley Longman, ISBN 0 582 36856 1 Faltinsen,O.M.(2000),“HydroelasticSlamming”,Journal of Marine Science andTechnology,vol. 5, pp 49-65.