Tech­ni­cal: Vertical bows pros & cons

Superyacht - - What’s On The Market - by An­drea Man­ci­ni

Are bla­de li­ke vertical bows be­co­ming in­crea­sin­gly po­pu­lar on small and lar­ge yachts ir­re­spec­ti­ve­ly as to whe­ther they’re mo­tor or sai­ling ones, or is it on­ly a tren­dy fa­shion? Are they use­ful or not? Are they sui­ta­ble for eve­ry sort of wa­ter craft or is it that sha­pe is de­ter­mi­ned ac­cor­ding to func­tion? For so­me they are even dan­ge­rous. Is this true? Let’s try to an­swer...

Ta­ke a chair, an arm­chair, a stool even. They ha­ve dif­fe­rent na­mes be­cau­se they’ve got dif­fe­rent func­tions and yet all th­ree are used to sit on! The sa­me is true for boa­ts: a ya­cht, a fi­shing tra­w­ler, a fer­ry, all ha­ve dif­fe­rent na­mes but all th­ree are used to sail wi­th on seas, la­kes, ri­vers and so on. Ob­viou­sly they don’t ha­ve the sa­me ha­ve func­tions still they’re all built to sail, but ea­ch one ser­ves a di­ver­se pur­po­se. Ac­cor­din­gly, for eve­ry ty­pe of ves­sel pos­ses­ses phy­si­cal fea­tu­res and ex­ter­nal li­nes and si­lhouet­tes whi­ch dif­fer from one ano­ther even when they are of the sa­me si­ze. This exam­ple is qui­te plain enou­gh but it un­der­sco­res the ob­vious fact that: boa­ts ha­ve di­ver­se sha­pes be­cau­se they are built to ser­ve dif­fe­rent func­tions and pur­po­ses. Or bet­ter they should ha­ve! When con­si­de­ring the world of yachts or re­crea­tio­nal craft lar­ge and small so­me pro­vi­so mu­st be ma­de sin­ce this sec­tor has been in­crea­sin­gly and stea­di­ly con­di­tio­ned by fa­shio­na­ble trends. Skil­led car de­si­gners from the au­to­mo­bi­le in­du­stry and ca­pa­ble in­te­rior de­co­ra­tors/ar­chi­tec­ts ha­ve in­fluen­ced the sec­tor, of­ten thou­gh wi­th ve­ry lit­tle know how on spe­ci­fic su­b­jec­ts whi­ch we re­fer to as na­val ar­chi­tec­tu­re. No doubt as ma­ny of you know, na­val ar­chi­tec­tu­re is all em­bra­cing: from hull sha­pes to in­te­riors, whe­re all is dic­ta­ted by spe­ci­fic func­tions whi­le being com­pliant to stan­dards de­tai­ling sta­bi­li­ty, sea wor­thi­ness, drag and mu­ch mo­re. Ine­vi­ta­bly the­re­fo­re, yet un­cri­ti­cal­ly, sty­ling and trends de­ri­ving from sec­tors other than tho­se of the ya­ch­ting in­du­stry ha­ve been adop­ted in to­day’s yachts as well. Not to men­tion the so cal­led ya­cht “ex­perts”, in short sa­le­smen, pseu­do sur­veyors, or tech­ni­cians that all too of­ten pass them­sel­ves off as ex­perts whi­le kno­wing no­thing or ve­ry lit­tle about what a hull is, what drag means, the sa­me goes for sta­bi­li­ty, pro­pel­ler ef­fi­cien­cy and in spi­te of this hu­ge lack of kno­w­led­ge pro­fess pre­cious ad­vi­ce to would be fir­st ti­me buyers pe­rhaps who are fa­sci­na­ted by the ya­cht they wi­sh to buy. Fa­shio­na­ble trends af­fect and con­di­tion the ya­ch­ting world and al­so hear­say plays an im­por­tant part. When a gi­ven mo­del is at­trac­ti­ve enou­gh she im­me­dia­te­ly becomes tren­dy and becomes the ya­cht to copy whe­ther she’s a ‘na­vet­ta’ or a speed boat. Ne­ver mind, she’s be­co­me sim­ply fa­shio­na­ble! In exac­tly the sa­me way as fa­shio­na­ble clo­thes in­du­ce us to do away wi­th all kinds of things we nor­mal­ly wear, from sui­ts to shirts sim­ply be­cau­se the co­lour or pat­tern is no lon­ger ‘in’ or be­cau­se the sty­ling has chan­ged! And this is exac­tly what has been of­ten hap­pe­ning in the ya­ch­ting world, whe­re fa­shio­na­ble trends ha­ve de­ter­mi­ned choi­ces whi­ch are a world, apart from any­thing nau­ti­cal. The exam­ples are not few and far bet­ween but ma­ny: they com­pri­se ty­po­lo­gy of the en­gi­nes, hy­brids, dri­ves, hulls’ sha­pes, decks and lay­ou­ts. In the cour­se of this ar­ti­cle we’ll ta­ke a clo­ser look at this to­pic to bet­ter un­der­stand the poin­ts we wi­sh to ad­dress and un­der­sco­re wi­thout get­ting in­vol­ved wi­th tech­ni­cal de­tail, al­beit it is an ex­tre­me­ly im­por­tant aspect when de­ter­mi­ning yachts’ nau­ti­cal cha­rac­te­ri­stics, sea-kee­ping qua­li­ties and sa­fe­ty. So we co­me to the sha­pe

of the bow. We’ll be ana­ly­sing tho­se sleek vertical bows wi­th ve­ry lit­tle fla­re or no­ne wha­tsoe­ver. Over the pa­st few years they ha­ve be­co­me ex­po­nen­tial­ly mo­re po­pu­lar on eve­ry sort of ves­sel: fa­st pla­ning ones and slow di­spla­cing ones, ve­ry of­ten for no pre­ci­se, or func­tio­nal rea­son other than the fact they’re tren­dy. The adop­tion of this choi­ce wi­thout a spe­ci­fic tech­ni­cal rea­son and func­tio­nal pur­po­se for doing so, but one whi­ch is me­re­ly dic­ta­ted by the fact it’s tren­dy can not on­ly turn out to be a choi­ce whi­ch does not work ef­fec­ti­ve­ly in the true sense but one that can be­co­me a dan­ge­rous choi­ce!

But let’s pro­ceed in steps. Bows used to slant for­ward wi­th fla­res of va­ry­ing de­grees but al­ways clear­ly vi­si­ble. Loo­king at a fi­shing tra­w­ler for exam­ple, a ves­sel whe­re the bow is de­si­gned to gua­ran­tee, thanks to its vo­lu­me, less or dam­pe­ned pit­ching mo­tion as the boat cra­shes again­st head seas the gi­ven sha­pe of the bow stops wa­ves from ri­sing up and spil­ling over on­to the main deck. The­se sa­me fea­tu­res in va­ry­ing de­grees are al­so found on pla­ning hulls from the se­ven­ties whi­ch spor­ted Del­ta or Hunt sha­ped bows whi­ch soon be­ca­me uni­ver­sal­ly re­no­w­ned. They we­re ve­ry si­mi­lar to one ano­ther but ca­me from dif­fe­rent sour­ces na­me­ly from The Ita­lian na­val ar­chi­tect Son­ny Le­vi and from US ci­ti­zen Ray Hunt. Fa­st pla­ning hulls wi­th si­gni­fi­can­tly slan­ted bows and ge­ne­rous fla­re we­re spe­cial­ly de­si­gned to li­mit broa­ching, whi­ch can

hap­pen wi­th lit­tle war­ning when for exam­ple the bow dips deep in­to a wa­ve as the­re is not enou­gh vo­lu­me to keep the bow up out of the wa­ter. When this hap­pens at so­me speed the ves­sel will sud­den­ly chan­ge di­rec­tion (so­me­thing whi­ch can be va­gue­ly com­pa­red to a car spin). But we’ll ta­ke up this su­b­ject in de­tail la­ter. And why is it that an ever in­crea­sing num­ber of yachts, be they mo­tor yachts, speed boa­ts, na­vet­te, (small ships), open or day crui­sers, ha­ve slim vertical bows wi­th ve­ry li­mi­ted abo­ve sur­fa­ce vo­lu­mes? Be­fo­re tac­kling this point, let’s ta­ke one step back and try to com­pre­hend how and when this trend star­ted. The tur­ning point ca­me wi­th the pre­sen­ta­tion of the Wal­ly Po­wer 118, the ve­ry fir­st mo­tor pro­pel­led Wal­ly from the pre­sti­gious ship yard wi­th Lu­ca Bas­sa­ni at the helm. He in fact re­vo­lu­tio­ni­zed the looks and re­vi­si­ted the func­tio­na­li­ty of the sai­ling ya­cht ran­ge. It was 2002 and the Wal­ly 118 whi­ch was la­ter fol­lo­wed by se­ve­ral other smal­ler Wal­ly Po­wer mo­dels, and a few Wal­ly Ten­der mo­dels, was ne­ver­the­less a bold de­ci­sion whi­ch ge­ne­ra­ted mu­ch ar­gua­ble di­scus­sion, in so­me ways even sheer fol­ly star­ting from the in­stal­la­tion of as ma­ny as th­ree gas tur­bi­nes de­ve­lo­ping 5,600 HP ea­ch one lin­ked to th­ree hy­dro-je­ts whi­ch to­ge­ther rea­ched an ab­surd speed of 60 kno­ts. Even when in terms of sa­les Wal­ly Po­wer 118 was no suc­cess, this ya­cht was pro­vo­ca­ti­ve and real­ly roc­ked the ya­ch­ting sce­ne and be­ca­me kno­wn as a cult boat wi­th a spe­cial de­si­gn, to the ex­tent she’s the on­ly ya­cht to ha­ve been ex­hi­bi­ted at the San Fran­ci­sco MOMA (mu­seum of mo­dern art) in 2004. The 118’s mo­dern li­nes and fu­tu­ri­stic

de­si­gn, li­ke ma­ny of the de­tails rea­li­zed on this ya­cht be­gan to be of in­spi­ra­tion to ma­ny others whi­ch fol­lo­wed. At ti­mes so­me of the mo­re ou­tstan­ding de­tails we­re sim­ply co­pied un­cri­ti­cal­ly. This ex­plains how we be­gan to no­ti­ce su­per­struc­tu­res and decks wi­th taught clear­ly de­ter­mi­ned li­nes and mi­ni­ma­li­st in­te­riors. But ina­smu­ch as a su­pe­rya­cht is not on­ly a lu­xu­ry col­lec­ti­ble, in prac­ti­cal terms it can­not ju­st be an ob­ject of spe­cial de­si­gn ei­ther. Re­cal­ling the point about sha­pe and func­tion men­tio­ned at the be­gin­ning, the­re would be mu­ch to say about how the­se aspec­ts im­pact on a ya­cht whi­ch of cour­se needs to be at­trac­ti­ve al­beit wi­th a pre­ci­se func­tion. A ya­cht is an ob­ject whi­ch tra­vels and the pos­si­bi­li­ty that any­bo­dy can at so­me point ac­ci­den­tal­ly cra­sh in­to a sharp ed­ge of the coa­chroof for exam­ple is fo­re­seea­ble and con­se­quen­tly sharp ed­ges are clear­ly avoi­ded as it is bet­ter to hit up again­st a roun­ded ed­ge than again­st a sharp one. In mu­ch the sa­me way as

few grab rails can­not be ju­sti­fied ju­st to mat­ch up wi­th a mi­ni­ma­li­st de­cor. But let’s go back to the Wal­ly Po­wer and to her sharp nar­row vertical bow and al­mo­st vertical top­si­des in the bow whi­ch con­tri­bu­te con­si­de­ra­bly in de­li­ve­ring a ve­ry ag­gres­si­ve and mo­dern ap­peal. The vertical bow be­ca­me tren­dy and one way or ano­ther ma­ny de­si­gners and shi­pyards played along. So yachts wi­th vertical bows ha­ve be­co­me ve­ry tren­dy but it’s no­thing new for nar­row and vertical bows fir­st be­gan way back, to when ships be­gan to be pro­pel­led wi­th en­gi­nes and wi­th a spe­ci­fic rea­son: to ma­ke wa­ter­li­nes lon­ger whi­le mi­ni­mi­zing wa­ve for­ma­tion in the bows to get mu­ch clo­ser to the ves­sel’s cri­ti­cal speed wi­th af­for­da­ble pe­nal­ties in terms of drag (cri­ti­cal speed re­pre­sen­ts the phy­sio­lo­gic li­mit of a di­spla­cing ves­sel, the speed at whi­ch the hull pro­du­ces a tran­sver­sal wa­ve whi­ch is equal to the leng­th of the ves­sel itself beyond whi­ch point and ex­plai­ned in un­scien­ti­fic terms but ne­ver­the­less ex­pla­na­to­ry ones, the stern end of the hull si­ts back on the self pro­du­ced wa­ve. At this point the drag ef­fect in­cur­red by the wa­ve pro­du­ced be­gins to in­crea­se sud­den­ly). We’re tal­king about lar­ge ships but not on­ly. If you wan­ted speed then nar­row sleek hulls wi­th vertical bows cou­pled to es­sen­tial­ly flat bot­to­med stern areas used to be the on­ly so­lu­tion, as can be clear­ly seen when ob­ser­ving old pic­tu­res of the fir­st tur­bo char­ged ship the “Tur­bi­nia” whi­ch was over 30 me­tres long and rea­ched 35 kno­ts in 1894, or the tor­pe­do ar­med speed-boat de­ployed in bo­th world wars by the Ita­lian Na­vy, (fig.5). The sa­me sha­pes at the ti­me we­re obli­ga­to­ry choi­ces for the fir­st ra­cing speed- boa­ts (fig.6). This ty­pe of bow is not so­me­thing new to­day and is de­ployed in se­ve­ral con­tex­ts for di­ver­se sco­pes, but al­ways in con­nec­tion wi­th a spe­ci­fic func­tion. We’re tal­king about small uni­ts whi­ch en­su­re com­mu­ni­ca­tion in de­man­ding hea­vy wea­ther bet­ween the coa­st and off­sho­re rigs in the Nor­th Sea for exam­ple (fig.7). The­se sport nar­row vertical bows whi­ch li­mit pit­ch and slam­ming. The lat­ter of the two could bring about struc­tu­ral even ir­re­pa­ra­ble da­ma­ge to the craft in ad­di­tion to de­li­ve­ring a ve­ry un­com­for­ta­ble ri­de to tho­se on board. Thanks to nar­row vertical bows the­se spe­cial craft are ma­de to be li­te­ral­ly wa­ve pier­cing and can keep up mu­ch hi­gher speeds than other­wi­se (fig.8). Ha­ving thus ascer­tai­ned that this ty­pe of bow whi­ch is so tren­dy no­wa­days, is in tech­ni­cal and hi­sto­ri­cal terms no­thing new. Let’s try now what the ef­fec­ts de­ri­ved from this are, whi­le re­mem­be­ring the bow is an in­te­gral part of the ves­sel and its sha­pe is grea­tly re­spon­si­ble for the ship’s be­ha­viour and fea­tu­res.

A wet­ter boat. This is the fir­st con­se­quen­ce when a nar­row sleek bow is adop­ted. Lack of grea­ter abo­ve sur­fa­ce vo­lu­me, cau­ses the craft to pier­ce in­to wa­ves ra­ther than ri­de up­ward to meet them. This means mo­re spray wi­th mo­re wa­ter on deck spe­cial­ly in head seas in hea­vy wea­ther and when you do not want to re­du­ce speed mu­ch.

Di­mi­ni­shed in­te­rior vo­lu­mes. This one is al­so an ob­vious con­se­quen­ce whi­ch has not been du­ly con­si­de­red when slim bows are adop­ted me­re­ly for ae­sthe­ti­cal rea­sons. In fact the sha­pe of the bow has con­si­de­ra­ble ef­fect on a good third of the hull and re­du­ces in­te­rior vo­lu­me as well as deck spa­ce. All of this of­ten in­vol­ves shif­ting the su­per­struc­tu­re fur­ther aft at lea­st in smal­ler ves­sels whi­ch trans­la­tes in­to a dra­stic re­duc­tion of in­te­rior spa­ce and al­so in­vol­ves the si­ze of the aft area de­di­ca­ted to loun­ges and con­vi­via­li­ty. On lar­ger ves­sels thou­gh mo­ving the su­per­struc­tu­re fur­ther aft means ha­ving a mo­re ag­gres­si­ve yet slen­der si­lhouet­te.

Hull ty­po­lo­gy. This re­qui­res a lit­tle tech­ni­cal but ne­ces­sa­ry de­tail. Bea­ring in mind the abo­ve men­tio­ned con­si­de­ra­tions, in broad terms we can say a vertical slen­der bow can be­fit di­spla­cing or se­mi di­spla­cing hulls by whi­ch we mean hulls whi­ch nor­mal­ly voya­ge wi­th bows im­mer­sed at lea­st in nor­mal fair wea­ther. In this in­stan­ce lon­ger wa­ter­li­nes ob­tai­ned by vertical hulls gi­ve ri­se to hi­gher speeds whi­ch clo­se mu­ch of the gap when com­pa­red to the re­spec­ti­ve cri­ti­cal speeds men­tio­ned ear­lier wi­th af­for­da­ble drag coef­fi­cien­ts. Ho­we­ver when con­si­de­ring fa­ster se­mi pla­ning or pla­ning craft for the­se ha­ve mo­re op­tions sin­ce they can crui­se along in the sa­me po­si­tion they adopt when ly­ing to an an­chor in nor­mal si­tua­tions, or they can pla­ne the­re­by lif­ting up their bows, as they pick up speed. In this mo­de slim vertical bows be­co­me a ha­zard as they’re mo­re su­scep­ti­ble to broa­ching, and con­se­quent spin out. But what cau­ses this? Ba­si­cal­ly a sud­den va­ria­tion in the craft’s lon­gi­tu­di­nal ba­lan­ce, a wa­ve even can cau­se the bow to di­ve in­to the wa­ter and when the im­pact is not suf­fi­cien­tly sym­me­tri­cal to the pla­ne the flat stern end will ri­se up as the bow dee­pens in­to the wa­te­rand the speed mea­n­whi­le will cau­se the craft to spin (sad­ly we’re all aware of dan­ge­rous spin ou­ts wit­nes­sed du­ring off­sho­re speed boat com­pe­ti­tions). In prac­ti­cal terms the mo­re the bow end is slim and deep the mo­re it will tend to di­ve in­to the wa­ter and will pi­vot, and li­kewi­se the stern the mo­re it is flat the mo­re it will tend drift off cour­se (figs 9 and 10). Re­tur­ning to the que­stion po­sed at the start, why are the­re ever gro­wing num­bers of slim bla­de li­ke vertical bows on pla­ning yachts to­day wi­th li­mi­ted abo­ve wa­ter­li­ne vo­lu­mes? Is su­ch sha­pe ju­sti­fied by the func­tion the bow has to de­li­ver? Or is it ju­st a pas­sing trend? The an­swers, If I ha­ve ma­na­ged to be clear enou­gh in my ex­pla­na­tions, should by now be clear. In ac­tual fact the speed boat ra­cing world has de­li­ve­red the an­swers to the­se que­stions over tens of years whe­re near­ly al­ways the bow slan­ts hea­vi­ly for­ward spor­ting am­ple fla­ring. And not­wi­th­stan­ding this, the po­ten­tial dan­ger of spin­ning out still exists. In a nu­tshell, vertical sleek bows are ful­ly ju­sti­fied when in­stal­led to fill a spe­ci­fic func­tion as hap­pens wi­th Axe Bow hulls whi­ch, let’s re­mem­ber are se­mi-di­spla­cing ones. They can’t be ju­sti­fied on pla­ning ones sin­ce they can cau­se broa­ching and po­ten­tial­ly spin ou­ts as well. Ima­gi­ne what can be ex­pe­rien­ced when spee­ding along at 20,30 kno­ts and sud­den­ly the ya­cht bears off shar­ply and stops: tho­se on board will pro­ba­bly fall and or hit on so­me­thing and can even fall over­board, whi­le ob­jec­ts fly li­ke bul­le­ts. I ha­ve per­so­nal­ly ex­pe­rien­ced a spin out and for­tu­na­te­ly it was Fi­gu­re 13 – As men­tio­ned ear­lier when the si­ze of a ya­cht is sub­stan­tial a vertical bow can be a good so­lu­tion even when con­si­de­ring sea-kee­ping qua­li­ties and sa­fe­ty fac­tors. In fact di­spla­cing and se­mi-di­spla­cing hulls sin­ce they voya­ge wi­th a ‘stan­dard’ lon­gi­tu­di­nal set up whe­re the bow is al­ways im­mer­sed at lea­st in fair wea­ther, a slim and vertical bow of­fers ma­ny ad­van­ta­ges sin­ce it leng­thens wa­ter­li­ne whi­le mi­ni­mi­zing the for­ming of bow wa­ves and is fa­ster wi­thout gi­ving mu­ch away to drag ef­fec­ts. Ob­viou­sly head seas will pro­ba­bly spill wa­ter spray on the bow end of the deck as can be seen in the pic­tu­re fea­tu­ring M/Y Ka­mi­na built by Feadship ( a 33 me­tre laun­ched in 2016) crui­sing at 20 kno­ts all out: the bow wa­ves for­med, thanks al­so to the sha­pe of the bow sec­tion is, all things con­si­de­red, con­tai­ned but the on­co­ming head sea has no­thing to stop it from ri­sing up on­to the top­si­des. not a ve­ry vio­lent one. It hap­pe­ned in the cour­se of a se­ries of speed tests on a small boat when all of a sud­den at 20 kno­ts the boat went off at right an­gles and stop­ped. We we­re all clear­ly con­cen­tra­ted and hol­ding on wi­th grip­ping hands and for­tu­na­te­ly no one was hur t. The­re­fo­re asi­de from a hy­dro-dy­na­mic func­tion (bet­te­ring ef­fi­cien­cy when in di­spla­cing mo­de- wa­ve pier­cing ef­fect) adop­ting a slim vertical bow on a pla­ning hull has got cer­tain si­de ef­fec­ts whi­ch ma­ke it dan­ge­rous and inad­vi­sa­ble. Ob­viou­sly the dan­ger of broa­ching gro­ws ex­po­nen­tial­ly as boat speed in­crea­ses, the­re­fo­re if a boat is ca­pa­ble of 40 kno­ts a slim bla­de li­ke vertical bow would be a cra­zy thing. Broa­ching thou­gh can hap­pen al­so at con­si­de­ra­bly lo­wer speeds in cer tain con­di­tions and /or rou­gh seas. Let’s the­re­fo­re try to al­ways un­der­stand the func­tion or ro­le the ob­ject in que­stion has to ful­fil whi­le it en­joys ephe­me­ral suc­cess (as long as it’s tren­dy) be­fo­re being se­du­ced by it...if we can. If not we could wind up as so­me of tho­se mo­tor car buffs who in­stall spoi­lers on the backs of their com­pact cars in imi­ta­tion of For­mu­la 1 class ve­hi­cles, wi­th no be­ne­fit wha­tsoe­ver, on the con­tra­ry wi­th de­tri­ment to fuel con­sump­tion. But we know, va­ni­ty li­ke whims has no pr ice!

Fi­gu­re 10 – He­re’s what de­si­gner Son­ny Le­vi wro­te in his book: “Mi­le­sto­nes in my de­si­gns”, from whi­ch we’ve ta­ken the two dia­grams abo­ve con­cer­ning broa­ching and of how bow sha­pes bring about the phe­no­me­na “Ex­ces­si­ve V in bow sec­tions can cau­se...

Fi­gu­re 11 – The dif­fe­ren­ces in the bow sha­pes of Re­na­to Son­ny Le­vi’s Sur­fu­ry and Wal­ly Po­wer 118 are well de­fi­ned. The­se bring about two di­ver­se func­tions: Sur­fu­ry’s bow is de­si­gned to stay out of the wa­ter at all ti­mes whe­reas Wal­ly’s is de­si­gned to...

Fi­gu­re 9 - Broa­ching is the ter­mi­no­lo­gy used when the ves­sel sud­den­ly bears off cour­se as the bow di­ves be­low the sur­fa­ce and the stern tends to ri­se. Fi­gu­re 9 clear­ly sho­ws what can hap­pen when the ya­cht’s bow ‘digs’ in­to a lar­ge wa­ve and tends to...

Fi­gu­re 8 - A ty­pi­cal wa­ve pier­cing bow fea­tu­ring a slim stem head whi­ch slan­ts bac­k­wards. This ver­sion can be found on a lar­ge mi­li­ta­ry ves­sel li­ke a DDG-1000 whi­ch ser­ves as a mul­ti-mis­sion 183 me­tre long ship built for the US Na­vy. She is al­so kno­wn...

Fi­gu­re 7 – The ”Axe­bow”,re­pre­sen­ts an exa­spe­ra­ted ver­sion of a vertical one whe­re the dia­gram clear­ly sho­ws Doña Dia­na’s si­lhouet­te. She’s a fa­st 51 me­tre sup­port ves­sel re­cen­tly built by Da­men shi­pyard from Hol­land. She’s to pro­vi­de trans­port to and...

Fi­gu­re 6 – The hull li­nes of the Le­gru-hot­ch­kiss, one of the fir­st speed boa­ts built in 1903 in En­gland. Thanks to a vertical slim bow and the 12 me­tre wa­ter­li­ne wi­th a beam of ju­st 1.5 me­tres and flat stern sec­tions this boat rea­ched 30 kno­ts wi­th an...

Fi­gu­re 5 – Tur­bi­nia left the fir­st tur­bo char­ged boat wi­th an LOA of 30 me­tres rea­ched 35 kno­ts in 1894. To the right a tor­pe­do equip­ped mi­li­ta­ry ves­sel of the Ita­lian Na­vy in 1917. No­ti­ce the slight Axe bow whi­ch con­fers an ag­gres­si­ve ap­pea­ran­ce whi­ch...

Fi­gu­re 4 – A slim nar­row al­mo­st vertical bow and top­si­des we­re one of Wal­ly po­wer 118’s fea­tu­res whi­ch ha­ve be­co­me ve­ry tren­dy.

Fi­gu­re 3 – Re­na­to Son­ny Le­vi’s fir­st off­sho­re ra­cer de­si­gned in 1965, sports a Del­ta hull. In ad­di­tion to deep V sha­pe all along its leng­th it is pos­si­ble to see a ve­ry pro­noun­ced for­ward slan­ting of the con­vex bow. This mo­del won ma­ny pri­zes in that...

Fi­gu­re1 – In the fo­re­front a clo­se up of a vertical bow wi­th al­mo­st vertical top­si­des of Azi­mut’s Ma­gel­la­no, be­hind it the ty­pi­cal slan­ted bow of a pla­ning hull wi­th slightly con­vex top­si­des.

Fi­gu­re 2 – view of a slan­ting ste­m­head and well de­si­gned fla­re cha­rac­te­ri­ze the bow of the fi­shing ves­sel. This sha­pe gi­ves ex­tra lift to the bow that can in head seas de­flect on­co­ming wa­ves whi­le re­du­cing pit­ch and pre­ven­ts the bow from going under.

A cut­tin­gly deep and thin vertical bow of a ten me­tre speed boat ex­hi­bi­ted at one of the re­cent Ge­noa Boat Sho­ws. Wi­th su­ch sha­pes ( con­si­de­ring the flat­ness of the stern ends) broa­ching is gua­ran­teed and mo­re so when pro­pel­led at 50 kno­tstop speed...

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