FUNCTIONING AND COLLATERAL EFFECTS

CMC Ma­ri­ne ope­ned the doors of the new HQ si­tua­ted in Ca­sci­na Ita­ly to whi­ch the com­pa­ny mo­ved to in the be­gin­ning of 2017. The mo­ve was dic­ta­ted by the im­pel­lent need to fa­ce up to the sub­stan­tial in­crea­se in pro­duc­tion and by the need to take on mo­re st

Superyacht - - Technical - by An­drea Man­ci­ni

Bow th­ru­sters are pro­ven use­ful aids whi­le ma­noeu­vring ya­ch­ts in re­stric­ted wa­ters, they be­co­me ab­so­lu­te­ly ne­ces­sa­ry when tal­king about su­per and me­ga ya­ch­ts. Of­ten enou­gh thou­gh bow th­ru­sters are in­stal­led ei­ther ap­pro­xi­ma­te­ly well whi­ch is ba­re­ly enou­gh or even clear­ly in the wrong pla­ce to the ex­tent that ef­fi­cien­cy is re­du­ced and hy­dro­dy­na­mic drag is en­han­ced, so are vi­bra­tions and fur­ther­mo­re struc­tu­ral da­ma­ge can re­sult from this as well. The text that fol­lo­ws aims to ana­ly­ze cau­ses and pre­cau­tions whi­ch need to be ta­ken in­to ac­count and other con­si­de­ra­tions to en­su­re cor­rect in­stal­la­tion. Use of a side thruster in­stal­led in the bow and / or the stern whi­ch will at the pu­sh of a but­ton or joy­stick mo­ve the bow or stern of the yacht to one side or the other ac­cor­din­gly to en­han­ce ma­noeu­vring in the smal­le­st of slo­ts whi­le ber­thing for exam­ple. And this is the rea­son for whi­ch al­mo­st eve­ry yacht abo­ve a gi­ven si­ze will be equip­ped wi­th a bow thruster and sometimes a stern thruster too. De­ploy­ing this tech­no­lo­gy ma­kes things sim­ple enou­gh when wan­ting to ber­th for exam­ple in real­ly re­stric­ted spa­ces even, and/ or wi­th cross winds and or cur­ren­ts pu­sh the boat in the op­po­si­te di­rec­tion you want to go, this tech­no­lo­gy be­co­mes mo­re than han­dy and a lot sa­fer to ha­ve than not. But li­ke eve­ry­thing el­se the in­stal­la­tion of the who­le, mea­ning th­ru­sting pro­pel­ler and hou­sing tun­nel mu­st be car­ried out cor­rec­tly whi­le kno­wing that a hull con­cei­ved and de­si­gned to mo­ve th­rou­gh wa­ter whi­ch is a thou­sand ti­mes den­ser than air will be mo­di­fied. Ca­re­less, thoughtless in­stal­la­tions can be seen of­ten, as you ob­ser­ve hou­sing tun­nels, as the ya­ch­ts are hi­gh and dry on their crad­les.

The thought being the sa­me one al­ways: well af­ter all its no­thing but a “ho­le” ! But it’s a ho­le and it’s be­low the wa­ter­li­ne un­der­wa­ter! What’s mo­re it’s inside a mo­ving hull and when do­ne bad­ly it can co­st an arm and a leg and mo­re, spe­ci­fi­cal­ly it will im­pair pro­pel­ler ef­fi­cien­cy and ove­rall per­for­man­ce due to grea­ter drag ef­fect whi­ch means ad­ded fuel con­sump­tion, noi­se and in­du­ced vi­bra­tions. Let’s the­re­fo­re take a clo­ser look at so­me of the hy­dro­dy­na­mic aspec­ts in­vol­ved in con­nec­tion to the bow pro­pel­ler whi­ch is the mo­st com­mon­ly used and its hou­sing tun­nel. In ac­tual fact the pro­pel­ler in­stal­led in­to the hou­sing can be a fi­xed bla­ded one, a va­ria­ble pit­ch or even a coun­ter ro­ta­ting sy­stem wi­th two props.(any­thing is mo­re ef­fec­ti­ve than a fi­xed bla­ded prop. But the pur­cha­sing co­st is hi­gher and is mo­re com­plex to run and main­tain: be wary thou­gh of ex­traor­di­na­ry per­for­man­ces being pro­mi­sed lightly). Wha­te­ver the choi­ce of pro­pel­ler it lod­ges in­to a co­duit whi­ch mu­st pos­sess gi­ven fea­tu­res in terms of wear and tear, struc­tu­re and mu­st be wa­ter tight and mu­st com­ply to a gi­ven set of hy­dro­dy­na­mic re­qui­si­tes ac­cor­ding to the hull sha­pe. LONGITUDAL POSITIONING So as to de­li­ver ma­xi­mum ma­noeu­vra­bi­li­ty bow th­ru­sters mu­st be in­stal­led as for­ward as pos­si­ble. In fact the lon­ger the di­stan­ce to the hou­sing tun­nel from the stern, the grea­ter the ma­noeu­vra­bi­li­ty. A sim­ple exam­ple is sup­plied in the technical da­ta sec­tion at­ta­ched to this ar­ti­cle. Ne­ver­the­less the­re’s a do­wn­si­de to in­stal­ling bow th­ru­sters as far for­ward as pos­si­ble: sin­ce, when the yacht is pro­cee­ding for­wards slo­w­ly the bow th­ru­sters loo­se ef­fi­cien­cy by com­pa­ri­son to one whi­ch is in­stal­led fur­ther astern. Tests car­ried out on se­ve­ral mo­dels in­di­ca­te that the bow th­ru­sters’ ef­fect at ju­st two kno­ts are re­du­ced by as mu­ch as 50%. Wi­th a speed bet­ween 1 and 2 kno­ts 40% loss of ef­fi­cien­cy can be re­cor­ded but by mo­ving the hou­sing and prop fur­ther astern the ef­fect is re­du­ced and the pro­pel­ler main­tains hi­gher ef­fi­cien­cy even when the yacht is not mo­ving. Ob­viou­sly this de­tail is of re­la­ti­ve im­por­tan­ce be­cau­se when the boat is not mo­ving the­re’s no rud­der ( in rea­li­ty it works pas­si­ve­ly as de­via­tor of the flux

crea­ted by the pro­pel­ler) as speed in­crea­ses the rud­der bla­de be­co­mes mo­re ef­fec­ti­ve: and the­re’s less need for la­te­ral th­ru­st pro­du­ced by the bow th­ru­sters. Cer­tain­ly in so­me ca­ses, in mo­tor ya­ch­ts for exam­ple whe­re rud­der bla­des are ve­ry mu­ch on the small side ( this is do­ne so as not to ha­ve ad­ded drag at hi­gh speeds) and are the­re­fo­re prac­ti­cal­ly use­less at ve­ry low speed. This da­ta can be use­ful when as­ses­sing whe­re the be­st com­pro­mi­sing li­ne or cut off point is bet­ween the grea­te­st pos­si­ble di­stan­ce from stern to bow thruster or ma­xi­mum le­ve­ra­ge and the mi­nor loss of thruster ef­fi­cien­cy at pro­gres­sing lo­wer speeds.

IM­MER­SION The ru­le is sim­ple: to work cor­rec­tly the bow pro­pel­ler is be in­stal­led as far do­wn as pos­si­ble be­low the wa­ter­li­ne. This is for two rea­sons: 1.In su­ch a way to pre­vent air from the sur­fa­ce from being suc­ked in. This would grea­tly re­du­ce th­ru­st pro­du­ced by the pro­pel­ler ( the pro­pel­ler would no lon­ger be pu­shing wa­ter but a mix of wa­ter and air) 2.To ha­ve wa­ter enou­gh to gua­ran­tee suf­fi­cient pres­su­re to avoid pro­pel­ler ca­vi­ta­tion and con­se­quent loss in pro­pel­ler ef­fi­cien­cy. In prac­ti­cal terms bow thruster pro­du­cing companies re­com­mend that pro­pel­lers be in­stal­led so that the up­per part of the hou­sing tun­nel be pla­ced be­low the wa­ter­li­ne for at lea­st ¾ of the hou­sing tun­nel’s dia­me­ter, or at any ra­te at lea­st one foot (30.48 cm) be­low the wa­ter­li­ne whi­che­ver is the grea­ter. I wi­sh to un­der­sco­re this is a mi­ni­mum va­lue and it is bet­ter to pla­ce the pro­pel­ler as low as pos­si­ble un­der wa­ter. Fur­ther­mo­re hou­sing tun­nels on pla­ning hulls should be in­stal­led so they are out of the wa­ter abo­ve wa­ter­li­ne when the yacht is crui­sing in pla­ning mo­de. LENG­TH OF HOU­SING TUN­NELS When positioning the bow pro­pel­ler, it is not enou­gh to find the right com­pro­mi­se bet­ween the lon­gi­tu­di­nal positioning ( ge­ne­ral­ly as far for­ward as pos­si­ble wi­th the re­min­ders al­rea­dy men­tio­ned) and the im­mer­sion dep­th. A third aspect mu­st al­so be ta­ken in­to due con­si­de­ra­tion: the tun­nel’s mi­ni­mum leng­th across in­to whi­ch the pro­pel­ler will be in­stal­led. To do this the pro­pel­ler mu­st be in­stal­led in an area of the hull whi­ch is suf­fi­cien­tly wi­de across or bea­my enou­gh, whi­ch pro­ba­bly can­not be found nei­ther in the ex­tre­me bow area nor at the bot­tom of the hull in the bow sec­tion. In fact the mo­re we mo­ve to­wards the bow and to­wards the bot­tom of the hull, the mo­re the vo­lu­mes sh­rink mea­ning that beam de­crea­ses. The ideal tun­nel leng­th across is com­pri­sed bet­ween 2 and 4 ti­mes the dia­me­ter of the tun­nel itself. Grea­ter leng­ths cau­se loss of ef­fi­cien­cy due to wa­ter at­tri­tion flo­wing along the si­des and walls of the sa­me. The loss of ef­fi­cien­cy in­cur­red

is ho­we­ver slight up to tun­nel leng­ths equal to six- se­ven ti­mes the si­ze of the dia­me­ter. Les­ser leng­ths be­low 2 to 4 ti­mes the dia­me­ter cau­se loss of ef­fi­cien­cy be­cau­se the pro­pel­ler, con­cei­ved to work in wa­ter wi­th a uni­form flux and pa­ral­lel to the axis of th­ru­st, finds itself wor­king par­tial­ly inside the tun­nel: for the lo­wer part of the tun­nel, whi­ch is con­si­de­ra­bly smal­ler, does not per­mit to ha­ve a uni­form and pa­ral­lel flux as in the up­per sec­tion. Con­se­quen­tly the pro­pel­ler’s th­ru­st is less ef­fi­cient and di­mi­ni­shes si­gni­fi­can­tly due to whir­ling and ca­vi­ta­tion. To sum up when positioning a thruster three Car­te­sian axis need to be ta­ken in­to ac­count: lon­gi­tu­di­nal ( leng­th), ver­ti­cal, ( im­mer­sion) tran­sver­sal ( hull beam). The­re­fo­re nor­mal­ly a ‘ pos­si­ble’ area in whi­ch to in­stall the thruster has to be se­lec­ted prior to com­men­cing in­stal­la­tion .

JOI­NING TUBING TO HULL To pre­vent ef­fi­cien­cy loss of the th­ru­sters and to re­du­ce noi­se to mi­ni­mum le­vels it is ve­ry im­por­tant to per­form a roun­ded cut out bet­ween tun­nel and hull whi­ch is sea­led and not less than 10% of the dia­me­ter. Should this de­tail be omit­ted the re­sul­ting ed­ge bet­ween tun­nel and hull will cau­se tur­bu­len­ce and ca­vi­ta­tion along the tun­nel’s walls when wa­ter en­ters at hi­gh speed. This phe­no­me­na re­du­ces the si­ze of the ‘ ef­fi­cient’ dia­me­ter li­mi­ting the vo­lu­me of wa­ter and the con­se­quent th­ru­st. The sa­me tur­bu­len­ce and ca­vi­ta­tion can al­so af­fect the pro­pel­lers the­re­by re­du­cing per­for­man­ce and in­crea­sing noi­se. Fur­ther­mo­re the roun­ded ex­tre­mi­ties of the tun­nel en­han­ce ta­king wa­ter in and the di­schar­ge of the wa­ter inside the con­duit. The wa­ter is ‘ suc­ked in’ along the si­des of the hull and crea­te a lar­ge area in de­pres­sion whi­ch tends to draw in, the boat la­te­ral­ly. Su­ch de­pres­sion whi­ch of­ten enou­gh co­vers a lar­ger area in the ca­se of ‘ soft’ con­dui­ts, can be con­si­de­red as an ad­di­tio­nal sour­ce of th­ru­st: when in­stal­la­tions are per­for­med fla­w­les­sly, su­ch ex­tra th­ru­st can be si­gni­fi­can­tly hi­gh as mu­ch as 20% mo­re. HULL SET UP NEAR THE TUN­NEL We are tal­king about a mi­nor de­tail when com­pa­red to the who­le yacht and one whi­ch is ne­gli­gi­ble to ma­ny ( even to so­me of tho­se who in­stall side bow th­ru­sters). Ne­ver­the­less in terms of drag effects and noi­se in­crea­se it is wor­th men­tio­ning. Ba­si­cal­ly we’ll be loo­king at a mi­nor mo­di­fi­ca­tion of the hull li­nes near the thruster. The­re are two ways of doing this: ei­ther by buil­ding up a small mould for­ward of the tun­nel whi­ch ac­ts as a wa­ter de­flec­ting ele­ment or wa­ter flow de­via­tor, or by crea­ting a small con­ca­ve dip in the hull ju­st in li­ne wi­th the stern end of the

tun­nel to at­tract the wa­ter flow co­ming from the bow. In bo­th ca­ses the goal is to pre­vent that flo­wing wa­ter along the hull si­des hit the stern walls of the tun­nel crea­ting a bra­ke ef­fect or ge­ne­ra­ting mo­re drag, whir­ling and noi­se. Bo­th so­lu­tions work but the fir­st one is be­st sui­ted to pla­ning ya­ch­ts, whi­le the se­cond one be­fi­ts di­spla­cing hulls mo­re . LET’S NOW TAKE A CLO­SER LOOK. • Hull se­tup for­ward of the tun­nel – We’ve clai­med that this so­lu­tion is mo­re ap­pro­pria­te for pla­ning hulls sin­ce their bo­ws are si­gni­fi­can­tly out of the wa­ter when crui­sing nor­mal­ly. Con­se­quen­tly the tun­nel is ge­ne­ral­ly abo­ve the sur­fa­ce. The se­tup in this ca­se mu­st de­li­ver two func­tions: the pri­me one is to de­via­te wa­ter flow at low speeds as long as the bow and tun­nel the­re­fo­re are im­mer­sed be­low the wa­ter­li­ne. The se­cond func­tion is to de­via­te the wa­ter im­pac­ting the bow whi­le in pla­ning mo­de in the pre­sen­ce of wa­ves, and to pre­vent ri­sing wa­ters

from cra­shing in­to the tun­nels’ walls. Whi­le pla­ning along, the wa­ter flow is ma­de up of two fac­tors com­pri­sing boat speed and the way in whi­ch the boat hi­ts the wa­ves in a head sea, or a cross sea and so on. This is whe­re the mould co­mes in­to play as it will de­via­te bo­th the wa­ters co­ming from the bow and the ones co­ming from be­low ( as seen in pho­to 1) when pro­per­ly in­stal­led. But, set­ting up the hull wi­th this ‘ mould’ for the en­ti­re cir­cum­fe­ren­ce of the tun­nel ( as seen in pho­to 2) will can­cel at lea­st in part the de­si­red effects. In fact so­me of the wa­ter de­via­ted will in any ca­se im­pact again­st the op­po­si­te in­ter­nal wall of the tun­nel. Pho­to 3 sho­ws a tun­nel built wi­th no pro­tec­ti­ve se­tup: it is ea­sy to ima­gi­ne how wa­ter ri­sing from be­low and from the bow will hit up again­st the inside wall of the tun­nel. • Hull se­tup aft of the tun­nel – This so­lu­tion is ge­ne­ral­ly de­ployed on ships be­cau­se it re­du­ces drag mo­re. As said it means crea­ting a con­ca­ve or shell li­ke dip in the hull whi­ch will ‘ col­lect’ the flow aft of the tun­nel pre­ven­ting it from cra­shing in­to the tun­nel’s stern walls. The con­ca­ve dip starts from the aft side of the tun­nel and ta­pers off to- wards the stern. This con­ca­ve dip mu­st be at lea­st equal to the tun­nel dia­me­ter and mu­st slant do­w­n­wards to­wards the stern to be­st adapt to the wa­ter flow. This so­lu­tion will re­du­ce drag brought about by the tun­nel ge­ne­ral­ly from 1 to 2 % but can be as mu­ch as 5% in ca­se of small ships and / or when tun­nels sport lar­ge dia­me­ters. Phy­si­cal and vir­tual tests are car­ried out to de­ter­mi­ne the be­st an­gle of slant at di­ver­se speeds to ob­tain the be­st com­pro­mi­se be­cau­se the drag coef­fi­cient is hi­gh enou­gh to war­rant the­se. The flow an­gle is de­ter­mi­ned by the sha­pe and si­ze of the bow wa­ve whi­ch va­ries ac­cor­din­gly wi­th the speed of the hull. Pho­to 4 sho­ws an im­pres­si­ve bow wa­ve for­mat ge­ne­ra­ted by a lar­ge mo­tor yacht crui­sing at 16 kno­ts. Pho­to 5 sho­ws the le­vel of con­si­sten­cy of the flow on the hull, at the sa­me speed using paint or ‘ drop’ me­tho­do­lo­gy whi­ch trans­la­tes in­to ap­ply­ing plen­ty of paint on the hull whi­ch is then to­wed at a gi­ven set speed. The en­suing wa­ter fric­tion along the hull will drag the paint de­pic­ting the di­rec­tion of the flow. The re­sul­ting ‘ pic­tu­re’ ma­de by the flo­wing wa­ter along the hull gi­ves a good in­di­ca­tion as to whe­re to in­stall the tun­nel hou­sing and the bow thruster ( in cor­re-

spon­den­ce wi­th rib num­ber 18) as paint tracks, show the an­gles of slant whi­ch can be as mu­ch as 20°. Pic­tu­res 6,7,8 show a fa­st mi­li­ta­ry ves­sel pro­cee­ding at 29 kno­ts: whe­re the wa­ve is not as steep and the tun­nel is si­tua­ted fur­ther astern ( rib num­ber 17). Crea­ting a con­ca­ve shell li­ke dip in­to the hull near the tun­nel is af­ter all ea­sy enou­gh to do and not ex­pen­si­ve when com­pa­red to the be­ne­fi­ts ob­tai­ned spe­cial­ly on lar­ge ya­ch­ts. Un­for­tu­na­te­ly this con­cept is ne­ver­the­less not clear­ly un­der­stood even by tho­se who in­stall bow th­ru­sters. Con­se­quen­tly seeing ve­ry co­stly ya­ch­ts wor­th mil­lions, equip­ped wi­th bow th­ru­sters that ha­ve not been adroi­tly sea­led and who­se hulls ha­ve not been pro­per­ly set up is no ra­re thing. In pic­tu­re 9 the­re’s a lar­ge 30 me­tre lu­xu­ry yacht whi­ch has no hull se­tup in pro­xi­mi­ty of the tun­nel wha­tsoe­ver and what’s wor­se, is a se­ries of ver­ti­cal rods ha­ve been sol­de­red on­to the bulb in the bow whi­ch is com­ple­te­ly con­tra­ry to wha­te­ver prin­ci­pal con­cer­ning hy­dro­dy­na­mics: whoe­ver thought this up has clear­ly no idea as to how hulls be­low the wa­ter­li­ne func­tion. Seeing con­ca­ve shell li­ke dips on pla­ning hulls is ano­ther fre­quent eye­so­re, and is cer­tain­ly not so be­fit­ting as the mould si­tua­ted for­ward of the tun­nel. In pic­tu­re 10, thanks al­so to the way the pic­tu­re was ta­ken it is pos­si­ble to ma­ke out why: when hit­ting a wa­ve ver­ti­cal­ly wa­ter is not in­du­ced to slip off, but it is held in by the con­ca­ve dip in the hull as if it we­re a spoon. This trans­la­tes in­to a hi­gh pres­su­re area con­cen­tra­ted lo­cal­ly en­gen­de­ring vi­bra­tion and an im­me­dia­te in­crea­se of drag. • Hy­brid So­lu­tions – Fi­nal­ly pla­ning hulls are of­ten seen spor­ting hy­brid so­lu­tions whi­ch en­tail ha­ving bo­th so­lu­tions in­stal­led: the shell li­ke, spoon li­ke con­ca­ve dip aft of the tun­nel as well as the mould in­stal­led for­ward of the tun­nel ( pho­to 11). Even when the­se so­lu­tions can work well they should be in­stal­led ac­cor­din­gly wi­th ade­qua­te pro­ject de­si­gn work pre­ce­ding in­stal­la­tion. Ma­ny ti­mes the­se so­lu­tions are me­re fan­ta­sy work by im­pro­vi­sed de­si­gners and ha­ve no rea­li­stic ju­sti­fi­ca­tion. In pho­to 12 a mould for­ward of the tun­nel is de­fi­ni­te­ly vi­si­ble but it con­ti­nues al­so aft con­tou­ring the shell li­ke dip to end up on the ska­tes: a clear sty­li­stic exer­ci­se! But will it be enou­gh! It is ob­viou­sly clear that so­lu­tions as the one in pho­to 13 can­not be ju­sti­fied tech­ni­cal­ly spea­king and are me­re­ly fruit of igno­ran­ce. What can be seen is a pla­ning hull wi­thout a mould for­ward of the tun­nel, whi­le a con­ca­ve shell li­ke dip can clear­ly be seen but it is too short and the­re­fo­re of no use at all. The ac­tual con­ca­ve dip is ve­ry deep and ex­tends well abo­ve the tun­nel. The re­sult of this work trans­la­tes in­to a sort of giant wa­ter col­lec­ting spoon whi­ch wi­th­holds wa­ter co­ming from be­low and from for­ward of it and pro­du­ces vi­bra­tion lo­cal­ly and in­crea­ses drag. Su­re­ly a plain ho­le de­ployed as a tun­nel would ha­ve been bet­ter and no­thing el­se!

CMC is plan­ning to pre­sent three in­no­va­ti­ve sy­stems to broa­den the firm’s cur­rent ran­ge, by trans­fer­ring Sta­bi­lis Elec­tra tech­no­lo­gy (elec­tric sta­bi­li­sers) to ya­ch­ts un­der 20 metres wi­th Short Ran­ge plan­ts as well as HS , Hi­gh Speed and LR Long Ran­ge ones. The­se ha­ve all been spe­cial­ly de­si­gned to suit pla­ning ya­ch­ts wi­th speeds in ex­cess of 24 kno­ts, se­mi- di­spla­cing ones and con­si­de­ra­bly slo­wer di­spla­cing ones too. This new ma­chi­ne­ry de­ri­ves from mu­ch of the ex­pe­rien­ce gai­ned in re­cent years when Sta­bi­lis Elec­tra fir­st be­gan to hit the mar­ket wi­th a small but con­si­de­ra­ble revolution in 2009: to over­co­me the pro­blem of low ef­fi­cien­cy me­cha­ni­cal, hy­drau­lic gy­ros ap­pli­ca­ble to smal­ler ya­ch­ts, wi­th a new electrical ac­tua­tor whi­ch mo­ves sta­bi­li­sing fins ge­ne­ra­ted by DC elec­tric mo­tors whi­ch are lighter, hi­ghly ef­fi­cient and mo­re com­pact than pre­vious sy­stems. CMC’S in­tui­tion paid off and they are now the mo­st im­por­tant com­pa­ny in the sec­tor. The ran­ge of Sta­bi­lis Elec­tra – SE mo­dels has been

gro­wing ex­po­nen­tial­ly sin­ce 2013. To­day the­re are about 30 pos­si­ble con­fi­gu­ra­tions thanks to 7 di­ver­se se­ries of ac­tua­tors cou­pled to as ma­ny as 14 dif­fe­rent si­zes of fins and to 12 clas­ses of mo­tors. SE sy­stems can cur­ren­tly be in­stal­led in­to a wi­de ran­ge of di­ver­se ya­ch­ts from fa­st pla­ning ones to slow di­spla­cing ones mea­su­ring from ju­st 20 metres up to 80. La­te­st ge­ne­ra­tion en­gi­nee­ring means that SE gua­ran­tees ea­sier to in­stall mo­re fle­xi­ble sy­stems. The la­te­st se­ries sports an au­to or self adap­ting soft­ware un­der Ita­lian pa­tent cal­led Dia­lo­gue whi­ch gua­ran­tees ex­cel­lent per­for­man­ce and en­han­ced ef­fi­cien­cy. Sin­ce Dia­lo­gue pos­ses­ses mo­re ver­sa­ti­li­ty it can in­te­gra­te SE sta­bi­li­ser sy­stems wi­th other CMC Ma­ri­ne gear su­ch as elec­tric th­ru­sters of the com­pa­ny’s Dua­lis Elec­tra se­ries run th­rou­gh a single CMC Ma­ri­ne con­trol sta­tion si­tua­ted in the whee­lhou­se. This pre­sen­ts ob­vious ad­van­ta­ges in terms of ea­se of use and mo­ni­to­ring. The in­te­gra­tion in­to a single con­trol sta­tion trans­la­tes in­to ac­crued ef­fi­cien­cy whi­ch is ener­gy sa­ving. At en­try le­vel of the SE ran­ge the­re’s the 40 mo­del for ya­ch­ts bet­ween 20 to 25 metres th­rou­gh to the lar­ge­st 200 SE whi­ch is de­di­ca­ted to ya­ch­ts from 60 metres up wi­th fins whi­ch va­ry ac­cor­din­gly from 0.4 squa­re metres to 5.00 squa­re metres. Flan­king this, CMC Ma­ri­ne as men­tio­ned ear­lier, to sa­ti­sfy gro­wing re­quests has pro­du­ced three di­ver­se sy­stems di­vi­ded

in­to three se­pa­ra­te ca­te­go­ries: the SR Short Ran­ge, the HS Hi­gh Speed and the LR Long Ran­ge. The SR Short Ran­ge – re­gi­ste­red in 2016 cur­ren­tly co­ve­red by tem­po­ra­ry pa­tent is sui­ta­ble for ya­ch­ts less than 20 metres. This pro­duct fea­tu­res great in­no­va­tion, it in­vol­ves a Bru­shless Tor­que electrical en­gi­ne cou­pled to a re­du­cer (The­re are three dif­fe­rent po­wer hou­ses avai­la­ble). The de­si­gn is uni­que, com­pact, weight sa­ving, of low con­sump­tion and is ea­sy to in­stall. The sy­stem can al­so be po­we­red by 24V DC. The HS sy­stem has been de­si­gned for pla­ning ya­ch­ts wi­th crui­sing speeds abo­ve 24 kno­ts.this la­te­st, sports se­ve­ral no­vel­ties when com­pa­red to the pre­vious ran­ge among whi­ch: op­ti­mi­zed pro­fi­ling of the fins whi­ch per­form bet­ter and re­du­ce drag. The adop­tion of new smal­ler mo­re per­for­ming elec­tro­nic com­po­nen­ts whi­ch can mo­ni­tor the po­si­tion of rud­der bla­des and other per­for­man­ce re­la­ted sur­fa­ce areas as well as the sta­bi­li­zing fins them­sel­ves. The new LR sy­stem is ideal for di­spla­cing and se­mi-di­spla­cing ya­ch­ts. He­re again mo­re per­for­ming and mo­re com­pact ac­tua­tors by com­pa­ri­son to pre­vious SE sy­stems de­li­ve­ring the sa­me out­put of­fer ob­vious ad­van­ta­ges flan­ked by new fin de­si­gns for di­spla­cing ya­ch­ts wi­th sur­fa­ce areas of up to 5 squa­re metres. Thanks to new elec­tro­nics of­fe­ring mo­re ca­pa­ci­ty it is now pos­si­ble to in­te­gra­te, mo­ni­tor and run up to 8 se­pa­ra­te mo­ving parts be­low the wa­ter­li­ne su­ch as two pairs of sta­bi­li­ser fins, rud­der bla­des

and so on. Sen­sors to

mo­ni­tor Roll, Pit­ch and Yaw can al­so be in­stal­led on re­que­st so as to fur­ther op­ti­mi­ze the de­gree of com­fort per­cei­ved on board. Ales­san­dro Cap­piel­lo MD at CMC Ma­ri­ne com­men­ted as fol­lo­ws: “The new sy­stems de­ri­ve from con­stant feed­back, ow­ners’ re­quests and shipyards’ re­quests ha­ve hi­ghlighted their need for what was up un­til ve­ry re­cen­tly an unad­dres­sed re­que­st in the field of sta­bi­li­sers. Well CMC Ma­ri­ne took on the challenge and re­spon­ded by crea­ting three spe­cial­ly de­vi­sed new li­nes. When I men­tion my electrical plan­ts I al­ways say the­re are three ad­van­ta­ges to be had: one for the shi­pyard, one for the end user and one for us. The yard be­cau­se in in­stal­ling elec­tric sta­bi­li­ser sy­stems is by com­pa­ri­son ea­sier, ti­me sa­ving in man hours. To whi­ch we can add lo­wer con­sump­tion, less pur­cha­se co­st, less bulk. For ow­ners this la­st point is al­so re­le­vant when

tal­king about si­ze whi­ch plays a mu­ch mo­re im­por­tant ro­le then other­wi­se. The ow­ners find them­sel­ves wi­th ea­sy to run, cheap to use in terms of con­sump­tion, lit­tle main­te­nan­ce and la­st but not lea­st low noi­se le­vels. Tal­king of whi­ch, our plan­ts’ ave­ra­ge noi­se le­vels mea­su­red in de­ci­bel are around 40/45 de­ci­bel, whi­ch is con­si­de­ra­bly less than the 58/60 de­ci­bel hy­drau­lic sta­bi­li­sing plan­ts pro­du­ce. But what’s im­por­tant to us what is a great ad­van­ta­ge for CMC is to ha­ve been able to pro­du­ce a re­lia­ble long la­sting pro­duct, whi­ch is al­so ea­si­ly adap­ta­ble to di­ver­se ty­pes of ya­ch­ts, and is al­so sim­ple enou­gh to hand­le in terms of ser­vi­cing”. CMC Ma­ri­ne plan­ts ha­ve al­rea­dy been cho­sen among the mo­st re­no­w­ned Ita­lian shipyards as Benetti, Sanlorenzo and Ros­si­na­vi, Azimut, Man­gu­sta and Overmarine and by so­me Eu­ro­pean ones li­ke Moo­nen and Sunseeker. For fur­ther in­for­ma­tion www.cmc­ma­ri­ne.com The Man­gu­sta Grand­sport 54 whi­ch is cur­ren­tly in construction at the Overmarine Pi­sa shi­pyard,is the fir­st flag ship ini­tial­led by Al­ber­to Man­ci­ni and is due to hit the wa­ter in mid 2018. It has been in­stal­led wi­th CMC Ma­ri­ne elec­tric sta­bi­li­sers and bow th­ru­sters. The ad­van­ta­ges re­por­ted by the shi­pyard, hi­ghlight the low noi­se im­pact fir­st and fo­re­mo­st sin­ce the noi­se le­vels near the guests’ quar­ters don’t ex­ceed 45 de­ci­bels whi­le pre­ce­ding hy­drau­lic mo­dels pro­du­ced 80 de­ci­bels.

Bow Thruster wi­th en­gi­ne wing ta­ken from VETUS and re­mo­te ca­ta­lo­gue) (Dra-

Pho­to 1 - “mould”for­ward of the tun­nel whi­ch de­via­tes wa­ter co­ming from the bow and from be­low.

Pho­to 2 - “Mould”in­stal­led on the tun­nel’s en­ti­re cir­cum­fe­ren­ce: whe­re the ef­fect of the lo­wer/ bow part of the mould is par­tial­ly re­du­ced

Bow Thruster wi­th coun­ter ro­ta­ting pro­pel­lers (Dra­wing ta­ken from B.C.S. ca­ta­lo­gue)

Pho­to 3 – Tun­nel wi­th no hull se­tup: it isea­sy to ima­gi­ne how the wa­ter ri­sing up from be­low and from the bow hi­ts on the in­ter­nal walls of the tun­nel.

Pho­to 5 – wa­ter flow re­pro­duc­tion 16 kno­ts: the an­gle of slant sug­gests it will re­qui­re a shell li­ke con­ca­ve dip in the hull in li­ne wi­th the stern part of the tun­nel (GUER­RA-INSEAN)

Pho­to 4 – Im­pres­si­ve wa­ve for­mat on the bow of a lar­ge mo­tor yacht crui­sing at 16 kno­ts (by M.GUER­RA-INSEAN)

Pho­to 6 – Bow Wa­ve for­mat of a mi­li­ta­ry ves­sel at 29 kno­ts. (Pho­to M.GUER­RA-INSEAN)

On the left - Dia­gram of the wa­ter flow suc­ked in­to the tun­nel when it ha­sn’t been ade­qua­te­ly roun­ded off wi­th the hull (whir­ling and ca­vi­ta­tion). On the right - Dia­gram of the wa­ter flow inside a tun­nel wi­th fla­w­less roun­ding off. Dra­wings ta­ken from SIDE-PO­WER Thruster Sy­stem ca­ta­lo­gue.

On the left – Dia­gram of the flow inside a tun­nel whi­ch is too short. (whir­ling and ca­vi­ta­tion) On the right - Dia­gram of the flow inside a tun­nel whi­ch is ade­qua­te.

Se­lec­ted positioning area for the thruster in the bow (Dra­wings ta­ken from SIDE-PO­WER Thruster Sy­stem ca­ta­lo­gue)

On the left - Dia­gram of the flow wi­thout se­tup. In the midd­le - Dia­gram of the flow wi­th se­tup for­ward of the tun­nel. Bet­ter sui­ted to pla­ning hull. On the right - Dia­gram of the flow wi­th se­tup aft of the tun­nel. Bet­ter sui­ted to di­spla­cing hulls. Dra­wings ta­ken from SIDE-PO­WER Thruster Sy­stem ca­ta­lo­gue.

Pho­to 8 – Rea­li­za­tion of a con­ca­ve shell li­ke dip in the hull in li­ne wi­th the stern part of the tun­nel in­stal­led on a mi­li­ta­ry ves­sel.(pho­to by M.GUER­RA-INSEAN)

Pho­to 7 – Wa­ter flow re­pro­duc­tion of a fa­st mi­li­ta­ry ves­sel at 29 kno­ts: the an­gle of slant sug­gests it will re­qui­re a shell li­ke con­ca­ve dip in the hull. (Pho­to M.GUER­RA-INSEAN).

Pho­to 10 – con­ca­ve shell li­ke dips in pla­ning hulls: the­se are not re­com­men­ded in pla­ning hulls be­cau­se when hit­ting wa­ves ver­ti­cal­ly wa­ter is held back by the con­ca­ve dip whi­ch ac­ts li­ke a spoon.

Pho­to 9 - Hou­sing tun­nel for the Bow thruster of a 30 me­tre lu­xu­ry yacht wi­th no hy­dro­dy­na­mic shield whe­re no hull se­tup has been ma­de.

Pho­to 13 – What mu­st not be do­ne: no ‘mould’ for­ward of the tun­nel whi­le aft of it a shell li­ke con­ca­ve dip whi­ch is not long enou­gh and the­re­fo­re use­less. The con­ca­ve dip ex­tends well abo­ve the tun­nel and is ve­ry deep. The re­sult is a sort of hu­ge spoon whi­ch col­lec­ts and wi­th­holds wa­ter ri­sing from be­low! Su­re­ly a plain tun­nel and no­thing mo­re would ha­ve been bet­ter!

Pho­to 11 –Hy­brid so­lu­tions on pla­ning hulls: whe­re con­ca­ve shell li­ke dips are per­for­med aft of the tun­nel as well as a ‘mould’ for­ward of the tun­nel. It is con­cei­va­ble this so­lu­tion may work if car­ried out pro­fes­sio­nal­ly fol­lo­wing due pro­ject de­si­gn work

Pho­to 12 – Bow end mould whi­ch con­ti­nues aft con­tou­ring the shell li­ke con­ca­ve dip and ta­pers off. A clear sty­li­stic exer­ci­se! But will it be enou­gh?

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