FOI­LING IN LO­VE

Ma­rio Ca­pon­net­to talks foils

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It was a lo­ve­ly calm day out on La­ke Mag­gio­re in Nor­thern Ita­ly. Con­di­tions we­re ju­st per­fect for ae­ro­nau­ti­cal en­gi­neer En­ri­co For­la­ni­ni’s te­st run for the la­te­st model of his hy­dro­foil, a long mo­tor hull on the un­der­si­de of whi­ch he had af­fi­xed a lad­der sy­stem of foils he ho­ped would lift the boat out of the wa­ter as she mo­ved. The te­st was a suc­cess. The year was 1911. “The foil era be­gan that ve­ry day,” ex­plains 57-year-old na­val and me­cha­ni­cal en­gi­neer Ma­rio Ca­pon­net­to, a ve­te­ran of the 1992 Ame­ri­ca’s Cup wi­th Il Mo­ro di Ve­ne­zia. He fol­lo­wed this up a stint wi­th Lu­na Ros­sa bet­ween 2004 and 2007 be­fo­re going on to head Ora­cle’s Com­pu­ta­tio­nal Fluid Dy­na­mics De­part­ment, de­li­ve­ring victory in the Cup in bo­th 2010 and 2013. In 2004, Ca­pon­net­to be­gan col­la­bo­ra­ting wi­th Fran­cis Hue­ber al­so, a part­ner­ship that led to the foun­da­tion in Va­len­cia of Ca­pon­net­to-Hue­ber SL, a spe­cia­li­st na­val en­gi­nee­ring com­pa­ny that was al­so com­mis­sio­ned to de­si­gn Lu­na Ros­sa’s foils for the 36th Ame­ri­ca’s Cup.

When did peo­ple star­ting tal­king about foils in sai­ling? Peo­ple star­ted tal­king about foi­ling for sai­ling craft in the 1960s but the­re are ear­lier exam­ples still, su­ch as Mo­ni­tor from 1955. Ho­we­ver, the­se we­re ex­pe­ri­men­tal craft.

When did you start wor­king on foils?

Wi­th Ora­cle for the 2010 Ame­ri­ca’s Cup when we we­re up again­st the ca­ta­ma­ran Alin­ghi. We in­ve­sti­ga­ted the pos­si­bi­li­ty of get­ting our 34-me­tre tri­ma­ran wi­th its 70-me­tre wing­sail ma­st, foi­ling. We had al­so te­sted a shor­ter hi­gh-wind foil-as­si­sted tri­ma­ran: the for­ward half of the hull was out

of the wa­ter and the stern was im­mer­sed. But in the end we li­ked the big di­spla­ce­ment foil-free tri­ma­ran mo­re whi­ch was op­ti­mi­sed for the calms that we we­re ex­pec­ting at Va­len­cia in Fe­brua­ry. Then in the Cup at San Fran­ci­sco, we star­ted out pret­ty con­ser­va­ti­ve­ly in the Ora­cle De­si­gn Team but we re­spon­ded well to the Ki­wis’ foi­ling wi­th a boat that was su­pe­rior in terms of its ae­ro­dy­na­mics.

What are foils and how do they work?

They are es­sen­tial­ly wings that work in the wa­ter ra­ther than the air. Cen­tre­boards and rud­ders are wings too. The­re is no dif­fe­ren­ce bet­ween them in phy­sics terms. But ra­ther than being ver­ti­cal wings, foils are ho­ri­zon­tal to pro­du­ce grea­ter ver­ti­cal ra­ther than la­te­ral th­ru­st and so be able to lift the boat out of the wa­ter. They al­so work li­ke any other wings. The sha­pe and an­gle of the wing to the air or wa­ter flow crea­te an asym­me­try in the pres­su­re field of the fluid itself and thus a pres­su­re dif­fe­ren­ce bet­ween the up­per and lo­wer sur­fa­ces of the wing. This dif­fe­ren­ce in pres­su­re is what crea­tes lift whi­ch rai­ses the air­craft or boat up.

We’ve seen ma­ny dif­fe­rent ty­pes of foil. Why?

Fir­st and fo­re­mo­st, the big dif­fe­ren­ce is bet­ween sub­mer­ged and se­mi-sub­mer­ged foils. The se­mi-sub­mer­ged foils can self-sta­bi­li­se. If the­re is ex­ces­si­ve lift and the boat ri­ses too hi­gh, a part of the wing co­mes out of the wa­ter and thus no fur­ther lift is crea­ted. Con­se­quen­tly, the boat lo­wers itself un­til the foil esta­bli­shes equi­li­brium again. In ful­ly sub­mer­ged foils, whi­ch are al­ways en­ti­re­ly un­der wa­ter, this doe­sn’t hap­pen and, as wi­th air­craft, you need a sy­stem that

will al­low you to ad­ju­st the an­gle of the en­ti­re foil or a part of it at lea­st (flaps, ed.’s no­te) to suit the lift that you need to ge­ne­ra­te. The­re are al­so hy­brid foils whi­ch is why so ma­ny dif­fe­rent sha­pes are out the­re.

Asi­de from its sha­pe, what ma­kes a foil mo­re or less ef­fi­cient?

Foils aren’t ju­st use­ful in terms of up­ping speed. One of our pro­jec­ts, Sea­bub­ble, is a ta­xi-boat for the Sei­ne whe­re the speed li­mit is 15 kno­ts. The ad­van­ta­ge of foils in this in­stan­ce is that they crea­te prac­ti­cal­ly no wa­ves and can cut th­rou­gh wa­ves cau­sed by other boa­ts wi­thout im­pac­ting pas­sen­gers. But the­re are al­so the rud­der sur­fa­ces…

In theo­ry, the­re could be su­ch a thing as a sin­gle foil boat but real­ly you need at lea­st two poin­ts to keep the boat ba­lan­ced. On a foi­ling sail boat you ha­ve to try to put ma­xi­mum load on the wing that is mo­re do­w­n­wind to boo­st righting mo­ment. The rud­der, or tail wing, thus works to sta­bi­li­se pit­ching. Aboard the AC50s in the 2017 Cup, be­cau­se the­re we­re al­ways two rud­der sur­fa­ces in the wa­ter, you could play around al­so wi­th the an­gle bet­ween them to add righting mo­ment and thus po­wer on the sails.

The next Cup will be com­pe­ted using the AC75, a foi­ling mo­no­hull. What will ma­ke the dif­fe­ren­ce bet­ween the teams?

The AC75 Class Ru­le is com­ple­te­ly un­pre­ce­den­ted and eve­ryo­ne is star­ting from scrat­ch. Al­thou­gh the­re are ele­men­ts that are the sa­me for eve­ryo­ne (in­clu­ding the foil mo­ve­ment sy­stem, ed.’s no­te) and a re­la­ti­ve­ly strict ru­le, I’m

su­re all the teams will co­me up wi­th so­me ori­gi­nal ideas and fi­gu­re out any way pos­si­ble of get­ting around the rules that exists. It’s a la­te­ral thin­king ga­me. Whoe­ver does that be­st will win. As is al­ways the ca­se.

Is it pos­si­ble that foils will ma­ke the tran­si­tion to pleasure sai­ling craft?

You don’t al­ways ha­ve to go fa­st. You can go slow and be re­la­xed too. But whe­re­ver per­for­man­ce is a prio­ri­ty, foi­ling will used mo­re and mo­re. The area I see mo­st po­ten­tial in is mo­tor­boa­ts. The­re is no com­pa­ri­son bet­ween cut­ting th­rou­gh the wa­ves in si­len­ce on a foi­ler and slap­ping again­st them in a con­ven­tio­nal hull.

Are foils an end point or is the­re mo­re to co­me?

I be­lie­ve and I al­so ho­pe that the­re will al­ways been so­me­thing new to in­vent. In the short term, I see po­ten­tial in au­to­ma­ti­cal­ly-con­trol­led ful­ly-sub­mer­ged foils whi­ch pro­vi­de bo­th im­pro­ved per­for­man­ce and com­fort at sea. Then, abo­ve cer­tain speeds, ae­ro­dy­na­mic lift in the air ra­ther than wa­ter be­co­mes ef­fi­cient. I’m thin­king of re­vi­si­ta­tions of the Ekra­no­plan whi­ch is a cross bet­ween a hy­dro­foil and a ho­ver­craft, and used ground ef­fect. Wor­king in ra­cing has taught me to keep a ve­ry open mind to the unu­sual. The na­val sec­tor does suf­fer from a cer­tain iner­tia when it co­mes to in­no­va­tion. I think pro­gress needs peo­ple pre­pa­red to gam­ble on chan­ge.

Mar­ti­na Or­si­ni

Har­ryKH/ INEOS TEAM UK

Abo­ve, Ma­rio Ca­pon­net­to ( right) wi­th Fran­cis Hue­ber. Left, Sea­bub­ble. Pa­ge op­po­si­te, INEOS Team UK try­ing out the te­st boat for the next Ame­ri­ca’s Cup.So­pra, Ma­rio Ca­pon­net­to ( a de­stra) con Fran­cis Hue­ber. A si­ni­stra il Sea­bub­ble. Pa­gi­na a fian­co, INEOS Team UK pro­va la bar­ca te­st per la pros­si­ma Cop­pa Ame­ri­ca.

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