Fre­quent Flyer

JAR­RETT BAY, PRINCESS AND SEAIR ARE JUST A FEW BUILDERS EX­PER­I­MENT­ING WITH FOILS TO IN­CREASE SPEED AND EF­FI­CIENCY. ALAN HARPER RE­PORTS ON THE TREND AND IF IT WILL TAKE OFF.

Power & Motor Yacht - - IN THIS ISSUE -

It’s not sci­ence fic­tion. Fly­ing yachts uti­liz­ing the foil­ing tech­nol­ogy seen in Amer­ica’s Cup boats have ar­rived.

It I was at the 1958 Amer­ica’s Cup tri­als off New­port, Rhode Is­land, that Dick Ber­tram had his eu­reka mo­ment. As the story goes, he was the sail trim­mer aboard Vim in chal­leng­ing, choppy con­di­tions that had the chase boats strug­gling to keep up, so the way that one par­tic­u­lar 23-foot power­boat was able to main­tain its speed through the steep seas was all the more no­tice­able.

The boat was one of C. Ray­mond Hunt’s first deep-V de­signs. Ber­tram sought him out, sea-tri­aled the boat and com­mis­sioned Hunt to de­sign a 30-footer for the Mi­ami-Nas­sau off­shore power­boat race. Ber­tram won, the su­pe­ri­or­ity of the deep-V con­cept was clearly demon­strated and the rest—as they say—is his­tory.

Ber­trand Castel­nérac had a sim­i­lar eu­reka mo­ment in Quiberon Bay in 2015. An in­trepid, dare­devil yachts­man of the sort that France seems to have a knack for pro­duc­ing, he was sail­ing a GC32—one of those hy­dro­foil cata­ma­ran sail­boats for which in­san­ity seems to be the prin­ci­pal qual­i­fi­ca­tion in a crewmem­ber—when he no­ticed that his team’s ten­der, a RIB con­tain­ing tools, spare sails and the long-suf­fer­ing coach, was fall­ing be­hind in the rough wa­ter. “So I thought, ‘why not have foils on the RIBs, too?’” he re­calls.

Hy­dro­foils are those coun­ter­in­tu­itive wings that when fit­ted to boat hulls jut out into the wa­ter­flow, yet some­how im­prove ef­fi­ciency. It’s all about lift, of

course: What­ever drag the foil might pro­duce, once it has per­formed its func­tion and raised the boat’s body out of the wa­ter, it re­duces the far greater drag caused by the hull’s wet­ted sur­face area.

The prin­ci­ple has been doc­u­mented for decades, and there are many hy­dro­foil fast fer­ries in ser­vice to­day around the world. But the un­der­wa­ter wing has been slow to find fa­vor in leisure craft—un­til now. Re­cent im­prove­ments in elec­tron­ics and ma­te­ri­als tech­nol­ogy, com­bined with big-bud­get spon­sor­ship for sail­ing events, have led to a rekin­dled in­ter­est among naval ar­chi­tects and ma­rine en­gi­neers in their search for su­pe­rior per­for­mance and speed. Just check YouTube. From South Africa we have the Hy­su­cat sys­tem in which a hy­dro­foil wing spans the gap be­tween the hulls of a cata­ma­ran. In Slove­nia, Quadro­foil has de­vel­oped an ex­tra­or­di­nary elec­tric-pow­ered per­sonal wa­ter­craft that looks like a two-seater con­vert­ible on four legs. There are surf­boards that ride along on sin­gle T-shaped foils while seem­ingly con­found­ing all known laws of physics. And then there are the sail­boats, with ter­ri­fy­ing craft like the Amer­ica’s Cup mono­hulls and GC32 cata­ma­rans at one end of the spec­trum, and foil­ing ver­sions of the Moth and Op­ti­mist sail­ing dinghies at the other.

Jar­rett Bay, builder of cus­tom sports­fish­ing boats, is per­haps a sur­pris­ing name to find on the hy­dro­foil ros­ter. But as re­ported in Power & Mo­to­ry­acht’s July 2018 is­sue, the builder’s new 90-footer sports a foil—a 14-foot wing slung be­neath the hull, to add lift and in­crease top speed to a barely be­liev­able 50 knots. Tests of a fixed pro­toype foil made of alu­minum and car­bon were ap­par­ently suc­cess­ful; now the plan is to de­sign a re­tractable ver­sion.

In Eng­land, Princess Yachts has also had a rush of blood to the head in the form of its new R Class debu­tante, the R35, to be un­veiled this fall. The R stands for Rev­o­lu­tion. Two re­tractable T-shaped foils, each 39 inches long and 10 inches wide, are in­stalled in the hull of the 35-footer, which even with­out them will have no trou­ble at­tract­ing at­ten­tion with its all-car­bon struc­ture and swoopy Pin­in­fa­rina styling. This head-turn­ing ma­chine sports a pair of 430-hp Volvo gas V8s on Duo­prop stern­drives that will re­port­edly make it the firstever 50-knot Princess, while the ac­tive foils, mounted 3 feet in front of the tran­som, rake for­ward or aft by plus or mi­nus 5 de­grees, creat­ing lift or down­force as needed.

“When first push­ing the throt­tles for­ward, you ex­pect the bow to lift and the stern to dig in un­til the boat starts to plane,” ex­plains R35 project man­ager Paul Macken­zie. “It’s what nor­mally hap­pens. But on the R35 there’s no hump—it stays flat, as the foils sup­ply lift to the stern.” Keep­ing the stern up trans­lates into ef­fi­ciency, with the R35 able to plane at lower speeds than con­ven­tional hulls.

As the foils move in­de­pen­dently, they can in­flu­ence lat­eral trim as well, for ride com­fort. The sys­tem will also in­clude a sport set­ting, al­low­ing greater an­gles of heel and a more dy­namic ride. The soft­ware has been de­vised by Ben Ainslie Rac­ing, the Olympic and Amer­ica’s Cup yachts­man’s high-tech firm in Portsmouth, Eng­land, which also worked on the R35 hull de­sign.

Orig­i­nally de­vel­oped in Switzer­land but now funded and built by Enata in the UAE, the 33-foot Enata Foiler is eas­ily the most dra­matic and per­haps the most am­bi­tious of this new breed of leisure hy­dro­foil power craft. A diesel-elec­tric hy­brid, the Enata is fit­ted with two 300-hp diesels that power two elec­tric mo­tors and also charge the bat­ter­ies to al­low the boat to cruise, briefly, in pure elec­tric mode. Two huge for­ward wings, which re­tract and fold out of the way when dock­ing, com­bine with a pair of ver­ti­cal-de­ploy­ment foils aft, each fit­ted with a tor­pedo-shaped elec­tric drive—solv­ing the prob­lem of get­ting the pro­pel­lers into the wa­ter while the hull is fly­ing above it. The foils are de­signed to de­ploy once the hull reaches 17 knots, and with the boat lifted clear of the wa­ter on its foils the Enata’s max­i­mum speed is re­ported to be 40 knots.

Like Princess’ Rev­o­lu­tion 35, the Enata Foiler’s struc­ture is molded en­tirely in car­bon—the par­ent com­pany’s spe­cialty—and with an eye on the su­pery­acht ten­der mar­ket, it has been de­signed to fold up neatly for stowage on board the mother ship. Its wingspan re­duces from 24 feet to 11 feet with the foils re­tracted, and stowage height comes down to just 8 feet.

It was a chance meet­ing with fel­low French­man and tele­com en­trepreneur Richard For­est that gave Ber­trand Castel­nérac the chance to test out his ideas for a foil­ing RIB, start­ing with an 18-foot tech­nol­ogy demon­stra­tor.

Along­side the dock it looks a lot like any or­di­nary rigid in­flat­able, for the foils re­tract al­most com­pletely into their hous­ing in the helm con­sole, with just the blade tips vis­i­ble be­neath the tubes. This pro-

to­type was built and adapted to SEAir’s spec­i­fi­ca­tions by Zo­diac, which will also pro­duce the first few pro­duc­tion boats sold through SEAir, but even­tu­ally the foil­ing sys­tem will be made avail­able to any boat­builder who wants it. The RIB was fit­ted with a 115-hp Yamaha out­board when I caught up with it on Lake Geneva this sum­mer, although SEAir would ac­tu­ally rec­om­mend an 80-hp unit as eas­ily pow­er­ful enough, and more eco­nom­i­cal on fuel.

The foil wings on the 18-foot RIB pro­to­type are hand­made in solid car­bon fiber, a process which took two weeks. Pro­duc­tion foils will be built of pre-preg car­bon in a mold and UV-cured in a con­trolled at­mos­phere, which will take two days. The larger foils on the next model, a 23-footer, will have a foam core.

The con­ven­tional look and straight­for­ward helm lay­out of the pro­to­type are re­as­sur­ing. “It needs to be sim­ple,” says For­est. “Just one but­ton. Peo­ple don’t need to know how the self-park­ing thing on their car works, they just need it to work.” Castel­nérac ex­plains that the wings ac­count for 80 per­cent of avail­able lift when the boat is fly­ing, while the car­bon hor­i­zon­tal sta­bi­lizer fit­ted to the out­board leg, rather like an out­size cav­i­ta­tion plate, sup­plies the re­main­ing 20 per­cent.

If you’ve ever taken the helm of a boat with trimmable sur­face drives, such as Ar­nesons, driv­ing the SEAir RIB will feel strangely fa­mil­iar. Engine trim is key to per­for­mance. Set the throt­tles with the boat on the foils, trim the engine out a lit­tle, and the ac­cel­er­a­tion that re­sults is like the surge you get when rais­ing sur­face drives into thin­ner wa­ter. The cause is dif­fer­ent, though: On the SEAir RIB it’s all about find­ing the cor­rect an­gle of at­tack for the foils, so they pro­duce max­i­mum lift and min­i­mum drag. There’s a sweet spot that re­veals it­self af­ter a lit­tle trial and er­ror. If you overdo the an­gle of at­tack as I did, and then ap­ply some helm, one foil can stall like an air­craft wing. The re­sult­ing lat­eral os­cil­la­tion was in­tense enough to re­mind me to han­dle this pro­toype with care.

On pro­duc­tion boats it will be pos­si­ble to ad­just the rake of the for­ward foils while un­der way, giv­ing more con­trol over their an­gle of at­tack and re­fin­ing your trim op­tions. In the mean­time, SEAir is also work­ing with NKE Ma­rine Elec­tron­ics on sen­sors and au­to­mated ride-con­trol soft­ware which, they say, will take all of the guess­work out of driv­ing the boat.

In­de­pen­dent tests pit­ting a con­ven­tional 18-foot Zo­diac against the SEAir foil ver­sion re­vealed higher speeds across most of the rev range and some sig­nif­i­cant gains in fuel ef­fi­ciency. But the other thing that foils are good for is the rea­son Castel­nérac wanted to build a foil RIB in the first place: the qual­ity of the ride. With the hull out of the wa­ter there’s no slam­ming as you charge through rough seas, which should en­able those un­for­tu­nate sail­ing coaches to keep up with their fly­ing, foil-born charges. Ob­vi­ously on Lake Geneva I couldn’t put this to the test, but the RIB’s gen­tle de­meanor as we crossed the wakes of the big lake steam­ers sug­gested that he has a point; there was a dis­tinct cush­ion­ing ef­fect.

So, are hy­dro­foil power­boats go­ing to make his­tory in the way that the first off­shore deep-Vs did? It’s go­ing to be fun find­ing out.

The SEAir sys­tem is based on pre-preg car­bon fiber foil wings and a car­bon hor­i­zon­tal sta­bi­lizer fit­ted to the leg of an out­board.

The new R35 from Princess Yachts has two re­tractable T-shaped foils in­stalled in the hull to cre­ate lift or down­force as needed.

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