A while back,

Yachts International - - Sternlines -

I had some meet­ings in New York and At­lantic City with a prom­i­nent real es­tate de­vel­oper to dis­cuss the con­struc­tion of a rather sub­stan­tial mo­to­ry­acht. Even in those days he was a hard guy to get into a room to talk, di­vid­ing his time as he did be­tween his Fifth Av­enue pent­house and a grand ocean­side res­i­dence in Palm Beach. I can only imag­ine it’s even harder to­day: Man­hat­tan, Palm Beach, Wash­ing­ton D.C. Any­way, dur­ing each of our con­ver­sa­tions, he would in­quire sev­eral times about the de­sign fee. Each time, I’d an­swer with the same num­ber. Even­tu­ally, seem­ingly ex­as­per­ated, he ex­claimed, “That can’t be. After all, the com­puter does all the work, right?”

I rolled my eyes. If only. That was more than 30 years ago. And although we have most def­i­nitely made tech­no­log­i­cal ad­vances since then, when it comes to test­ing hulls to pre­dict per­for­mance, not much has changed. Com­put­ers still do not de­sign boats. Peo­ple do. Com­put­ers sim­ply as­sist in the process. After all, CAD stands for com­puter-aided de­sign.

And even though our cur­rent com­man­der-inchief might em­brace Hol­ly­wood’s fu­tur­is­tic de­pic­tion of glass-clad labs where se­cret agents sum­mon glitzy de­signs of sub­marines, air­craft or top-se­cret giz­mos on de­mand, the fact re­mains that, de­spite the ev­er­in­creas­ing util­ity of new tech­nolo­gies, the evo­lu­tion of the tools used to con­firm hull de­sign has been

grind­ing along at a com­par­a­tively glacial pace.

Con­sider: The Scot­tish ship­build­ing com­pany William Denny and Broth­ers opened the first com­mer­cial ship model basin in 1883. Since then, nearly all ad­vances made in hull, pro­pel­ler and ap­pendage de­sign have been tested in com­mer­cial or pri­vate model basins or in spe­cial­ized model tanks, such as cav­i­ta­tion tanks.

In the in­ter­ven­ing years, soft­ware devel­op­ment has con­tin­ued to ma­ture as sur­face- and solid-mod­el­ing has be­come more and more ac­cu­rate. Many ap­pli­ca­tions have achieved com­mer­cial suc­cess, among them pre­dic­tive and de­vel­op­men­tal pro­grams for hy­dro­dy­nam­ics, ve­loc­ity per­for­mance, fi­nite el­e­ment anal­y­sis, and the cur­rent fair-haired prodigy of the dig­i­tal de­sign world, com­pu­ta­tional fluid dy­nam­ics (CFD). Each helps de­sign­ers pre­dict what will hap­pen in real-world con­di­tions, but clients con­tinue to be­lieve that a com­puter can now de­sign the per­fect hull form. But can it?

Sev­eral naval ar­chi­tects told me this phe­nom­e­non has struck them as well, in­clud­ing those a gen­er­a­tion older and a gen­er­a­tion younger than I.

“Tank-test­ing is very in­ter­est­ing for the clients,” said Ronno Schouten, man­ager of de­sign at de Voogt Naval Ar­chi­tects (Fead­ship’s naval ar­chi­tec­tural firm), which uses CFD to pre­dict sea­keep­ing and tank test­ing for fi­nal anal­y­sis. “Watch­ing the de­sign­ers and tech­ni­cians at work in a model basin is both cap­ti­vat­ing and stim­u­lat­ing, but watch­ing the anal­y­sis of CFD live in the de­sign of­fice can be in­ter­est­ing to them as well. [Re­gard­less], we use CFD [to pre­dict] sea­keep­ing, but it’s backed up for fi­nal anal­y­sis by tank-test­ing.”

Quite of­ten, model tests show re­sults that dis­agree with de­sign soft­ware pred­i­ca­tions. Don­ald Blount learned this be­fore start­ing his own naval ar­chi­tec­tural firm, while serv­ing as head of the U.S. Navy’s Com­bat­ant Craft De­part­ment at the David Tay­lor Model Basin.

“Kids go to col­lege and study CFD,” he said, “but what both­ers me is that they know how to en­ter the equa­tions and code num­bers into a com­puter, but the whole se­cret of the thing is [to] ac­tu­ally rep­re­sent— in de­tail—the shape that they’re study­ing. It makes a big dif­fer­ence in the dis­tri­bu­tions, the geo­met­ric rep­re­sen­ta­tions. For some fea­tures, you don’t need a lot of el­e­ments to de­scribe that shape, and for [oth­ers], you need more than you could be­lieve to get a re­al­is­tic an­swer.

“Do you have to do some­thing in the wa­ter or can you do it dig­i­tally?” he con­tin­ued. “The an­swer is, You can do it in the wa­ter, and some things you can do dig­i­tally very well, and some you have to be an

ex­pert in un­der­stand­ing the wet part be­fore you can get good re­sults from CFD and a dig­i­tal ap­proach.”

Com­puter geeks call this con­cept GIGO (garbage in, garbage out), re­fer­ring to the qual­ity of data in­put for any given pre­dic­tion. The more ac­cu­rate the data that is in­put into the ma­chine, the more ac­cu­rate the re­sult will be.

Naval ar­chi­tects agree that hav­ing a wealth of good data on file is ex­tremely im­por­tant to any test­ing reg­i­men. CFD can be used for cal­cu­la­tions that used to be the sole prov­ince of wind tun­nels. Nowa­days, the soft­ware can han­dle flow cal­cu­la­tions for such fac­tors as air con­di­tion­ing, su­per­struc­ture de­sign and place­ment of ex­haust vents.

“It’s all about re­duc­ing de­sign-cy­cle time,” Schouten said. “After all, model tanks, wind tun­nels and com­puter time are quite ex­pen­sive, so the key is

The key is to in­te­grate the avail­able tools to find a bal­ance that works best to go from ini­tial to fi­nal de­sign as ac­cu­rately and cost-ef­fec­tively as pos­si­ble.

to in­te­grate the avail­able tools to find a bal­ance that works best to go from ini­tial to fi­nal de­sign as ac­cu­rately and cost-ef­fec­tively as pos­si­ble.”

In ad­di­tion to the cost of the ro­bust hard­ware needed to grind out pre­dic­tions, the soft­ware it­self is quite pricey, with li­censes for each pro­gram run­ning in the many thou­sands of dol­lars (per work­sta­tion, per year).

Nowhere in the recre­ational ma­rine in­dus­try has com­pu­ta­tional de­sign ad­vanced farther than in Amer­ica’s Cup rac­ing. To­day’s re­mark­able AC cata­ma­rans—and their equally re­mark­able cost—il­lus­trate what hap­pens when one takes com­pu­ta­tional de­sign to the ex­treme on a per-boat ba­sis. The amount of data col­lected in each race is stag­ger­ing, and all of it is vi­tal to re­fine not only the over­all de­sign, but also each and ev­ery op­er­a­tional pa­ram­e­ter as well. The re­sult is a de­signer’s most cov­eted sce­nario: data from full-scale test­ing un­der ac­tual op­er­a­tional con­di­tions.

So, how long will model basins be used be­fore they go the way of the horse and buggy? Were I a bet­ting man, I’d say don’t count them out just yet.

“CFD is not a proven tech­nique for pre­dict­ing sea­keep­ing char­ac­ter­is­tics of ves­sels mov­ing through the wa­ter in waves,” Blount said. “That’s prob­a­bly the next big hur­dle that needs to be done, but part of that hur­dle is, How do you model a ran­dom or ir­reg­u­lar sea math­e­mat­i­cally? You can do this in a tow­ing tank, but the math­e­mat­i­cal rep­re­sen­ta­tion of that is, I think, maybe five years or more away be­fore you should even have balls enough to spend mil­lions of dol­lars on a boat [that’s] been de­signed en­tirely by us­ing CFD and dig­i­tal tech­niques for some­thing that is sup­posed to per­form well in rough wa­ter.”

For more in­for­ma­tion: de­voogt­navalar­chi­tects.nl dlba-inc.com; marin.nl; oos­sa­nen.nl

BE­LOW: Basins are specif­i­cally de­signed for spe­cial­ized tests such as sea­keep­ing and ma­neu­ver­ing. FAC­INGPAGE: (from top) CFD mod­els de­pict­ing vor­tices cre­ated by a sub­merged sub­ma­rine un­der­way and wave pres­sures when sur­faced; The test sub­ma­rine op­er­at­ing semisub­merged in a model basin.

ABOVE: A CFD model de­pict­ing a mo­to­ry­acht equipped with Hull Vane dur­ing re­sis­tance tests. TOP: A high-speed mo­to­ry­acht un­der­go­ing calmwa­ter re­sis­tance test­ing at the Wolf­son Unit at the Uni­ver­sity of Southamp­ton (Eng­land).

Above: Whether us­ing CFD soft­ware or tank-test­ing, mod­els must be as ac­cu­rate as pos­si­ble to en­sure re­li­able re­sults. For some tests, only the cor­rect hull­form and scaled weight are re­quired, as shown here.

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