Aloha Jay Ja­cobs

Passage Maker - - Letters To The Editor - —Ken Ficket, Pres­i­dent Mirage Man­u­fac­tur­ing, & Brooke Wil­liams,

Thomas, co­in­ci­dent waves only came up in the trial be­cause of the un­ex­pected tes­ti­mony by my ex­pert on oceanog­ra­phy and wave for­ma­tion, Rae Strange.

Since there were no sur­vivors or eye wit­nesses, no one will ever know what hap­pened for sure, but I went into the trial con­cerned that the other side might of­fer as an ex­pla­na­tion for the loss of the Aloha that the boat was nav­i­gated too close to the western edge of Bonita Chan­nel and a big wave came over the Bar and sank it. This is what hap­pened a year prior to the in­ci­dent when three men were washed over­board.

Con­cern­ing Rae Strange’s tes­ti­mony, “Waves are formed in only one way … by the wind,” I be­lieve is an ac­cu­rate over­all state­ment. Your com­men­tary that waves can be formed by pass­ing large ships is cor­rect, but I think most boaters would cat­e­go­rize “waves” cre­ated by a large pass­ing ship as a wake rather than a wave, and know to keep well away from the ship.

I also agree that the state of the tides and cur­rents can and do in­flu­ence in­com­ing swells. An out­go­ing tide of 3 to 4 knots or greater, in con­fined ar­eas such as the mouth of a river or the en­trance to the Golden Gate, can cause in­com­ing waves to “rise up” to some de­gree.

An alert skip­per will keep a close eye out to avoid one of th­ese “stack­ing” waves from af­fect­ing his boat.

There was no ev­i­dence of tsunami con­di­tions any­where in the Pa­cific on the day of the in­ci­dent.—

CALDER PROP THE­ORY IN PRAC­TICE

En­gine man­u­fac­tur­ers uni­ver­sally spec­ify that boats be propped to run at rated max­i­mum rpm at Wide Open Throt­tle (WOT). In the last is­sue (In Praise of Big, Pas­sage­Maker Nov/Dec 2014), Nigel Calder sug­gests that this long­stand­ing man­date needs to be rethought. Specif­i­cally us­ing a com­bi­na­tion of larger props and slower rpm will im­prove over­all per­for­mance with few draw­backs. We, Ken Fick­ett owner of Mirage Man­u­fac­tur­ing and I, the owner of a Mirage Great Har­bour 47, ac­tu­ally de­parted from the prop man­date with suc­cess.

We ven­tured off the man­dated path not out of a de­sire to re­search and ex­plore. We did it to cor­rect prob­lems cre­ated by an ear­lier at­tempt to meet our en­gines’ spec­i­fi­ca­tions re­quire­ments. This de­par­ture in­volved go­ing to slightly larger props and in­creas­ing the pitch rather than chang­ing a trans­mis­sion. A lit­tle his­tory . . .

East Pas­sage was com­mis­sioned in 2004. The en­gines were twin 71hp Wester­bekes. As con­struc­tion was start­ing, Wester­beke changed en­gines specs in­sist­ing that we use hy­draulic trans­mis­sions in­stead of the pre­vi­ously used me­chan­i­cal trans­mis­sions. Their reps claimed we would see no dif­fer­ence, but we did. Max­i­mum run­ning rpm were way be­low rated max­i­mum. Wester­beke’s lit­er­a­ture clearly spec­i­fies that the en­gines be propped to max­i­mum rated rpm and clearly states that im­proper use of the en­gines will void their war­ranty—an un­pleas­ant com­bi­na­tion.

So we cut down the props to 11inch pitch by 23-inch di­am­e­ter from 13 by 24. We got some of our rpm back but lost top end speed. Still couldn’t meet spec­i­fied rpm but Wester­beke signed off on war­ranty re­quire­ments.

Fast for­ward to early 2014: We re­power. In go Yanmar 74 hp en­gines. The old props get the en­gine to rated rpm eas­ily—too eas­ily—the en­gine would run over rated max­i­mum. The re­duced pitch pro­duces rpm speed but not enough for­ward thrust. Speed is off. We seem to be re­gress­ing.

The po­ten­tial so­lu­tion comes in a pair of props on the shelf at Mirage. Acme de­vel­oped a set of in­creased pitch props (15 by 24-inch) for the larger line of Mirage boats. Th­ese pro­pel­lers are not only larger, have in­creased pitch but also are in­her­ently heav­ier be­cause they are ma­chine milled props. We ex­pected re­duced rpm, in­creased speed and in­creased fuel ef­fi­ciency at run­ning speeds. As the owner, I was cer­tainly will­ing to pay for the swap.

Con­fi­dence was high be­cause I—now this is Ken Fick­ett talk­ing—grew up in the com­mer­cial boat business in Mi­ami. Work­boat own­ers have long in­creased prop pitch to im­prove per­for­mance and fuel ef­fi­ciency. Fur­ther­more, my ex­pe­ri­ence with light air­craft teaches me that best per­for­mance, in cruise, the type Nigel Calder seeks, comes from run­ning “over squared,” higher man­i­fold pres­sure, lower rpm.

I have built all my trawlers with in­creased pitch with this ex­pe­ri­ence in mind. They don’t quite meet rated max­i­mum rpm. This prac­tice has been called over-prop­ping. We call it prop­ping right. Now, with Calder’s data, per­haps we can re­move the stigma of that term. Our changes worked and here’s how: With our Wester­beke en­gines we cruised at 2850 rpm pro­duc­ing a stan­dard 7.3 knots. Fuel burn av­er­age was 3.5 gal­lons per hour. New prop set up al­lows us to cruise at 2300 rpm pro­duc­ing 8 knots of speed. Pre­lim­i­nary fuel burn cal­cu­la­tions in­di­cate we are burn­ing 3.3 gal­lons per hour.

We ex­pect the burn rate to drop with more run­ning hours in the cal­cu­la­tions. But let’s as­sume no drop. We are burn­ing 5 per­cent less fuel while go­ing 10 per­cent faster with 20 per­cent less ro­ta­tional wear. Slow speed ma­neu­ver­ing is not af­fected. Of course the en­gines’ man­i­fold pres­sures are up. And we have no more sense of where the sweet spot ac­tu­ally is than Calder does with his ex­ten­sive data col­lect­ing.

Man­i­fold pres­sure gauge ports are non-ex­is­tent on the small Yan­mars. Over­heat­ing would be our tell­tale, and they run rock steady, only go­ing up one de­gree dur­ing WOT runs.

WOT run­ning has never been a habit of ours. We are mind­ful of Yanmar’s ad­mo­ni­tion about time lim­its for sub WOT high rpm run­ning and WOT run­ning. You still need to make sure your cruise rpm is 10 to 15 per­cent off WOT rpm. Some will say that we are leav­ing horse­power that the en­gine is ca­pa­ble of pro­duc­ing un­avail­able, and they are right but the in­abil­ity to get the last few per­cent of max horse­power is way over­shad­owed by the other ben­e­fits.

Bot­tom line: We are con­vinced our set up is proper for this fulld­is­place­ment cruis­ing boat and feel vin­di­cated by Nigel Calder’s work. Per­haps it can re­ally be a new day for pro­peller as­sess­ment.

East Pas­sage’s new pro­peller, at right, is not only big­ger but it has greater pitch.

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