BOATYARD

Power & Motor Yacht - - BOATYARD -

reach its end stops at which time it is then no longer pro­duc­ing a torque. The sphere will re­main on its end stops un­til the boat comes out of its turn. “

The key phrase here is “on its stops.” The Sea­keeper re­acts the same as the toy gy­ro­scopes we all en­joyed play­ing with as kids. When a gy­ro­scope, whether bal­anced on a string held by a 10-year-old, or mounted in a gim­baled sphere on a boat, is acted on by a side force, it re­acts by mov­ing, or “pre­cess­ing,” at right an­gles to the di­rec­tion of that force. (If you want to know ex­actly why, Google it. It’s all about an­gu­lar torque.) Pre­ces­sion cre­ates an im­me­di­ate counter force, at right an­gles to the pre­ces­sion and in the op­po­site di­rec­tion of the orig­i­nal force, which re­stores equi­lib­rium. When the pre­ces­sion stops, the counter force stops, too.

The Sea­keeper’s gyro is a heavy, rapidly spin­ning ro­tor in­side a mount that can only tilt for­ward or aft, in what en­gi­neers call the “pitch plane.” It’s fixed in the athwartships plane. When the boat rolls, the Sea­keeper senses the roll as a side force, and the ro­tor in­stantly pre­cesses at right an­gles to it—ei­ther for­ward or aft, de­pend­ing on the di­rec­tion of roll. This cre­ates the counter force that damps the roll. The strength of the counter force de­pends on the speed of pre­ces­sion. In nor­mal rolling at sea, the boat heels one way, then the other, and the gyro re­sponds ac­cord­ingly, pre­cess­ing this way and that, and maybe never hit­ting the stops.

But crank the helm over and the boat leans and stays put; the gyro pre­cesses and quickly reaches the end of its range, with the heel­ing force still act­ing on it. When it stops, its coun­ter­force stops, too, and so does sta­bi­liza­tion. With­out pre­ces­sion, no op­pos­ing force is gen­er­ated. Af­ter an in­stant of min­i­mal re­sis­tance, the boat steers, and heels, nor­mally, with the ro­tor all the way for­ward or aft. When the boat lev­els out, the ro­tor re­turns to nor­mal op­er­a­tion. If this were not the case, the Sea­keeper could dou­ble as trim tabs—au­to­mat­i­cally off­set­ting any heel from wind, poor trim, fat Aunt Sally sit­ting on the gun­wale, and so forth.

Pre­ces­sion hap­pens on its own—it’s physics—but in an ac­tively con­trolled gyrostabilizer like the Sea­keeper, the hy­draulic cylin­ders con­trol the rate of pre­ces­sion and the pre­ces­sion os­cil­la­tion range, con­strain­ing it to op­ti­mal lim­its. Left to its own de­vices, in cer­tain con­di­tions, such as bois­ter­ous seas, the dras­tic rolling of the ves­sel could, the­o­ret­i­cally, cause the gyro to pre­cess too rapidly and de­velop coun­ter­act­ing torque too great for the mount­ing struc­ture to han­dle. Again, that’s the ar­gu­ment against pas­sive gy­rosta­bi­liz­ers. Gy­ros work bet­ter when they’re un­der con­trol.

The Sea­keeper 3 is de­signed for boats from 30 feet.

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