Keep the Pres­sure On


Power & Motor Yacht - - 115 - BY MIKE SMITH

Hy­draulics, or, more ac­cu­rately, oil-filled hy­draulic power sys­tems, are a boater’s dream. Af­ter all, they de­mand al­most no at­ten­tion yet do lots for any skip­per lucky enough to have them as ship­mates. A hy­draulic wind­lass, for ex­am­ple, will usu­ally crank from now un­til dooms­day with­out over­heat­ing; ditto a hy­draulic thruster—al­though if you need to run one un­til the end of time, you should work on your dock­ing skills. Dav­its and hy­draulics go to­gether like Bos­ton and Whaler, and will snatch a beefy ten­der out of the wa­ter fast. And need I men­tion the value of hy­draulic sta­bi­liz­ers when a beam sea rises and pas­sen­gers start turn­ing green?

Hy­draulic power sys­tems aren’t new. Fluid un­der pres­sure has been used for pro­duc­tive pur­poses since at least 6,000 B.C., at first sim­ply for turn­ing wa­ter wheels, with grav­ity as the driv­ing force. With enough belts, gears, pul­leys, and en­gi­neer­ing imag­i­na­tion, the turn­ing axle of a wa­ter wheel can do all kinds of things. In the mid-19th cen­tury, at the height of the In­dus­trial Rev­o­lu­tion, English­man Wil­liam Arm­strong in­vented a hy­draulic crane for han­dling cargo in the busy sea­port of New­cas­tle upon Tyne us­ing wa­ter flow­ing from a nearby reser­voir for power. Arm­strong then in­vented a hy­draulic ac­cu­mu­la­tor to power the cranes when a wa­ter sup­ply wasn’t avail­able. His ac­cu­mu­la­tor com­bined an iron wa­ter tank with a heavy plunger; once the tank was filled (wa­ter was drawn in when the plunger was hoisted), the weight of the plunger forced the wa­ter into the hy­draulic lines with suf­fi­cient pres­sure to op­er­ate the ma­chin­ery. It worked like a gi­ant hy­po­der­mic nee­dle.

Most hy­draulics aboard boats use a pump to pres­sur­ize the fluid, usu­ally oil, in a closed sys­tem that typ­i­cally in­cludes a reser­voir, oil lines, pis­tons, rods, and other parts. Since the hy­draulic fluid is in­com­press­ible, the pres­sure cre­ated by the pump at one end of the sys­tem is main­tained through­out the rest of the sys­tem, even if it is large. Add a hy­draulic ap­pli­ance like a mo­tor or a steer­ing cylin­der to the sys­tem and the pres­sur­ized fluid will earn its keep by do­ing some work.

Elab­o­rate hy­draulic sys­tems are com­mon aboard larger yachts, but on smaller boats they’re used mostly in steer­ing sys­tems and trim tabs. Whether a yacht has so­phis­ti­cated hy­draulics or just a sim­ple sys­tem, pe­ri­odic main­te­nance is re­quired. Sim­ple sys­tems mean sim­ple main­te­nance, com­plex sys­tems are more in­volved—still, hy­draulics de­mand very little TLC to keep them work­ing com­pared to other on­board tech­nolo­gies. Here’s an in­tro­duc­tion to the sub­ject, al­though the best source for specifics is your op­er­a­tor’s man­ual.

Check the Oil

Some ves­sels carry a sin­gle hy­draulic pump in the en­gine room, plumbed to ap­pli­ances through­out the boat. Na­iad’s ( na­iad .com) In­te­grated Hy­draulic Sys­tem (IHS), for ex­am­ple, pow­ers sta­bi­liz­ers, thrusters, dav­its, passerelles, and other hy­draulic gear from a sin­gle pump. Each IHS is cus­tom-de­signed, op­er­ates in­de­pen­dent of the main en­gines (via an elec­tric mo­tor), and makes main­te­nance much eas­ier, since there’s only one sys­tem to main­tain. But IHS is the gold stan­dard. More com­mon, and re­quir­ing more in­volved main­te­nance, are self-con­tained hy­draulic units: each with its own pump, or maybe one pump driv­ing two ad­ja­cent ap­pli­ances, e.g., a thruster and a wind­lass, since the two sel­dom op­er­ate si­mul­ta­ne­ously. No mat­ter the de­sign of your hy­draulic sys­tem(s), how­ever, the ba­sic main­te­nance pro­ce­dure is sim­ple: Check the oil.

Oil is the lifeblood of hy­draulics, so keeping a sys­tem filled is a pri­mary con­cern—and pretty easy, too, since un­less there’s a leak the oil level will rarely drop, and leaks are rare in a prop­erly en­gi­neered and main­tained hy­draulic sys­tem. Many

hy­draulic sys­tems have a sight glass, so you don’t have to open any­thing or even pull a dip­stick. Keeping the oil scrupu­lously clean is im­por­tant, though, so open things up only when nec­es­sary. If the oil level drops, top-up and then find and fix the leak. Oth­er­wise two bad things hap­pen: The ap­pli­ance won’t work as well, or not at all; and the leaked oil will mi­grate into the bilge.

When adding oil, by the way, use a clean fun­nel and pour through a paper strainer. Change the oil at the in­ter­val spec­i­fied in your man­ual, or sooner if the sys­tem over­heats or the oil shows con­tam­i­na­tion. Na­iad rec­om­mends chang­ing the oil ev­ery three years or 4,000 hours of use for sta­bi­liz­ers, ev­ery three years for thrusters. (Most skip­pers go by the cal­en­dar; four thou­sand hours is about 40 years of use for the typ­i­cal yacht.) Shaft seals should be changed at the same in­ter­val. Change fil­ters as re­quired, too; there’s of­ten a pres­sure gauge or other indicator show­ing when it’s time.

Take a Sam­ple

Ev­ery year, or with heavy us­age at six-month in­ter­vals, take a sam­ple of your hy­draulic oil and send it to the lab for anal­y­sis. This is most im­por­tant with sta­bi­liz­ers and thrusters, and wind­lasses, too, if you do a lot of an­chor­ing. The used oil should re­tain its orig­i­nal color, or maybe get just a little darker, but even if it looks okay, get it an­a­lyzed any­way. If the oil’s dark and syrupy, chances are it’s been over­heated, a prob­lem with sta­bi­liz­ers that run con­stantly while the ves­sel is un­der way, and some­times at an­chor, too. Black oil is se­ri­ously con­tam­i­nated. Ex­cess wear in a hy­draulic pump can in­tro­duce metal par­ti­cles, mean­ing it’s time for an over­haul or pump re­place­ment; such possibilities will man­i­fest un­der anal­y­sis. Or there may be wa­ter or dirt in the oil. All of the above mean the oil should be changed, and maybe the sys­tem flushed by sim­ply chang­ing the oil and fil­ter a cou­ple of times, al­beit af­ter a con­sult with an ex­pert.

Keep Your Cool

If a hy­draulic ap­pli­ance is in al­most con­stant use (sta­bi­liz­ers, for ex­am­ple), the oil will get very hot un­less there’s an ef­fi­cient cool­ing sys­tem. Usu­ally that means do­ing pe­ri­odic main­te­nance on a sea-wa­ter-type heat ex­changer. So, change the rawwa­ter im­pellers on sched­ule, keep the strainer clean, and check the zincs ev­ery month. And call a pro for other sus­pi­cious is­sues. Over­heated oil can burn the paint on an oil reser­voir, a sure sign the cool­ing sys­tem needs help. When the sta­bi­liz­ers are in use, check the oil tem­per­a­ture reg­u­larly.

Check the Steer­ing

Not ev­ery skip­per has a hy­draulic sys­tem like those de­scribed above, but most boats have hy­draulic steer­ing, and the main­te­nance of these sim­pler sys­tems is much the same as it is with larger, more com­pli­cated set­ups. Prob­lems are rare, un­less the

New steer­ing hy­draulics im­prove an old boat.

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