How to Maintain the Hydraulic Systems on Your Boat

Hydraulic systems are extra-reliable but they need regular maintenance to stay that way.
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Hydraulic systems are extra-reliable but they need regular maintenance to stay that way.

Keep the Pressure On.

New steering hydraulics on an old boat

New steering hydraulics improve an old boat.

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 raw-water 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 system is damaged, e.g., by somebody throwing something on the steering ram in the lazarette. Typically, the pump is the helm itself. Power steering systems are a bit more complex, since there’s a separate pump involved, but they’re still ultra-reliable and easy to maintain. Most boat owners check the steering oil infrequently—a euphemism for never—unless the steering becomes less responsive, feels rough, or has other issues. Usually problems are due to low fluid level and/or air in the lines. A simple and inexpensive fix: Just add oil.

However, different systems use different procedures for topping-up. Fill either at your highest helm station (in a two-line system, more common in today’s boats) or (in a three-line system) at a remote reservoir tank.

In a two-line system, the helm pumps oil through the lines, helped by gravity in multi-helm boats: A compensating line between the helms lets oil flow down to the lower helm while trapped air rises and escapes through the vent fitting at the upper helm. Most two-line systems require a plastic filler tube with a screw-in fitting that connects the fill port on the helm with the bottle the oil comes in. Very little oil is typically required for a top-up.

If air gets into the hydraulic lines, or a lot of oil has been lost—from a leaky hose, damaged steering ram or, as in my case a few years ago, a faulty autopilot installation (that’s what I get for hiring an “expert”)—refilling the system is more complex, and will require a helper. Basically, the standard “fill and purge” procedure consists of cranking the helm hard over in one direction then releasing air from the lines through a bleeder. That’s where the helper comes in—one person holds the wheel while the other opens the bleeder and catches expelled oil. Then the procedure’s repeated with the wheel cranked the other way. Most owner’s manuals offer more detailed instruction.

Three-line systems are typical of larger yachts and fill at a separate reservoir that’s pressurized. Such systems are more complex to engineer, but they’re easier to check and top-up with oil; you simply add it to the reservoir. Of course, you release the pressure first, then pump it back up with an air pump.

Once a system’s topped-up, blow out any air by cranking the helm hard over in both directions. To find leaks, pressurize the oil by cranking the wheel hard over again but then hold it there (you’ll need a helper for this one, too) while wiping all the hose connections with a paper towel that shows oil stains. Swap the helm and repeat.

If a hose end leaks, incidentally, you usually need to replace the whole hose, but a leaking seal on the steering ram is frequently the problem. Replacing a seal is a job for a mechanic with a clean shop; contamination is just as bad in a simple steering system as it is in the sophisticated hydraulics aboard a megayacht.

This article originally appeared in the October 2017 issue of Power & Motoryacht magazine.

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