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Transferring Power


Depending on the size and type of boat, it likely has a system operated by hydraulics. Understanding how they work and how to maintain them is an essential skill.

Hydraulic systems are everywhere, even on the smallest of boats, controlling trim tabs, engine tilt and trim, and steering. (Photo: Lund)

All hydraulic systems use the same basic system of operation: Fluid under pressure from a pump (either manual or electric) moves through a system of hoses, lines, or channels. The fluid direction can be controlled by valves to move an object one way or another. Since the fluid can’t be compressed, the pressure created by the pump or motorized pump is maintained throughout the entire system, even if it is large and complex.

This is not a new concept. Using fluid under pressure has been a good way to move things for a very long time. The first documented systems, using water, date back to 6000 B.C. Today’s marine systems, which use oil instead of water, are remarkably similar in operation. Additionally, they’re not hard to maintain, as long as the maintenance is performed on a regular basis by an owner or technician who knows the system and understands how it works.

These systems often include hydraulic and power-assist hydraulic steering, power trim and tilt, trim tabs, and hydraulic jacking plates for outboards. Some larger craft feature items such as bow thrusters, davits, stabilizers, hatch covers, and windlasses.


Many boats have a hydraulic steering system. It has become the standard for steering many modern craft. Not so many years ago; in the 1960s, ’70s, and ’80s, mechanical push-pull cable was the standard. Hydraulic systems became popular in the 1990s and have proven to be reliable, safe, and relatively inexpensive to buy, install, and service.

Filling and bleeding the hydraulic steering helm reservoir.

It’s not uncommon today to buy a complete system online, even from an online retailer, and install it yourself. System selection and installation is not difficult, but careful study of application charts and installation/bleeding instructions is necessary to choose the correct helm and engine cylinder assembly. Time must be spent measuring for the proper hose length, completing the installation correctly, and performing proper bleeding so the system works without skipping, looseness, or sloppy steering. Bleeding is pretty easy, but it is a two-person job as most owners won’t have access to the power bleeders that dealerships and professional installers use.

Maintenance is pretty straightforward. An annual check and maintenance regimen should be followed, but just like pilots and race drivers do, a quick visual inspection combined with a lock-to-lock steer-through should be performed each time the boat leaves the dock. This provides the helmsman with good feedback as to the health of the system visually and reactively.

The steering should not be leaking or compromised in any way, and it should turn the engine(s) or rudder(s) smoothly through the full lock-to-lock cycle without any issues. While there is often some play in every system — between steering wheel turn and helm response — it should be minor: less than a half-inch of travel.

Owners should examine the complete system annually. This includes checks for:

  • Fluid leaks. Look for fluid traces along the hydraulic lines, the hose connections at the rear of the helm, and the steering shaft seal that is behind the steering wheel. Similarly, look for leaking fluid at the engine steering cylinder from the ram seals and the hose connections.
  • Skipping, missing, or poor response when the wheel is turned. As noted above, operate the steering lock-to-lock several times and feel for anything unusual. It may be that a follow-up bleeding is necessary to remove lingering air bubbles from the system.
  • Corrosion. This is more of a problem in saltwater areas than fresh. Regardless, corrosion can be a problem because there are dissimilar metals in the installation. Aluminum is commonly used for the helm housing, cylinder, and steering arms, with stainless steel for the shaft, ram, and other hardware. Carefully check for corroded, chipped, and peeling paint, and pitting on the stainless ram, hose fittings, and hardware. Corrosion left unchecked can render the system inoperative and make it nearly impossible to remove and disassemble.
  • Bent and binding brackets. These indicate improper application and/or installation. Hydraulic steering systems are common, and it’s not unusual to see older systems resold after years of use. These can easily be improperly installed on engines not designed for the brackets involved. This is highly dangerous! Steering is a safety mechanism, and the wrong application or installation could mean loss of control.
  • Secure nuts and bolts. A quick wrench check will ensure that fasteners are tight and right.
  • Worn bushings and connections. Having a partner steer the system lock-to-lock while you eye the helm, engine cylinder, and attachment points can reveal a potentially dangerous situation.
  • Power. Check to ensure that the power steering motor, where fitted, is receiving 12-volt power when energized and is transmitting that power to the system. Check connections and fittings for corrosion and leaks. Ensure that the power wires and hydraulic supply lines are not chafing or kinked.
  • Air in the lines. Bleeding hydraulic steering is similar to brake bleeding on a car. The procedure consists of turning the wheel hard over in one direction then releasing air from the lines through a bleeder on the hydraulic cylinder. This is why a helper is needed. One person holds the wheel while the other opens the bleeder and catches expelled oil. Then the procedure is repeated with the wheel turned hard over the other way.

Power Trim & Tilt

Just about every larger outboard (40 hp and higher) is either factory-equipped with hydraulic-electric power trim and tilt, or it’s available as a dealer-installed option. In addition, for those smaller engines not available with this feature, or for owners of older engines who wish to add it, there are aftermarket trim/tilt plates that provide the function by means of a hinged aluminum engine-mounting transom plate with electrohydraulic motor and pump.

Typical leak in a power trim cylinder. The tilt ram seal is leaking fluid with every up stroke.

Either way, the maintenance of power trim/tilt units is similar no matter the manufacturer or type. The electric and hydraulic systems are combined, in that the electric motor is usually attached directly to the hydraulic unit. An exception is the Mercury Marine High Performance units, where the electric motor and pump are mounted in the boat, connected with hydraulic hoses to the engine trim/tilt cylinder.

Lack of routine maintenance has destroyed the electric motor on this power trim system.

Maintenance of these systems should be performed at least once per year. Similar to the maintenance of hydraulic steering, here are the checkpoints to review:

  • Tilt and trim cylinder/rams. Check for hydraulic leaks, especially around the ram/cylinder seals and hydraulic line connections. Check for excess engine movement when trimmed/tilted up or down, which means the plastic or brass bushings inside the cylinder rams are worn out.
  • Debris and excess grease/dirt. Often the wiper seals (the outermost seals that keep dirt from entering the cylinders) get compromised and start to leak due to excess grease, dirt and debris on the tilt/trim rams themselves. A simple wipe down of the ram can keep this from occurring.
  • Corrosion. This is especially problematic in salty environments, and even in fresh or brackish water when the boat is kept in the water and the trim unit is therefore sitting in the water for extended periods. It’s important to remove the boat/engine from the water and clean off the engine stern brackets and power trim unit. This can usually be easily accomplished with a soft brush and soap, but it sometimes requires scraping off barnacles and galvanic corrosion (that white powdery debris buildup).
  • Fasteners. If the unit ever needs to be removed from the engine for service (this is more common than you might think), it could be problematic due to the corrosion inherent when putting dissimilar metals (aluminum and stainless steel) together in a corrosive environment. It’s not a bad practice to remove the fasteners (e.g., bolts, tilt pins) and apply a film of synthetic waterproof marine grease. This will make it much easier to remove the unit.
  • Electric motor. On many units, the motor assembly is made using a steel housing. Some are made from plastic, which won’t corrode. The steel housing units do corrode badly if left unchecked. Best practice is to check often and catch corrosion before it spreads; use a stiff wire brush to clean off any rust, clean the motor with acetone, and apply spray paint.
  • Electrical connections, relays, and harness. Check connections for corrosion and clean them. Ensure wires are not kinked or otherwise compromised. Look for abraded/bare wires and correct these areas if possible with heat shrink tubing or liquid electrical tape (both available at marine supply stores). It’s a good practice to remove the up/down circuit relays and coat the connections with dielectric grease to keep moisture out.

Outboard Jack Plates

Found mainly on performance and bass boats, but now increasingly installed on other fishing and family craft, hydraulic jack plates allow the operator to change engine height while underway. This gives many performance advantages such as a quicker holeshot, higher top speed, better fuel economy, and improved handling. The jack plate is a simple affair, consisting of a transom mounting plate and engine mounting plate joined together by some type of sliding or moving mechanism, activated by (of course) a hydraulic electric cylinder and motor.

Trim tabs are especially susceptible to corrosion and breakdown, as they are constantly submerged.

Inspection and maintenance are critical. Lack of attention could lead to a serious safety problem as the plates could crack, fasteners could loosen, and the engine could literally come detached from the transom. Therefore, regular inspections are a necessity and should include:

  • Checking for hydraulic leaks around ram seals, fittings and hose connections.
  • Checking fastener tightness. It’s highly recommended to perform this check at least every few weeks when in use.
  • Inspecting the aluminum plates with a close eye for cracks or separation. This is critical and could prevent engine loss.
  • Inspecting electric motors, harness, and connections for corrosion, kinked or separated wires, and bare wires or connections.

Other Systems And Accessories

Many accessories such as trim tabs, bow thrusters, davits, hatches, and systems are built into the boat when it’s manufactured. Therefore, you may have difficulty accessing and servicing them without special tools or knowledge of their mounting systems.

Hydraulic steering using an electric-assist motor is becoming increasingly common, even on smaller boats.

Some larger vessels utilize one hydraulic pump in the engine room that controls all or most of the appliances throughout the boat. For example, a company called Naiad Dynamics offers the Integrated Hydraulic System (IHS) that controls many accessories using one pump. These are high-end custom-designed systems that operate independently from the main engines using an electric motor.

Despite the perceived complexity of such a system, maintenance is actually easier because there’s only one pump to maintain. Self-contained hydraulic units, each with their own pump, are much more common. Some of the points that may require service include:

  • Inspection for cracks, loose fasteners, corrosion, and stuck components.
  • Loose fasteners preventing the cover from closing all the way.
  • Electrical connection problems causing inoperative parts (e.g., a trim tab won’t go up or down due to a poor electrical connection).
  • Fluid leaks that cause parts to operate incorrectly.
  • Accessories, such as davits, that won’t operate properly because of cracking and failing under load.
  • Systems that constantly sit in water. Trim tabs, stabilizers, and thrusters will always suffer the worst due to the harsh environment they live in. Continual checking and addressing corrosion, damaged parts, and stuck assemblies is therefore paramount to their continued operation.


John Tiger

Contributor, BoatUS Magazine