How to Inspect and Troubleshoot Hydraulic and Electric Trim Tabs

Look inside the stern lockers or bilge for a pump with a clear reservoir (hydraulic). If you only find wires going to the actuators, it is electric. Note the brand and model from the helm control or the pump label so you can find the right manual and parts.

Look at each tab from behind the boat. Check for bent blades, cracks near the hinge, a worn or missing hinge pin, and loose or missing screws in the transom. Wiggle each tab by hand: a little play is normal, a clunking hinge is not. Loose screws can let water into the transom core, so reseal them with marine sealant.

In salt water, each tab normally carries its own zinc anode on top of the blade. Bennett says the zinc must make direct contact with the stainless steel, must never be painted, and the tabs should not be bonded to other underwater metal. Replace anodes when they are about half worn away (typical; confirm with your tab maker), cleaning the contact spot with a wire brush first.

Scrape barnacles and slime off the blades, hinges and the exposed actuator rams. BoatTEST notes that growth on the ram can wear the seals over time. If you keep the boat in the water, Bennett's guidance allows its tabs and actuators to be primed and painted with antifouling; keep the anodes bare. For electric actuators, check your maker's instructions before painting anything. An orange tint on unpainted stainless is normal surface staining, not corrosion; pitting is the warning sign.

Run both tabs fully up first. Then check the reservoir level against the mark or height given in your manual. Bennett's guide uses automatic transmission fluid and says brands can be mixed; other makers may specify a different fluid, so use what your manual lists. Top up slowly with a funnel and refit the cap.

Check the pump fittings, the tubes where they pass through the transom, and the actuator fittings for wet spots or dripping fluid. An oily film around one actuator usually means a leaking seal or fitting. Low fluid that keeps dropping means a leak you need to find before it gets worse.

At the helm, check the back of the control for loose or green, corroded terminals. Check the fuse in the power wire. On hydraulic systems, check the pump's ground wire and its plug connector. On electric systems, check each actuator's plug and the cable where it passes through the transom for chafe or cracks. Bennett asks that its pump be mounted in a dry spot; one that gets soaked will fail early.

With the boat on the trailer, run each tab fully down and up from the helm while a helper watches. Both should move smoothly and at about the same speed, and an indicator (if you have one) should match. Listen for the pump or motors: a strained or grinding sound is worth noting.

Check that the battery switch is on and the battery is charged. Then check the fuse in the helm control's power wire, the ground connection and any plug connectors for looseness or corrosion. With a multimeter, confirm battery voltage reaches the pump or actuators while you press the switch. No voltage points to the switch, fuse or wiring; voltage with no movement points to the pump or actuator.

Start with the wiring for the dead side: plugs, connectors and the switch. On a hydraulic system, Bennett's troubleshooting guide suggests swapping the two hydraulic lines at the pump. If the problem moves to the other tab, the pump or its valve is at fault; if it stays on the same side, suspect that actuator or its line. On an electric system, check for voltage at the dead actuator's plug while pressing the switch: power there with no movement means the actuator has failed.

On hydraulic systems, Bennett lists low battery voltage as a main cause: check the voltage while the pump runs, because the valves may not open if it drops too low. Clean and tighten the helm and pump connections next. On electric systems, a failed actuator or water in a connector is the usual cause. If a tab stays down on the water, run slowly back to the dock, keep the load centered and avoid sharp turns.

Retract the tabs at the dock and before trailering so they are less likely to be hit. BoatTEST also recommends retracting them after use so growth does not build up on the rams. Bennett states that leaving its actuators extended will not damage the seals and that its hydraulic system needs no winterizing; for electric or other systems, follow the maker's storage advice.