Author: Boat Accessories Australia Date Posted: 8 February 2017
Trim tabs are a worthwhile addition to most boats. They give your boat an additional lift that helps to decrease your boat’s weight while making it easier to control. The increased lift reduces stress and resistance on the hull to provide you with a more comfortable ride.
Installing trim tabs can be a DIY job if you're comfortable using a drill though it can take a little time so give yourself more than half a day to complete.
Bennett Marine manufacture the majority of the trim tabs Boat Accessories Australia supplies. The Bennett Marine YouTube channel has some videos that may give you some additional information about installing trim tabs, but the instructions supplied with their products are clear and detailed.
The summarised steps for installing trim tabs are below but read the instructions supplied with your purchased trim tabs before beginning the project.
Step 1 — Position the trim tabs against the transom and check to see that the upper mounts of the hydraulic actuators do not centre on an inside obstruction. Position tabs 3" to 4" from the chine (side of boat) and run towards the centerline of the boat.
Step 2 — Attach the mounting plates and trim tab with #10 x 1-1⁄4” stainless steel screws along the bottom of the transom. Using the backing plate as a template, mark screw hole locations. Drill 9/64" pilot holes for mounting screws and test. Assemble backing plates and hinge plates, dip screws in marine epoxy before running in. Slide trim tab between backing plate and hinge plate before running screws tight. Snug screws down to secure mounting plates and trim tab to transom.
Step 3 — Secure the lower hinge of each actuator to the tab with 1/4-20 x 3⁄4" Phillips head machine screws. Using a straight edge under the hull bottom, set the “negative angle” of the tab’s trailing edge.
Step 4 — With tabs set at a negative angle, position the upper mounts of the actuators against the transom. Slide the actuator template behind upper mount, align and tape to transom. Drill holes accurately as indicated on templates. Drilling a small pilot hole first helps you locate accurate centres.
Step 5 — Install the pipe nipples (dry) snugly into the actuator upper mounts. Do not use Teflon tape. Apply waterproof sealant on surface around pipe nipple and screw holes. Insert pipe nipples through transom and secure actuator upper mounts to transom with #14 x 1-1/2" screws.
Step 6 — Install Hydraulic Power Unit (HPU) in a convenient location with a dry environment. Important: The HPU must be mounted in a dry enough location to avoid submersion and drenching. Allow space above the HPU so that it may be slid into its mounting bracket (about 3"). Lay out upper holes on HPU mounting bracket 4-5/8" apart and start #10 x 1" screws using 5/32" pilot holes. Then drill 5/32" pilot holes for lower screws and secure bracket. Slide HPU into bracket.
Step 7 — Inside the transom, apply Teflon tape on male threads of pipe nipples and tighten 90-degree brass elbows to pipe nipples.
Step 8 — Run hydraulic tubing from brass elbows to HPU and cut to length. Put masking tape on tubing ends to prevent debris from entering system. Remove masking tape before making connections. Use tube bending clips at desired 90 degree bends in tubing to prevent kinking.
Step 9 — At brass elbow, insert tubing through the nut with ferrule. Push until it bottoms in the fitting. While continuing to bottom the tubing in the fitting, tighten nut “finger tight,” then just one full turn with a 1/2" wrench.
Step 10 — With plastic hangers, secure hydraulic tubing along hullside or bulkheads to HPU. When facing HPU, the brass fitting on the left of the pump face connects with the tubing from the port actuator, the fitting on the right connects with tubing from the starboard actuator. These fittings are identified “P” & “S” for port and starboard by small letters directly above each one.
Step 11 — Connect the HPU ground wire to any convenient ground then the run wiring harness from the HPU to helm. (Follow control installation instructions enclosed with your control.)
Step 12 — Remove plug from filler stack located at the front left corner of the reservoir. Fill reservoir to “Full Line” using any type automatic transmission fluid.
Step 13 — Using the control, hold the “Bow Down” position for 15 seconds, then “Bow Up” for 15 – 20 seconds. Repeat three times. This will purge any air from the system. No bleeding is necessary.
Step 14 — Place both tabs in the “full down” position and check all hydraulic connections for leaks. Bring the tabs to the full up position and check fluid level.