Several manufacturers offer trim tab kits intended for do-it- yourself installation by boat owners. These kits come complete with all the necessary hardware and step-by-step instructions. The installation instructions provided with popular brands of trim tabs are clear and accurate. There is little sense in duplicating those instructions here. Instead, here are a few tips gleaned from the professionals who install tabs at boat factories.

Homemade Trim Tab Gauge

One of the hardest jobs in installing tabs is getting the 1/4- inch setback from the bottom. The tabs are not installed absolutely flush with the bottom of the boat. Instead, they are located on the transom a 1/4-inch above the sharp corner where it meets the bottom. Trying to draw a line and then install the tab to that line is difficult at best. It's much easier to build a "trim tab installation gauge" out of scrap lumber. This gauge automatically establishes the setback for you.

Any handy scrap can be used for this gauge. Looks aren't important. Start by cutting a piece of 1/4-inch plywood to the approximate size and shape of the tabs. Then, screw two pieces of straight scrap lumber to the plywood as shown in the drawing. The top edges of these pieces (which we'll call "the prongs") must be absolutely flat.

Mark the location of the outside edge of the trim tab on the transom. Have a helper hold the gauge so that the prongs are in full contact with the bottom and the plywood makes a "shelf" at the transom. The top of the plywood gives you the exact 1/4-inch setback required. Simply rest the tab on the plywood while you mark and drill screw holes at either end of the hinge. Take the gauge down and goop up the back of the hinge with polyurethane adhesive/sealer (3M 5200 or Sika 540). Install the tab using the two pre-drilled holes. Then drill the mounting holes for the remaining mounting screws.

Extending Control Cables

Trim tab kits come with standard length cables that are usually long enough for boats up to 26 feet. Standard cables are often too short to reach flying bridges or inside steering stations on longer boats. Check first to see if the manufacturer of your tabs offers either a longer cable set or some sort of plug-in extension. If either one is offered, obtain it prior to beginning

If you must extend the cables yourself, be sure to purchase wire that is at least the same gauge as the wire in the supplied cable set. Also, buy wire that has the same color insulation as used in the cable set. This will avoid wiring mistakes which could damage the trim tab pump unit. Crimp-on "butt" connectors are the easiest way to extend the individual wires. Skin the wires and crimp the connectors in strict adherence to the instructions. It's not a bad idea to waterproof crimp connectors with a wrapping of electrician's tape.

Routing The Wiring

The wiring from the trim tab pump to the helm station should be run as high out of the bilge as possible. This keeps the wiring from being shorted out by the inevitable bilge water. Nylon wire ties are available that have a mounting eye which allows them to be screwed to bulkheads or stringers. These wire ties can be used to mount the cable as needed. An alternative is to use electricians' tape to hold the trim tab cable in a bundle with pre-existing wiring in the boat.

Locating Control Switches

Trim tab control switches are used often. They should be located where the helmsman can see and reach them easily. If possible, the helmsman should be able to rest the heel of his hand on something solid while operating the tab controls. This will prevent his hand from being bounced off the switches in choppy water.

Don't Forget The Funnel

Trim tab units come with a small funnel that is necessary when filling the hydraulic reservoir with oil. Most people use this funnel only once, when they install the pump unit. A year or so later, the funnel has disappeared when the time comes to top off the reservoir. One way to keep the funnel handy is to secure it to the pump with a nylon wire tie. You'll have to cut the tie when you want to use the funnel, but wire ties are cheap while funnels are hard to find out on the water.