Outboard motors come in handy when used on sailboats as auxiliary or "kicker" engines. Small boats that have C-clamp outboard motors can benefit from the installation of a permanent transom bracket that will properly support engines of different sizes and weights. Before mounting an outboard motor bracket to your boat's transom, consider motor shaft length and transom rake to set the motor at the proper angle and water depth.
Make sure your boat sits on a trailer over level ground. Do not attempt to mount a bracket to your transom with the boat moored in water. Refer to your boat owner's manual for the proper horsepower, size and weight limitation for your craft if you need to install an outboard motor on your boat. You must stay within the manufacturer's specifications so that the hull will sit at the proper profile in the water.
Place the motor in a mobile outboard motor stand. Wheel the motor and stand it up against the rear of the transom and, using the raising feature on the stand, bring the outboard motor up to the approximate mounting height next to the transom. Determine the angle of the transom in degrees by dropping a weighted string from the top of the transom rail and measure the angle at the bottom of the boat hull with a protractor. Write the figure down with a felt pen on the transom for easy reference.
Locate the approximate waterline on the hull by looking at the discolouration of the paint on the hull that shows a the dividing line, or look at the waterline paint stripe. Make sure the water intake on the outboard motor sits at least 3 inches below the waterline, and that the exhaust port sits at least 1 inch above the waterline. Refer to an outboard motor height chart, such as the one found at MarinePartsMan.com, to determine the mounting position of the outboard motor bracket on your transom (see Resources).
Use a sabre saw to cut a square of 3/4-inch marine plywood large enough to accept the mounting holes of your motor bracket, with at least 1-inch margins on all sides of the four mounting holes. Make certain there are no obstructions like stringers or components on the inside of the transom. Use marine silicone adhesive to glue the plywood square to the inside of the transom, no higher than even with the bottom of the top rail. Let it dry for an hour.
Place your mounting bracket on the outside of the transom. Use a tape measure to align the bracket so it will centre in the middle of the plywood square, making sure the mounting holes will sit inside the plywood square outer edges. Mark the bracket holes with a felt pen on the transom exterior. Use a drill motor and drill bit to drill the four holes through the transom.
Place a kit washer on each mounting bolt and shove all four bolts through the mounting bracket and then through the transom. Place a kit washer, lock washer and nut on each bolt thread on the inside of the transom and tighten them with a socket and wrench.
Position the bracket tilt and elevation bolts in the approximate position for your motor, according to a motor height chart or your boat owner's manual. Make the final adjustments on the bracket tilt and elevation bolts once you launch the boat in the water.
Pay strict attention to the motor height chart when determining how to mount your specific outboard motor to you transom. The same rules apply to sailboat transoms.