Jack Plate Home -- Page Two: Adding a trim bracket

Jack Plate Plans Construction Notes

(Purchase Plans, if you haven't already.)

If you are mounting a longshaft motor on a 15" transom, make the moving part of the the jackplate 5" longer than shown in the plans drawings.

Start with four 12" lengths of 4" x 4" x 1/4" aluminum angle. Layout the hole locations, as shown on the drawings.

I use a hacksaw to join the holes into slots. First square the holes somewhat with a small file (a triangular file works well).

You may be able to use an electric jigsaw instead of a hacksaw, but in my experience the aluminum clogs up the blade.

File out the slot, as needed, to fit the square boss under the head of the 1/2" carriage bolts. Make the slot just large enough for the carriage bolt to slide along without binding.

Round the corners as shown on the drawings, or as you see fit. File all the edges smooth.

The motorboard can be considered optional. Your motor can be clamped and bolted directly to the aluminum.

I like to use the motorboard because it ties the two halves of the jackplate together, parallel and properly spaced, before they are installed on the boat. It also provides an extra 1.5" of set-back.

The cut-out is only required if you are setting up a trim system similar to the ones I use. The exact size and shape of the cutout will depend on the requirements of your equipment and setup.

Glue up the motorboard from plywood. Scraps from a building project will often do the job. Final thickness should be 1.5 to 1.75 inches.

Epoxy is always a good glue choice. However, I have made these using Titebond II and Titebond III woodworker's glue. My boats spend their downtime on trailers. If your boat lives in the water, epoxy might be best.

I only use one bolt to hold the motor board to each half of the jack plate, plus one screw each side just to keep things aligned. Your outboard motor will further serve to hold things together, first when you clamp it down, and second when you bolt in on. Bolting on your motor is required for racing, and a good idea in any case.

I use regular plated bolts, nuts and washers to bolt my jack plates together and to bolt them to my boats. If your situation makes rust a worry, then by all means go with stainless.

Use nylon insert nuts all around. Other types of locking nuts or washers may also work.

Bolt the jack plate to your transom using at least two 3/8" bolt for each half of the unit. Locate the upper bolt close to the corner of the aluminum angle so that the motor is unable to pull it away from the boat.

I have not specified an exact location for your mounting bolts, since you may have structure or equipment in your boat to work around.

Exact mounting location of your jackplate will also depend on how much height you are trying to gain. On my own designs, the initial motor height is quite high, so you would mount the jack plate such that it initially adds no height at all, and plan to work upward from there.

On boats with a lower transom height, you will want to mount the jack plate so that it adds height even at its lowest setting. Obviously it helps to know approximately how high you need to go. Only experiment, and perhaps experience, will tell you that.

To raise and lower my jack plates, I use the jack from pickup truck.

(Purchase Plans, if you haven't already.)

Jack Plate Home -- Page Two: Adding a trim bracket