How to Build a Fiberglass Outboard Bracket for a Small Sailboat

By John C. Harris - 2010

The instructions below show how to build a light, strong, elegant outboard bracket for PocketShip.  Since we have a lot of scrap six-ounce fiberglass laying around that's what we used, along with Peel Ply. 



Here's the drawing showing dimensions of the finished outboard bracket.
 

A very simple "female" mold is built from cheap plywood and scraps.

 

The mold is coated with generic paste wax before the fiberglassing begins.  It's hard to have too much wax on the mold.

A wooden spacer will be laminated into the motor mount to give the outboard's clamps a good grip. Make this form to fit inside the mold with a small gap between the pieces.

 

To begin, put a layer of peel ply into the mold so it will have a smooth exterior. Peel ply also aids in releasing the bracket cleanly from the mold.

 

 

Brush more wax onto the peel ply, and take care to eliminate all the wrinkles.

 

Use a fiberglass roller like the one below to saturate the many layers of fiberglass cloth.

 

 

 I used 50 layers of six-ounce fabric (!) wetted-out in two 25-layer units.  This was overkill.  For a 2- or 3-hp outboard, a total of about 28 layers of six-ounce fabric would have been sufficient, in two 14-layer units.

 

 

The fabric is wetted out in a simple wooden tray I built for the purpose, to keep the excess resin from going all over the place.  100% of the air must be rolled out.  This takes a lot of work, and you have to work very fast, as you'll need nearly a gallon of epoxy.  And it wants to set up in a hurry!

 

 

Here are 25 layers of fiberglass completely wetted out, ready to put in the mold.

 

 

Fiberglass is set into the mold, pressed and rolled tightly to eliminate air bubbles.  Then the block of wood is set in place.

 

 

Quickly make a big, strong fillet between the wood block and the fiberglass going up the sides of the mold. The fiberglass should still be uncured.  

 

 

Press the second and final 25-layer glass into the mold, sandwiching the wooden block.

 

When it cures, trim the overhanging material off with a 4-inch cutoff wheel. This type of cutting wheel is used by welders and metalworkers.

 

Lift the bracket out of the mold, and peel off the peel-ply.  Peel Ply is available by the yard

 

The bracket will need some heavy-duty sanding.  Fill any air bubbles that you find.

 

The exposed edge of the wooden filler block must be thoroughly coated with epoxy.

 

Finish the bracket with several coats of paint, and through-bolt it to the stern of your boat. The finished bracket is light, clean, strong, and unobtrusive!