Does anyone know the best way to fit an auxiliary out board bracket to a boat.?

Question

When you bolt it to the boat do you put a board on the inside of the boat to take the strain of the bracket on the outside of the boat as I bought the bracket on ebay and I got no instructions with it. The bloke I bought it from is as a much use as an ashtray on a motor bike.

Answer 1

just offer it up to the boat where you want it to go, then you will see which way to do it.

Answer 2

A lot depends on the material of your transom and the power of your aux outboard.  You will be fitting something to part of the boat which was not designed to be stressed in that way so you definitely need to add some strength yes.  How much strength and what you can use does depend as above.  Assuming your transom is fibreglass or plywood, I would start with two plywood pads one for outside and one inside the transom.  For a small 5 or 6 hp outboard you might get away with 4 to 6 mm marine ply cut to spread the load from the actual mounting bolts to an area of about 25 cm by 25 cm.  For a larger outboard I would use a single 6mm outer pad between the bracket and the transom and then make up multiple layers inside, each from 6 mm marine ply with the first pad (against the transom) larger than the next, so you get a shallow pyramid kind of shape.  In this case my largest pad could be 40 by 40 cm if adding 3 layers with 30 by 30 next and 25 by 25 next.  I would simply waterproof the outer ply before applying with some soft sealant but the inner ones I would actually laminate to the inside of the transom with epoxy and the same between each of the pads so it forms more of a solid reinforcement inside than just loose plywood pads.  Neither fibreglass nor plywood reacts well to small points of stress and in a new boat designed to have such a bracket, you might expect to find a block of wood 10 mm to 20 mm thick actually bonded into the inside of the transom so you can bolt through.  Of course you can always laminate some fibreglass sheet also over the inside pads to make a good reinforcement and spread the load of the outboard.  In this case dont leave the ply pads with 90 degree edges but fair them off to give more of a sloped edge which is better to laminate over.  Remember also to use good large and thick washers on the through bolts.

Answer 3

It is always better to strengthen the transom.  To start get some 3/4" ply. cut it bigger that bracket size to spread weight.  Offer it up to inside of transom to see that it will fit in.  Paint it well to stop water/damp penetration and fit  it.