Thread: transom replacment

To give advice I have to ask what size & type of boat??.....any photographs??
...........I have replaced a few over the years but it will be better to advise you once I know what we are dealing with!!

the boat is a velero dart, i think around 14 ft long, the transom was that rotten i could remove most of the timber buy the handfull, im amazed it actually held together with the wieght of the 70hp outboard and the strain of towing two biscuits, says alot for the strength of fibreglass,

Typically, older 'glass powerboats, need to have their transoms replaced after about 20 years of hard service. There are many reasons for this and I've replaced dozens. Sailboats less often, unless a big old honking outboard has been hanging back there.

Yes, you should use a marine grade of plywood, but there are tricks to keep costs down.

You can use construction plywood grades too, but the trick is to use multiple layers to increase veneer count (the layers on the edge of plywood).

An example is (sorry I'm a Yank) most transoms are about 1.5" thick (before sheathing). Generally the manufactures use two pieces of 3/4" plywood, glued together and tabbed to the hull shell. This provides at least 14 veneers of wood in the laminate. If you use 3 pieces of 1/2" (5 plys each) then you get 15 veneers inside the laminate and you can employ a slightly lower grade of plywood (construction grade).

Secondly, since plywood has a cross grain veneer every other layer, it's wise to "cant" each layer. Basically you want the bulk of the strength to go athwartship (side to side), but you also want to transfer transom loading to the bottom, with some cross grain strength. You can increase this "stiffness" element by canting each sheet about 12 degrees in relation to each other.

Pictured is three sheets of plywood, with a transom section on it. You'll note it's pretty wasteful of wood, but it's a lot stronger, so you can use cheaper plywood.

Originally Posted by PAR

it's wise to "cant" each layer.

Ozzies never say can't


Sorry, couldn't help myself