What fibreglass to use on my 12ft boat

Hi there,

I recently purchased a 12ft fibreglass boat, it has a 6hp 2stroke mariner motor which I am going to keep on. Sadly, the transom has a crack which requires repair otherwise my outboard will be coral reef soon. The boat currently has a 5mm glass transom, onto which the engine wood mounts are bolted on. Can't believe it's so thin!

I would like to improve the strength and stability of the the transom by introducing a 9 or 12 mm transom, but I want to epoxy/glass it in permanently.

After some research I will do the following:

1. strip and sand with 80 grit sandpaper to prep the survaces.
2. cut a template of the transom
3. epoxy the ply after it's been cut from template, and wrap it with FG
4. Using epoxy resin and wood flour, I create a putty/peanut butter and spread it on the existing FG transom, and the new ply transom then bolt/clamp it into place
5. Once cured, sand and apply the same putty around the edges to get round corners
6. Apply FG tape around the edges
7. Apply FG to the entire new transom, about 4 layers.

I may have missed a step like sanding etc but that's the general idea.

Only thing I'm unsure of is what weight or type of fibreglass to use and hoped someone could point me in the right direction.

Here are some pics for your persual.
https://drive.google.com/folderview?id=0Bzms3yzVpcovUUwycmdQMUZuUHM&usp=sharing

Thank you.
Byron