transoms

HI, im new to this forum, i have a 21' wellcraft, 18" setback transom w/ 6" hyd.jackplate and 150 merc efi. my transom is rotten, since i have a lot of experence with epoxy and glass work im going to re-build it myself. i,ve seen some repair shops that use 1/4" luan plywood (phillipine mahogany) saturated with slow setting epoxy and f.g. mat untill they build up to the desired thickness. i'd like some opinions on this as opposed to using layers of 3/4" marine plywood thanks fishhawk

 

About half way down this document is the description and repair technique recommended for transom core replacement.

http://www.westsystem.com/ss/assets/HowTo-Publications/Fiberglass-Boat-Repair-and-Maintenance.pdf

 

Assuming a 1.5" core (two layers of 3/4" plywood), you can save some money with 6 layers of cheap 1/4" lauan, though it's likely not as strong as the two pieces of marine grade 3/4", in spite of all the mat and goo.

On highly loaded transoms I use three layers of 1/2", with the grain oriented at 12 degrees to each layer (further increasing strength). Since you use epoxy, you know that you don't need, nor is it desirable to use mat. I laminate each layer in place on the boat, typically with through bolts or temporary screws to hold everything together as the goo sets up. Then of course the tabbing to the hull shell.

The basic issues with the cheap lauan from Lowe's?depot is the glue used may not be WBP and the thickness of the long grain veneers. This isn't an issue with marine grades. Some will have you use a BS-1088 grade, which is fine, but unnecessary on a transom, so save some money and use a BS-6566 grade plywood.

 

Two layers of 3/4 is how iI always do it. I agree with par on the rest.

 

thanks for the advice, the original transom was 2" guess i'll go with 4 sheets of 3/4, as the weight of the setback is about 100 lbs, the jackplate about 50 lbs. and the engine 450lbs, and its sitting 24' back.