Re: Transom Wood

[Pete]

Plywood glue specs are WBP(water and boil proof for marine and high quality exterior grades) and MR (moisture resistant usually for interior grades). High quality exterior (HQE) plywood like AB exterior grade uses the same glue as marine plywood. I have built boats with marine and HQE plywood with equal success and HQE costs less. There are ply thickness standards used, Ex: I have seen 5 ply 3/4" and 7 ply 3/4". When I was a PM engineer at a Marine Research facility in West Palm Beach, Fl in the 70’s we built numerous sea water use large and small tanks, flumes, large pump forbay sumps, transport tanks for long haul on land and air, etc. I specified AB Fir exterior plywood for these and to use 2 part epoxy and 3 coats of polyester resin. There never was a failure and they held up excellent for exterior and interior use with sea water. Fiberglass cloth was used in some areas where extra joint strength was needed. We used the plywood because it was quick to build and to modify as conditions arose and relatively inexpensive. Metals (SS, Monel, marine Aluminum) were also used in special cases along with the plywood. Then and now before using any plywood a WBP test was done on a small piece. The AB never failed the test.

Fir plywood will have some grain checking and needs good sealing to temper that, the polyester resin did a good job doing this in our outside applications. Overlay with fiberglass completely solves the checking.

For my race boats I use Okume plywood (3mm, 6mm, etc.) and AB exterior for transom boards laminated with Okume for a bright finish, clear coat with epoxy + fumed silica in epoxy for a structural thickener for bonding.

Lots of info here on glue and plywood:

http://www.christinedemerchant.com/mari … glues.html

http://www.christinedemerchant.com/mari … rades.html