Aluminum boat motor mount replacement with HDPE?

[kaliona]

I obtained a 12' aluminum boat that's been sitting in a back yard for about 16 years. It's still sound with no leaks but the plywood at the transom where the motor mounts is pretty bad. I thought I could replace both pieces (outboard and inboard) with some Seaboard high density polyethylene and seal the mounting screws with 3M 4200 sealant. It's easy to cut and drill and readily available. Is this a good idea? Bad idea? Should I stick with marine plywood? Thanks for any input. This is how it looks right now.

 

[titaniumneck]

I'm just going to give my two cents in, I am not familiar with the poly board your talking about, buttttt, if it is strong enough, hell yea go with it. I believe if you have a boat and plan to keep it and use it for awhile, replacement of All wood and going with synthetic materials that don't rot is a great idea. Also always go with stainless steel fasteners.

 

[kaliona]

Definitely will go with stainless fasteners. Can anyone speak to the purpose of that plywood? If its just to provide a "meatier" surface for the outboard to clamp on, then I'll probably go with the HDPE. If it provides structural stability, then I'll probably go with the plywood since I'm not an engineer and know nothing about the bending or breaking strength of HDPE.

 

[GA_Boater]

Your transom is a single thickness of stamped aluminum from the looks of it. Without the plywood, transom isn't thick enough to mount a motor and the transom will fracture.

I would use plywood inside and out for a stiffer motor mounting surface. And replace all the rusted steel hardware. Steel and aluminum do no play nice together and will cause corrosion issues.

 

[Chaser 32]

I too was looking at using a $20 HDPE cutting board from Wal-Mart in place of plywood for my O/B back plate, but I was going to laminate a piece of 1/16 aluminum on the outside to prevent vibration wear. I used an inch of plywood for my main transom board, treated with a Spar Varnish mixture and another 5 or 6 coats of Spar varnish on top. Don't think I'll have any issues.

 

[Scott Danforth]

NO

HDPe doesnt have any strength and you will fatigue your transom from all the flexing and it will bust.

wood was there for over 50 years of neglect. replace the wood and with a bit of maintenance it will last more than 100 years. HDPE will break down from UV (even the UV stuff) in 15-20 years. however the transom will let loose in about 1-2 years from oil-can fatigue and the boat will sink

wood is still the best material in this case.

 

[Watermann]

Yeah replace with good quality exterior grade plywood, sealed and painted with oil based paint to protect it from the elements.

Use the cutting board to clean the fish you'll catch. :lol: