Scout Transom replacement

[PAR]

It's important to talk apples and apples folks.

Mat isn't used, nor is desirable when using epoxy.

Bondo absorbs moisture and is prone to "shake out" from vibration, which is fairly common on a transom.

You don't need to wrap the plywood in fabric.

You do need to bond the pieces of plywood together and to tab the plywood into the hull shell (not the liner).

Again many previous threads have covered this topic, but a quick over view:

Grind and cut out all the bad stuff inside the transom. Use a very coarse paper, like 16, 24 or 36 grit and insure all contact areas are clean and well roughed up. Grind back the edges of 'glass pieces to be bonded back together several inches in each direction. This provides a place for the epoxy to bond and make the transition from polyester to epoxy, without a hard point. All areas where the plywood will touch or tabbing will contact should be well "toothed".

Cut and fit the plywood pieces. Drill all holes and cut all notches for a fairly close fit, but it doesn't have to be exact. Remove the plywood, apply two coats of unthickened epoxy all over the plywood. Every side, especially the edges and each hole or cutout, needs epoxy on it.

Bond the two 3/4" plywood pieces (or three 1/2" pieces, which is stronger) together, by applying an epoxy, thickened with a structural filler (50% silica, 50% milled fibers will work) with a 1/16" notched trowel. Some people like to drill a thousand little holes so the two pieces will lie flat and let air escape, but I've found if you start at one side, wedge up the other side with a piece of scrap, then trapping air isn't a problem. Screw the two together with 1 1/4" stainless, flathead screws. Use a tight screw pattern like 3" or 4" center spacing. Apply another coating of unthickened epoxy to the plywood. It should shine on every square inch or it's not completely sealed.

Next wet out the contact areas with unthicknened epoxy, inside the hull shell (again not the liner, unless it's a structural liner, which it's probably not). The wet out areas should include a healthy tabbing area, well back into the hull shell.

Mix up more thickened epoxy and coat the contact surfaces with it. In areas where you expect to fill some gaps, apply more, but generally a reasonably uniform coating min. 1/16" thick. This doesn't include the tabbing areas, these should just be wet from the unthickened epoxy coating.

Install the plywood, you'll see thickened goo oozing out around the edges of the plywood. This is good. If you don't see ooze out, you haven't enough stick'um on the contact areas. From the outside, use a few dozen or so screws to suck the plywood back against the cracked and broken up 'glass transom skin. You could wedge it against this outer skin from inside, but you have enough damage back there that you'll have to paint it anyway, so a few filled screw holes isn't a big deal.

Now the plywood is locked place and the goo oozing out everywhere. Smear the ooze out epoxy into a nice neat corner radius, which we call a fillet, around the inside edges, where it meets the hull. A tongue depressor is the perfect tool for this and I make them up from scrap bits of wood and a belt sander. If you haven't enough ooze out to completely fillet around the inside edges of the plywood, then make some more and do so.

Next apply your tabbing. I use biax, just because its a fair amount stronger then regular woven fabric, don't cost much more, it drapes around things better and places more fibers across the joint then 90/90 weave fabrics do and I have a bunch of it. You can use regular 'glass fabric or cloth tape. Fabrics are sold by weights. There's a many different weights. 3 layers of 8 ounce or 2 layers of 12 ounce will work, which ever is available for you. The tabbing should reach back onto the hull shell several inches. This ties the old to the new. Too short of tabbing will fail. Too long of tabbing will not hurt a thing, error on the too long side.

If the fillets are still wet or green (which is preferred) then just lay the strips of cloth on the transom, crossing over the fillet and back onto the hull shell. The wet epoxy will start to change the color of the cloth. Using a chip brush apply unthickened epoxy to the cloth, until it pretty much seems to disappear. Wipe away excess epoxy with a squeegee, moving it to areas that need more epoxy. When all the tabbing layers are applied, you're pretty much set to finish thing off.

[MikeV]

I finally opened this cracked transom
i see when it was assembled there was no contact between the core you can see the gap in the picture glue was put in but there was still a void.

[MikeV]

hey Par - dock dave or anyone
i was all set to use the plwood then i accuired the original foam insert as it was from the mfg...
now what ?
I cut from the inside will post a picture i have 1/2 in foam left on the skin .. i was think of glassing this the adding the new material the 1/2 does have a crack I repaied the outside skin.

the foam is 1.1 thick original was 1.5 with fiberglass skins .. i was still think of using plywood on this to support the 70 hp mariner


Thanks
MikeV

[MikeV]

added one more picture

Thanks MikeV

[dockdave]

Your off to a good start. Time to get sticky.

[MikeV]

Yes I just am not sure of the glue epoxy oredre should i coat the foam first?
should i glass the inner transom i have some heavy biax plus som kevlar
can i still put a layer of ply over it glassed ?