Transom extension on a 74' 20' seacraft

[sparrow]

Hey guys,
first post for me, have found everyone's posts and replies inspiring and educational. I am trying to finish out a rebuild, which someone couldn't complete. He replaced the stringers, transom, and put in a brand new 50 gallon gas tank. I hope he did a good job. Right now, I have a hull which is starting to shape up on the inside, lots of filling and leveling. So far I have used epoxy fairing compound to join all the cuts together that this fella made to pull the boat apart, do his handiwork and then put back together---west system actually--which is probably taboo to most fiberglass veterans. But I am happy so far with the results---I think. Lots of sanding. But the transom is only 20" from the bottom of the keel. My research says i need to extend the transom up another 5" to allow for a newer style motor and so I don't risk large breakers coming over aft, or worse, taking on water while at dock---while no-one is there to notice. I think I could just add plywood to the top of the existing transom and lag bolt it down, w/ resin coated generously between each layer of plywood and then wrapping it all in fiberglass cloth, soaked in resin. The lags would take most of the weight, and the plywood would essentially become one uniform piece, right? The other option is to cut out a large swath of the transom, and try to sister on a couple sheets of marine grade ply, like guys have demonstrated on this site. Any thoughts? Also, is ACQ or pressure treated plywood the same thing as marine grade plywood?

[warthog5]

So far I have used epoxy fairing compound to join all the cuts together that this fella made to pull the boat apart,

It might just be your wording here? Did you glass the part' back together, or just use fairing compound?

Also, is ACQ or pressure treated plywood the same thing as marine grade plywood?

I think you ment ACX? ACX and most preasure treated plywood is Pine. It's heavier in weight than Fir.

The standard for Marine plywood is BC Fire Marine. However there are other's that are more expensive.

There's to many void's in ACX and standard preasure treated plywood is to wet and inhibit's the bond of resign and glass.

[Trayder]

As for the transom extending the transom another 5" you could also use a jack plate, see Scott Mcleod;s 23 in the 23 section. Although your concerns of a low transom for water intrusion in your boat are real they only become a major concern if powering the boat with a heavy engine or when one does not look after their boat.

What are your plans for power?

As for West System being "Taboo" not really, just expensive.


Welcome to the site.

[sparrow]

Yeah, actually, I did just epoxy it back together, the seems are about 1/4"to 3/8" apart. I was worried about this and still am but it sure set up solid. What's your take? Do you think that torsionally-- my seem joinery could fail and crack? If so is it too late to lay some cloth over the joints that are still umprimed and sanded to 60 grit? As for repower, I am of course thinking about a large size motor, say 150 to 200 hp. I was considering for the transom extension, a piece of steel that wraps both inside and outside as well. As for the joints, this weekend I'll get some digi pics. out so all from csc can see how I screwed this up. haha Thanks for any input.

[warthog5]

That's not the way to repiar fiberglass.

It's fine to glue the piece's in place to hold them in position, but now you need to grind all the seam's back in at least a 12 to 1 ratio.

That means if the panel is 1in thick you grind it back 12in, with the center at the seam ground back to almost zero thickness.
A 1/4in thick laminate would get ground back 3in.

Light weight fiberglass tape is not gonn'a get it. You want multi layer's of +45/-45 biaxal with the strand's running across the joint.