Replacing core under tower legs

[msteimer]

Guys,

Looks like I have some water in the core that the tower legs are attached to. Pretty certain all four legs have balsa coring underneath. They are all thru bolted and bedded, but when holes were cut to run wires through the legs, the balsa wasn't epoxy coated. Bedding may be shot and water getting in through there as well.

What do you think the best fix would be. I'd like to spend the time/money to do it right now and not ever have to worry about it again. Should I just build up with epoxy and 1708? Or use G-10 or similar as a core? Other options?

Thanks for the input!
Mark

[Tony Meola]

Are you talking about the wood under the gunnel? On my 31 it is 3/4 ply and not balsa.

[msteimer]

Hey Tony,

Thanks for the response. Nope, I'm not certain it's balsa. The front two legs are attached to the bow deck, the rear two are under the gunwhales. Felt like wet balsa when I reached underneath, but I guess it could be rotten ply as well. Either way, it still has to come out, and not sure what to replace with.

Mark

[CaptPatrick]

Mark,

Is this a B31?

[msteimer]

Capt Pat, it is a B35.

[CaptPatrick]

Mark,

Sorry, but I'm not familiar enough with the construction of the 35 or other Napier designs to be of much use to you... However, as a general rule, wet balsa core is a major problem that never has an inexpensive or easy solution. Once balsa core is wet there's no way to fix the problem other than major removal and replacement. Your best replacement material will be a Coosa Board type material, (Coosa, Thermo-lite, & Penski Board) bonded in place with epoxy & Cabosil.

[msteimer]

Capt Pat,

Thanks for the advice. I was worried about the compression strength of a polymer material as the core under the tower legs, but if that will get the job done without future rot, then that is what I'll do.

One other question...I will bond the Coosa in place with epoxy and cabosil, but is there a best practice for glassing over the Coosa overhead? I'm wondering if it would be easier if I wet the glass out on wax paper first. Will wetting out 1708 on wax paper and then laying it up on the Coosa work? Will I be bringing contaminates from the wax paper to the laminate that will prevent adhesion?

Sorry for the novice questions but am trying to make sure I get it right the first time.

Mark

[CaptPatrick]

Mark,

Getting wet glass to behave upside down is a real trick... It would be best to carefully fit the Coosa Board as precisely as possible before epoxying into place and glassing it over while you can lay it up on a table upside down. After the underside sets up, then mud it into place with the epoxy and Cabosil. Use vertical battens to hold the Coosa firmly in place while that cures and then tab over that joints. It'll be easier to control the tabbing than it will be to try and manage a larger sheet of wet glass. Hope that makes sense to you, if not call me...

[msteimer]

Thats perfect, thanks Capt Pat.

[Pete Fallon]

Mark,
If I remember correctly the core under the 35 Bertram gunwales and foredeck is marine plywood. I would follow Capt. Patrick's advise on how to replace the rotted plywood. Also I always used a backing plate as large as it will fit under each tower leg, it can be a piece of aluminum flat stock or piece of fiberglass. The aluminum can be gotten at a local tower manufacturer and the fiberglass can be gotten at a local boat builder. Try and get pieces of fiberglass from deck cutouts, deck flanges, or you can lay them up yourself. I always tried to make the backing plates twice the size of the area that your going to support. On my 31 Express all the rod holders and outrigger bases had plywood backing plates that were thru bolted with extra large washers, it was before I got into building boats and used what was available to me. If your using Coosa board or high density foam core board use the highest density you can get (either 60 or 80 pound rating). If using aluminum plate at least 3/'8" or 1/2" thick material and if you can drill and tap the aluminum for good holding power. Just a few thoughts from past experience.
Pete Fallon