Balsa Core Deck Repairs

[reiner]

My boat ( 40ft Challanger) has a deck stepped mast and the deck is balsa core.
The rigging is getting replaced and the mast is removed. I found some rot under the mast foot. After further investigation I found that the junction box in front of the mast has let water in the core.
The damaged part is about 12 inch by 8 inch. My thought was to dig out the rotten balsa and replace it with a solid piece of hardwood glassed in with polyester resin. I left the inner glass layers in tact .I am getting rid of the junction box and make sure the whole repair is waterproof. Would it be better to build up with glass to make it more solid for the mast foot or is the hardwood block a good way to go?
Should it have had the balsa core under the mast foot in the first place?
I would think that something more solid would have be a better way to go when the boat was build.
Cheers
Reiner

[sdowney717]

Balsa is a soft wood. Why not get some Pressure treated deck boards or dimensional lumber? Pick out tight grained pieces.
That would have to be better than something that will rot.
IPE is a very strong heavy hard wood or a white oak, neither will rot for a long time. Red oak or Ash, both common hardwoods will rot in a few year if it gets wet.
I also use a lot of PL premium polyurethane construction adhesive which is waterproof.

[Beersmith]

If you have the patience for it, I would build up solid glass right there.

[mitiempo]

I agree - solid glass is best. You could buy some G10 of the correct thickness instead of laminating to that thickness. I would use epoxy.

[minaret]

+1 for G10. The only way to go for this.

[perchance]

I just redid mine and removed the rotten balsa and replaced it by casting it in west epoxy mixed with west 404. The area in question was about 4x6x3/8. the actual step is a raised section of marine ply which I replaced with same after sealing all surfaces with straight epoxy resin and built it up using layers of glass mat. The boat is a 1975 so the repair should outlast me. I have a few dodgy stanchion bases that will get the epoxy 404 treatment.

[reiner]

I didn't know G10 fibreglass boards, I have to find out where to get them here in OZ. Looks like a smart way to go.
Thanks for your replies. What would we do without the Cruisers Forum.

Cheers
Reiner

[mitiempo]

If you can't find G10 locally it can be made easily.

[foggysail]

For those who have never worked with G10, you will have a quick learning experience. The stuff even growls at you. Good stuff but a bitch to work.

Foggy

[minaret]

Originally Posted by mitiempo

If you can't find G10 locally it can be made easily.

I build a lot of fiberglass flat stock, but no you can't make G10 at home. G10 is compressed in hyrdaulic press mold while it's still a wet laminate, at about 60k lbs. force if I remember correctly. This means the resin/fiber ratio is down around 30%, even lower than the best vacuum bag can make. You cannot reproduce this in a non-industrial setting. For high strength plate G10 is the way to go. In this case I agree that any flat stock would be more than strong enough, but there is a big difference between the two.

[mitiempo]

I didn't mean you could make G10 but you can lay up a panel that is plenty strong enough.

[roverhi]

Any non compressible core will do. You could even use 'starboard' as the core for that small a patch. Are you sure it's balsa core, btw. I doubt that any boat builder would use Balsa Core where it would be subject to compression by the mast. SOP was to use plywood core in the mast area.

[mitiempo]

Not much sticks to Starboard - no sealant that I know of nor epoxy. If the skins aren't bonded to the Starboard it couldn't be structural.

Plywood - although not the best choice - would be better than Starboard.

[Celestialsailor]

I would use G 10 with Epoxy/Cabosil/Mill fiber slurry. A little slurry at a time so no heat is produced.
McMaster-Carr has G 10. Hope this helps

[daddle]

Balsa core is is very incompressible. The problem was the leak not the material. I tend to respect the original designers choice and would replace with the same by removing an inner or outer skin and rebuilding appropriately.