San Juan 24 floor re-core

[Peter]

Well, it looks like I'm going to have to join the legions of amateur recorers out there. I discovered wet balsa in the floor of my San Juan 24.

WET AREA

For those of you unfamiliar with the boat, there is a section of cored hull on the starboard side of the keel attachment to strengthen the hull. The port side is adequately supported by the dinette and locker bulkheads and liner. The coring extends sideways from the 'bilge' to the edge of the galley, and bow to stern from the raised floor in the head, aft to about 6" behind the rear cabin bulkhead: a section about 2 feet by 6 feet overall.

This is a common problem area on these boats, and if let go too long, allows the keel to waggle to such an extent that the fairing at the hull-keel joint cracks and falls out, not to mention giving the boat interesting sailing characteristics.

A few 2" holes through the inner layer of glass revealed wet and rotten core material in the forward 4 feet of the floor, so I have cut that section out, back to the area of solid dry balsa coring.
After the initial cleanup it looks pretty good.

CLEANED FLOOR

As usual I'm wrestling with finding the best way to fix this. My intention is to put it back the way it was, as that lasted over 30 years and only failed because of water intrusion.
I can't re-use the old piece of glass floor as it came apart where the core was undamaged. Boy, that stuff was stuck on there really well!

ROTTED FLOOR SECTION

For the small area I have to repair (2 feet by 4 feet) I've decided to use strips of 3/8" plywood 2 1/2" wide glued lengthways fore and aft with thickened epoxy as an adhesive.

PROPOSED NEW CORE

and braced from the cabin top while the epoxy sets.

BRACING DRY RUN

Covering this, I plan to use 2 layers of 18 oz woven roving, one layer at 45 degrees to the other, then a layer of 9 oz cloth as a finish layer. The roving and cloth will overlap the surrounding floors as much as possible for a strong joint.

I suspect the repair will be stronger than the original floor ... at least I hope it will. I'm using a Canadian epoxy called "Cold Cure" which is useable down to about 36 degrees F. Even so, I'm going to wait for some 50 degree weather to do the job, and maybe provide a bit of additional heat to help the curing process.

I haven't gone beyond the prep stages yet, and am interested in ideas and opinions from my fellow forumites on my repair method.

[Tim]

The repair idea looks fine to me. It's probably worth it to seal each strip of plywood in epoxy before installation as an added barrier to moisture infiltration. Use lots of thickened epoxy to secure the plywood, and fill all seams and gaps as much as you can. You're actually recoring a section of the hull, not just a sole. Your new repair will be substantially stiffer and stronger than the original.

In case the question arises, I recently read that epoxy-coated wood can be successfully bent without damage to the epoxy coating.

Can I apply mixed epoxy to a piece of wood and then bend it without cracking the epoxy?
Yes, while the cured epoxy may be stiffer than an equal thickness of wood, the epoxy coating is much thinner and can be bent further than the wood it coats without cracking.

However, also be sure to address--and repair--the leaks that caused the damage in the first place. It looked like the keel-hull joint was leaking, probably through the keel bolt holes? Sounds like time to drop the keel and rebed. Before proceeding with the core repair, see whether it makes sense to address the keel issue first.

Good luck on the repairs!

[dasein668]

RE: Epoxy flexibility

Yes, a thin coat of epoxy is actually quite flexible. At one of the boat shows, the West rep had a thin strip of wood which was painted with a sealer coat of epoxy. He could tie the wood in a knot without cracking the epoxy.

[Peter]

Ahhh ... just the kind of advice I was looking for. The hull-keel joint appears to be good, on the outside. After I removed the bottom paint I raised the boat off the keel and tried to move it laterally to see if any cracks showed up. Looked good. The dark marks are where I got a little too ambitious with the sander.


Re-examining the interior joint after reading Tim's comments I can see that water could migrate from the bilge to the coring.

I'm going to end the new coring just shy of the joint and fill the rest with thickened epoxy, isolating the floor core area from the keel cavity. Then I'll run a reinforcing strip about 4" wide along the whole joint.

My next project (today) is to drill a few small holes in the bilge looking for any more moisture. My other thought is to remove, caulk and re-torque the keel nuts one at a time.
After spending all of last year on dry land I'm not in the mood to pull off the keel ... yet. I'm going sailing this spring, leaky keel or not :)

[Tim]

Complete isolation of any coring from the keel sump area should help prevent future core problems. However, it would be prudent to add the keel rebedding project to your list for a future season, after you've had time to enjoy the boat for a while! Water is insidious and makes its way to places one would never imagine, even when no obvious means of transfer exists.

Good luck!

[Peter]

Tim. I found the (hopefully only) source of water intrusion. (See above close-up photo on the rightside). The layer of glass layed on top of the coring was folded over the edge of the shallow bilge and glassed in.

In the picture I had cut along the bend in this layer, planning on leaving the part extending down into the bilge in. Today I drove a chisel between the layer and the bilge side and half the works popped right off. The rest of it came off with very little resistance. Any water sitting in the bilge was free to work it's way up through to the balsa coring, past the partially sealed coring top.

[Tim]

If you spend some time smoothing that transitional area (it looks pretty rough as originally built), you should be able to successfully reglass with watertight integrity.

The best way to learn how to build a boat is to discover all the wrong ways to do it by tearing apart old boats (and there are many, many wrongs on our beloved plastic classics...). Once you eliminate the wrongs, figuring out the right way is pretty easy!

[Peter]

The dirty deed is done ... and went a lot better than expected. A little more fairing, as Tim suggested, glued in the new pieces with thickened epoxy, then 2 layers of heavy woven roving, and sealed the edge in the bilge with thickened epoxy and a layer of cloth ... all covered with another coat of unthickend epoxy, and capped with a new bilge cover (yet to be painted)


Now to get on with the fun stuff: fairing the old non-skid decks and cabin top :)