Replace Balsa core with coosaboard/ fg roving?

[jholovacs]

I was replacing my windlass which had exploded on me about 6 months ago. undid the bolts, wedged it off the deck... found that some of the holes were completely waterlogged; black water just oozing from the balsa core. Well, crap.

So I'm going to be fixing leaks (I have some large holes to fill in too, it's a different windlass than my previous, the hole locations are different) and filling holes, and I thought to myself, do I need to replace this with balsa? I have plenty of 6oz roving and a sheet of 1/2" coosaboard, either one seems like it would be a better option... but would it?

Strengthwise, can I replace the ripped out balsa core with coosa or fg roving without issue?

[Chotu]

Sort of. But ultimately, there will be a stress riser between the Coosa and existing balsa. I’m imagining the moment where you actually rip the winless straight out of the deck. It will rip where the Coosa and balsa come together. If it were all balsa you would probably get a more uniform bend to the deck without a stress riser.

That’s just the extreme situation. I like to think of those. I doubt you will be tearing your windlass out of the deck, so the Coosa will remain more solid than the rotted balsa ever was. You’re good to go.

[rslifkin]

A large enough backing plate to extend beyond the transition in core material would help with that potential strength concern, I think.

[SVHarmonie]

You do not need to replace it with balsa.

On boats with a premium build, and there are way too few of those in the world, the area under the windlass would have been sold glass in the first place so feel free to go there.

If the damaged area is large enough to need core replacement, use whatever works best for you. If you seal it up and exclude water 100% balsa is good. But any of the foam products would work as well. Just match up thickness as close as you can.

There is NO rational for a "stress riser" where one type of core meets another. If you have ever seen ready to install balsa core it is made of littles squares of wood held together for assembly by gauze. It is not one piece. The loading on the core is 100% shear. There is no place for "stress risers" in such a case.

[Differentroads]

I've had to do similar under my windlass and my foredeck cleats recently for similar reasons (there's a special place in hell for people who use silicone as a sealant).
I cut out the underdeck under my windlass, fitted in a piece of good quality ply shaped to the curve of the deck, bonded it in place with lots of thickened epoxy and then four layers of biaxial mat. I couldn't get at the underside of the cleat so had to chop out the upper deck to replace the ply core with good ply and then mat over it.
Elsewhere hat I've found soft core I've taken less drastic action (allen key in my drill to rip out 12mm or so of core, backfill with epoxy). But anywhere with such severe stressing, best not do half a job in my book.

[phillw]

Originally Posted by jholovacs

I was replacing my windlass which had exploded on me about 6 months ago. undid the bolts, wedged it off the deck... found that some of the holes were completely waterlogged; black water just oozing from the balsa core. Well, crap.

So I'm going to be fixing leaks (I have some large holes to fill in too, it's a different windlass than my previous, the hole locations are different) and filling holes, and I thought to myself, do I need to replace this with balsa? I have plenty of 6oz roving and a sheet of 1/2" coosaboard, either one seems like it would be a better option... but would it?

Strengthwise, can I replace the ripped out balsa core with coosa or fg roving without issue?

I know nothing about coosaboard. I am currently building a schionning cat out of balsa. The fact that the area under the winch was not decored is alarming. You should not have any cored material underneath a windlass or winch. The correct process should be to

Decore the area around and underneath leaving the bottom fibreglass skin in place. I would decore at least 100mm radius around the windlass. If the area is wet let it dry out and if the water damage extends past the area require for the pad you will need to either extend the ply pad or replace that area with more balsa or deck material of your choosing.

Glue marine ply base in the decored area to the thickness of the balsa core and glass with 2 layers of 460gsm double bias making sure the first layer extends 150mm outside the ply base and the second layer 100mm.

You then need to place a backing plate under the deck and glass it in with 2 layers of d/b.

You can substitute aluminium or solid glass in place of the ply for the steps above as some people do not like ply.

The secret is to oversize the bolt holes for the windlass, fill the holes with epoxy glue mix (West 403) and redrill the holes into the epoxy.

Sounds like a lot of work but it is not. If the area you are decoring straddles any bulkheads under the deck just run the glass down the vertical side of the bulkhead. Hope this helps.