Wet Plywood backing board on my Through the hull

[drysuit2]

I finally went out on Seque Wednesday evening. Instead of sailing ...I spent my 3 hours scrubbing the bird crap for the cormorant , seagull, or osprey that has taken up residence on deck. Checked my bilge pump, and she is still working after the deep cycle sat onboard all winter with a solar trickle charger.

When I checked my sea cock I noticed that the plywood backing board was wet.
This could just be age
It could be that I stored her on the hard vs the water this winter. So maybe she dried out and is just now getting moist and expanding again.

I noticed a little evidence of weeping on the bronze seacock. But not that much. I'll use some lapping compound and see if it's the sea cock, or the bond between the hull / plywood/ and, or /sea cock.

What should I look for?

I'm fearful of poking it with an awl or something in case it is really soft or rotten.
My guess is with all the snow, and not being properly covered I had some fresh water intrusion this winter. [Some of the cushions were wet.]

So how would you handle this?

Short of having her hauled and replacing the ply. I'm going to try and let her dry out today. See if I can assess the situation better.

What should I look for?

Would you use ,"Git Rot", or "Captain Tolley's" penetrating epoxy? or maybe wrap the disk , in place, with some west system and glass tape?

I am not sure how to tell if the Plywood is just surface wet from weeping, humidity, or a leak. And now that it is wet...maybe the swelling is OK, and what's sealing everything up.

I'm willing to listen to ideas? and I obviously do not want to haul her till fall.

Thanks for the suggestions...

[Anthony P. Jeske]

Hi Frank:

Search "thru hull backing" on this website. You'll find lots of answers.

Good Luck,

Tony Jeske

[Steve Laume]

I would poke it with an awl to see if it is soft. The area around the fasteners would be of particular concern. If it is just wet then it isn't a problem. Do not start covering it with any sort of glass or epoxy as it will not add any strength to where it is needed and will only mask or make the problem worse by trapping moisture in the plywood. If you are feeling particularly brave, you could put a foam plug in the through hull and service the seacock while the boat is in the water. You will have to live with the backing plate until you are hauled again. You really need to determine if the backing plate is soft to gain some peace of mind. I doubt if it is very serious if you just started to notice it being wet, Steve.

[Paul D.]

Always poke with an awl or swiss army knife. You may not like the results but you will have a line of sight reality on the issue.

[drysuit2]

Steve,
I had more time to inspect it today. Plus I had a friend, my Club Steward actually, look at it.
Looks like I’m in luck. The water seems to be coming from. The sea cock itself.
I’ll take some lapping compound to it next time I’m out. I’ve done it in the water before. The bilge pump keeps up.

Should make it through the season but I will have to replace the backing plywood this winter.

But I and my friend agree with you about not trying to epoxy or tighten the actual through the hull fasteners. Though I may put a few dollop of 4200 in some strategic spots. And I’ll definitely keep some cone dowel s close at hand.

Thank you guys for your help.

[jbenagh]

And I’ll definitely keep some cone dowel s close at hand

Don't get too comfortable with the idea those will help with backing plates. When mine failed, it allowed water to enter behind the thru-hull and enter the boat between the hull and the backer plate.

When I replaced all seven the next winter, at least two others showed signs of impending failure where the adhesive had failed.

I've noticed that nearly all the original adhesive on the boat is giving up around the same time. The backing plate failure was '15, the companionway teak began to fail in '16, speed sender in '18 and most of the deck fittings now need rebedding. I think maybe it just has a 30 year lifetime.

Jeff

[drysuit2]

Thank you all,
For letting me see this potential problem through another set of eyes than my own.

[steve poulin]

Having just replaced the backing board of my port side scupper (following the excellent advice on these boards), I too was alarmed at the condition of the decades old marine plywood. I will be replacing the remaining ones next haul. On that note, I discovered quite by accident that the small end of this $9.95 Home Depot tool fits perfectly the external flange of the 1 1/2 Spartan seacocks:

https://www.homedepot.com/p/Husky-Doubl ... /304217585

Steve

[fmueller]

Frank,

I'm not understanding how you lap the seacocks with the boat in the water ? "the bilge pump keeps up" !!!

Also, consider using G10 instead of plywood, which you epoxy into place - if you replace backing plates.

Stronger, by far, than plywood, and will never rot. In fact you can tap it and avoid having the thru hull screws.

cheers Fred

scupper thru hull before tapping G10 plate

44 Jerezana refit @ Carbon Ocean Yachts.jpg

[Bill Goldsmith]

Those plywood backing plates were never meant to last forever. On Loonsong, I have replaced 5 of the six seacock backing plates with G10 (head in/out; head sink drain; galley sink drain, holding tank out), as they were all soft. I also replaced the speed impeller through hull backing plate in the bilge. Oddly, the one plate that sees the most water go by it (but not on it) is still dry and solid--the engine intake. I do poke it every spring to gauge its health.

Combining bronze seacocks and FRP backing plates epoxied in place makes for a much sounder installation than plywood (or any wood).