Temporary repair to through-hull backing plate

[anchorbend]

Saw this but I have no experience with it

https://www.amazon.com/Stay-Afloat/d...08S3PRF4&psc=1

[Jolly Roger]

Take a look at this neat little product from England, which I sell from North Carolina.
SEA STOPPER (schooner-britannia.com)
The article is self-explanatory, but the stopper certainly works and enables you to remove not only a seacock but also the nut securing the through-hull. I have done this in the water to replace a damaged seacock.
It’s also possible, if you are careful, to replace or strengthen the ply backing plate.

[adjo]

From the looks of it the plywood is not "rotting" but "delignifying" due to alkaline salts concentrating by evaporation. The alkaline salts (sodium hydroxide) are formed at the cathode (bronze skin fitting) due to electrolysis or galvanic corrosion.

The first thing to do is wash away the sodium hydroxide with plenty of warm fresh water and then swab the plywood with vinegar to help neutralise the residue. This will slow down the deterioration of the plywood. Litmus paper is useful but not necessary.

You could then dry the area and try to epoxy saturate the plywood (Everdure or equivalent) but this is unlikely to be very successful. Better to remove the skin fitting asap and replace the backing plate with a good FRP one.

[RaymondR]

Since the penetration is not in use I would make it as short as possible so there's no leverage and leave it alone until you put the boat on the slip. The backing plate is there to reinforce the penetration in case lateral forces, such as what would occur if an attached hose was pulled on. are applied. However drying it out and epoxy saturating the plywood would provide increased peace of mind.

[Kd9truck]

You could clean that up with a battery drill grass grinding wheel, the backing plate is steel no?

[Kd9truck]

You could clean that up with a battery drill brass brush grinding wheel, the backing plate is steel no? I re-seated my stanchions and backing plates with white Sikaflex 291, after grinding off the rust and then I painted 3 coats of white oil base (rustoleum ).

[AKA-None]

Going back on what I said earlier
If it’s not all dry and crumbly you could just leave it be as any futzing around could make a problem that doesn’t currently exist

[Noahr]

Stick a plug in from the outside. Clean inside and slather with Splash Zone epoxy? It should dry, but it will be an added mess to remove later and clean-up once hauled.

[Cheechako]

Yeah, I would just leave it alone for now and watch it. You cant really fix the wood and will be sealing moisture into it. Most thru hull fittings are sealed to the hull itself pretty well with the sealant.

I can think of schemes of fixing it without haulout, but of course they involve risk without a yard nearby. But minimal risk in my opinion.

With someone there to help you:
- Make sure the fitting stays in place by having the helper hold it up against the hull by holding it from inside the boat.
-Carefully loosen the nut and gouge/scrape/chisel all the rotten wood out. Hold the fitting with a pipe wrench if the nut does not loosen easily.
-Smooth the debris off the fiberglass.
-Put some 5200 around the threads.
-Simply tighten the nut onto the fiberglass hull. It will be fine, you cont need a backing plate that is just a capped through hull fitting.
-Your helper is there to simply make sure the fitting stays in place against the hull. It's likely the fitting is held tight against the hull with the original sealant, but you want to make sure. Every through hull fitting I have ever taken out I had to drive out with a hammer or etc.

PS: if the cap comes off the fitting easily, you could actually replace the backing plate this way if you premade it. Remove cap, remove nut, remove the old backing plate, caulk, install the new backing plate, nut and cap.

[Happ]

Originally Posted by TCL

I need to replace this (unused, capped) BTW through-hull; the backing plate is deteriorating and obviously has evidence of moisture.

As a **temporary** repair until I can get to the boat yard and haul out (preferred yard is about 90-95 nm away), I'm thinking of covering the backing plate with thickened epoxy resin. Someone suggested 5200, but I'm inclined to go with epoxy.

Have regular West System and a variety of hardener. Wondering whether I should get G-Flex.

I know that ideally all surfaces should be really clean, but I'm worried about causing some critical damage in trying to clean. I'll likely at least put a heat gun on low to remove any moisture.

Any opinions or suggestions would be greatly appreciated.

Use G10. Put it in and forget about it.

[Rumrace]

Lexel clear one large chalk tube. No worries. Available on line Home Depot. Stuff is amazing. You’ll need to cut it off with sharp knife. Cures soaking wet

[Sailmonkey]

I vote don’t touch it.

If it’s not running water now, it’ll likely last a month or two until you haul. It’s not going to suddenly catastrophically fail.

[Rumrace]

IIve used Lexel underwater to seal a friends stern drive cable leak. We couldn’t get good access on the inside behind the power steering arms. About an Oz glob and he was good to go. His bilge pumps were loosing the battle. So no worries to go under the hull and apply a coat

[bstreep]

When we had our thruhulls replaced a couple of years ago, upon the advice of our surveyor (who is VERY well known), it was suggested that since we have a very thick solid hull, to eliminate the backing plates. So we did.

However, in your case, I think I'd just leave it. People freak out about holes in the boat. I've twice drilled holes in a boat for thruhulls, while the boat was still in the water. Freakish? Sure. But it's a piece of cake. A gallon or 2 of water. The heel of a foot, or a rag in a hand over the hull stops the leak.

[Rumrace]

That was a great read. Thank you.
Is your marine surveyor well known cause he’s on the list of licensed marine surveyors, or out spoken and talks like Noah or Popeye. The Noah type are my favourite.

Some through hulls require a board. It’s suppose the eventually crush. Nylon may last longer. PEEK likely a like time. But the lame fibreglass boards are popular.better than slowly Embedding a bolt in the hull. If you don’t have bronze flanged ballcocks then you don’t need them as there is no benefit.

Drilling a hole under the water line should have been filmed. Sounds fun.