Rot in my battery compartment

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ChrisMKingBerkeley
Bottom Sanding Grunt
Posts: 3
Joined: Sat Aug 27, 2011 11:25 pm
Boat Name: Puffin
Boat Type: Alden 44

Rot in my battery compartment

Post by ChrisMKingBerkeley »

I sail a 1978 Alden 44. This boat has two pilot berths in the aft cabin. Under each berth is a fuel tank and an area for batteries. The other day I was checking the fluid level in my batteries when I noticed the battery was not level. In fact I could push on it and it would move up and down slightly. Hmm... I pulled everything out and removed the floor of the compartment and sure enough, rot.

Things brings up lots of questions.

This is the only place in the boat that shows any signs of rot. It seems dampish under the compartment floor but there are no signs of damp anywhere nearby. Could it be that that something about the battery fumes causes rot?

The compartment floor of the compartment is marine ply covered with a thin covering. It is about 1/8 thick. It looks like chopped strand mat in epoxy but it doesn't look like it was molded but cut from a sheet. Is there some sheet product that looks like this?

The inboard side of the compartment is ply with a nicely finished mahogany veneer. Unfortunately it shows signs of rot and yet it would be a huge chore to replace. I'm tempted to try treating it with penetrating epoxy. What chance does this have of working?

The floor was originally supported by a framework that I think is douglas fir (or was before it rotted). It turns out I have some oak and poplar that would fit well. Are there pros and cons to using different wood species in this sort of application?

The original floor supports were not coated at all. Should I coat this stuff in epoxy or is that overkill? Would paint make things less rot prone?

Thanks
Chris
Quetzalsailor
Master of the Arcane
Posts: 1100
Joined: Fri Aug 26, 2005 9:53 am
Boat Name: Quetzal
Boat Type: LeComte North East 38
Location: Philadelphia, PA

Re: Rot in my battery compartment

Post by Quetzalsailor »

We have a 1970 LeComte NorthEast 38. Batteries were in a 'glassed plywood box under the sole and over the fuel tank. Some PO noticed rot/deterioration and filled the space between the box and the tank with Home Despot-type urethane foam. Only the box bottom and lower sides were affected. Naturally, trapping water and/or battery acid only made the problem worse. I moved the batteries from over the tank to the lazarettes. (Bill Tripp naturally put the weight down low and central.)

Normally a charging lead-acid battery only vents hydrogen gas; an over-charged or boiling battery will spray a bit of acid out the vents. Thus the attention given to corrosion on battery posts, and the rusty battery shelf in your older car. Battery acid attacks wood; the damage looks like dry rot. Battery acid does not seem (to my observation) to attack polyester resin; it does attack epoxy resin.

I think you can simply rebuild what was original w/o undue coating-out but with a 'simple' modification: buy a couple cheapie plastic marine battery boxes and arrange the new supports to accommodate the additional space they'll take up. I would not use wood that is not a traditional boat-building species. Certainly Poplar is pretty poor in rot resistance and the damp of under a boat sole would be a bad place for it. I have used Red Oak for a sole joist, but this piece did not land on the fiberglass. That said, I've used a fair amount of Home Despot's best Red Chinese cheap plywood for backing boards and battery shelves. I coated that stuff with epoxy and it's been fine for about 7 years so far.
Carl-A259
Master Varnisher
Posts: 104
Joined: Fri Jan 15, 2010 3:07 am
Boat Name: Romper
Boat Type: Pearson Triton hull705
Location: Georgia

Re: Rot in my battery compartment

Post by Carl-A259 »

Batteries have an uncanny ability to attract moisture/ condensation (sweat). Are your batteries in a plastic battery box? After rebuilding the wood go with a battery box to encase the batteries.
Tallystick
Skilled Systems Installer
Posts: 177
Joined: Fri Sep 09, 2011 10:54 am
Boat Name: Nostalgia
Boat Type: Pearson Triton Yawl

Re: Rot in my battery compartment

Post by Tallystick »

Sulfuric acid is hygroscopic, so if any battery acid fumes escape, the small amount of acid coating the enclosure could attract moisture.
sscoll
Master Varnisher
Posts: 116
Joined: Fri Sep 25, 2009 8:26 am
Boat Name: Medora Jane
Boat Type: Pearson Triton #532 E.C.
Location: Wisconsin

Re: Rot in my battery compartment

Post by sscoll »

Poplar is excellent in dry locations. It dissolves when wet.
ChrisMKingBerkeley
Bottom Sanding Grunt
Posts: 3
Joined: Sat Aug 27, 2011 11:25 pm
Boat Name: Puffin
Boat Type: Alden 44

Re: Rot in my battery compartment

Post by ChrisMKingBerkeley »

My batteries were in boxes, but the boxes had no lids. Also I think my battery charger is relatively aggressive. It seems like I have to top off the batteries pretty often. So it sounds like battery acid fumes were definitely a issue.

Here is where I am so far in my repair work. I have pulled out all the old wood work in the battery compartment. I treated the back or the visible veneered panel with penetrating epoxy sealer. I don't have sky high hopes for this stuff. I can see how maybe it helps it you soak the wood in it. In may case I had a vertical panel and I brushed it on. I probably didn't wait long enough for it to dry out. I gave it a couple of days with a low level heater and a couple of hours with a more aggressive one. I get the impression for this stuff to do anything substantial you need to dry stuff out for weeks.

I have build all new wood work from douglas fir and coated everything with epoxy. The floor of the battery compartment is supported by a couple of beams that were just screwed into the panel I mentioned above. I don't trust that panel to support the weight anymore so I plan to add reinforcements.

Tomorrow I can start reassembling with new battery boxes with covers and proper tie downs. I will have to modify the wiring some what. The existing wiring won't go up under the covers.
Zach
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Re: Rot in my battery compartment

Post by Zach »

Remove the untrustworthy rotten wood from your support panel and build it back to about the same scale that it was. It worked well for this long. If you leave rotten wood, it has a tendency to spread as it is alive... fungus and spores that like to eat the next piece of wood.

A layer or two of fiberglass is a good thing over your resin coated wood.

If you dent the resin coated wood hard enough to expose a way for moisture to get in, it has no way out. (Epoxy works as a barrier coat from both directions!)
Douglas fir, is easy to dent. Don't paint directly under the battery if you choose not to glass it, and inspect when you have the battery out for any black spots where the epoxy is compromised.

I would have gone for marine grade plywood and fiberglass cloth. 3/4 bottom and 1/2 inch sides.

Look into a smart(er) battery charger if yours is boiling your batteries. Some are very dumb, and the dumbest of them like to catch on fire when their voltage sensing circuit fries and they stay set to charge.

Zach
1961 Pearson Triton
http://pylasteki.blogspot.com/
1942 Coast Guard Cutter - Rebuild
http://83footernoel.blogspot.com/
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