Marine or CCA treated wood?

[BuzzChamp]

I had to replace my bildge pump this week, in the process I had to pull the batteries and oil tank to get to the bildge pump. The board that the 2 TM batteries, 1 starter battery & oil tank sit on was very rotted and is falling apart. I'm wanting to replace the board!

What type of wood should I use for this? I can get my hands on today CCA treated 1/2 plywood or wait until next week for Marine grade 1/2 inch and pay $80.00.

The old board is 1 1/4 inch thick. Do I need to replace with 1 1/4 inch board?
Can I enlarge the new board some? Make it 8 inch longer, it will be about 2 inches from the back of the boat!

[BASSCAT7]

You can replace it with standard plywood that you treat with resin. Anything wood that is in the bilge should be waterpoofed with resin first or the moisture in there will start to rot the new wood also.

You cannot use treated wood as the resin will not react well with it.

Standard or marine grade ( void free ) plywood is fine. Put 3- 4 coats of resin on the entire piece of wood to keep it from rotting.

What size is the board in there now ?

[northrivergeek]

Are you talking about a removable battery tray or the back floor ? If its the floor .. you prob have rotted floor all the way up under the rear deck, generally the transom and stringers are rotted as well or have rot.
The rear floor battery areas 99% of the time go up under your rear deck and can go all the way to the front cockpit.. under that floor section is flotation foam, that holds the foam in place if the boat ever sinks or starts to sink.

Most boats that have that area rotted out is because screws are used to hold oil tanks and battery box straps with out being properly sealed, and even when sealed over time water will enter the wood around a screw.
I always epoxy micarta blocks about 2 inch thick for screw blocks taping the micarta for screws. Micarta is a epoxy resin fiberglass material used for circuit boards and other electrical items such as insulator boards in industrial electrical breaker boxes.
This way the water never enters the floor again, after repairing the floor section.

As far as the wood .. marine grade is not needed.. nor was it originally made with marine grade.. they used exterior plywood covered with polyester resin and fiberglass cloth and or fiberglass 1.5 oz mat usually mat 2 or 3 layers thick.
If you want a more permanent fix use epoxy resin and epoxy cloth instead of polyester resin.. dont use pressure treated.. the resin wont stick to it properly and it will peel loose soon after it cures.

Of course you could also use micarta sheets to replace the floor sections, as well as coosa board, and several other composite decking materials .. but wood is the most cost effective.. you will still have to use fiberglass and resin even with the other materials as well

[RipNLips]

If it is what I am thinking he is talking about it is just a sheet of plywood cut in the shape of a T that holds 3 batteries and an oil tank. I am working on a 89 champion and pulled the tray out and it was rotted. It just lays on the floor of the boat. So you can have rot without it affecting the transom or stringers.

[northrivergeek]

Yes in that case you would be ok from rot on the rest of the wood .. maybe .. Id replace it with a non wood material even Aluminum Plate like diamond plate scrap 1/4" cut to fit .. no more rot on that tray

[BuzzChamp]

Yes, the 'T' shape plywood holding the batteries & oil tank.

I went with CCA treated plywood coated 2 time with risin. Thanks for the help.

[bighaida]

I made the T a two piece unit. I straight piece for the batteries and I piece for the starting battery and oil tank. I don't have to remove every battery to get to my bilge and areator.
I had some oak and put Rhino liner on both pieces.