What to mount a new water heater on

[helm]

Our old Atlantic Marine water heater is finally leaking. Replacement will be a quick 12 gallon all stainless water heater.
The Atlantic marine water heater is mounted on 2 rails molded into our fiberglass holding tank, which was all designed for that specific water heater.
So I will need to mount the new water heater on some type of support, that would then be bolted to the existing rails. I don’t want to use a plywood sheet because of the future rot issue, but was leaning towards a 24x24 sheet of 3/8 starboard or maybe a similar piece of Coosa board.

The full weight of the water heater will be on whatever support I have underneath, starboard or coosa. My only concern with the starboard is it sagging over time. Let me know your thoughts
Thanks
Eric

 

[rslifkin]

I wouldn't be too afraid of plywood in that application. My water heater is mounted to a sheet of marine plywood bridging the top of 2 stringers. 38 years later the plywood is still in perfectly good shape. Basically, as long as it's not in a location where it's likely to get wet regularly (or worse, stay wet) it will last a long time.

 

[psneeld]

A properly painted or resin coated piece of plywood that doesn't sit in water and the fasteners properly sealed, will last as long as the heater lasts. It's usually the heater leaking that rots what it is fastened to.

Your call but plywood would me my goto for price and convenience.

 

[tiltrider1]

What’s cheaper, plywood + paint or starboard. Both will be satisfactory.

 

[TJM]

I am not a fan of starboard in structural uses over time, sagging is an issue.
I would use Marine rated plywood, sand all of the edges round, drill your thru bolted holes and encapsulate it in resin , paint it to make it match the hull. Thru bolting is better than threading in wood screws.

 

[Comodave]

I agree that Starboard isn’t a good choice here. I would use a 3/4” plywood sheet and seal it with epoxy resin. Then paint it and you will be good almost forever if it isn’t sitting in water.

 

[helm]

Thanks Gentleman
My concern with starboard was that it might sag over time. I’ll go the marine plywood approach. Thanks again very much for the guidance!
Eric

 

[Comodave]

For an application like this you don’t really need marine plywood. Exterior plywood will do just fine and at a much lower cost. Marine plywood has no voids but if there is a void under the water heater that would not make much difference.

 

[Delta Riverat]

Yup, that's what I do, exterior 3/4" and I put a coat or 2 of paint on it.

Marine plywood is brutally expensive.

 

[rgano]

Everybody keeps restating the "encapsulate-in-Epoxy-resin" refrain, but more specifically, I encourage saturating wood in Clear Penetrating Epoxy Sealer (CPES) because unlike simple resin which forms a crackable layer over the surface with little penetration, CPES has a long cure time enabling it to get deep into the wood fibers and do a better job of sealing the wood. I coated the entire wooden underbody of my Grand Bank 42 with it years ago with great, long-lasting results.

 

[SIBERNUT]

There's another thing to consider, how long will you keep the boat.
Guy tried to sell me Trex decking, 20 yrs warranty. I'm 78............

 

[rgano]

There's another thing to consider, how long will you keep the boat.
Guy tried to sell me Trex decking, 20 yrs warranty. I'm 78............

Ah, but think to the curb appeal of that XX-year warranty left on it when you sell.

 

[Marco Flamingo]

Regular plywood. Cut it out and paint lightly with your used crankcase oil. Set in the sun until all the oil is absorbed. Sounds awful but I helped an old shrimper captain do this decades ago. The boat has probably rotted away, but that ER shelf is likely still okay. Odd as it sounds, I would guess that it is more environmentally friendly than Starboard.

 

[rgano]

Regular plywood. Cut it out and paint lightly with your used crankcase oil. Set in the sun until all the oil is absorbed. Sounds awful but I helped an old shrimper captain do this decades ago. The boat has probably rotted away, but that ER shelf is likely still okay. Odd as it sounds, I would guess that it is more environmentally friendly than Starboard.

I'd be afraid of the smell as the water heater warms the board. Then there's the added fuel if a fire broke out nearby. If a water seep developed that passed over this board soaked in motor oil, what then? A sheen on your bilge water. I'm just spit-balling here.

 

[Steve DAntonio]

Exterior ply, cut and drill holes, sand, chamfer edges, a coat of primer and a top coat of enamel and you'll never give it another thought, it's done all the time on high end new vessels. Definitely not Starboard, it's terrible for structural projects and too heavy for the poor stiffness it provides.