Building a shelf

[BCBertie]

I have a small boat (C-Dory 16) that's pretty tail-heavy, so I want to move the batteries from the stern to up under the v-berth. I need to build a shelf to give the batteries something flat to sit on, but I don't want to just glass in a piece of plywood bridging the keel valley (if that makes sense). I think that would just create stress risers on the hull.

I'm wondering if there is any technique that would allow me to build a plug that conforms to the inner hull shape - maybe putting a horizontal dam and using self-leveling compound, letting it dry, and then making a mold and part from that, or would a fiberglass shelf with foam injected be strong and supportive enough, or...

I got no clue, but I'm pretty sure some of you have done something like this before! Help!

Please?

Cheers!

John

[Peter]

Why not just glass a couple of pieces of ply flat against the hull where either end of the shelf would sit? This would distribute the loads to the hull skin and avoid creating stress risers or cracks at that point.

Furthermore you could then just add a "land" or "cleat" (not the sort that you tie a line to, but a piece of slightly protruding structure to support the shelf) to each ply patch on the hull and actually make the shelf removable. If you then put oversize holes in the shelf, and screw down through them into the cleats using large washers it would allow some movement as the hull works and thus not transmit nasty forces to the hull skin, plus you can get it out to get under it to clean out or inspect the bilges.

Now the shelf cleats should have a provision at the forward end in particular, but hopefully at both ends so that it can't slide fore-and-aft. In most boats stuff tends to shift forward when running in seas. You want these forces to be taken by a hard- stop, not the loose-fit tie down screws. Don't ttry to make everything fit too perfectly. Give yourself a little extra room, like maybe 1/8 inch to 1/4 inch, so stuff goes in and out easily. This is a battery shelf, not a paneled living room!

Built in this manner gravity would probably hold the shelf in with no fasterners at all, but you need something so that in nasty situations the batteries don't come free and start crashing about. You also need to use battery boxes of some sort (either the sort you buy or ones you build yourself) to contain any spills from cracked batteries etc. And don't neglect tie-downs for the batteries themselves.

I'm a big believer in the KISS method: Keep It Simple, Stupid!

Peter

[BCBertie]

Thanks, Peter!

I'm thinking that with the kind of surface area the two pieces against the hull would have, I could just use 3M 4000 or 4200 to retain them. Then the connection would be flexible and removable with no holes into the hull... in case some future owner wanted it as original.

You're a lifesaver. Although as soon as I read your reply I thought "Duh!", it's clear I wasn't gonna come up with it on my own!

John

[Peter]

as soon as I read your reply I thought "Duh!", ....

That is what this board is for. Exchange of ideas.

The only dumb questions are the ones that don't get asked.

BTW don't neglect to provide some ventilation for the batteries. You don't need much but you do need a little.

Peter.