A little shelf building advice, please...

[TimScearce]

I have a teak-hulled Robb 35 yawl. She is a heavy full-keeled cruiser so weight is not a major concern.

I need to build a shelf behind the starboard settee to support two 65 lb. 6V AMG batteries. The aft part of the space is a 3/4" plywood bulkhead. The frames and planking are outboard. The space is 12" deep, 26" high and 5' long

My thought is to use 2" X 2" solid wood (Oak or Marine plywood?). I will predrill, epoxy, paint and then screw and glue it to the bulkhead to support the floor of the enclosure. I will then use similarly treated marine plywood for the outboard, inboard, top and forward sides of the box. I will drill several 1/2" ventilation holes in the upper part of the enclosure. The batteries will be secured to the wood. I will probably need to screw and glue the forward side to the ceiling beams. A shelf attached to the lower aft side of this will support the forward part of the floor of the box.

This will be my first try at marine carpentry. Ulp!

Does this sound like a sound plan?

Any thoughts on solid vs plywood?

Thanks in advance for your thoughts.

Tim

[Bruce Hooke]

I can't really fully visualize the plan you have in mind but I do have a couple of general thoughts:

1. If possible, especially on a boat of traditional construction, which it sounds like your is, I would try to make sure that whatever structure you put in can be removed by just taking out fastenings. In other words, it is fine to use epoxy coating and assembly techniques to put together the box, but I would avoid gluing stuff to the existing structure in the boat unless you really need to. One of the nice things about traditional construction is that it allows for disassmbly if something needs to be replaced, and it would seem to make sense to me to stick to that approach at least where the new work comes in contact with the existing structure.

2. On plywood vs. solid wood, because plywood is always, to some degree, vulnerable to water getting into the end grain from any edge, and because plywood really only takes fastenings well from 2 directions, where solid wood takes fastenings well from 4 directions, I would only use plywood where it has a clear advantage. Two examples of this are: A) places where you need large sheets of material (thus the sides and bottom of box shaped structures are an obvious candidate) and B) places where plywood's roughly equal strength in two directions is critical (for example, gussets and similar pieces. So, for things like a "shelf" attached to a bulkhead and to the floor of a box, I would use solid wood to make it easier to screw into the shelf from both the side and the top.

However, others may have other ideas and opinions so we'll see what they say...

[John Blazy]

Excellent points Bruce. I would lean a little more toward plywood (cabinetmaker in me speaking) if making an open top (or front) box, because epoxying rabbet or Tng&Grv joints can be quite strong, if the joint is prewet long enough before clamping. Allow for plenty of ventilation for heat, like allowing wide margins of air space around battery, even tho AGM Batts don't gas-off like wet cells (I think).
Design into the 'box' a hanging board like you see inside kithen cabinets, so that you can screw it into the bulkhead like Bruce mentioned.

[Dave Fleming]

For battery storage it has been found best to build a stout plywood box, line it inside and out with ***feeberglaz set in resin*** and paint.
Hold downs are usually marine grade stuff found in most catalogs. For custom size batteries, neoprene lined SS brackets bolted to the box.
And don't forget to vent the box to the outside even with these newer sealed batteries. I just don't trust that idea, on general principles, that is.

[ 06-27-2003, 07:35 PM: Message edited by: Dave Fleming ]

[Frank Wentzel]

Tim

Heat is a very real consideration with AGM batteries. In flooded batteries excess charge current electrolyzes water in the electrolyte into hydrogen and oxygen gasses which leave the cell (gassing). In AGM batteries the gasses are recombined back into water. This means that, in effect; the hydrogen is "burned" inside the battery. This generates considerably more heat than the normal venting process so the battery installation needs to be designed to dissipate this heat.

/// Frank ///