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S/V Sabbatical
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I have a Pearson 365 Ketch and I need to expand my current battery box. My idea for a new battery box looks like a partial bulkhead with steps cut into it. I will tab two partial bulkheads to the hull and build shelves for the batteries between the two bulkheads. The end product will look like a staircase. Batteries 1 and 2 will go on the lowest step. Battery 3 will go on the second step in line with the first two and battery 4 will go on step two, but aft of battery 3.

My question is how should I tab the bulkheads to the hull? Should the plywood fit snuggly against the hull? I have heard that I should leave a gap so there are no pressure points against the hull. If I do need to leave a gap, how big should the gap be and how do I hold the box in the correct position while I am tabbing? Is there a filler I should apply to the bottom of the partial bulkheads before I tab them? Any ideas, tips or advice would be appreciated. Thank You.
 

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Get some airex or corecell to use as a spacer between the hull and the framing piece. Cut cardboard and tape it in place to hold the piece while you are tabbing.

Good luck !
 

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I can't tell from your sketch, but I would hesitate to in any way restrict access to a seacock. Envision needing to reach under those steps to turn off the seacock, to change a hose, to tighten a clamp or, Neptune forbid, to jam in the wooden plug I know you have conscientiously tied to the seacock with string...

Also, while I'm all for short cabling runs, isn't having four batteries on the same side going to throw out your trim? Can you not put Batteries 3 and 4 on the opposite side, nice and low, and perhaps relocate your water heater? Just some thoughts, as batteries are best kept low and not, in my view, stacked.
 

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Telstar 28
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A few points...

First, i would agree that you should probably split the batteries port and starboard, as Valiente suggests, to keep the boat better balanced.

Second, I'd hesitate to block access to a seacock, since, in an emergency, you may need fairly decent access to plug it.

Third, adding a box to the hull only on one side may cause problems... generally, you should try and modify the hull in a somewhat symmetrical fashion, so that the hull doesn't have uneven loads on it.

Fourth, to keep the plywood from touching the hull, cut some foam, either Airex or Divinylcell, in a trapezoidal shape, and use it to hold the plywood in place. The trapezoidal shape will help you create a strong fillet joint and not bend the fiberglass too tightly—which would result in damaging the glass fibers.
 

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The foam stand-off is a good suggestion to avoid hard spots, SD. Don Casey's book on deck and hull repair, plus the West System booklet on basic fibreglassing, are going to be helpful here.

Also keep in mind that a "to code" battery installation is going to secure not the batteries, but the boxes in which they reside, usually with webbing tie-downs and either a belt-bucket or clasp sort of band. The lids go on the boxes, and the boxes are strapped to the platform (which benefit from some sort or lip or bits of 1 x 1 to keep them from moving). The straps are usually either run through slots in the glass or riveted through the glass.
 
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