Battery Box Installation - Bertram 31
The battery box for Patrick Hancock's B31 was constructed in fiberglass from two temporary molds made specifically for
the batteries to be used on his boat. A Coosa Board panel has been laminated on so the cable hold downs can be affixed.
 The box will be installed under the companionway between the engines and elevated to just below the level of the hatch covers.  To achieve both height of the box & strength in the floor for the 150 lb weight of the batteries, a 3/4" layer of H80 Divinycell was laminated between the box & a panel of 1/2" Coosa Board. Another panel of 1/2" Coosa Board will be glassed to hull. The box has been configured to bolt to the glassed in panel making a very high strength final installation.  3/8" hex head bolts will mate with T-Nuts installed into the panel to be glassed to the hull. After pre-drilling, the T-Nuts are driven in and additionally secured with Cyanoacrylate glue, (Superglue).  To achieve the desired height and make the box level with the companionway deck plates, the top was screwed onto the box & a piece of plywood screwed to the top. 3/16" spacer strips were added between the top & plywood to keep the box spaced lower then the underside to the deck plates. The plywood will hang the box by the companionway rails.  Below is the whole assembly ready to be epoxy bedded into place.  Two piles of epoxy bedding mud is laid down with the depth being greater where the lower shelf will ride. All bonding surfaces were pre-ground & primed with un-thickened epoxy.  The box is now pressed into the epoxy mud & centered.  About 1/4" of space will be between the top of the battery box and the underside of the deck plate.  After the bedding mix has cured, excess is ground away & additional mix is faired in to allow a smooth transition of the fiberglass. The bolts were placed back into the T-Nuts & the threads taped. This will keep epoxy from getting into the t-nuts. The bolts will be removed after the epoxy has cured for a few hours, but before it hardens.  Only a single layer of 1208 biaxle glass is used to tab the plate securely to the hull.  Once the epoxy has set up to a leather hardness, the excess glass will be trimed away with a razor blade.  Finished shelf...  Box bolted down, Coosa board spacer added to elevate batteries above bolt heads, ready to accept batteries.  Why do I prefer to install the batteries in the bilge between the engine? The primary reason is that of weight distribution. Batteries are heavy. By locating them between the engines & on centerline, trim weight is negated. By installing them as low as possible & on center, their weight helps counteract the roll duration of the hull. They're more conveniently located than outboard of the engines; servicing or replacing them is easier. But won't they get wet in the bilge? They can if the water level gets so deep that it overflows into the battery box. The bolts holding the box securely in place are bedded with 5200, making the box water tight up to the cutout for the cables. The bilge pumps will normally keep the water level far below the flood stage of the box. A high water alarm set to sound at about the half way mark will alert to any danger of the pumps not keeping up. Finally, when the batteries are installed, all electrical connections are thoroughly & heavily coated with a high temperature grease to prevent water getting to them, even if submerged. Which batteries will I use for this installation? Each engine will be serviced by an Odyssey DT1500. The genset will be serviced by the port engine battery. The house battery will be a PC1400. Odyssey Batteries have the following specs: Exclusive 8-12 year design life, military grade, with service life of 6-10 years 834 Scott Dr., LLANO, TX 78643 Telephone 325.248.0809 Web site questions or comments to: bertram31@bertram31.com |
