When Madrone is sailing, she harvests all the power she needs to move from the wind. But outside of moving the boat, nearly all of the systems that we use onboard rely on electricity. Most of Madrone’s electrical system is original to her build and first commissioning – while still perfectly functional, the electrical system deserves some upgrading.

Preparing the new battery box area under the settee by removing the old tie down points with an oscillating tool

First up is improving the way the battery bank is mounted in the boat. When Madrone was originally commissioned the batteries were set up in two physically separate banks, one next to the mast and one at the aft corner of the main salon port settee. This configuration means that the cables connecting the two battery banks are different lengths, which results in is a small difference in voltage between the two sets of batteries.

First step in building the new battery box- applying a layer of fiberglass and epoxy to each side of the plywood
Cutting the “fringe” of fiberglass off the edges of the plywood after both sides were finished being fiberglassed

That difference doesn’t really affect performance, but having an imbalance like that is not great for the long term health of the batteries. And it irritates the former electrical engineer on the crew. So, some time at the dock is a perfect opportunity to fix it.

After building the box, but before completing it by epoxying it together, we figured it would be a good idea to make sure all the batteries would fit. Luckily they did!
Moving batteries around is hard work. Time for a rest

Flooded lead acid batteries like Madrone’s need to be mounted in a watertight box to protect the boat against the possibility of battery acid leaks. The reason the batteries were split up in the first place is that there’s not enough room for them to fit together while using commercially available battery boxes. So, consolidating the batteries into a single bank means that we need to build a custom battery box.

It was too tight for the completed box to fit through the settee opening and then rotate to sit flat. So we slid the completed base with one wall into place and then built and epoxied the rest of the box in place
Screwing the box together in place required a bit of boat yoga on Mike’s part

We started with a sheet of standard plywood, and then coated each side with epoxy and a single layer of fiberglass to strengthen the plywood. After waiting for that to cure, we carefully cut the plywood into pieces that would form the bottom and sides of the box. Then, we added epoxy-coated hardwood battens to the edges and corners before screwing and gluing the box together. The final step was to add fillets of thickened epoxy to all the inside corners to ensure that the final box is completely waterproof.

Adding fillets of thickened epoxy to seal all of the seams within the box to make it “waterproof” or more importantly “battery acid proof”
Angie looking super pleased with the final product

As usual, the project took much longer than originally anticipated. But it turned out to be a great way to learn a bit about fiberglassing, and the end result is a much better solution for Madrone’s main battery bank.

Madrone’s house bank resting comfortably in the new battery box, wired up, strapped down, and ready to sail!