Having received a tremendously exciting electric motor for Skipper, I now need to fit a battery. There’s an easy way to do this; just put it in the stern locker. That would be a perfectly sensible thing to do. If there is a sufficient swell that the battery might get bounced about, we won’t be electric motoring (we won’t be on the water at all). If there are strong enough winds that we will be getting a decent lean on, or even capsizing, we probably wouldn’t bother bringing the motor. The motor is for cruising about on calm water.
But. There is just something fundamentally wrong to the nautical mind with having a heavy object insecurely stowed. Doubly so when it powers your engine. So I’m doing it the hard way, the right way
The right way is to put the battery in a box then epoxy a piece of wood in to the bottom of the locker and strap the box down to the wood.
Make the pieces of wood. I don’t have anything the right width to cut out a single piece so I’ve had to cut two lengths here. They’ll get joined together by the same process that attaches them to the boat so no loss of strength there, it’s just more hassle for me.
It’s not quite as simple as just cutting two lengths of wood. I want that strap to be able to pass underneath even once I’ve stuck the whole thing down so I need a channel for it to run through, I chiselled that out then filed it smooth.
Prepare strap. Since I want this to be able to run through, it needs to not stick to epoxy, so I’ve made a little plastic sheath (from the packaging the battery came in.)
Prepare surface. Any painting, bonding, etc job is mostly about preparing the area. You might be forgiven for thinking that this doesn’t look immaculately prepared but bear in mind that this is a boat which has been outside all autumn, gradually filling up when it rains and being bailed out by me and the boys intermittently. So I bailed and dried it with a towel. Water seemed to be seeping in from somewhere so I bailed the rest of the boat, and tried again. Water was still seeping in but eventually it slowed down enough that it wasn’t in the way and the heater started to make some headway in making the area feel dry. This was a good reminder that this boat is not constructed to the standards of a yacht, and rightly so we wouldn’t be able to afford it if it was and a leak rate of a few litres an hour is no problem at all for a dinghy which isn’t stored in the water. Even so, while I’ve got epoxy out I’ve pulled out some nails from the stringer which you can see passing down the centre line of the boat and removed the worst of the rotten wood.
The black marker lines are where the wood will sit. Irritatingly it can’t sit against the bulkhead because nothing is square on a boat, the hull slopes upwards at this point so the base of the battery has to be a little way out or the top hits. That is the sort of detail which leads to much frustration if you don’t notice it before applying permanent adhesives.
Prime surfaces. Just paint unthickened epoxy on to the wood and the hull. This step is pretty much the whole point of using a fancy West Systems epoxy rather than just some very strong glue. The unthickened epoxy is very runny which means it can penetrate the wood far better than an all purpose glue firstly that waterproofs the wood and secondly it makes the bond much stronger.
Apply epoxy thickened with milled glass to the bottom and sides of the wood and stick it all together. This is the bit where you start to feel the time pressure of working with epoxy. Actually it has quite a long pot life but by the time you’ve mixed it, added the filler, mixed again, caught the bits and pieces the wind has blown over, realised that something isn’t quite ready yet, sorted that out, layered it on, placed the wood in position and tried to create a fillet around the sides, it’s easy to feel like you’re running out of time. I also at this point (with a separate batch, always make small batches so there’s less to go wrong at any one time) covered the stringer damage. I had planned to fibreglass over it but I think that’s unnecessary; just this is already a pretty good match for the surrounding area and there’s no benefit to making it stronger than its surroundings.
To stop the box sliding around I wanted to create an indent on the top of the wood which matched the bottom of the battery box. So I covered the bottom of the box in cling film, spread thickened epoxy on the top of the wood and pressed the box down on to it until it had set.