Just to make details a bit clearer, here are a few photos showing the various stages of my outboard well infiller, including what the underside looks like when you take the existing flaps off. One side effect I hadn't expected, but like, is how my outboard works. Before I could only turn it very slightly side to side, so couldn't use it for steering. The cavitation plate hit the plywood holding the flaps in place. When I removed that plywood cover and the flaps, there is more clearance so that I can turn the outboard 90 degrees either direction, which can be useful for manoeuvring around marinas etc. The copper covered lump in the bottom left of the well is my through hull transducer. The two on either side of the hole are plywood clips the cross bar squeezes under. It is a doddle to fit when there is no engine, and not when there is. I had to plane the handle down to half the initial thickness to be able to fit it in. I didn't anti-foul the infill, because I take it out on the mooring, so there is no growth on it.