rotten floor, battery relocation etc??

[Tony Davis]

I think your all getting a bit carried away and forgetting this is a floor in a skiboat, that'll be over laminated.

The simplest is a butt joint, but for extra strength I'd screw a strap on the underneath. bit of 3/4" ply if there's space for it, perhaps some waterproof glue if your paranoid.

I'm sure the repair will outlast the rest of the boat!