I am glad all this talk of batteries, pump ratings
and solar panels has made you reconsider this idea. A heavy battery by itself on a 17' O'day would change the balance of the boat. Batteries are also filled with strong acid that would be bad for the boat, not to mention your skin if it got out somehow. The custom cover would probably cost less than the pump/battery/solar panel even if made by a canvas shop.I used to keep a 14' daysailor moored in LI Sound and I only kept a manual bilge pump, a bucket and an oar on board. Once the boat got swamped but there was enough positive flotation so it did not sink and the bucket helped to dry things out with a lot of work. I am pretty sure the O'Day 17' has similar positive flotation qualities. You could also try to make a cover out of a tarp from HDepot but I doubt that it would last as long as one made of canvas.I keep my 27' boat in Nyack on Hudson. Where on the Hudson is your anchoring cove?