what is the intention of the solar panels? if it is for battery maintenance, a 30-40 watt panel would be all you need, that is a small panel about 2' by 9" for when the boat simply sits not used.
if it is to charge batteries, a single panel would not be enough.
I know a good many live-aboards that have 5 or more solar panels for charging the house banks. usually 2-3 on top of the salon and 2-3 bracketed off the dinghy davits in the back and they still have a wind generator. the issue is that unless the panel is perfectly aimed at the sun, you dont get 250watts out of the panel. so with an array, you may get 300 watts out of 4 panels as the boat moves around in the swells.