I will assume you have a reasonable budget
to get this done if you want a proper job. I would still go with an instant tankless system, either gas or electric
. On a boat your size, your engine
can easily produce enough heat for hot water, but they may not be on when you want it. An electric
heater will require you run your genset, so I would go gas. If the tanks
are inside and the unit is inside, you may want to have a professional install it. Like your tank locker, the unit should be inclosed but open only to the outside, vented and flued. On a lovely boat like yours, that could get expensive, on a scow like mine I would bolt the sucker to the outside and drill a hole for the water pipe. Im getting ready to install one myself.