Just wondering if, when you bought boat
both the hot and cold water were working and whether this problem developed after the pressure pump went down? or if it was like this when you bought it?
Like some of the other contributors have mentioned the first thing to work
out is.. Is there cold water getting to the cold water inlet into your hot water tank? Once you have discovered that then it's a matter of filling (priming) the tank and hot water lines. This can only happen if the air is allowed to escape from the top of the tank via the hot tap, overflow or pressure relief valve (on some) as the cold water fills the water heater tank from the bottom cold water inlet. The usual suspects here would be. A valve is turned off, there is a blockage or an airlock. You could identify a leak as the pressure pump would continue to work
when all the taps are turned off. A blockage could be identified by working back to the pump from the H/W tank and checking all connections (or the other way). I'm in Australia
and some of the H/W tanks
we have here are configured differently with the hot water to tap being drawn through a heat exchange coil immersed in a static heated body of water in the tank so it might be worth checking with the H/W tanks
manufacturer to see if there are any tricks. If you are in a marina it might be worth back or forward flushing
with a garden hose from the mains to dislodge a block or expel air with the greater pressure.