To get "hot" water off of a AC, refrig, or central ac unit,water or air cooled, One would need a heat exchanger on the high temp high pressure line right off the compressor.(the discharge line before it goes into the present condenser)
That line is always well above 100 degrees when the comp is running. Most marine units under 24,000 btuh are too small to make enough hot water to be useful by use of a discharge gas H/X
The existing condenser (water or air) would become secondary but still necessary.
On larger water cooled units using geothermal, closed loop or well water there is a control that modulates the flow of water through the heat exchangers that keep the operation pressures constant. This modulating water valve is very common on larger units, it controls the water flow rate via the pressure of the refrigerant. In general, of any type unit will heat the condensing water only about 10 degrees, unless in reverse cycle, then then it would be 10 degrees lower.
Metrex Valve: Water Regulating Valves for HVAC Commercial, Marine&Nuclear
For any larger unit a discharge gas h/x is still the way to heat water and it requires cutting into the refrigerant lines and all the usual hvac routines to install it.
You would get more heat, from a diesel inboard H/X actually. or even a solar collector instead a little 16,000 btuh or so boat a/c.
Work vs return? not worth the trouble.