Hot water heating from engine

I am looking for owners experience with the time it takes to heat up the hot water tank from the engine. I have a 2030 Volvo engine and it takes between 1 and 2 hors depending on how hard the engine is working. On simlar sized non Beneteau vessels with the same engine the time for the same sized water tank appears to be between 20 and 45 mins again depending upon engine load.