Hi,
Outlet water temperature may be different. Normally, 70-75 deg C.
However, I experienced that it is up to 85-92 on some brands.
My experience covers only commercial fleet, but, I hope that physics also works in a superyacht industry,
So, some of commercial ships are equipped with a system, which utilizes the heat, produced by auxillary engines.
It works good. We even did not use the diesel oil boiler in winter time. The system could handle all domestics + heating of HFO storage, settling, service tanks.
If You are looking for heat exchangers, please consider:
www.gea-westfalia.com www.alfalaval.com www.apv.com www.ami-exchangers.co.uk
There are more brands of course, but I recommend only those, what I operated / dismantled / cleaned.
I hope, that this info will be useful for You,
rgds,
Andrei