We have an Ocean 38 and we were unhappy with the OEM calorifier/hot water heater (Nordic?) as we didnt like the volume provided by such a small unit so we designed and built one just for us.
We went from a 6 gallon horizontal oriented model to an 18 gallon custom vertical model as we had the space and vertical is much more efficient. It features both a 24 volt DC/600watt/25 amp electrical element and a 120 VAC/1500 watt /13 amp electrical element. It also has two independent heating coil loops, one for engine coolant and one connected to our Espar hydronic diesel cabin heater. One happy user reported that it sustained a party of four with daily showers, dish washing and all other needs for a week relying on just solar power. We have made others with 12 VDC and 220/240 VAC.
Hopefully this doesn't come across as self-promotion or advertising a product, it's just that I designed it privately for myself and my Bavaria Ocean 38 and it began selling itself to other boaters and yacht manufacturers. I snapped the enclosed photos today of one headed to Tiawan to be installed in a new Hylas 57, the Sailboat of The Year for 2022 by Cruising World. Note the upper heat exchanger coil is capped with black covers in the attached photo.
The unit stands 32.5 inches tall and the cylindar is 16 inches in diameter. It resides behind the saildrive in our engine room and sits on a self-leveling platform.
If you are interested in more please contact me privately.