120 Volt corrosion-resistant 6 gallon hot water heater with aluminum tank and front heat exchanger connections.
 
Equipped with 5/8" hose barbs for optional heat exchanger connection, and 1/2" NPT threaded ports for domestic hot and cold water allowing easy installation.

Complete with ignition-protected controls.

They use shore power when plugged in at the dock, and engine heat when available.