Whale Seaward 6 Gallon Hot Water Heater w/Rear Heat Exchanger - Galvanized Steel - 120V - 1500W - S600. Compact, Durable, and Efficient Marine Hot Water Heater. The Whale Seaward 6 Gallon Hot Water Heater with Rear Heat Exchanger provides reliable hot water in a compact, corrosion-resistant design. Built with a galvanized steel case coated for durability, this heater blends seamlessly into modern engine rooms while delivering consistent performance. The rear heat exchanger allows the unit to har