The invention discloses a marine hot water tank, and belongs to the technical field of marine hot water systems. According to the hot water cabin, a constant-temperature cabin and at least two heating cabins are formed by a ship structure cabin cabinet, heat preservation cotton is arranged on the outer side of a cabin body, and a
steam heating coil, an
electric heating device, a liquid level and temperature sensor and a control box are arranged in the cabin body. The control box automatically controls heating, heat preservation and hot water
lightering according to
water level and temperature signals, when the liquid level of the constant-temperature cabin drops, hot water in the heating cabin is supplemented as a hot
water source, and the heating cabin synchronously supplements water for heating and works in turn. The constant-temperature cabin directly supplies water to the outside, cold water is not supplemented, and the outlet
water temperature is stable. The ship body structure is arranged in an integrated mode, the cabin capacity can be flexibly configured, the
heating power is low, the heat source requirement is small, continuous, stable and large-flow
hot water supply can be provided for the crowded ship, and the
system is safe, reliable and low in cost.