Hot water heater system
If you are going to fit a hot water heater (calorifier) and let the coolant from the closed circuit of the engine heat the water for you, It is essential to get the plumbing correct so that you don’t have an overheat problem with your engine. Keep the supply and return lines between the engine and hot water heater as short as possible and avoid any big loops or dips in the hose. Remember that you fill the coolant at the cap that is on top of the manifold that is on the engine. This must be the highest point of the cooling system because you cannot pour water uphill. If the shape of the boat forces you to mount the hot water heater above the engine, then you need to follow the drawing (link below) to ensure that your cooling system works correctly.