Boiler on a boat. What to know to always have hot water on the boat

In order to have hot water on the boat as at home you need to install a boiler or water heater on board. Here is how to choose the most suitable type and what to check before, during and after installation. And above all how to take care of it afterwards.

Basically, the operation of a boat boiler is almost identical to that of a civil boiler, it changes the outer coating which, in addition to being highly insulating, is particularly resistant to the marine environment. There are two types of boiler: with heat exchanger or with heating element.

The boiler with exchanger

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In the first case the water is heated by means of a heat exchanger, nothing but a coil in which the water from the engine cooling circuit flows. The liquid reaches temperatures between 90 and 120 °C and heats the coil, which heats the water in the tank by irradiation. Each boiler shows in its data sheet the exchange surface value of the coil. The larger this measurement is, the more water is heated in the shortest time, and likewise the service life of the hot water in the boiler. When evaluating the performance of the exchanger, it is necessary to consider the water pressure drop induced by the pipe size and the construction curves that reduce the coolant flow and therefore the performance of the boiler.

The boiler with electrical resistance

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The boiler with electric resistance, through this last one, always uses a coil, but which increases in temperature with the passage of the run and, consequently, heats the water. In this case what makes the difference is the power of the resistor. An average value is about 1000 W, and in commerce you will find between 800 and 1200. Evaluate the power according to the power you have on board and what you expect to find on the dock. Sometimes the harbour columns barely reach 1 kW. Heating by means of a heating element is, of course, convenient as you don’t need to have the engine running to get hot water, but all you need is a generator or, as written, to be connected to the quayside.

The various parts of the system

The thermostat is used to activate the ignition when the water temperature falls below the set level. It is not a power regulator, but only a switch that works according to the temperature: above a certain value it is off, below it is on. Setting it to high temperature values (over 45 degrees) does not heat the water first, it only consumes more. An international standard, in terms of safety, requires the presence of a safety valve to allow the venting of the boiler when the internal pressure becomes excessive and dangerous. The mixing valve, often supplied as an optional, is very useful to prevent too much hot water from coming out of the taps, so as to optimize the contents of the boiler and avoid scalding. To simplify the system, the tank should be positioned as close as possible to the engine. In this way the cooling water circuit of the engine, which must also pass through the heat exchanger, will be reduced to a minimum.

Choose thinking about measures

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A typical diagram of a boat’s water system. Fresh water arrives at the boiler from the central tank. The diagram shows that the cold water inlet is at the bottom and the hot water outlet is at the top. This is to use the hottest water, which by physical law is higher. On the sides of the central part of the crankcase, the inlet and outlet of the engine cooling system.

Choose well the pipes, normally the dimensions and the type are indicated by the manufacturer; in any case they must be well resistant, because the water of the circuit easily reaches 90 degrees, stressing the system. The boiler itself, if used correctly and installed correctly, does not require continuous or demanding maintenance. The only element that can be replaced is the electrical resistance. Usually the connection is positioned on the side where all the taps are located. Check that this part of the boiler is easily accessible and that the heating element can be easily removed. The shapes of water heaters on the market can be cylindrical, some companies, such as Quick, Indel Marine or Ati, have recently produced square, parallelepiped models to optimize the space in the boat. The water heaters on the market have two clamps that slide along the drum. If they are fixed, take a good look at the space available in the compartment you have chosen for your accommodation because if they are not adjustable, they do not slide along the entire boiler, and assembly becomes difficult if not impossible.

Tips for the cold

For those who sail in the North Sea, companies recommend emptying the bin during wintering, because in case of very low temperatures the water inside could freeze and strain the welds. An important element for both ordinary and extraordinary maintenance of a boiler is the size of the electrical resistance connection and its power. The most common resistances, in any shop even in the nautical sector, are 1200 W, with the 1″ and 1/4″ threaded connection, standard size also for civilian use.