Heating system for boats, motorboats and yachts
It's warm in the cabin!
For heating on boats, car heaters or small-sized stoves are often used, but with their help it is not possible to maintain the desired temperature for a long time, for example, at night.
In our opinion, it is advisable to install a heating system with a special heating tank filled with hot water on ships operated in cold areas of the country. With good thermal insulation of the cabin, 30-50 liters of hot water ensure that room temperature is maintained for 8-14 hours.
Preheating of the cabin, as well as heating of the water for the tank, is carried out either by a running engine or by a fireplace. It is impractical to use independent heaters for this purpose, for example, the heater from the «Zaporozhets» car, since they consume electricity during operation (at least 30 watts), are difficult to install and, most importantly, cannot be considered absolutely reliable in fire-fighting attitude.
The first task is to provide thermal insulation of the cabin.
To evaluate the effectiveness of thermal insulation, Fig. 1 shows graphs showing the temperature t in the cabin (in the absence of a heating tank) depending on its volume V 1 hour after the heater stops working at an outdoor temperature of 0° and an initial temperature in cabin 20°.
Fig. 1. Efficiency of various cabin insulation systems
Curve I refers to a single-layer plywood or fiberglass skin 3-6 mm thick. It is interesting to note that the difference between the steel and plywood skin will be felt only in the first 10-20 minutes; in the future, in both cases, the cabin will be equally cold. Large heat losses through the sides and walls lead to the fact that with a cabin volume of more than 7-10 m, it is usually necessary to install two car heaters. However, even with their joint work, the conditions of habitability in the room cannot be called comfortable, since the temperature inside it will be uneven: from 20-25° in the area of the heater to 2-4° near the walls.
Curve II refers to a board or plywood skin with a thickness of 15 mm, and curve III refers to a two-layer skin with a distance between the layers of 20-60 mm (while the thickness and material of the internal stitching have little effect on heat exchange). It should also be noted that increasing the air gap over 30-40 mm practically does not improve thermal insulation. This is explained by the fact that at small intervals heat transfer is carried out by means of thermal conductivity, and, as is known, the thermal conductivity of air is much lower than that of any solid bodies. With an increase in the thickness of the air gap, air circulation occurs between the layers of sheathing and stitching; at the same time, heating up at the warmer inner wall, the air rises up, and then, cooling down, falls down, heating the outer, colder wall, which leads to an increase in heat exchange.
The thermal insulation properties of the foam are significantly higher. Curve IV refers to foam insulation with a thickness of 40 mm laid directly on the outer skin, and curve V refers to the option when there is an air gap of 20-30 mm between the skin and the foam (the foam is laid on top of the stringers).
With good thermal insulation of the cabin, significant heat losses occur through the glass. Curve VI refers to thermal insulation according to option V, but with a glazing area of 2 m². Hence the conclusion: in heat-insulated cabins, it is desirable to reduce the glazing area in every possible way or to provide double glazing with an air gap of 30-40 mm between them.
It should be borne in mind that a small amount of heat is reported by the crew itself. Curve VII characterizes the temperature drop in a cabin with thermal insulation according to option V, but with three people in it and with minimal ventilation (4 m/h per 1 person). As you can see, with a cabin volume of less than 5 m, the temperature in the cabin will even rise without any heat source.
In real conditions, temperatures may differ slightly from those shown on the graph, since the cooling processes are influenced by the strength of the wind, the weight of furniture in cabins, the intensity of ventilation and many other factors. Usually, the walls of the cabin and the basement are insulated; there is no need to isolate the slats, but they need to be well fitted.
Approximately the amount of water heated to 80° G required to maintain a temperature of 18-20° in the cabin for one hour can be determined according to the schedule shown in Fig. 2 (the designations of the insulation curves are the same as in Fig. 1). Good thermal insulation of the cabin allows you to reduce the required amount of hot water 5-8 times, as a result, placing the tank in the cabin will not cause serious difficulties. We see that for a cabin with a volume of 7.5 m³ with insulation according to option V, 40-60 liters of water is sufficient for heating for 10 hours (multiplied by 10, the value read on the G scale).
Fig. 2. The required amount of hot water and the area of the heater tank, depending on the insulation system
The figures shown in this graph are calculated for normal cabin ventilation at the rate of 15-20 m/h per person. In this case, the amount of heat spent on heating the cold air coming from the fans turns out to be of the same order as the amount of heat generated by one person in the cabin. With the minimum permissible ventilation (4 m/h per 1 person), water consumption can be reduced, conditionally assuming that one person replaces 1 liter of hot water per hour.
Optimal ventilation is obtained in the case of the use of two supply and exhaust fans. The design of the fan should provide the possibility of changing the area of the flow section so that it is possible to maintain a constant air flow regardless of the speed and direction of the wind. The cross-sectional area of the fan to ensure normal ventilation of the cabin in light winds should be at least 100-150 cm per person, while in strong winds only 1 cm is sufficient. From these figures it can be seen that when insulating the cabin, it is necessary to pay attention to sealing cracks in doors, hatches, etc.
For the first time after the engine is turned off, the temperature in the cabin may even be excessively high, so it will be necessary to cover the heating tank with some kind of cover. By the end of the estimated heating period, when the water temperature in the tank drops to 40-50°, the side surface of the tank may not be sufficient to heat the cabin. The approximate required lateral area of the tank F (m²) can be determined by the same Fig. 2. Structurally, the tank area can be increased, for example, by soldering ribs to it; the easiest way is to slightly increase the water supply.
Water heating can be carried out from the cooling system of a stationary engine using heated water from an external circuit. By another method, the external cooling circuit is connected to the internal circuit using a thin tube with an internal diameter of about 10 mm. In the upper part of the expansion tank, a drain hose fitting with an internal diameter of 20-25 mm is strengthened. When opening a tap mounted on a thin connecting tube, water from the external circuit will flow into the internal one, as a result of which the water level in the expansion tank will rise and excess water will drain into the heating tank through the drain hose. The same faucet is used to adjust the temperature of the flowing water. In the case of heating a small cabin according to this scheme, two or three cans can be used as a radiator. At the same time, it is advisable to take the drain hose out of the transom, outside of which the filled canister is attached (this eliminates the ingress of water into the boat when the canister overflows).
It is advisable to fill the heating tank with hot water on the course of the boat, since in the parking lot, even when the engine is running at medium speed, the tank filling time is much longer.
With a single-circuit engine cooling scheme, the outlet water temperature does not exceed 60°, therefore, the efficiency of serial car heaters («Moskvich», «Zhiguli») sharply decreases. In this case, it is advisable to install two or three radiators in series and use a higher-pressure centrifugal fan instead of an axial fan.
Such a heater can also work with a powerful outboard motor if, with the help of an additional pump (for example, using a dehumidifying pump in the «Moscow-30» motor), part of the heated water is pumped out of the cooling jacket. Given the lower temperature of the incoming water in this case, its amount will have to be increased by 1.5 times compared to the recommended one in Fig. 2.
A very effective device for heating the cabin is obtained if a heating tank is strengthened over the fireplace, i.e. a miniature hot water column is built. For small, well-insulated cabins, water can be heated on heating devices designed for cooking. However, it should be borne in mind that the operation of gasoline stoves and household primuses in the cabin is not allowed both for fire safety reasons and due to excessive release of carbon monoxide dangerous to health. Gas stoves, a tourist primus or a wick kerogaz can work in the cabin for a long time only if an exhaust hood with a cross section of at least 100x100 mm is reinforced above them.
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