9. Up to 4 kWh required per day (170 Watt average )
9.1. Introduction
It is now time to go on board and see how things work out in practice.
Of course all boats are different, depending on purpose, budget and ownership. Some boats are equipped to cross the Atlantic or to sail around the world. Others are intended to travel along rivers and canals. And still others go out fishing for a day. Some boats are sailed and maintained by the owner, others are part of a charter fleet. Then similar electric installations can be found in mobile homes for example, or off-grid houses.
I have chosen here to take sea-going yachts as the example, because that is what I know about first hand. It is not very difficult to adapt the reasoning given in this and the following chapters to other applications.
The first boat we will board is fairly simple in terms of electric installation, and electric power consumption has been kept as low as possible. It would typically be a motorboat of up to 9 metres or a sailing boat of up to 12 metres. The boat has a 12 V electrical system and, to start with, we list all electric equipment and current consumption.
9.2. Equipment and current consumption
9.2.1. Navigation instruments (wind set, log, depth sounder, etc): less than 0.2 A
9.2.2. GPS : about 0.2 A
9.2.3. VHF
Standby consumption is low (approx. 0.1 A). Transmitting does take a good deal of current (approx. 5 A) yet is brief, so that consumption in Ah remains quite low.
9.2.4. Tricolour navigation light or anchor light : 25 W (25 W / 12 V = 2.1 A)
9.2.5. Autopilot
The autopilot can be one of the biggest consumers if used for long periods of time. The motor’s current consumption is easily 5 A. When running with a duty cycle of 30 % the average consumption would be 5 x 0.30 = 1.5 A. Please bear in mind that this is a very rough approximation. Power consumption of the autopilot will in practice depend on the boat, trimming, the seas, etc.
9.2.6. Radio
Particularly on longer cruises, the (car) radio is often turned on. Its current consumption is about 1 A.
9.2.7. Cabin lighting
These days lighting consists of halogen lamps (10 W to 20 W) and fluorescent tubes (approx. 8 W). Incandescent bulbs are not recommended because they take up to 5 times more current for the same amount of light produced. Assuming 10 lighting points and thrifty use, consumption would be limited to approx. 10 Ah per 24-hour period.
9.2.8. Refrigerator
Refrigeration has been discussed in sect. 6.2. In this example we will assume that we have a refrigerator on board with a 50 W compressor running with a 50 % duty cycle. In my experience this is an average refrigerator in terms of energy consumption, when cruising in a temperate climate.
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