Boat Electrical equipment

Each item of boat electrical equipment has particular requirements and by examining each in turn we will gain a better idea of the requirements for circuits, fuses, etc, in order to arrive at an installation which will be reliable and give minimum trouble. Let's start with some of the heavy current users because these tend to give the most trouble.

Anchor windlasses

Apart from starter motors, the anchor windlasses are probably the most powerful electric motors on board. When running without much load this motor could draw 40 amps or more from the battery on a 12 volt system. When under load or when starting, the load could be up to 140 amps on a 12 volt system. Whilst the windlass is in use for only a short time, it is the circuits required to handle this heavy current which can cause difficulties and which require very careful installation.

It is not just the heavy current which can cause problems. Anchor windlasses are located rightforward and whilst the hauling section is above deck, the electrics and the motor are below deck where you might think they were well protected. However, the chain locker where the motor is usually located is a damp, gloomy place which has just the right sort of atmosphere to encourage corrosion and short circuits.

There is also the problem of the chain thrashing around inside the locker, so the electrical circuits and motor have to be protected from physical damage as well. This need not be a problem if the anchor is dropped slowly using the motor power, but the anchor chain could rush out if the anchor is let go by hand.

Directing the power to the windlass demands long leads from the distribution box to the motor, which highlights the problem of voltage drop. Any significant drop in the voltage will reduce the power of the windlass and cause overheating, so the solution is to fit large cables which are adequate for the motor current. The connections in the system must also be adequate for the current. There really is no room for economy in windlass circuits if you want the system to work properly.

One alternative to running heavy wiring the length ofthe boat is to have a separate battery for the windlass. This could be stowed forward, as close as possible to the motor, so that the heavy duty wires are short. This battery could be charged from the alternator via a blocking diode. Such a battery could also be a useful spare in an emergency, but finding a safe location at the bow may be difficult.

When the windlass is controlled from the helm position a relay is used. This avoids running the heavy duty wires to the dashboard; instead you have light wires from the dashboard control which operate the relay or solenoid to switch in the heavy current for the motor (much in the same way as the control for the starter motor, except that a reversing switch is necessary because you want the windlass motor to operate in both directions).

The damp atmosphere in which the windlass motor operates is not kind to boat electrical equipment. The motor will, hopefully, be a sealed unit which will not be prone to corrosion, but the connections are often exposed and these should be coated with one of the proprietary products which both insulate and keep out the damp. It still pays to have a look at the installation every month or so to check for corrosion before it gets a firm hold. A regular spray with silicone grease will help to keep everything in working order.

Bow thrusters

Electrically powered bow thrusters are becoming increasingly popular on boats to improve close quarters handling. With the motor located low in the bow it has many of the same problems as windlass motors, and it can take a similar load from the batteries. Both windlass and thruster motors are only used for short periods, so the battery drain is not excessive. The thruster motor and its control system need to be installed and maintained in much the same way as the windlass system.

Yacht Air conditioning

Air conditioning systems are becoming popular on boats operating in hot climates. There is a choice of individual units for each compartment or a system built into the boat. There is also a choice of air or water cooling for the system, and on some units the system can also include heating. An owner is likely to opt for the compact semiportable units if the equipment is being retrofitted, and these now tend to come as bolt-on units which can be fitted to the top of the wheelhouse. They invariably operate from mains voltage, 115 or 230 volts, and can simply be plugged in to the ring main.

Be aware that an air conditioner with heating circuits will be a heavy current user and may need separate circuits wired into the distribution box. Obviously, if you want to use an air conditioner at sea you will need a generator on board. Beware of fitting units designed for homes or motor vehicles on the exterior of boats, as they are rarely designed to be corrosion resistant against seawater.

Trim tabs and power trim stern drives

Power trim comes as an integral part of stern drives or outboard motors, and the wiring is complete apart from connecting in the power supply. Trim tabs tend to be separately installed but the principle is the same, and after installation only the power supply needs connecting. Both of these units operate on the electric/hydraulic principle, with an electric motor driving a hydraulic pump which in turn provides the power to the activating cylinders.

Reversing the direction of operation is usually done by means of solenoid valves controlled from the dashboard switch. The electric motor driving the pump can be quite a large current user, particularly with the larger units fitted to high performance craft, and on a 12 volt system they could absorb up to 30 amps. However, these motors are only used intermittently so that the overall load on the battery is small.

The motors are invariably fitted in the engine compartment with stern drive units, but could be in the steering compartment on boats with conventional propulsion. In the latter position they could be subject to damp, and any exposed connections will need protection. In the engine compartment the heat will tend to keep corrosion at bay; here the heat itself could be a problem, so try to keep the motors as far away as possible from hot exhausts.

Autopilots

Although these units are classed as electronic systems as far as the control is concerned, they usually include electric motors which either drive the steering directly through a chain drive system or are used to power a hydraulic pump which then links into a hydraulic steering system. The electric motors used for autopilots are designed to consume the minimum amount of current, and the units specifically aimed at the sailboat market are very good in this respect.

Overall they use very little current (5 watts per hour is the figure quoted for some units), but you have to remember that whilst the overall consumption may be low, the intermittent current can be quite high (up to 15 amps for some of the larger units) so the circuits and fuses must be rated for this level of current.

The dashboard control unit is the focus for the autopilot, but the rest of the autopilot's components tend to be hidden away out of sight. Many of the electrical circuits are included in the manufacturer's specification, but the installation may require the provision of low power circuits between the distribution panel of the autopilot and the relays which control the main drive motor, and of course the supply of power to the autopilot control panel and to the motor itself.

Different autopilots will require a different approach, but where one has a motor which switches on and off, then be aware of the higher starting current which is required for the motor. Protect all exposed terminals and connections, particularly when these are located in the steering compartment and allow for cable one size larger when long cable runs are involved. The main power supply must be routed through the distribution box and have its own fuse or circuit breaker.

Bilge pumps

Electric bilge pumps are now common on boats of all types. They can be the exception to the rule of taking all supplies through the battery isolating switch, because the bilge pump is one circuit you may want to leave on when the boat is left unattended. Most electric bilge pumps are fitted with an automatic float switch which turns on the pump when the water level in the bilge reaches a prescribed level, hopefully keeping the boat dry when left unattended. I say hopefully, because the average electric bilge pump will not deal with a major leak, a cooling water pipe failure for example, whilst any minor leaks such as a dripping stern tube gland should be dealt with rather than left for the bilge pump to manage.

An automatic bilge pump may be necessary on a wooden boat where there is seepage, but a modern GRP boat should not have any leaks, at least of the sort a bilge pump can cope with. However, automatic bilge pumps are often fitted, so if they are to be used in this mode they need to be wired up separately from the main distribution load which is isolated once the battery switch is turned off.

The best place to connect the bilge pump is to the live side of the battery master switch. The circuit will still need protecting against short circuits, so a fuse or circuit breaker of the appropriate rating must be fitted. This fuse is doubly important on this circuit which is left live when the boat is unattended.

The rating of a bilge pump will depend on its pumping capacity. A 12 amp 12 volt pump will move around 7500 litres per hour, but such a pump is at the top end of the range, and a small 2amp l2volt pump would only handle 1500 litres per hour. The latter type is probably adequate for leaving on when the boat is unattended, and would run for maybe 50 hours before running the battery down. Neither type will be able to cope with a sudden in rush of water.

The bilge pumps are generally submersible pumps, with sealed wiring from the pump. Any connections should be made well above a possible internal water level, and batteries should not be placed too low in the boat where they might be affected by rising water before the pump can rectify it.

Boat Refrigerators

Like most electric motors, the refrigerator motor will use a high current when starting up, after which the current will drop back to the continuous use level. Yacht refrigerators may be rated with the current they will use when the motor is running or they may have the average consumption per hour listed.

When you arrive at your boat the refrigerator will have to run continuously for an hour or more before it gets down to its normal operating temperature after which it will run intermittently. A typical small boat refrigerator will consume around 4 to 5 amps per hour, although during the time the motor is running the consumption could be as high as 12 amps, so the circuits must be rated higher than this to cope with the higher starting power needed.

The refrigerator is one of the few motor units on board which runs on a more or less continuous basis. This means that when the engine is stopped it will be one of the main users of current and the most likely cause of a flat battery if care is not taken. Some refrigerators include a device in the control circuitry to warn if the battery voltage is dropping. In some cases this will automatically switch off the refrigerator if this occurs in order to prevent the battery from becoming deeply discharged.

It is possible to buy dual voltage refrigerators so that they can operate on battery power at sea and mains power in harbour. Another option is a refrigerator which can operate from either bottled gas or battery power.

Water pumps

These are installed on boats to provide a water flow when a tap is opened. They operate either with a micro switch which activates the pump when the tap is opened, or by means of a pressure tank which is topped up by the pump when the pressure starts to fall. The intermittent use of these pumps makes their overall consumption low, but the pump motor may use 5 amps on a 12 volt system when it is running.

The flicker often seen in the cabin lights when a tap is turned on is an indication of the higher loads on the motor at switch on.

Whilst on the subject offresh water suppl ies it is now possible to buy water makers operating from a 12 or 24 volt supply. New technology allows these to operate efficiently to produce around 12 litres per hour with a power consumption of about 8 amps. They can add a useful extra amount of fresh water on a long voyage when the engine is running to keep the batteries charged up.

Boat Heaters

Marine heaters tend to be gas or diesel powered because the electrical loads would be too high unless shore supply or generator power were available. The main requirement with the diesel type of heater is for a power supply for the fan and ignition circuit; here the electrical load is low, probably around 2 amps on a 12 volt system at the higher rated units, and perhaps 0.5 amps on smaller units. Some heaters can incorporate water heating, using diesel or gas. The hot water system is usually controlled and powered by the cold water pressure pump.

Windscreen wipers and horns

These units operate out in the open or are at least partly exposed so there is no substitute for quality here. If possible the wiper motor should be inside where it can be protected from water, but the higher quality units use a waterproof motor which allows the unit to be mounted on the windscreen of open boats. If the motor is watertight. then the connecting circuitry must be to the same standard.

Wipers come in two types, the normal swing arm type and the rotating arm or screen. The current requirements of both types is around 4 amps on a 12 volt system, with the swing arm wiper being preferred on modern boats because of the larger area it clears. Three wipers may be required for a wheelhouse, making a considerable load in total, but they tend only to be used when the engine is running.

With the wiper motor often close to the compass, the magnetic influence has to be considered and the minimum safe compass distance respected.

Horns have a hard life on the outside of the boat and again only the best quality will survive. An electric horn may use 6 amps at 12 volts but the use will be very intermittent and it will only have frequent use in fog, when it becomes an important part of safety equipment. An alternative to the normal electric horn where the wiring and electric components are outside is to have an air horn with the compressor driven by an electric motor. The electrical components can then be inside, protected from water; the power consumption is similar.

Marine Lighting

Boat lighting choice in fittings generally lies between filament bulbs and fluorescent tubes. The latter tend to have a longer life in the marine environment, and give considerably more light for a given power consumption, but not everybody likes the harsh white light they produce..-The best compromise is to have a mixture of light fittings, some filament and some fluorescent, so that the lighting can be set for the particular mood. However, standardisation reduces the number of spares required.

Any outside lighting, wherever it is located, must be waterproof. This applies to cockpit lighting in sheltered locations just as much as to the exposed navigation lights. If you use recessed light fittings for outside, then only the fitting needs to be watertight on the outside; it can be linked by standard wiring which is protected on the inside. Fittings such as navigation lights and searchlights can be connected by a watertight deck plug and socket which allows them to be removed easily.

The socket should have a waterproof cover to screw in place when the plug has been removed so that water can't get to the live connections in the socket.

Try to keep switches in protected places. It is convenient to have a light switch just inside a door or hatch, but make sure that water can't drip on to it when it is raining or when spray is flying about outside. Even with an enclosed wheelhouse, any switches mounted flat on the dashboard should be waterproof, or at least splashproof, because water can drip onto them from wet oilskins or hands.

Marine Electronics

The increasing use of marine electronics on boats of all sizes has led to increasing concern about providing suitable power supplies for it. This concern can be measured by the number of proprietary 'black boxes' on the market which are offered as a means of providing the correct type of smooth power to the electronic instruments, free from voltage spikes and surges. Spikes and surges are mainly caused by switching equipment on and off, but they also emanate from the charging circuits.

We have already seen how the starting battery can be separated from the auxiliary, which helps to remove the effects of voltage drop created by operating the starter motor. If the electronics were supplied from the same battery the voltage drop could be enough to cause them to temporarily switch off. This usually happens in harbour, so it is not serious from the point of view of safety, but it is irritating when you have just set up the electronics for the start of your voyage.

Separating the starter and auxiliary circuits solves this problem, but it could also occur when heavy power users such as the windlass or the bow thruster are operated. Ifthis is a problem the solution could lie in separating the auxiliary circuits onto different batteries, one for sensitive equipment and one for general purpose use.

VHF radios do not normally cause problems in the supply circuits, but powerful HF or MF radios can cause major problems with their high transient power requirements when transmitting. Unlike the windlass or bow thruster, the radio will be used out at sea, so its effect on sensitive electronics should be checked on temporary circuits before finalising its installation.

Apart from the radio, the electronics are used mainly for navigation. The power requirements for logs, echo sounders and navigation receivers are not high, usually in the order of I amp or less on a 12 volt system, but navigation receivers and autopilots can be particularly sensitive to the quality of the power supply. Some incorporate smoothing devices in the power input circuitry to improve the quality of the supply but much can be done simply in the layout of the circuitry.

Each piece of electronic equipment should have its own power supply with a separate fuse and switch, and as far as possible isolated from circuits supplying electric motors which switch on and off.

The quality of the power supply can be improved by fitting one of the surge suppressors now on the market, but if the quality of the power to the electronics is poor, then think about the option of a separate electronics supply battery.

Poor quality power supplies can be recognised by internal fuses blowing in the electronics, by unstable displays, and by generally poor performance. Some of these symptoms can result from interference such as radio transmissions.