Powerboating - Part Four

For those with good memories, the previous article on electricity was written in glorious sunshine on the back of my boat. At the moment it's raining hard enough to give Noah some concern, I'm in the saloon in the company of a wet dog who smells like a dead fish, and the leak in the forward cabin I've been meaning to fix is there with a vengeance. Sometimes, living on a boat is not the paradise people imagine.

Hence, a good time to drag out the laptop and continue with the fascinating story of electricity.

WIRING FUNDAMENTALS
The photo below shows the state of the wiring on a typical 20-year-old cruiser. Constant fiddling and additions over the years have produced this electrical nightmare. There are two options: rewiring (which is expensive) or a tidy up. The second option is time-consuming but rewarding, and not as difficult as it first seems.

Fig One shows a basic wiring system applying to most single-engine boats that have been professionally wired. Look at some of the features of this circuit. For a start, the batteries have been arranged into two banks, with the two house batteries being connected in parallel for greater capacity; and all the consumer circuits are drawn from this bank.

Thus configured it's impossible to draw off the starting battery unless the paralleling switch is closed. This means that if excessive consumption of electricity occurs, the engine will always be able to be started - an important safety consideration.

As a backup for emergency start, placing the paralleling switch to the ON position puts all three batteries in parallel. This is used should the starting battery fail. Immediately the engine starts, place the paralleling switch back to the OFF position to prevent using the start battery to feed the consumer circuits.

The feed cable from the batteries distributes to two buses: main and essential. Both of these are isolated when the house isolator is turned off.

This is important if an electrical emergency should arise, such as a fire.

For this reason, all battery isolators should be placed in a readily accessible position outside the engineroom. When leaving the boat for any length of time, the main switch is turned off, ensuring that only essential circuits such as bilge pumps, stereo memory, etc, are left on.

Power from the buses is distributed to the various circuits via fuses and selector switches. These two items could be combined in one circuit-breaker, which is the more common approach.

Fig Three shows a well-planned DC switchboard. The essential circuits are illuminated with green LED lights when activated and the main circuits with red.

The electric anchor winch is wired from the house battery isolator via (in this case) a 150amp circuit-breaker. These circuit-breakers are necessary. I was onboard a charterboat in Sydney Harbour one night when a guest stood on the foot switch for the anchor winch unwittingly. The anchor was hard in its stops and the winch wiring caught alight in minutes - disconcerting until the fire was brought under control.

Note here, the winch isolator in the line, rendering the winch completely dead unless it's being used. (As an aside, electric anchor winches can be dangerous, especially around children. A more effective method than foot switches is all-electric winch control, enabling both up and down operation).

The output from the alternator to charge the batteries is taken to two points - one to charge the engine battery, the other through a diode to charge the house bank. Remember that a diode is a device which will only allow electricity to flow in one direction, thus in this application, the diode stops the house bank feeding into the start bank when the alternator is not charging.

WIRING TECHNIQUES
The basics of good wiring practice, when working on low-voltage circuits, is to use the correct size wire and to finish with a good connection. The amount of electrical current a wire can carry depends on its cross-sectional area and its operating temperature.

If the wiring is going to be bundled together (ie. if it runs through hot enginerooms and if it runs a long distance from the battery), then use the next size up from that recommended in the table (Fig Four).

Because there is no written rule for indicating cross-sectional area, some mathematics may be involved. For instance, automotive cable is often quoted in the number of strands of basic size strand (eg. 41/0.032 means a cable having 41 strands, each 0.032in diameter). The cross-sectional area of the strand is pi times the radius squared - in this case 3.14 x (0.016)2 which equals 0.0008.

Multiply this by the number of strands (41) and the answer is 0.328sqin, which is close enough to 8AWG. (again see table above).

ELECTRICAL TERMINATIONS
When the correct cable has been selected for the particular circuit, the next job is to put the correct termination on the end.

A photo above right shows a variety of these. The different colours indicate the wire size to be used.

Make a rule not to just twist the ends of the wire and stick them under a screw terminal. This will always fail. The vibration over a period of time, coupled with a harsh environment, will cause a high resistance joint and allow our old enemy (voltage drop) to get the upper hand. Invest in good quality crimping pliers and purchase the various styles and sizes of lugs.

The method of crimping the lug onto the end of the wire is shown hereabouts (Fig Five-Seven)...

A special type of connector is the heat shrink butt. This is applied to the cable and crimped. Do the same to the piece of cable to be joined. Heat the butt connector with a hot-air gun or hair dryer. (see Fig Eight-12)

This will form an almost watertight join for severe applications, such as bilge pumps, navigation lights, etc.

The ability to make quality electrical connections will go a long way to ensuring a trouble-free electrical system.

If the wiring on your boat is a bit of a mess, use these techniques to improve the situation. Even the worst job can be lifted to an acceptable standard. Start with small areas at a time and eliminate all the bad connections one by one.

While you're at it, try and mark the wires with some sort of wiring code to make future troubleshooting easier.

ESSENTIAL CIRCUITS
As explained previously, these circuits are necessary for the safe operation of the boat and under normal circumstances should not be turned off.

There are no hard and fast rules, but generally the bilge pumps and bilge alarm are fed from this bus, as well as anything else that proves necessary.

A case in point is the drain water from airconditioning. Often this is directed to a sump box with an automatic float switch. If the DC master is turned off but the airconditioning left on, then this sump would flood unless it was supplied from the essential bus.

Fig 13 (opposite) shows a typical wiring diagram for a bilge pump. Note the selector switch, which can operate the pump manually if required. This is a useful feature for testing the pump.

An indicator light is also incorporated and this will illuminate every time the pump operates. This indicator light can be in a special panel (with other lights) to alert the owner when circuits are energised, such as engineroom lights, etc.

When wiring bilge pumps, only use the heat shrink butt connectors and make sure these connectors are well positioned above the level of the float switch. This wiring should be inspected on a monthly basis as it is very susceptible to corrosion due to its location in the bilge area.

Finally, always make sure the float switch is higher than the pump. This will ensure the pump will stop.

Another circuit on the essential bus is the high water alarm. This is simply a float switch mounted higher than the float switches for the main bilge pumps. This float switch is connected to an audible alarm (see Fig 14). In the event of a leak in the bilge area and the failure of the bilge pump, the float switch will cause the alarm to operate and alert the boat-owner.

HOUSE CIRCUITS
All circuits not fed from the essential bus take their supply from the house bus. As can be seen from the introductory basic single and twin engine wiring diagrams, this is energised through the main switch and it's a good idea to turn this off when leaving the boat for any period.

For example, if a leak were to develop in the freshwater plumbing and this plumbing was supplied by a pressure pump, this pump would run until it either burned out (these pumps are not designed for continuous operation) or the batteries went flat. However, turning off the main switch before leaving ensures this cannot happen.

Some of these circuits do not control the device directly, merely the actuating solenoids. High-power equipment such as the anchor winch, bow thruster and inverter are among these.

The following is a list of some of the house circuits:

CLEANLINESS IS NEXT...
As mentioned earlier, the wiring on a modern powerboat can rival a small aircraft in complexity. This is the main reason that as a boat ages, and all the latest toys are added by successive owners over the years, the wiring tends to become more and more muddled.

I have seen some boats with only four DC circuit-breakers controlling nearly 15 circuits. This means that a fault in, say, the bait pump, prevented the wipers, sound system, autopilot and shower sump pump from working! Hardly ideal.

Repairing the wiring on your boat is not as difficult as may appear at first glance when contemplating the mess behind the switchboard. The first step is to decide what type of repair is necessary.

I find that these tend to fall into one of three categories: a tidy-up, partial rewire or the full monty.

THE TIDY UP
This is done when the system is basically wired correctly with the correct sized cable, etc, and sufficient fuses or circuit-breakers to service all the circuits.

What I tend to do in such circumstances is to disconnect the switchboard at the main bus, if there is one. If not, it is the first thing to be installed.

Bring all the boat's wiring to the main and essential buses and terminate neatly and mark each cable. All the negatives will terminate at the neg bar, but it is not usual to mark these wires.

When everything is neat and securely saddled, the switchboard can be wired to the buses. Make these wires a reasonable length so that the switchboard can be swung aside to allow for easy fault-finding and additional work.

PARTIAL REWIRE
Partial rewires are generally necessary when all the additional wiring (post-manufacture) is unsatisfactory - a common occurrence.

Generally, the standard circuits such as navigation lights, interior lights, etc, will be okay but the wiring for radios, depth sounders and the like will be ordinary.

In most cases it's easier to pull all these defective cables out and start again using the correct wire.

The switchboard will usually have to be increased in size as invariably three or four circuit-breakers or fuses will be protecting up to 20 circuits.

Sometimes it's easier to install a sub-board near the main switchboard and transfer a whole group of similar circuits to this, such as navigation instruments. Thus this board might protect GPS, radar, radios, depth sounder, plotter, etc.

Moving these from the main board to the sub-board makes a lot more room on the main board for additional work.

Once all the cables have been pulled into the switchboard, complete the work in the same manner as a tidy up.

THE FULL MONTY
If the boat has been so poorly wired initially that constant electrical breakdowns occur, then perhaps you may just have to bite the bullet and start again.

That said, such a case is unusual in my experience - generally the basic cables are okay but completely new switchboards are necessary and every cable requires re-terminating properly.

If the work is approached in an orderly fashion, with a definite plan based on a basic wiring diagram, then there should be little trouble.

If a new switchboard is necessary, then the option to purchase or make it yourself will require addressing.

Indeed, in this case it's important to no our limitations... And perhaps the telephone number of a qualified marine electrician...