Rewire for reliability

When re-wiring a small boat, you want a reliable system that won’t leave you stranded. Select the correct materials and make sure all joints are watertight.

One of the last steps in restoring my Sea Nymph Commander from its near-wreck on a rocky foreshore was the fit-out of electrics, battery and fuel systems.

The first task was the initial wiring. There were a lot of systems for a small boat but the job was well within the capabilities of a motivated amateur. The wiring in a boat is similar to that of a car, so a DIYER with automotive experience will find it pretty straightforward. Where necessary, I engaged the help of a local automotive mechanic. However, there are a couple of differences between car and smallboat wiring – mainly in the selection of materials – and they are important to get right.

TINNED COPPER

The classic beginner’s mistake is failing to use the appropriate wiring for the boating environment – the sort of stuff available at Repco or similar, intended for automotive use, will begin to corrode as soon as it enters a marine environment.

Marine wiring is a different grade, known as tinned copper. That is, the entire length of wire inside its protective sheath is covered in protective solder, similar to the tinning process when you make a soldered joint of two wires.

This type of wire should be used wherever the wiring will be exposed to moisture: areas like the bilge pump, floor lighting in the cockpit and any critical wires such as the main feed from the battery. In some areas, for example the cabin lights, you may get away with standard wiring, which is cheaper and easier to source.

If your boat is permanently in the water I would suggest using tinned copper wiring everywhere. I didn’t, because my boat lives on a trailer in a workshop a long way from the water. The general rule is: if in doubt, use tinned wire.

It is available from some chandleries and your local marine electrician may sell to you from a bulk roll. For modern LED lights, you need to run the smallest size wiring available; for battery feeds, you will need one of the larger sizes, so you will need several different gauges of wire depending on the current draw.

You don’t need to work out the area section of wire required for current draw; if in doubt, just use a larger size. The increased size will provide less voltage loss, a margin for the inevitable corrosion at the joints and is a little more costly in weight and price for the lengths used. I assume you’re not building production yachts and trying to maximise profits here.

SOLDERING ON

Joints in the wiring are particularly vulnerable to corrosion, and if the affected joint is in a main battery cable, its failure could see you out at sea, unable to start your motor to get home – so it pays to take special care ensuring your joints are well-protected.

Soldered joints are preferable to the crimped type, and heatshrink tube with a glue liner is preferable to the normal non-glue lined type – see discussion next column. If you haven’t done any soldering, get someone who has to show you the correct use of fluxes and how to tin the wire. If the preceding two terms are new to you, you definitely need a lesson. It’s not hard, and with the right equipment and instruction anyone who is good with their hands will soon be turning out neatly soldered joints.

These soldered joints will need to be covered in heat shrink. Remember to put the heat shrink on the wire before you solder it. This is easy to forget, and unless you can slide the heat shrink down the wire from one end, you will be unsoldering your joint to put on the heat shrink, and then re-soldering.

Any soldered joint will require at least two pieces of heat shrink: one to insulate the wires from each other and one to cover the whole joint.

Heat shrink comes in a couple of grades. The basic stuff is cheap and exactly that: basic. It won’t protect the joint in areas where it may get wet, like in the bilge for the pump. For potentially wet areas, you need to use Dual Wall heat shrink. It has a glue liner; ie, a second wall inside it, so it doesn’t just shrink onto the job, but actually bonds to it to create a truly waterproof joint.

It’s more expensive than the normal stuff so it pays to be economical with it. The usual electrical wholesalers sell it – I get mine from Ideal Electrical. There are a couple of wall thicknesses available too. Where you are wiring something well away from moisture on a trailer boat – for example, the cabin lights as mentioned above – the normal grade will do.

PROTECTING YOUR POWER

Once you have everything in place and have soldered or crimped joints wherever necessary, I suggest wrapping the wiring loom

“Wire intended for automotive use will begin to corrode as soon as it enters a marine environment.”

in a protective covering. Fibreglass boat interiors sometimes have sharp spikes hidden up under the coamings and aluminium boats tend to have sharp edges in the same sorts of places; any of these can damage your wiring systems. Modern wiring systems are expensive to buy, particularly types like Canbus, so it is worth protecting your investment, especially as the protective sheaths are inexpensive.

There are a few types available, either the split type or spiral wrap type – there are several thickness and size options available. The split type is easier to install and is much easier to come back to if necessary for repairs, but it’s horses for courses. I use the split type where the wiring is concealed and the wrap type for short runs where it’s visible. Use cable ties to keep the cables tidy and to bundle up any excess length; for example for the GPS and fish finder – you can’t shorten these wires.

I elected to go with dual batteries for my electrical installation as I like having a back-up system for anything critical. As Coastguard likes to remind us: fuel problems and battery issues are the major reasons for call-outs. Two batteries give you peace of mind, but involve more work and cost.

MARINE BATTERIES

I went for a normal marine battery for the main unit. Externally it looks similar to an automotive battery, and this fools many people into getting a car battery

TIP: Use tinned copper wire on a boat wherever the wire and its joints will be exposed to moisture.

ride than usual, so I went for an AGM battery (absorbed glass mat). These are more robust than normal marine batteries and are fully sealed against leakage.

Once the batteries were installed, I wired them with suitable size cable and connected them to a dual battery switch which allows charging both batteries at once, or running one at a time. Next, I installed a solar charging system to keep the batteries trickle-charged between outings. In the last few years, these have come down significantly in price and, with the advent of flexible solar panels, are much easier and neater to fit on a boat.

Two batteries required a slightly larger solar panel than needed for one battery, and I had to connect the solar panel to a solar regulator. Fitting the flexible panel was straightforward – a matter of pinching it down on to the cabin roof with some stainless screws and making sure they didn’t protrude inside the cabin. The panel came with some simple screw-through grommet/seals to keep them watertight.

The solar regulator was one of the smaller and cheaper units available, as the panel doesn’t produce a huge amount of current to trickle-charge the batteries. You need the regulator to stop the solar panel overcharging during the day and discharging the batteries during the night. I screwed it inside the cabin, under the deckhead and near to where the panel was mounted on the topside; it was easy to wire it in. Simple LED lights on the regulator indicate whether it is charging or discharging.

Wherever I ran wires from outside the boat to the inside, I used rubber grommets to ensure they were waterproof. These I either made myself or used those available on the market, drilling them a bit bigger if necessary to suit the wire size. They should be tight on the wire if possible to stop leakage – this is why you are fitting them. It is always better to slide them onto the wire whole from one end if you can, but in some cases I had to cut them with a razor blade and put them on once the wires were in place. If you have to cut them, glue them back together and to the boat with Superglue. They give a professional finish for little effort which is exactly what we amateurs want.

I took a fair bit of care with the installation of all these systems as I wanted to get them right first time. As a refit progresses, fittings tend to get built-in so it’s important to do items in the right order so you don’t have to go back and remove cabinetry or trim to get access to wiring. I’m a firm believer in: do it once, do it right. B