Shock Tactics

Travis Godfredson and Michael Fitzallen | VOLUME 32, ISSUE 2

The seven deadly sins for boat electrical systems.

Michael Fitzallen is a former aeronautical engineer for the Royal Australian Navy. He has worked with high-voltage hardware in harsh, salt-laden environments, so he knows a floating time bomb when he sees one. In his role as manager of Nautek Marine in Melbourne, Fitzallen sees any number of boats a week that have major electrical problems, which he says are usually avoidable.

In this article, Fitzallen delves into the ‘dark art’ of boat electrics and provides some tips on how to protect your precious pride and joy.


Most boat owners think that everything electrical should be isolated with rubber and buffers like Sikaflex. This is actually a good way to kill your boat. By isolating the components, you’re effectively creating a dissimilar metal potential, like a battery, which will create voltage and accelerate corrosion in your boat.

The experts say everything on your boat needs to be electrically bonded, bringing the electrical potential (voltage) for all items down to the same level. The way to do this is with bonding straps made from tinned copper or copper. These bonds will form a ‘grounding circuit’, connecting all the boat fittings and appliances. Ideally, a grounding circuit is fitted at construction stage. Alternatively, it can be retrofitted. Either way, it will need to be regularly inspected by a qualified marine technician.


Fitzallen says that poor wiring can turn a boat into a live battery – as was the case with an imported fibreglass boat that was delivering 1.2V from the through-hull fittings, which was enough to light a small torch. The cause was loose wires dangling in saltwater in the bilge. The water was acting like an electrolyte, or battery acid, sending current through to the hull fittings. As a result, the owner would get a tingling sensation when he put his hands in the livebait tank. Eventually, the electrical components on the boat started failing and the boat had to be fully rewired.

Whenever possible, inspect the electrical wiring on your vessel to ensure it hasn’t worked loose.


In Fitzallen’s experience, poor wiring can create problems. He says the most common wiring problems are not using tinned copper, wiring that is too thin and poor looming.

Tinned copper wiring is the most suitable in a marine environment because it prevents corrosion. Corrosion is best avoided because it creates resistance – and resistance creates heat. Heat can create further circuit resistance or even a fire. Thin wire can also cause heat caused by carrying to much current, leading to resistance or corrosion. Fitzallen’s rule of thumb is that every independent circuit needs a wire adequately sized and fused for its own requirements. For the technically minded, these are set out in the Australian Standard AS3000.

The length of the wire is also critical. Long wires can cause voltage drop, while short wires can pull on terminals, creating a bad connection (in turn, creating resistance and heat), or potentially can break.

Likewise, too much wiring – especially when coiled together – can create a heater, technically known as electromagnetic induction. Unfortunately, your multi-meter won’t pick up this hazard, because it’s designed to measure volts, not heat. So never coil wires if they’re too long; use the correct length and secure them to the vessel.


The term ‘marinised’ is commonly misunderstood. Sometimes it refers to the water and dust integrity of a component, but it can also refer to the way an appliance is isolated from an electrical system.

Fitzallen often sees automotive parts fitted to boats, particularly stereos. That’s a big no-no. The casing on a stereo is negative, allowing the current from the negative terminal of the battery to flow into the chassis or hull. That’s fine on a car, where the chassis is earthed, however sending current through a boat hull when it’s on the water will cause the vessel to corrode like an Aspirin in water. The water will act like an electrolyte, carrying current between dissimilar metals, creating electrolysis.

It’s not unlike wetting your fingertips and placing them on an AA battery – the fluid will act like an electrolyte, sending a gentle current through your fingers.

Metallic boats are more susceptible to this problem, but timber or fibreglass boats are not exempt either, particularly when moisture is present. Always opt for marine-specific radios on your boat, and be sure to avoid any automotive or non-marinised appliances.


Wiring appliances directly to the battery is a hazardous practice Fitzallen often sees. Most trailerboat batteries sit near the transom, which is the wettest part of the boat. It’s also a common place for fuel to reside – and it’s a major danger-zone for boat fires because of the risk of heat-related problems. Fitzallen recommends running one big cable to a dry, safe part of the boat that can act as a busbar, or distribution point, for the vessel circuit.

The wire to this busbar should be able to cope with all the current for all the circuits or systems if they were turned on at once. Recommended wiring sizes can be found in Australian Standard AS3000. Each wire from the busbar to the vessel systems should pass via a marine fuse or circuit breaker block.

Fitzallen also advises against using stainless steel for conductors. Stainless has some resistance properties and can generate heat. Tinned copper and brass are far more effective and much safer conductors of electricity.


It might come as a surprise to some that timber can also be a conductor of electricity, especially when it’s wet. Timber also absorbs salt, and the minerals themselves can create a circuit between dissimilar metals such as brass, stainless steel and copper. This, in turn, can create electrolysis. In simple terms, this is when an electric current is passed through a liquid that conducts electricity. It can cause the timber to break down at a cellular level, causing wood rot. A grounding circuit can avoid this.


Anodes have long been the catch-all to combat electrolysis. They achieve this by corroding away during the process of electrolysis. As they corrode, they are doing their job of sacrificing themselves, hence the term ‘sacrificial anode’. But studies have shown that excessive zinc anodes can encourage electrolysis, as zinc sits far apart from alloys and other metals on the periodic table. Nowadays, anodes are made from a range of alloys.

Fitzallen comes across several boats a year with no, or insufficient anodes, meaning somewhere on the owner’s boat, another part is slowly corroding away. It’s best to consult a marine electrical technician, who can assess your boat to determine the number and location of anodes required. If your boat needs excessive anodes, then it probably has more serious issues elsewhere that need investigation.


It cannot be stressed enough that, if in doubt, you need to contact an expert in the field. Electrical issues figure prominently in Club Marine’s claims data, with serious implications should things go wrong. Fires and electric shocks are the most grave outcomes and, overwhelmingly, the causes can be traced back to poor maintenance or shoddy workmanship.

Ultimately, lives are at stake when electrical systems go wrong. If you have any doubts whatsoever about your boat’s electrical system, have it looked at now rather than have it develop into a real problem.

How to-Safety