Little Compass
      RoseCaribbean Compass   July 2013

A ‘Leaking’ Boat

by Maurice Howland

Upon arrival at Marina Bas-du-Fort, on the south end of the French island of Guadeloupe in the Lesser Antilles, we plugged in to a 220 volt, 50 amp outlet — and promptly blew the circuit breaker on the power pole. A marina employee that was dispatched to assist quickly decided that there was something wrong with our boat — oui. I declared that our boat was fine at the last two marinas: Rodney Bay in St. Lucia and Port Louis in Grenada, so something must be wrong with their equipment.

Later, a French-Canadian electrician explained that yes, my boat probably worked fine on the English-speaking islands using US/Canadian equipment, but French islands use European standards that include a very sensitive Ground Fault Circuit Interrupt (GFCI) combined with a residual-current circuit breaker with overload protection (RCBO), and that I have a “leaking” boat.

In the US and Canada a residual-current device (RCD) is most commonly known as a ground fault circuit interrupter (GFCI) or shortened to ground fault interrupter (GFI). In other countries they are sometimes known as safety switches, trips or simply RCDs. RCDs are designed to disconnect the circuit if there is a leakage current. By detecting small leakage currents (typically five to 30 milliamperes) and disconnecting quickly enough (<30 ms), they may prevent electrocution.
Leakage current threshold, response time and the method of deployment of RCDs varies from country to country. RCDs operate by measuring the current balance between two conductors. If these do not sum to zero, there is a leakage of current to somewhere else (to earth/ground, or to another circuit), and the device will open its contacts. More on how we can use this information to test our boats later.
The technical definition for a ground fault with Alternating Current (AC) is: an unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors, i.e., metallic enclosures, metallic equipment or earth. 
Boats built according to ABYC standards have the AC and DC grounding systems connected together at the back of the boat's electrical panel, and the boat’s bonding system connects all the underwater metal objects like bronze sea cocks, rudder posts and strut mounts together electrically via a green 8 AWG wire. An AC leak will exit via the underwater metal as it tries to find a path back to its source. If, (a big if) you are plugged into the dock, and if that dock’s grounding system is in good shape some of the leakage current will follow your power cord back to the source.

We were oblivious to our boat’s electrical leak for hundreds of miles and numerous marinas before that finicky French marina would not play nice with us. So, what is the big concern? A leaking boat can kill. If a swimmer enters into the current path in the water around the boat, they are going to get shocked. Depending upon the actual amount of current they get run through their heart, the shock can range from undetectable to lethal. Most of the research that led to RCDs/GFIs was accomplished by Charles F. Dalziel, a professor of electrical engineering at the University of California at Berkeley. In his 1961 paper he describes subjecting 134 men and 28 women to electrical shocks and measuring the “let-go threshold.” He was then able to determine the values needed to prevent electrical shock. “Other tests were made with dry hands, hands moist from perspiration and hands dripping wet from weak acid solutions.” They just don’t make college students like that anymore, or let you do those kinds of tests on them! 

Even current below lethal amounts (1 amp AC) will cause extremely fast and damaging corrosion. If you are replacing your shaft and hull zincs at a rapid pace, you or your neighbor probably has an electrical leak.
If you are not catching fish, you may have an electrical leak. Yes, scientific research has proven that fish are both attracted and/or repelled by electricity. Commercial fishermen have effectively used electricity to help herd menhaden and shrimp into purse seines. Attracting fish using electricity is probably best left to the “experts.” We should probably only concern ourselves with not repelling dinner.
But, how do we know if our boat is leaking? For the electrician in Guadeloupe, finding the offending electrical equipment was easy. He simply had me turn all the breakers off, reset the GFCI/RCBO switch at the power pole, and then watch as I individually turned the equipment back on. It turned out that we had two offenders, the inverter/charger and the oven. The First mate’s solution for the oven was that we could eat out. However, we found that by disconnecting the seldom-used broiling element the leak was plugged. The offending inverter/charger had to be replaced.

But what if you are not plugged into a finicky French marina? Remember above where I said that the way RCDs work is by measuring the current balance between two conductors? If these do not sum to zero, there is a leakage of current to somewhere. Normally when using a clamp-on amp meter you are measuring amperage flow through a conductor so you clamp only around one wire. To look for current leakage clamp around the whole cord. With alternating current (AC) the current flow is really in two directions, it is alternating. It must cancel itself out, or be a sum zero situation. If your boat is not leaking the amp meter should read zero. The best way to take this measurement is to turn on your AC appliances one by one and see if the reading changes, just like the electrician in Guadeloupe had me do. If you get a reading that keeps going up as you turn on appliances, then you have what is called a “false ground” whereby there is a neutral to ground connection (common in land-based electrical connections) either at the panel board or at an appliance that should not exist.
A check should also be made for stray current in the water especially to ensure your boat is not driving fish away and eating zincs. This is best performed away from the dock so that you are not reading your neighbors leakage. A silver chloride electrode is the best type of reference electrode for detecting stray current and testing for cathodic protection corrosion systems (zincs) in seawater environments. The one available from has an electrode that plugs into your multimeter for ease of taking readings (directions included).

An improvised stray current detector can be constructed by attaching a 5-by-7 inch sheet of copper flashing to a broomstick. Then attach a wire to the copper and use cable-ties to secure it to the pole. Set your multimeter to DC voltage and connect the wire from the copper plate to the positive side of your multimeter. The negative side of the multimeter should be connected to a negative battery terminal or a reliable ground. Stick the copper plate in the water and walk around the boat’s parameter looking for a voltage change. The voltmeter should show a natural reading of around 0.6 to 0.9 volts. If, as you activate DC components you see a jump of 0.05 volts or more, you have found at least one of the leakers. Now, switch your multimeter to AC and do the same thing with the AC components. 
Once you have detected and repaired any leaks, you are ready to catch the big ones — happy hunting.

Maurice and Pollie Howland are cruising the Caribbean aboard the DeFever 49 Motivator.


Top of Page

Copyright© 2013 Compass Publishing