Dear Linda,
Congratulations on your new sailboat! You asked me what electrical information you need to know to maintain your boat. Here is the topic that causes the most problems for our customers. Actually it is two topics, shock hazard and corrosion, that can’t be separated.
As you know, the combination of water and electricity creates shock hazards. This is the reason GFCI outlets are installed in wet locations such as bathrooms and kitchens. I’m sure you’ve had to reset the GFCI button on your bathroom outlet when your hair dryer overheats and trips it. The GFCI compares the balance of electrons entering and leaving the outlet and trips when it senses a loss of a few electrons. Please make sure all AC circuits on your boat are protected by GFCI’s or GFCI outlets.
Next, do you know the difference between AC and DC electricity? AC is your home’s electrical system and also what your boat’s shorepower plugs into. DC is how batteries work. When your boat is unplugged away from the dock, it runs off DC, except some larger boats have inverters, which invert battery DC into AC. Since your 24 ft. sailboat is relatively small, its AC shorepower probably runs only a battery charger, and perhaps an outlet or two. On larger boats there are often numerous AC devices such as AC/DC refrigerators, water heaters, etc.
AC electricity is more dangerous. When your boat is plugged in to shore power at a dock with other boats, there is more risk of shock. AC shorepower runs in one big circuit along the dock through all the boats plugged in, and is grounded back on land at the marina’s main power panel. Corroded or miswired boats create AC stray currents that try to find a path back to ground. Stray current seeking ground can run through the water, along metal docks, and through other boats trying to get to ground. Divers and swimmers have been electrocuted by such currents.
To keep boaters on board safe from AC shock, most boats have their AC and DC grounds tied together. Then if there is short in the AC system, it can go to ground through the DC system: out the engine and other through-hull connections to the water.
This AC DC ground or “green wire” connection creates another problem. Stray AC current also builds up on the dock’s shared ground wire, carrying it onto your boat and causing corrosion in the DC fittings and emanating stray current into the water.
The solution is to install an isolation transformer on your boat. It isolates your boat’s AC from the shore. Your boat’s new AC ground will be on your boat, at the isolation transformer. Your GFCI’s will still work, and will protect you from faulty appliances within your boat. You will be separated from stray current on the dock’s AC ground. The isolation transformer will also correct reversed polarity coming from your dock’s shorepower connection. And your AC and DC grounds no longer need to be tied together.
Some vendors recommend galvanic isolators. We don’t. See the Practical Sailor August 15, 2002, “AC Shore Power: An Invitation to an Electrocution?” for a complete discussion of isolation transformers versus galvanic isolators.
Even if you have no AC onboard, your boat will slowly corrode as its various metals and other materials break down. There are two main types of corrosion: galvanic and stray current. Usually when boaters say they have corrosion problems they are talking about AC stray current corrosion. Basically, AC or DC stray current adds to the natural process of galvanic corrosion.
Prevent galvanic corrosion by attaching zincs that will corrode instead of the metal fittings they protect. The zincs will work only if your boat is properly bonded. See Chapter 5 of Boatowner’s Illustrated Handbook of Wiring, by Charlie Wing, 1993, to learn about bonding and grounding. You also need bonding for lightning protection purposes.
Again, prevent AC stray current corrosion by installing an isolation transformer. In the past, isolation transformers weighed about 200 lbs. and cost over $1,000. Now they weigh less than 60 lbs. and cost $700 for a medically shielded isolation transformer. We sell only the medical type to avoid the health effects of electro-pollution. See www.microwavenews.com or www.emfservices.com for further information on health effects of electro-pollution. See www.silencingthefields.com for how to reduce your boat, home and workplace electrical fields.
Have fun and be safe on your new boat!
Joyce Garner, Garner Services