Shore power must be one of the greatest inventions of all time. We can sit on our boats in the Marina enjoying all the comforts of home, TV, heater and kettle all contribute to a life of comfort. All the time we are blissfully unaware that down below the waterline our beloved boats metal bits are happily dissolving away.  Now you may be asking, why is there a picture of the surface of the moon on this page?  Sadly this is not a lunar landscape but the surface of an anode fitted to a boat which was linked to shore power. The anode was only two months old and was 75% eroded. The problem here is that it was not the only anode on the boat and they were all as bad.  The cost of having the boat lifted and the anodes changed came to several hundred pounds. Imagine having to do that several times a year. Worse still imagine what would happen if all the anodes dissolved. The next thing to go is your more expensive metal bits, like aluminium casings of the out-drives, maybe your rudder, or propeller, how about the odd skin fitting below the waterline.

Why does this happen?  Well as we all know sea water and metal don’t mix, but if your boat is built correctly all the underwater metal bits will be electrically connected together with an earth wire.  This helps protect the metal from corrosion. That is until you plug into shore power. You then become part of a large floating battery.  Forget the 240Volts of the mains power, this does not cause any damage to your boat, it is the small galvanic voltages of this giant floating battery (usually less than 1.2 volts DC) that cause the problem.

So how do you prevent it? Well you could lift he boat out of the water, permanently, or leave the marina and never plug into shore power. There are a couple of other alternatives.

The cheap alternative is to fit a galvanic isolator. This is basically two diodes which will allow the mains power to pass but stops the small galvanic voltages that cause the problems. They work reasonably well but there are no guarantees. They will not stop galvanic corrosion but they will slow it down. They are budget priced at around £100 and are ideal for the boater on a budget. They must be installed correctly, if not they may, at best, simply not work, or at worst be dangerous.

The professional alternative is to fit an isolation transformer. A Mastervolt isolation transformer will help preserve your valuable boat and provide you with security through a correctly earthed AC power system.

The Mass GI is an extremely small and light (only 6 kg) isolation transformer supplied with the latest high-frequency electronics switch technology. Suitable for 120V and 230V AC systems, its capacity of 16A/3.5 kVA per unit can be parallel coupled for higher capacity. Two 16A/3.5 kVA units correspond to 32A/7 kVA. This isolation transformer can be fitted in any position on a wall or floor. No rubber mountings are necessary because it does not vibrate or hum. The integrated Soft Start manages the current resulting from connection to the shore.

A LED indicator on the box displays load data. Remote operation is possible via a remote panel. There is also a connection for the automatic activation of the generator if shore power is overloaded. The Mass GI features marine aluminium casing and professional connections with strain relief cable gland. All Mastervolt isolation transformers comply with the CE and ABYC (US norm) guidelines for vessels.
 

For more information call us for free help and advice.

Marine Electrical Ltd 17 Margaret Street Beaumaris, Isle of Anglesey, LL58 8DN Company Number 4640817