Galvanic isolator (steel boat)

[masterofnone]

How high up the need list should this item be? On shorepower most of time, replaced anodes last year.

 

[Gumpy]

Some form of galvanic isolation is essential with a steel boat.
Personally I use a transformer one of these:
http://www.airlinktransformers.com/transformer/wp3230-waterproof-transformer.asp
You will however need a decent 16amp supply.

There have been some questions as to the effectiveness of GI when there are computers and other things with SMPSU on board depending on where you keep your boat.
http://www.smartgauge.co.uk/galv_tran.html

Hope this helps

BTW that's on the other boat not the one in the avatar

 

[rogerthebodger]

[ QUOTE ]
There have been some questions as to the effectiveness of GI when there are computers and other things with SMPSU on board depending on where you keep your boat.

[/ QUOTE ]

Pls explain this some more

 

[Gumpy]

SMPSU are Switch Mode Power Supplies as found in many household electrical objects, for a technical explanation of what happens see here:
http://www.smartgauge.co.uk/galv_tran_02.html
Having said that its a problem in freshwater rather than salt water but I always err on the side of caution.

 

[Phoenix of Hamble]

In summary (and simplification), in an SMPSU, RF is reduced by using capacitors (which are in all practical situations a straight through connection to RF) between the live and earth..... this draws stray RF down to earth, but also potentials creates enough voltage across the GI to allow it to pass DC as well, thus negating its effectiveness..

 

[VicS]

Also brings into question the advisability of having one of those "polarity" testing plugs permanently plugged in and indicating the correct "polarity", earth continuity etc. They will presumably be sending a current down the earth wire and putting the GI into "conduct mode".

Maybe not a problem in saltwater. Maybe can be overcome with a capacitor across the GI. Maybe simplest not to leave it plugged in all the time.

 

[nedmin]

Quite high, having had steel boats for many years the wear rate of the anodes should tell you whats happening.In my experience anodes should last a minimum of 3 years ,I,ve still got the originals on at the stern after 7 years.I found that the bow anodes were wearing quite fast .So I fitted a G.I. and this seemed to slow reaction down.One prob. I had a few years ago was that the prop. was going pink. I measured the continuity between the hull earth and propshaft and got a reading of a few milliamps, this could only have been the insulation properties of the oil in the gearbox.I fitted a set of brushes to run on the coupling and this solved the prob. Isolation transformer is better but they are expensive and v.large. I would try the G.I. first.