Galvanic Corrosion?

[Phil Ambrose]

So would a 12v only boat not hooked up to shorepower be subject to galvnic corrosion in any way at all?

In a word yes, as mentioned above you can still get stray DC currents seeking somewhere to roost.

Phil

[MunkeyBoy]

In a word yes, as mentioned above you can still get stray DC currents seeking somewhere to roost.

Phil

Any ideas on how to prevent stray DC currents?

[Ray T]

Any ideas on how to prevent stray DC currents?

 

Take your boat out of the water ?

[MunkeyBoy]

 

Take your boat out of the water ?

Lol nice one!

[comfortably numb]

Much of this thread has gone above my head, but as some posters have said, corrosion can occur but not necessarily. When we bought our 16 year old boat last year the surveyor said the hull was in excellent condition and it had spent every winter since new moored in Braunston Marina with no galvanic protection.

 

So presumably it must be down to luck regarding where you are moored. I've since fitted a galvanic isolator for peace of mind as much as anything.

[trackman]

It certainly can be very random.

Boaters have nothing to worry about compared with railways though. On the 3rd rail routes where there is 600 or 700 V DC, the stray currents get really interesting when things go awry!

Rails can corrode so badly they break, and here we're speaking of bits of steel about 6" tall and weighing 113lb/yard or more. As with boats, the most strange things seem to cause problems, yet in other cases what looks likely to be an issue turns out not to be.

On vulnerable things like pipelines, they use impressed cathodic protection. A voltage is applied deliberately to make the pipes the cathode and a buried lump of sacrificial metal the anode. The current flows through the ground between the two, eating away the anode and stopping corrosion of the pipe.

[MunkeyBoy]

Don't get too smug, galvanic corrosion can still occure with stray DC current.

Phil

What can cause stray current?

[mark99]

Railways (DC) can be a big problem.

Edited May 7, 2014 by mark99

[Phil Ambrose]

What can cause stray current?

Faulty wiring

Phil

[canalboat]

On ‎11‎/‎04‎/‎2014 at 13:20, Loddon said:

The major cause is mains cables connected to the boat and shore with no isolation

It doesnt matter what others are doing if your hull is bonded to mains earth with no isolation it will dissolve.

Scuse me for being thick but does that mean if you have a normal 240v extension lead plugged into the shore and used on the boat only for drills or chargers etc that are NOT earthed to any part of the boat then we should be safe from that type of corrosion?

[Chewbacka]

2 hours ago, canalboat said:

Scuse me for being thick but does that mean if you have a normal 240v extension lead plugged into the shore and used on the boat only for drills or chargers etc that are NOT earthed to any part of the boat then we should be safe from that type of corrosion?

If there are no faults then yes, BUT if there is a live to vessel hull fault on the boat and the RCD on the supply (assuming there is one) does not trip, then anyone touching the boat whilst standing on the bank or in the water would receive an electric shock, possibly large enough to kill them.  If you are using an extension lead in good condition for a few minutes to drill a hole then the risk is low, but for a longer term use - such as powering a battery charger then the risk becomes sufficiently large that you must not do it.  This is why using an unearthed shore supply to the vessel is forbidden by the regulations.  A permanent or semi-permanent supply must be installed correctly.