galvanic corrosion

[Terryryan]

hi every one, I have recently bought a narrowboat and took it out of the water to find there is a lot of galvanic corrosion on the bottom and the chines, I have done a google search to find out how to cure it but all it gives me are ways to prevent it PLEASE can anyone help as it is very worrying. thanks in advance Terry

[Alan de Enfield]

If by "cure" you mean replace the lost metal (fill in the holes) this can be done by either having a welder fill in the 'pits' (if the corrosion is localised) or if the corrosion is excessive then you can overplate the bottom, sides or wherever needs it.

 

Whilst it is out of the water - have the depth of corrosion measured, it maybe (for example) that you have a 10mm bottom and 6mm sides and the pits / corrosion is 2mm in which case you have no worries.

[Ray T]

If you moor in a marina and have 240v hook up, it may be a good idea to fit either a Galvanic Transformer of Isloator.

[Leo No2]

My BSC man has always told me, and I have seen the results on a boat with no 240v, that the majority of galvanic corrosion is caused by the 12v system on a boat especially where items have been fitted and use the hull as the earth return. i.e. A standard, I understand, motoring way of earthing an item.

[ditchcrawler]

Page 31 Towpath Talk March an advert from Star Line Boats you can probably look at Towpath Talk on line.

[Flyboy]

My BSC man has always told me, and I have seen the results on a boat with no 240v, that the majority of galvanic corrosion is caused by the 12v system on a boat especially where items have been fitted and use the hull as the earth return. i.e. A standard, I understand, motoring way of earthing an item.

Precisely why a boat hull should never be used as an earth return.

[Grace and Favour]

Terry, I suspect that there are three courses of action you should take, (or, put another way - this is what I'd do)

 

1/ Get a qualified surveyor to look at the hull, measure the corrosion, and follow his recommendations - if the 'pits' require to be filled, they can normally be welded. . . Whilst the boat's out of the water, (and after any remedial work) make a darn good job of blacking it.

 

2/ Determine what has caused the galvanic corrosion, IS any wiring on the boat using the hull as a return, (if it is, rewire correctly), or is there another cause?

You may find the services of an effective boat electrician useful, here.

 

3/ Invest in an isolation transformer/a good galvanic isolator