ELECTROLYSIS

[Guest]

ELECTROLYSIS

I have a 70' foot boat, with a fiberglas hull.
Zincs have been appropriately installed on the shafts, struts and rudder.
The boat has been moved to several different local locations.
THE PROBLEM:
The zincs are getting eaten up at an extremely fast rate. The impellors show signs of corrosion, as do the
rudders.
I am looking for help in how to actually measure the amount of stray current flow which is obviously
eating up these parts. (This seems to be a major secret!)

PS: I am not looking for outside sources to do the job; but looking for ways to tackle the job myself.

Sincerely,
Richard A. Sales, Captain
EMAIL: Captainsales@cs.com

 

[Guest]

Hi, Is your boat moored anywhere close to welding work being carried out? if it is, stray current runs to ground into water and corrodes all metal parts!

The other possibility is that you are "leaking" electricity from your own vessel" do you live on board? or do you spend a lot of time linked up to shore power, if so make sure that all your 220/240v is earthed out correctly, no loose earth wires etc. Make sure that the whole system is eared back to the engine blocks and that the anodes are all correctly linked back to the engine.

Hope this helps

Barry

 

[Guest]

Try www.yachtsurvey.com. There's two articles there on corrosion that should either answer any questions you have or will leave you even more confused.

 

[Guest]

Hot to test for electrolysis

Check out our article on DIY electrolysis testing at

http://www.yandina.com/electrolysis.htm

 

[colinroybarrett]

Two types of anodes?

Richard,

As I understand it, there are salt and freshwater anodes? Salt are Zinc and V.Heavy, F/Water are Magnesium and considerably lighter in weight.

Magnesium ones will vanish very quickly in salt water, but are reckoned to be OK for a short occasional jaunt.

Are you buying the right ones?

 

[Guest]

on shore supply?

if on shore supply, you will probably need a galvanic isolator for in the earth line.

it is basically two schotky diodes with their polarities oppossed and connected in parallel. this is then placed in line in the shore earth.

 

[Guest]

Minor correction

For a galvanic isolator you use silicon diodes. Schotky diodes have very low forward voltage drop and are more efficient than silicone, however in this case you WANT the forward voltage drop. In fact the 0.6 volts drop of silicone is barely enough to prevent electrolysis currents. A steel boat protected by zincs can have an electrolytic potential of up to 0.8 volts which would start to turn on silicone diodes. For good protection there should be four diodes - two in series in each leg, and the two legs back to back.

Here is a link to information on the galvanic isolator and how to test it. http://www.yandina.com/galvanicIsolator.htm

tech@yandina.com