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Old 29-02-2008, 22:00   #1
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wiring through hulls and keel bolts to anode?

My question is whether to or not.
I currently have 'Yellow Bird' out of the water to have a leak repaired. (see posting in meet and greats) Turns out the through hull for the cooling water">engine cooling water had an external cowling with another bolt through the hull. It was this bolt that had corroded thus causing the leak. The thing is, this fitting and all others, including the keel bolts are all wired to the anode.
I don't know whether this contributed to the corrosion or not, but it didn't stop it.
The person doing the repair says he would not have them wired together, but rather have each bolt and fitting stand for itself. He was quick to add, however, that he thought I should seek further opinions on this.
I'm sure there are as many sound arguements for, as against.
Would love to hear some of them.
Cheers Steve.
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Old 01-03-2008, 00:19   #2
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We do have some good discussion on this in the archives. But it is a case of are they easy to find.
There are two schools of thought. Isolate everything and connect everything. Both have advantages and disadvantages. I lean toward the connect everything class. If you connect everything, you can not have current flow between as there is a short. The anode takes care of the "whole".
The isolate class consider, if you isolate then current can not flow because there is nothing to connect them. Where that falls down is when you have something that is slightly conductive connecting them. As in, maybe there is enough conductivity in a timber hull, or the plumbing to the enigne or what ever. But also the same thing can happen if you do not have a conductor of sufficient capacity to carry the very small current that flows. This can happen by resistance in either the cable itself, or in any connection to a fitting.
What I assume may have happened in your case is, the bolt has corroded enough to then reduce its conductive ability to the fitting. Thus the bolt then becomes seperated from the circuit protection. But as the anode is protecting all the other fittings, the voltage potential is different between the screen and the bolt. Enough resistance is between the bolt and fitting via the hull. The saltwater connects the otherside and away if goes.
The remedy is to ensure the new bolt has a good clean contact to the screen fitting. Maybe even place a small amount of sealant over the cap of the bolt to help keep water out.
Umm, I do assume the bolt was bronze as was the screen being bronze. If the two are dissimilar metal in anyway, it will cause the same action.
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Old 01-03-2008, 04:23   #3
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Quote:
Originally Posted by Jazman View Post
The person doing the repair says he would not have them wired together, but rather have each bolt and fitting stand for itself. He was quick to add, however, that he thought I should seek further opinions on this.
I'm sure there are as many sound arguements for, as against.
Would love to hear some of them.
A new fibreglass or timber vessel can be easily built so that anodes are not required at all and that is the best way to proceed (in fact a timber vessel should not have anodes on the hull due to the risk of alkali attack on the timber about the anode). But for an existing boat no one can give you any sound advice that you can rely on without having detailed knowledge of your particular boats metals, drive arrangement and electrical systems.

As an example it is even easily possible to build a steel pleasure vessel that requires no anodes at all. In our own steel sail boat's case I specified it in a manner that allowed it to be so but we do have just one anode on the whole boat and that is on one side of the fin keel - it is really for "just in case" should some problem arise. It is replaced every 2 years when the boat is lifted for antifouling and the loss of weight in the anode is probably only about what one would expect from the zinc itself corroding in salt water rather than from galvanic action.

Unfortunately it is very difficult to get reliable advice as to the best protection status for an existing boat and most marine electricians and other boatyard staff just follow old habits. Apart from not getting to grips with the problem there are other issues that can arise such as many small marine diesels are isolated ground now (all Volvos, for example, I believe) so bonding battery negative and/or anodic protection back to their blocks can lead to unexpected problems.

If you find a reliable advisor who has good knowledge of the boat then follow his advice, but otherwise I would suggest being very cautious in changing anything from what you have. For an existing boat built by reliable quality high volume production builders the best advice is always to leave the boat protected in the manner it was when built (if that is known).
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Old 01-03-2008, 06:21   #4
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See the previous discussions at:

“Zincs and the hot marina”
http://www.cruisersforum.com/forums/...rina-8445.html

“Bonding the Prop Shaft”
http://www.cruisersforum.com/forums/...haft-9124.html

“Avoiding Electrolysis”
Avoiding Electrolysi
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