Dumb Anode Wiring Question...

[cardinal_mark]

Hi all,

I've just changed the hull anode on Viking and noticed that whilst one of the bonding wires runs off and connects to the engine block, the wire from the other stud is connected back across to its opposite number (ie it just connects the 2 studs). Is this normal?? I've had a look at the MG Duff website but they don't have any diagrams for a sail-drive set-up so am none the wiser.

As always, any advice will be greatly appreciated!

Cheers

Mark

 

[damo]

Sounds like a spare wire, or one that used/should connect to a nearby through hull fitting. AFAIK you can connect to any stud, but I guess it is belt and braces, in case of a poor contact with one side of the anode.

 

[Bilgediver]

I guess it is belt and braces
*****************************

Exactly what I was going to say.... /forums/images/graemlins/laugh.gif

 

[VicS]

[ QUOTE ]
(ie it just connects the 2 studs). Is this normal

[/ QUOTE ] Not necessary at all.

The important thing is that the anode(s) must be connected via a good low resistance connection to the items to protect. (The MGDuff website recommends a gauge of wire to use) The anodes must also be reasonably close to those items. What do you think they will be?

I would expect your sail drive to have its own anodes which you should inspect any replace as and when necessary. Refer to the manufacturers literature/owners manual for full info on that. This is important.
Assuming that to be the case I cannot see why your hull anode is connected to the engine block. It won't protect the engine which very probably has its own internal anode, at least if it is raw water cooled, inspection and replacement of which should be part of the normal service routine.

 

[cardinal_mark]

Yes, the saildrive has its own anodes - all replaced today. I should have said 'I assume' it goes to the engine block! I'll have a closer look tomorrow and see just where the little devil does go...


Cheers

Mark

 

[VicS]

[ QUOTE ]
Yes, the saildrive has its own anodes

[/ QUOTE ] I was afraid you were under the impression that the hull anode was protecting your saildrive and that a connection to the engine was part of that.

Not that dumb after all

 

[cardinal_mark]

[ QUOTE ]
Not that dumb after all

[/ QUOTE ]

Thats the kindest thing anyone has ever said about me, I'm touched!!

Mark

 

[Sans Bateau]

Are you saying that if an additional anode was fitted that had engine, saildrive, rudder stock, skin fittings etc connected to it, there would be no benefit to the saildrive? Put another way, if a large robust anode was employed to cover all the above you would still need a saildrive anode?

 

[vyv_cox]

A hull anode can never protect an engine, under any circumstances. In the simplest case, say attaching an anode to a steel rudder or something similar, you are creating a cell, once the assembly is immersed in seawater. Electrons pass between the anode and rudder, via the seawater, then complete the circuit by passing from one to another where they are connected. However, there is a limit to how far the electrons can pass through the seawater. In pipework, offshore platform tubulars and similar items, the range is considered to be six times the pipe diameter. That's why, if you have ever seen film of a platform being launched, it is plastered with anodes, probably six or eight at every node.

In other cases the anode and item being protected might be connected by a wire instead of a direct connection. However, the basic rules still apply - the distance between anode and protected item cannot be too large and they must largely be able to 'see' each other. This is not absolutely the case but is near enough for our purposes.

So for an engine, the electrons would have to leave the anode, pass along the hull, turn a right angle bend into a skin fitting, pass along a hose, probably with bends in it, through a strainer and the seawater pump and eventually to the engine. It just isn't going to happen.

Similarly, the distance between your single anode and all your skin fittings will be just too great, unless your boat has a very unusual layout, for electron transfer.

 

[Sans Bateau]

OK, so with a fresh water cooled engine, an anode on the saildrive, should I consider any other anode protection? I am concerned about the skin fittings and the rudder stock, although the rudder stock is only in seawater when under way.

 

[vyv_cox]

Advice given by Nigel Calder and others is that tin bronze or silicon bronze skin fittings need no cathodic protection, whereas modified brasses such as naval bronze, admiralty brass, do need it. I assume that DZR bronze, actually a brass, might fall into the former category. I think, but could be wrong, that Blakes seacocks and skin fittings are 'proper' bronze but others are probably not.

I have no anodes except one on my propshaft and one on the prop itself. My Blakes and non-Blakes skin fittings appear to be in good condition, with no evident pitting or dezincification. I replaced my P-bracket after about 20 years service and cut it up to check condition. There was slight surface dezincification but no internal degradation. I see no problems on the small amount of rudder stock that is visible and I have never heard of anyone who had a corrosion problem of this component.

So answering your question, I would say that no other protection is necessary but inspect annually for any evidence of problems.

 

[Sans Bateau]

Vyv, As a respected authority on metallograpy its good to have your views, thank you. As much as anything you have saved me some work!