anode not eroding - what to check?

[antaris]

Hello all,

just pulled my new-old sailing boat out for 2-month winter (well, almost spring) cleaning.

First thing to notice is that the sacrificial anode on the axle has not eroded almost at all... I understand that after a year in the water, it should have signs of wear...

How do I go about it?

 

[Halo]

Do you mean on the prop shaft ?:

 

[antaris]

I imagine that there's a method to check why the anode is NOT eroding and how to alleviate this...

If I understand correctly, if the anode is not wearing away, the shaft itself (or other engine parts) will!

 

[Pye_End]

Check for continuity with a multimeter between prop and anode.

How long had the boat been in the water, and what is the set-up - inboard/outboard/grp/shaft or hull anode etc.?

 

[antaris]

Sure... Boat is a typical 31 foot sloop, Perkins Perama inboard (positioned in middle of coach, over the keel), stainless axle connecting feathering Kiwi prop!

I have noticed that all through-hulls are earthed (bonded to each other).

Boat has been in seawater for 1 year + (just bought her) and is covered in classic antifouling (no exotic coppercoat or similar).

So, yes, one thing is to check that anode actually bonds with stainless axle (I cannot see how this is not happenning, except if paint underneath)

 

[Tranona]

Almost certainly it is not eroding because there is nothing for it to protect. The purpose of a shaft anode is to stop galvanic action between the shaft and the prop. However, your prop is all stainless steel or plastic so there is no potential galvanic action between it and the shaft. Think you can safely remove the anode.

The anode will do nothing with the skin fittings because it is not electrically connected to them. Anyway in a GRP boat there is normally no need to connect anodes to them as again they are not connected to any other metal so no galvanic action. Think your bonding will just be joining them together which achieves nothing so can be removed.

 

[antaris]

That sounds great, since I was a little worried... but I thought that the axle anode also protected the rest of the engine?????...

 

[Tranona]

Nothing on the engine to suffer galvanic corrosion except possibly the heat exchanger, in which case it will have its own anode. Don't think your engine does if it has the same heat exchanger as the Volvo version of the engine.

 

[macd]

I thought that the axle anode also protected the rest of the engine?????...

No.
And please stop calling it an axle.
Then go sailing and have fun.

 

[antaris]

ok man, is shaft better?

I am going sailing.

Thanks for all replies!