Prop anode 'gone' in 6 months

[Ru88ell]

I had my boat lifted out today for a six month check, jetwash and prop service. I was very surprised to find that the anode on the Featherstream was almost gone, and would have probably fallen off in less than a month, yet the hull anode was almost 'as new'. Both were new in November.

I've asked the yard sparky to have a look, but thought I'd ask here if anyone has any ideas why one would fare worse than the other. How should they be bonded?

I don't have an all singing a dancing shore power arrangement, just a camping type RCB not connected to any on board systems.

 

[SimbaDog]

My reply isn't going to help you really, but: I had my boat in Yachthaven for 3 years on a marina berth with power. It ate the prop anode every 6 months but hardly touched the hull anode? I had 3 different specialists look at things & nobody could find why, even fitted a galvanic isolator which made no difference! never did find the answer

 

[VicS]

I had my boat lifted out today for a six month check, jetwash and prop service. I was very surprised to find that the anode on the Featherstream was almost gone, and would have probably fallen off in less than a month, yet the hull anode was almost 'as new'. Both were new in November.

I've asked the yard sparky to have a look, but thought I'd ask here if anyone has any ideas why one would fare worse than the other. How should they be bonded?

I don't have an all singing a dancing shore power arrangement, just a camping type RCB not connected to any on board systems.

The Featherstream prop is I believe made of nickel aluminium bronze with 316 stainless steel blades.

A relatively small chunk of zinc connected directly to a relatively large area of nibral and stainless steel is going to be consumed quite quickly.. Thats the electrochemistry of the situation. Dissimilar metals connected together and immersed in an electrolyte will lead to galvanic corrosion of the more anodic, in this case the zinc.

The prop anode will corrode more quickly than the hull anode because of its proximity to the prop. .. It cannot be any closer can it.

If the hull anode shows very little attack though Iwould check the bonding between it and the prop. You need to be sure that the bonding is good so that if the prop anode is lost completely you still have effective protection from the hull anode.
Check in particular that any flexible shaft coupling is properly bridged.

My reply isn't going to help you really, but: I had my boat in Yachthaven for 3 years on a marina berth with power. It ate the prop anode every 6 months but hardly touched the hull anode? I had 3 different specialists look at things & nobody could find why, even fitted a galvanic isolator which made no difference! never did find the answer

No reason to be confused ... it is what to expect!.... although maybe "stray currents" in a marina might make matters worse if from higher voltage sources than the small galvanic EMFs that a GI will protect against

 

[Tranona]

First check that your hull anode is actually doing something. It should be bonded to the shaft and prop and if properly sited in relation to the prop will provide some protection - that is it should be eroding as well as the prop anode.

 

[Modulation]

6-12 months seems normal for these. There's very little meat on them

 

[Ru88ell]

Thanks folks. Two per year isn't going to break the bank. I'll still have a bonding check done for peace of mind.

 

[Gone sailing]

I have a featherstream and my anode has lasted a year.
They do two different types a short nose and a long nose anode. The long nose anode has more meat on it. Which one do you have?
Have you had a word with darglow they are very helpful.

 

[vyv_cox]

Do you have a prop shaft? An anode on it will save the prop one considerably. Without a shaft anode my Brunton's prop anode lasts less than a season. With one it lasts two and more.

 

[Dockhead]

Lucky guy. My Brunton Autoprop eats at least two anodes a year, PLUS two shaft anodes Sometimes more. Hull anodes usually get changed at the same time, although they are usually not as completely depleted as the prop anode, and might be stretched a bit further.

And I am on a mid-river mooring with no electrical service, so no stray currents. I think it's a function of all that metal in the water. I'm thinking about painting the prop with anti-foul, which surely would reduce this.

 

[awol]

Possibly a daft idea but if the zinc prop anode erodes too quickly and the hull zinc anode is uneroded, changing the hull anode to aluminium might give longer protection.

 

[Ru88ell]

I've had it all checked out, and the bonding is all fine as per the meter with a bit dangling in the water. It's not hard to change the anode, so I just need to keep a spare one on the boat. Thanks for all the feedback.