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Thread: Anodes

  1. #1
    Join Date
    Mar 2013
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    Kemps Quay, Southampton
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    70

    Default Anodes

    Hi, When I bought my Colvic Watson , I replaced the 2 anodes on the rudder and one on the hull. They now need changing urgently after 2+ years.
    It didn't register at the time, but I now notice that the Hull anode is not connected to anything other than the GRP hull.
    I put this to a mate with more knowledge than me and he's convinced that it will still offer some protection as the 'reaction' creates some sort of 'field'.
    Is there any truth in this?... As a layman, I'm sure in an ideal world, there should be a copper strap from this anode to the engine offering some sort of protection to the shaft (very little exposed outside), and the Prop.
    The internal studs are a sod to get at....Is there any truth in his assertion? If so, the shaft/prop protection is more likely to have been 'borrowed' from the adjacent rudder anodes and the hull anode is irrelevant unless I can get a strap onto it.
    Hope that made sense, advice much appreciated.

  2. #2
    Join Date
    Jul 2002
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    Home: Kent. Boat: Chichester
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    41,983

    Default Re: Anodes

    Quote Originally Posted by ctroutz View Post
    Hi, When I bought my Colvic Watson , I replaced the 2 anodes on the rudder and one on the hull. They now need changing urgently after 2+ years.
    It didn't register at the time, but I now notice that the Hull anode is not connected to anything other than the GRP hull.
    I put this to a mate with more knowledge than me and he's convinced that it will still offer some protection as the 'reaction' creates some sort of 'field'.
    Is there any truth in this?... As a layman, I'm sure in an ideal world, there should be a copper strap from this anode to the engine offering some sort of protection to the shaft (very little exposed outside), and the Prop.
    The internal studs are a sod to get at....Is there any truth in his assertion? If so, the shaft/prop protection is more likely to have been 'borrowed' from the adjacent rudder anodes and the hull anode is irrelevant unless I can get a strap onto it.
    Hope that made sense, advice much appreciated.
    Your " mate" is wrong. There must be a good low resistance electrical connection between an anode and what it is fitted to protect. It must also be reasonably close and be "able to see" it.

    If the anode is bonded to the engine any flexible shaft coupling mus be bridged to complete the electrical connection to the prop

    http://mgduff.co.uk/support/fitting-...wooden-and-grp

  3. #3
    Join Date
    Mar 2013
    Location
    Kemps Quay, Southampton
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    70

    Default Re: Anodes

    Quote Originally Posted by VicS View Post
    Your " mate" is wrong. There must be a good low resistance electrical connection between an anode and what it is fitted to protect. It must also be reasonably close and be "able to see" it.

    If the anode is bonded to the engine any flexible shaft coupling mus be bridged to complete the electrical connection to the prop

    http://mgduff.co.uk/support/fitting-...wooden-and-grp
    Makes sense Vic, many thanks.

  4. #4
    Join Date
    Feb 2013
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    820

    Default Re: Anodes

    I agree.

    Can you get to the studs inside the hull and run a bonding wire. That is the setup I have.

    I find if I dont keep the contacts between the wire and stud serviced it does build up some corrosion which is perhaps indicative its doing its job!

  5. #5
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    Mar 2013
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    Kemps Quay, Southampton
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    Default Re: Anodes

    Quote Originally Posted by ip485 View Post
    I agree.

    Can you get to the studs inside the hull and run a bonding wire. That is the setup I have.

    I find if I dont keep the contacts between the wire and stud serviced it does build up some corrosion which is perhaps indicative its doing its job!
    Thanks ip. It's awkward but obviously it will have to be done. That anode it appears has been doing nothing so I'm a bit worried about my prop. I can access it at the next big 'Spring' in about a fortnight here, so I can clean it up and see how things stand. If OK I'll sort the anodes then.

  6. #6
    Join Date
    Feb 2013
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    820

    Default Re: Anodes

    I am afraid I dont know the Colvic.

    Usually the prop / shaft would have its own protection bonded to the shaft or prop which I think is pretty essential. The one on my prop usually falls off after no time but I have totally solved this using nylon bolts.

    The anodes on the hull I am not sure necessarily do a great deal. Mine shows very little sign of eroding despite being well bonded, together with all seacocks (although I know European builders dont tend to bond the seacocks these days). It seems to me the absolute key is anything that is metal below the waterline should ideally have a dedicated anode - bowthruster, keel coolers etc., and if they do, beyond which I am not entirely sure how much an anode screwed to the side of a fibreglass hull actually does?

    My rudder is hung at the bottom off a turtle bar which is stainless and an anode bolted to the bar. This tends to suffer the most erosion, the prop. anode next and I see very little erosion on the keel cooler, or bow thruster, although I know of another boat the same which suffered truly horrific damage to their bow thruster which was not protected. Obviously having some form of galvanic isolation I suspect makes a significant difference.

    I reckon I might need only to change the two main anodes every three years and the rest every five, although I have tended to repalce them every two years.

  7. #7
    Join Date
    Nov 2007
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    31,646

    Default Re: Anodes

    The norm is to have that hull anode bonded to the shaft to protect the prop as suggested in post#2. There are, of course other ways of protecting props in some circumstances but they would not work with the Colvic arrangement. Equally simple fixed blade props can often survive without any anode protection, particularly if they are of the older variety made of better alloys than is now common.

    The whole bonding issue is poorly understood by many, including boatbuilders and yards. There was period when boats became more complicated with lots of metals of different types being used and electricity being added and potential corrosion became more of a problem. The answer was to bond everything without fully understanding the consequences. Thankfully things have now changed somewhat. The approach now is to identify specific potential for galvanic action and protect a specific item, so you no longer see through hulls and seacocks for example bonded, at least on sailing boats.
    Last edited by Tranona; 20-04-18 at 14:43.

  8. #8
    Join Date
    Feb 2013
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    820

    Default Re: Anodes

    Quote Originally Posted by Tranona View Post
    The norm is to have that hull anode bonded to the shaft to protect the prop as suggested in post#2. There are, of course other ways of protecting props in some circumstances but they would not work with the Colvic arrangement. Equally simple fixed blade props can often survive without any anode protection, particularly if they are of the older variety made of better alloys than is now common.

    The whole bonding issue is poorly understood by many, including boatbuilders and yards. There was period when boats became more complicated with lots of metals of different types being used and electricity being added and potential corrosion became more of a problem. The answer was to bond everything without fully understanding the consequences. Thankfully things have now changed somewhat. The approach now is to identify specific potential for galvanic action and protect a specific item, so you no longer see through hulls and seacocks for example bonded, at least on sailing boats.
    Is that the case in the States? I think for example IP still bond all through hull fittings. I am not saying it is necessary, just whether it is still common.

  9. #9
    Join Date
    Nov 2007
    Posts
    31,646

    Default Re: Anodes

    Quote Originally Posted by ip485 View Post
    Is that the case in the States? I think for example IP still bond all through hull fittings. I am not saying it is necessary, just whether it is still common.
    Think it is, but still completely unnecessary. Suspect your seacocks are Perko which are bronze and have no need for an anode as they won't corrode at all even if connected with other bits on the boat, which they are not.

  10. #10
    Join Date
    Mar 2013
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    Kemps Quay, Southampton
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    Default Re: Anodes

    [QUOTE=Tranona;6409986]The norm is to have that hull anode bonded to the shaft to protect the prop as suggested in post#2. There are, of course other ways of protecting props in some circumstances but they would not work with the Colvic arrangement. Equally simple fixed blade props can often survive without any anode protection, particularly if they are of the older variety made of better alloys than is now common.

    The whole bonding issue is poorly understood by many, including boatbuilders and yards. There was period when boats became more complicated with lots of metals of different types being used and electricity being added and potential corrosion became more of a problem. The answer was to bond everything without fully understanding the consequences. Thankfully things have now changed somewhat. The approach now is to identify specific potential for galvanic action and protect a specific item, so you no longer see through hulls and seacocks for example bonded, at least on sailing boats.[/Q

    Thanks Tranona and ip again. I'm a simple soul. When I access my prop/shaft and anodes in a couple of weeks, it will probably be apparent what's been working and what hasn't......Nervous from Southampton.

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