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Old 15-12-2019, 10:56   #46
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Re: Prop shaft bonding brushes?

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Crevice corrosion will occur in areas of oxygen starvation, e.g.; the SS shafting inside a cutlass bearing. This area is oxygen deficient and the strongly adhering passivation film will break down exposing SS that is active and anodic to the rest of the shaft. Crevice corrosion ensues.
Also in deep pitting with stagnant water on say a flat surface with little to no drainage.
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Old 20-12-2019, 12:01   #47
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Originally Posted by suiramor View Post
On my Beneteau 46 the only sacrificial anode is at the end of the prop shaft (propeller end). However, it seems that the shaft is bonded to the rest of the system with a copper strap, which appears to be connected to the fiberglass (!) part of the shaft enclosure (see picture). Even if I am wrong and the enclosure is metal (I have not checked yet - difficult access), that's not the best connection to the anode anyway. I heard of carbon brushes one can get to create a better connection to the moving shaft but the only one I am finding on the web is ProMariner, which looks flimsy and has mainly bad reviews. Does anyone know where I can get something more substantial? Something where the contact carbon is on a spring so it fits more snugly to the prop? Am I correct even relying on the prop anode or should I be considering adding something fixed to the hull?
Do you have a cast ferrous keel?

I have a friend with a similar ex charter Beneteau it has a very beautiful cast ferrous keel sort of a wing keel, However it was not protected by anything except paint, and the prop anode used to dissolve like crazy (it is tiny), He found crevice corrosion of the keel during a haul out and had a nice shiny anode installed on it - end of problem
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Old 20-12-2019, 12:54   #48
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Re: Prop shaft bonding brushes?

Would be correct to understand all the above as saying that bonding all submerged metals spreads the risk of any of them deteriorating faster than other, assuming they are all made of same metal? Given the assumption is unlikely to be valid, that currently there is no bonding installed at all and if I do install it, it needs to have these strict resistance characteristics, should I even bother?
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Old 20-12-2019, 12:56   #49
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Re: Prop shaft bonding brushes?

@mdenize: yes, I have exactly the same keel and see exactly the same corrosion. I will definitely install and additional anode on it. Thanks for the tip.
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Old 20-12-2019, 13:02   #50
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Re: Prop shaft bonding brushes?

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Originally Posted by suiramor View Post
Would be correct to understand all the above as saying that bonding all submerged metals spreads the risk of any of them deteriorating faster than other, assuming they are all made of same metal? Given the assumption is unlikely to be valid, that currently there is no bonding installed at all and if I do install it, it needs to have these strict resistance characteristics, should I even bother?
That’s the great debate. Bonding allows for all submerged metals to have the same potential while doing so connects all dissimilar metals together. Been argued extensively.
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Old 20-12-2019, 13:08   #51
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Re: Prop shaft bonding brushes?

If it ain't broke, don't fix it.
If there are multiple attacks and you are on shore power, install a Galvanic Isolator. Around marinas you may need a DoubleGalvanic Isolator
Inspect underwater metal periodically. If it shows no signs of deterioration don't bond it and invite trouble.
If it is already bonded it might be time to see if disconnecting it solves the problem.
If none of the above are working it is time to provide a sacrificial anode.
If the anode cannot be directly attached to the object a more remote anode and bonding to connect it is needed.
The area of coverage in salt water is about 6 feet radius from the anode depending on how aggressive the electrical environment is.
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Old 20-12-2019, 18:11   #52
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Re: Prop shaft bonding brushes?

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Originally Posted by suiramor View Post
@mdenize: yes, I have exactly the same keel and see exactly the same corrosion. I will definitely install and additional anode on it. Thanks for the tip.
Sorry to hear that

I am not sure why Beneteau would put such a huge hunk of iron in salt water without protection part from cheapness over lead or design obsolesce however as others have said I would try to find out why and how it is supposed to be protected. What my mate found was very active and aggressive corrosion (clean iron/steel - no rust in the crevices) which made cleaning and epoxy filling easy ( lots to key to) an anode directly attach to the back of the keel fixed the symptoms but probably not the problem since it was launched without a keel anode... we do not know how long it had been doing it though!
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Old 21-12-2019, 12:58   #53
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Re: Prop shaft bonding brushes?

Quote:
Originally Posted by suiramor View Post
On my Beneteau 46 the only sacrificial anode is at the end of the prop shaft (propeller end). However, it seems that the shaft is bonded to the rest of the system with a copper strap, which appears to be connected to the fiberglass (!) part of the shaft enclosure (see picture). Even if I am wrong and the enclosure is metal (I have not checked yet - difficult access), that's not the best connection to the anode anyway. I heard of carbon brushes one can get to create a better connection to the moving shaft but the only one I am finding on the web is ProMariner, which looks flimsy and has mainly bad reviews. Does anyone know where I can get something more substantial? Something where the contact carbon is on a spring so it fits more snugly to the prop? Am I correct even relying on the prop anode or should I be considering adding something fixed to the hull?
I'm coming late to this post but you most likely keep your boat in a marina with many other boats present and it sounds like you are concerned about needing more anode protection. 1) If it will fit place another anode further up on the shaft. Many owners use multiple anodes. 2) If you have a fixed prop add a Bronze Prop Nut Fastener anode. 3) Drop an anode over the side of the boat when at the dock that is wired to one of the transmission bolts. You can make your own or purchase a CMP Grouper.

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Old 22-12-2019, 21:19   #54
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Re: Prop shaft bonding brushes?

Originally Posted by suiramor
On my Beneteau 46 the only sacrificial anode is at the end of the prop shaft (propeller end). However, it seems that the shaft is bonded to the rest of the system with a copper strap, which appears to be connected to the fiberglass (!) part of the shaft enclosure (see picture). Even if I am wrong and the enclosure is metal (I have not checked yet - difficult access), that's not the best connection to the anode anyway. I heard of carbon brushes one can get to create a better connection to the moving shaft but the only one I am finding on the web is ProMariner, which looks flimsy and has mainly bad reviews. Does anyone know where I can get something more substantial? Something where the contact carbon is on a spring so it fits more snugly to the prop? Am I correct even relying on the prop anode or should I be considering adding something fixed to the hull?


I have a Bene361 that when connected to shore power the propshaft anode disappears quickly. Prior to solar installation and subsequent disconnect from shore power the anode would last about 3 months. Make sure your AC neutral (white) and AC safety ground (green) wires are separate and not connected on board your boat. The prop shaft is not isolated (electrically) from the engine. I installed the infamous AC isolator as well but have not really taken the time to quantify any improvements other than to say it still disappears.


I bought the boat new so for the most part I can vouch for much of the equipment.



As mentioned by others, the copper strap definitely looks as if it could be a remnant of a RF grounding scheme for a radio rig. I use a thru hull myself. If a radio is connected to it (and it is being used as an RF ground) make sure the strap is DC isolated from ground so as to not upset your single point DC grounding scheme. A radio antenna grounding strap should incorporate several if not more RF capacitors for this reason.


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Old 27-12-2019, 10:52   #55
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Re: Prop shaft bonding brushes?

In reply to @CharlieJ:
1. What is the anode material (zinc or aluminum)? Zinc
2. How many anodes are installed? 1, on prop shaft; just added another on keel and will add more when boat hauled out next time.
3. Can your diver vouch for the quality (Mil-Spec) of the anodes? Not sure
4. Do you have a galvanic isolator installed? Is it functioning properly? Yes, installed 3 mnths ago. However I tested it as per https://www.boatingmag.com/testing-galvanic-isolator/ (suggested by someone else on this forum - thanks!) and it showed correctly going slowly to 1v when touched one way but all the way up to 2v and stopping (which may be my instruments max anyway) when connected the reverse way. Not sure what that means.

@UncleBob: how do I check/test whether my alternator is correctly connected to the engine block and battery negative? Is it just a visual check?
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Old 27-12-2019, 11:03   #56
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Re: Prop shaft bonding brushes?

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Originally Posted by suiramor View Post
In reply to @CharlieJ:
1. What is the anode material (zinc or aluminum)? Zinc
Yanmar service advisory on cathodic protection.
Attached Files
File Type: pdf Yanmar saildrive anodes.pdf (66.8 KB, 32 views)
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Old 27-12-2019, 13:32   #57
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Re: Prop shaft bonding brushes?

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In reply to @CharlieJ:
<SNIP>
4. Do you have a galvanic isolator installed? Is it functioning properly? Yes, installed 3 mnths ago. However I tested it as per https://www.boatingmag.com/testing-galvanic-isolator/ (suggested by someone else on this forum - thanks!) and it showed correctly going slowly to 1v when touched one way but all the way up to 2v and stopping (which may be my instruments max anyway) when connected the reverse way. Not sure what that means.
<SNIP>
That means your Galvanic Isolator has failed and needs replacing however that would not be having any effect on zinc anode depletion.
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Old 27-12-2019, 13:49   #58
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Re: Prop shaft bonding brushes?

I bought it new 3 mnths ago! Would I test a new one similar way: measure voltage build-up from either end of isolator?
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Old 27-12-2019, 13:56   #59
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Re: Prop shaft bonding brushes?

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I bought it new 3 mnths ago! Would I test a new one similar way: measure voltage build-up from either end of isolator?
Yes.
However test it again, isolator failure to "fail open" on one or both sides is extremely rare. To meet ABYC specifications it should be "fail safe" which would give a nearly zero reading in the faulty direction. More likely a manufacturing defect unless you have had a lightning strike in the vicinity recently. Yandina Isolators have unconditional warranty and no warranty returns in the last 18 years!
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Old 28-12-2019, 09:18   #60
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Re: Prop shaft bonding brushes?

@Yandina #57:
Quote:
That means your Galvanic Isolator has failed and needs replacing however that would not be having any effect on zinc anode depletion.
Please explain the underline part above. A malfunctioning galvanic isolator could have everything to do with accelerated anode wastage.

A galvanic isolator is installed, and if functioning correctly, will block cathodic protection current from leaving the vessel via the safety ground wire. Without a galvanic isolator, cathodic protection current can leave the vessel and:

1. protect underwater metal components connected to the safety ground system; e.g., metal sheet piling, exposed concrete rebar, etc.
2. protect adjacent vessels also plugged into shore power that have inadequate sacrificial anodes for their underwater metal components.
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