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suiramor · 13-12-2019, 13:16

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?

rbk · 13-12-2019, 13:21

This is what you're looking for...
https://www.fisheriessupply.com/pro-mariner-shaft-brush

...but from the picture it looks more like a copper strap from a counterpoise, although not sure why they'd want the shaft involved. Is it possible it was run in the area and simply fell off onto the shaft?

CharlieJ · 13-12-2019, 13:26

The more fundamental questions is why you are attempting to bond your shaft and to what are you bonding it to? Shaft brushes of the type referenced in Post #2 are generally not an efficient method of deploying cathodic protection current.

Here are some questions:
1. Are the underwater metal components bonded together with AWG 8 wire and with each connection < 1 ohm?
2. Are there any other anodes installed on the boat?

suiramor · 13-12-2019, 13:30

@CharlieJ: 1) No, does not look that way 2) no, there are no other. Re 'the more fundamental question' the answer is most likely ignorance. I have noticed some of my throughulls are getting damage so looking at what I can improve.

@rbk: What's a counterpoise? I don't see any other electrical connection between the shaft and the rest of the boat and since the shaft has the only sacrificial anode I would expect its needed.

Found another thread somewhere else which may have more: https://forums.ybw.com/index.php?thr...pshaft.531204/

CharlieJ · 13-12-2019, 14:09

@suiramor
With the system you described, you do not need a shaft brush. The anode on the shaft or propeller nut is there to provide cathodic protection to the shaft/propeller system.

The copper strapping does look like a counterpoise which acts as the other have of a whip antenna system such as those used form marine single sideband or ham radios. In a bilge it will deteriorate fairly rapidly and is a nightmare to install and maintain. If you do need a counterpoise, come back and post.

suiramor · 13-12-2019, 14:22

Great, thank you! I will trace the copper strip's connections to see what it is there for.

Would the fact that my anode dissolved to 20% of original within 2 months, with no more than 10h of propeller use indicate that I have bad a stray electricity problem in the marina (rather than leakage from within the boat)?

CharlieJ · 13-12-2019, 14:37

That is excessive wastage. Before going down the stray current path here are some more questions:
1. What is the anode material (zinc or aluminum)?
2. How many anodes are installed?
3. Can your diver vouch for the quality (Mil-Spec) of the anodes?
4. Do you have a galvanic isolator installed? Is it functioning properly?

boatpoker · 13-12-2019, 15:44

Since you have a Beneteau it is 99.9% sure that you have plated brass ball valves instead of real seacocks.

Strongly suggest you read the following two articles on that situation.

http://www.pcmarinesurveys.com/Paul%...20Seacocks.pdf

http://www.pcmarinesurveys.com/Paul%...0Mongering.pdf

**EngNate** · 13-12-2019, 21:37

Quote:

Originally Posted by suiramor

Great, thank you! I will trace the copper strip's connections to see what it is there for.

Would the fact that my anode dissolved to 20% of original within 2 months, with no more than 10h of propeller use indicate that I have bad a stray electricity problem in the marina (rather than leakage from within the boat)?

This would be indicative of a stray current issue on board, and the first thing I'd be looking for is a high power alternator that has it's negative connection to the engine block. When this is done, the slightest loss of integrity in the engine negative connection to the battery will cause an elevated voltage on the block and this will be passed to the shaft and propeller. This can also happen with a stock alternator when the connection integrity is poor. All high power alternator installations need an appropriately sized negative cable back to the battery or common negative buss (preferred).

That said, it could also be related to your copper strap mystery and there being no other zinc installed. There is a shaft strut, and it needs to be protected, also metal thru-hull fittings, yes? How much shaft is there in the water? The prop nut zinc is only sufficient to protect the prop. If there is more than some inches of exposed shaft then it should have a zinc too. If other metals are connected to the prop/shaft zinc it will go away quickly. Possibly you have Marelon (non metal) thru hulls and the copper strap to the shaft was a shortcut to protect the strut. Or, there was another anode, a plate or maybe a round zinc on a single stud...(hmm, whats this silly bolt sticking out for, lets cut it off) In any case, you should have one square inch of zinc surface area for each 10 sq. in. of underwater metal (bare SS and copper alloys)(each 7 sq. in. of properly painted steel). A look at the bottom with this in mind will tell if there is supposed to be more anodes there. With or without consideration of radio grounding, boatbuilders often use copper strap for bonding the underwater metals, and often it is run and glassed over with only the connection areas exposed.

Uncle Bob · 13-12-2019, 22:57

Quote:

Originally Posted by EngNate

This would be indicative of a stray current issue on board, and the first thing I'd be looking for is a high power alternator that has it's negative connection to the engine block. When this is done, the slightest loss of integrity in the engine negative connection to the battery will cause an elevated voltage on the block and this will be passed to the shaft and propeller. This can also happen with a stock alternator when the connection integrity is poor. All high power alternator installations need an appropriately sized negative cable back to the battery or common negative buss (preferred).

That said, it could also be related to your copper strap mystery and there being no other zinc installed. There is a shaft strut, and it needs to be protected, also metal thru-hull fittings, yes? How much shaft is there in the water? The prop nut zinc is only sufficient to protect the prop. If there is more than some inches of exposed shaft then it should have a zinc too. If other metals are connected to the prop/shaft zinc it will go away quickly. Possibly you have Marelon (non metal) thru hulls and the copper strap to the shaft was a shortcut to protect the strut. Or, there was another anode, a plate or maybe a round zinc on a single stud...(hmm, whats this silly bolt sticking out for, lets cut it off) In any case, you should have one square inch of zinc surface area for each 10 sq. in. of underwater metal (bare SS and copper alloys)(each 7 sq. in. of properly painted steel). A look at the bottom with this in mind will tell if there is supposed to be more anodes there. With or without consideration of radio grounding, boatbuilders often use copper strap for bonding the underwater metals, and often it is run and glassed over with only the connection areas exposed.

Why is it that mainly north american boat owners are so obsessed with bonding every piece of metal on their boats. Is there something special about that part of the world that requires it whereas most of the rest of us don't have this problem, or is it some sort of custom or belief that one must follow that which is passed down, or what? I have zero bonding on my old fibreglass tub, with no issues, no one around me has either and the only bonded boats that I have heard of around here are steelies or American imports. Is this a routine practice in Europe as well?
Please, what would the cause of the differing experience/custom be?

**Wotname** · 14-12-2019, 04:03

^^ AFAIK, UK boats are generally "un-bonded" i.e. the same as Aussie ones.

CharlieJ · 14-12-2019, 06:17

OP:
Before wandering down the stray current road, my advice is to ensure that the cathodic protection current that your anode(s) is/are producing is staying on your boat to protect your shaft/prop system.

@EngNate:

Quote:

There is a shaft strut, and it needs to be protected, also metal thru-hull fittings, yes?

The strut only needs to be protected if it is connected to a dissimilar metal that is immersed in the same electrolyte.

Regarding the other underwater metal, there are advantages and disadvantages to bonding them together and then to a plate anode and B-. But first, the OP needs to determine if the engineered cathodic protection system installed by the boat builder is performing as designed.

**a64pilot** · 14-12-2019, 06:27

I’ve never understood the shaft brush thing, isn’t the shaft bonded to the engine through the transmission?
Couldn’t you confirm or deny that in just a few seconds with a multimeter?

YANDINA · 14-12-2019, 07:18

Quote:

Originally Posted by Uncle Bob

Why is it that mainly north american boat owners are so obsessed with bonding every piece of metal on their boats. Is there something special about that part of the world that requires it whereas most of the rest of us don't have this problem, or is it some sort of custom or belief that one must follow that which is passed down, or what? I have zero bonding on my old fibreglass tub, with no issues, no one around me has either and the only bonded boats that I have heard of around here are steelies or American imports. Is this a routine practice in Europe as well?
Please, what would the cause of the differing experience/custom be?

Thank you Uncle Bob, my sentiments exactly. To have current flowing you need a voltage difference and a current path for it to follow. Every piece of metal in the water acts a battery with a voltage from just above zero to as high as 0.9 volts for some Aluminium alloys. Until you complete the circuit no current will flow.

So an isolated piece of underwater metal is insulated with no current flow until you complete the circuit with a bonding wire. (This is not 100% true, salt water in the pipes between the engine and a thru hull is a conductor.) So when you bond the HOPE is that the 2 metals have the SAME voltage which will cancel out and no current will flow. This then provides a circuit for sacrificial anodes and provides protection that may not be needed.

My approach is don't fix it if it ain't broke. Bonding should only be connected if electrolytic action is detected on the surface and there is a sacrificial anode in range that could protect it.

Bonding also provides a destination target for surrounding metal on adjacent boats or metal structures that aren't as anal as you for blocking electrolysis.

Yandina has come out with a double galvanic Isolator with 2.5 volts of isolation compared to standard 1.2. With AC voltages on marina ground lines frequently greater than 1 volt it is double protection at a price less than many single isolators.