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Old 02-03-2018, 15:05   #1
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ohms/volts at shaft and rudder

After trying to solicit information locally and on the internet this seems to be a topic with a million experts, however can someone please try to give me an answer.
I have recently replaced my shaft end anode and rudder anode to a transom anode mounted on studs and bonded from the inside. I have only bonded to my shaft and rudder stock plus glands and tubes in both cases.
If zero ohms or volts is the optimum is there an acceptable maximum.
I have done this at the suggestion of my surveyor who also told me not to bond to the motor gearbox etc.
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Old 02-03-2018, 19:25   #2
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Re: ohms/volts at shaft and rudder

you need a silver silver cell in the water to measure against.

I would have left the shaft anode. those bonding shaft brushes are useless.

that bonding system should also connect to battery neg. at a main buss somewhere.

there are no experts in this field... maybe a couple in the world.
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Old 02-03-2018, 21:44   #3
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Re: ohms/volts at shaft and rudder

Thank you, ships earth is on the engine block on starter motor stud, so bond to there??
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Old 03-03-2018, 10:18   #4
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Re: ohms/volts at shaft and rudder

1. What did you bond the transom anode to?
2. You need to reinstall the shaft anode ASAP. The shaft/propeller system will get little to no cathodic protection from your transom anode unless you use a very elaborate shaft brush assembly such as those made by Electroguard.

Quote:
I have only bonded to my shaft and rudder stock plus glands and tubes in both cases.
3. How did you bond the shaft?

Quote:
If zero ohms or volts is the optimum is there an acceptable maximum.
4. Where do you intend to take these readings?
5. What is the hull material of your boat?
6. Are all of the underwater metal components bonded together with AWG 8 (minimum) wire?
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Old 03-03-2018, 10:29   #5
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Re: ohms/volts at shaft and rudder

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Originally Posted by smac999 View Post

there are no experts in this field... maybe a couple in the world.
Not quite. Here are 53 pages of ABYC Certified Marine Corrosion Analysts

As a retired Certified Marine Corrosion Analyst I say do not take internet advice on this issue. It is simply too complicated for one or two paragraph answers and 99% of the answers you will receive are pure bunk. Talk to a certified expert.
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Old 03-03-2018, 10:59   #6
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Re: ohms/volts at shaft and rudder

If you dig around on the web, or in the printed books from established authors, you will find there has been a long-standing debate (long-standing as in maybe fifty plus years) as to when/if/whether you should earth or bond or not. It is more of a religious or philosophical matter than one of simple engineering. There are pros and cons of going either way, and in the long run you need to run all those down and decide which are best for your specific situation. Bronze seacocks? Marelon? Metal hull? Cruising? Marinas with AC leakage? Shorepower? And possibly, phase of the moon.

The silver cell, and a calibrated voltmeter so the results from it are accurate, become a reasonable long-term investment if you really want to use any logic on this.
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Old 05-03-2018, 01:11   #7
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Re: ohms/volts at shaft and rudder

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Originally Posted by boatpoker View Post
Not quite. Here are 53 pages of ABYC Certified Marine Corrosion Analysts

As a retired Certified Marine Corrosion Analyst I say do not take internet advice on this issue. It is simply too complicated for one or two paragraph answers and 99% of the answers you will receive are pure bunk. Talk to a certified expert.
I am certified. it's a 2 day course. that doesn't make someone an expert.
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Old 05-03-2018, 07:37   #8
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Re: ohms/volts at shaft and rudder

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I am certified. it's a 2 day course. that doesn't make someone an expert.
The Corrosion Course is actually four 9hr. days, not two and the chances of passing that are slim if you do not already have electrical certification and even slimmer if you don't have years of background in the field. These four days do not include the weeks of studying the course material beforehand. Did you forget ?

That's like saying you became an Unlimited Master Mariner in one day (the day you took the exam). and forgetting all the other years of other courses and experience leading to the point where you had the basic knowledge required to pass the exam.

When you think of it, You could actually say you got certified in only 4hrs .... exam time.

it takes years to make an expert. Not one of those certified people woke up one day, took a 2 day (or four) course out of the blue and became certified.
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Old 05-03-2018, 07:45   #9
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Re: ohms/volts at shaft and rudder

+1 boat poker Post #8
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Old 05-03-2018, 17:48   #10
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Re: ohms/volts at shaft and rudder

Thanks guys, I think!!!!!!!!!!!!!!!!!!!!!!
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Old 06-03-2018, 20:07   #11
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Re: ohms/volts at shaft and rudder

As I had contact business wise with Wilson Walton Corp in the 70s I have taken a long shot and passed my query on to them, I know is is WAY below there expertise leve but I thought it was worth a shot, I am sure if there is an expert around it would be them!!!!!
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Old 06-03-2018, 20:26   #12
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Re: ohms/volts at shaft and rudder

I'm going to stick my neck out here and give some actual advice. I humbly request that if I am in any way wrong, somebody please let me know. Actually, forget "humbly" -- I hereby challenge anybody to prove me wrong.

If you have a reasonable sized zinc attached to the transom, then to see how well your rudder-shaft brush is doing, just measure the voltage between the rudder shaft and the zinc contact. It you see less than 0.01V, I'd say it's working well enough. If you can put a Silver Chloride reference cell in the water, then if you are measuring 700-900 mV at the shaft, things are OK.

Disconnect any shore-power connection before making these tests. If any of these voltages change when you reconnect shore power, then you probably need a galvanic isolator in your shore power circuit.

On my small power boat, I have zincs on the transom, and the rudder shaft has a copper braid strap bolted to it, and connected to the bonding system. The braid gives flexibility. I check this braid regularly for corrosion -- so far it looks fine.
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Old 07-03-2018, 07:44   #13
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Re: ohms/volts at shaft and rudder

phil 23
In Post #4 I asked you a series of questions to (1) better understand your level of knowledge and (2) to better understand the overall problem. You have not answered these questions. Rather than assuming that nobody knows anything, respond to reasonable questions, receive answers and then evaluate. "Go read a book" doesn't really help you.

Post #12 is well meaning but taking a voltage (or continuity) reading between two underwater objects on a boat is not meaningful as there will be parallel paths; the bonding system and the water path.

Quote:
If you can put a Silver Chloride reference cell in the water, then if you are measuring 700-900 mV at the shaft, things are OK.
Good advice but, we haven't established what your hull is made of. Different hull materials have different protection levels thus my original question in Post #4.

Quote:
Disconnect any shore-power connection before making these tests. If any of these voltages change when you reconnect shore power, then you probably need a galvanic isolator in your shore power circuit.
Great advice!

BTW, I am one of the names in the 53 pages mentioned in Post #5.
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