Slightly corroded pear anode studs and continuity (multimeter novice)

[FairweatherDave]

Been using my multi-meter to test the bonding between the pear hull anode and the prop shaft. The prop shaft has its own shaft anode but I have also tested and found I have continuity between the hull anode and prop shaft. My question is about the quality of contacts I was making with the multimeter as I went through this process - frequently I had no continuity due to dirty or corroded points of contact. Is that just normal when using a multimeter in the real world? I had to work to get the magic "peep" from the multimeter.
So, the detail,....
Initially no continuity between the two studs holding the anode to the hull. The studs are a bit corroded including where the wire comes off to the engine. Eventually with a bit of poking I "made continuity" but should I have been able to do this instantly and have spotless studs? The anode has plenty of zinc (75%) left although the surface is a bit crusty.... I could clean it up. The point is I did get continuity and the anode is obviously slowly wasting as it should, so do I need to do anything? I would obviously replace the anode if slightly corroded studs are a cause for concern.
Thanks for any advice.

 

[Tranona]

Corrosion of the studs is normal as they are mild steel. Should not affect continuity as this is through the terminal on the wire under the nut and washer.

 

[VicS]

Been using my multi-meter to test the bonding between the pear hull anode and the prop shaft. The prop shaft has its own shaft anode but I have also tested and found I have continuity between the hull anode and prop shaft. My question is about the quality of contacts I was making with the multimeter as I went through this process - frequently I had no continuity due to dirty or corroded points of contact. Is that just normal when using a multimeter in the real world? I had to work to get the magic "peep" from the multimeter.
So, the detail,....
Initially no continuity between the two studs holding the anode to the hull. The studs are a bit corroded including where the wire comes off to the engine. Eventually with a bit of poking I "made continuity" but should I have been able to do this instantly and have spotless studs? The anode has plenty of zinc (75%) left although the surface is a bit crusty.... I could clean it up. The point is I did get continuity and the anode is obviously slowly wasting as it should, so do I need to do anything? I would obviously replace the anode if slightly corroded studs are a cause for concern.
Thanks for any advice.

II would check for continuity between the anode ( clean a bit of surface to enable a good contact to be made with the prod) and the prop ( again clean a bit )

I would however have taken an actual resistance reading rather than just relying on the bleeper. The bleeper in my meter will sound at anything below 60 ohms but Id be looking for a resistance substantially lower than 60 ohms

 

[FairweatherDave]

Thanks Tranona and Vic.
If it has worked the photo probably makes the anode stud look quite gory. But your posts confirm my experience about the quality of the surface making contact difficult with the probes. I made no attempt to clean up before I experimented and I will go back and try and measure resistance between prop itself and anode.

 

[William_H]

Just another thought that it would be worthwhile reversing the leads on the digital multimeter. You should get the same resistance measurement of course. Unless there was some strange electrolytic action producing some small voltage. Digital multimeters operate on small voltage drop across the measured connection so could get different answers in different directions. But yes surface corrosion on metal is always a pain when you want an electrical connection. olewill

 

[FairweatherDave]

Well I've spent two further sessions sitting under my boat with the multimeter. Despite using a wirebrush on a grinder on the anode I have not found it easy to get the surface very good for making continuity. Even just across the surface of the anode! But I did finally get a stable reading of about 1 ohm to the prop which I believe is the maximum desirable reading. I am tempted to replace the anode, backing plate, studs and wire purely to see if I can get a better reading. Or am I getting a bit obsessed......? I can just about make out "Duff" on the anode which perhaps shows it is not a good bondined circuit as it is not eroding enough (it is two years old at least.)

 

[pagoda]

Well I've spent two further sessions sitting under my boat with the multimeter. Despite using a wirebrush on a grinder on the anode I have not found it easy to get the surface very good for making continuity. Even just across the surface of the anode! But I did finally get a stable reading of about 1 ohm to the prop which I believe is the maximum desirable reading. I am tempted to replace the anode, backing plate, studs and wire purely to see if I can get a better reading. Or am I getting a bit obsessed......? I can just about make out "Duff" on the anode which perhaps shows it is not a good bondined circuit as it is not eroding enough (it is two years old at least.)

I think you have about as good a connection as you could expect. Put the meter leads together on the low ohms range and you will probably still have 0.6 Ohm???
I was talking with the owner of a US owned ketch who is going round the world (W>E?) . Their hull is all steel. He said they tried various zinc anodes - and finally sourced some commercial ship anodes (about 4Kg?) which last him a couple of seasons. (using 2). I think the moral is don't skimp, zinc is cheaper than the damage.