What if the hull is Steel, Aluminum or wood?
Hull Potential is the base line potential , of your boat, without any galvanic protection.
That base line is dependent on the water's temperature, salinity and velocity of the surrounding water.
Jim....
Anodes, test cell, fresh water & hull potential.
- Thread starter SycloneDriver
- Start date
Hull Potential is the base line potential , of your boat, without any galvanic protection.
That base line is dependent on the water's temperature, salinity and velocity of the surrounding water.
Jim....
Now that I can actually get the anode on and off, I'll take some additional readings.
Today I remeasured the hull potential, it was -370mv. Then I added a shaft anode and it measured -505mv. The shaft anode has about 3 times the surface area of the prop anode. I feel better about this level of protection.
Bob Olsen recommends hanging the reference electrode within 1 foot of the prop or shaft in freshwater. Were you able to get that close? If so how?
I was not. I've just been hanging the test cell over the side near the prop and about the same depth as the prop. I've been using the same placement every time I test.
That would account for the slightly higher voltage reading than Olsen recommends, -.505 vs -550 to -.1100.
I'm going to have to develop a baseline for my boat as you suggested.Best thing to do to develop your Base Line
Jim...
I cleaned the anodes and prop a week ago with some scotchbrite. Today I tested the hull potential and got a surprise, 933mv. That's a lot higher than I've ever seen it. I don't think I've check it since I installed the new prop. The old prop was red/pink in color after i cleaned it up, I suspect galvanic corrosion.
You cleaned the galvanic protection. I assume you are in fresh water still.
Let the galvanic chemistry come to "Steady State Chemistry".
Depending on water temperatures that may take a week or so.
If you can measure it often, plot Hull Potential versus Time.
Jim...
Only because I just did the same test on my boat. Off the top of my head I had -.450 on the engine block and -.740 on a through hull in the bonding system. All in freshwater.
Lately I've only been checking it to the steering pedestal. With and without the shore power connected.
I wonder why you have such a variance in voltage, that doesn't sound right to me. The bonding system should be a low resistance path and thus have minimal voltage drop along the entire path.
I am in fresh water too.
I wasn't too worried about the -451 mv because the anode was several feet from the prop. I did think it was odd that the engine was higher than the through hull, my only explanation is the bolts have a coat of paint on them.
Please Note Fresh Water galvanic corrosion is a very slow Chemical reaction.
Sacrificial Anodes Surfaces, especially Aluminum, change with Time. Thus they deplete in Mass.
What is the Material of your Propeller?
Jim...
Sacrificial Anodes Surfaces, especially Aluminum, change with Time. Thus they deplete in Mass.
Let the newly polished surfaces chemically stabilize.
What is the Material of your Propeller?
Jim...
I believe the prop is bronze. It's a Campbell Sailor.Please Note Fresh Water galvanic corrosion is a very slow Chemical reaction.
Sacrificial Anodes Surfaces, especially Aluminum, change with Time. Thus they deplete in Mass.
Let the newly polished surfaces chemically stabilize.
What is the Material of your Propeller?
Jim...