83 2807 with a loose strut

[km1125]

The prop shaft is actually insulated from the strut, via the cutlass bearing. The anode on the shaft is really only for the shaft and the prop. You should have an anode on the rudder, and a "hull" anode that is connected to the bonding system and that bonding system should be connected via wires to any metal that goes through the hull underwater (water intakes, shaft logs, struts, rudder log, etc).

Now, the shaft is connected to the engine, and the engine itself should be connected to the bonding system, so there is SOME path for that anode to protect stuff... but not ideal.

[bud37]

QR_BBPOST I have owned the boat for three years. There is an anode on the prop shaft that shows no sign of degredation. I'm not sure what it's made of but the boat has always been in fresh water. It was also out of the water for at least seven years prior to me taking ownership. How would I check for stray current at the dock? (I know how to use a multi meter...) just not sure where or how I would check

My assumption here is that you are operating in fresh water not brackish or salt...correct ?
Can you take a close up pic of that broken bolt....the sheared end, maybe we can see if it is corrosion related . You will be checking continuity from all the metal fittings back to the engine block and to the divers dream ( a large usually square anode fitted to the transom ), if you have one.........but all these anodes should be Magnesium or aluminium......it is one giant circuit loop.

If the boat is out of the water, remove an anode....if it is heavy then it is a zinc alloy......mg and al are quite light and all the anodes need to be the same material.

Edit : corrected to say zinc alloy......geeezzzz

[Viper]

If the anode has not deteriorated in three years then you have the wrong anode on there. You can go with aluminum for your application. If you have other anodes, they all need to be the same material. And yes the shaft is part of the circuit and will have the same potential as all the gear that's connected to the bonding system. Having said that, there is special bonding hardware for shafts that float on them while they spin. Ideally it's preferable for there to be an easier electrical bonding path aside from the engine.

[CptnCrunch44]

The bolt that sheared off was definitely rusted through... There was some kind of non- carver applied "caulk" around the nut. It sheared off right at the fiberglass line. Boat is still in the water for another couple weeks then she's on the hard and the fun will begin....what is this "divers dream" you speak of. Guess I need to find all of my other "zincs" and see what's up with them.

So if I check between a random thru Hull with a bond wire attached, I should have continuity back to the negative on my batteries? Or the ground on my engine, or both?

[CptnCrunch44]

Ido cathodic protection tests at work for underground tanks....I wonder if this is the same....it's definatly similar!

[Viper]

QR_BBPOST.....what is this "divers dream" you speak of....

It's a rectangular anode (don't use the term "zinc", that is the material) usually mounted on the transom. Not all boats have them though, and it's not necessary to have anodes on each piece of running gear such as shafts, trim tabs, rudders, transom, etc., it really depends on your particular conditions. There is such a thing as too much anodidic protection that can actually do more harm than good. An anode doesn't have to be on every piece of equipment as it protects a wide area around it.

You need a special meter and probe to check stray current in the water around you. This is something the marina should be checking on a regular basis to ensure their dockside wiring isn't contributing to corrosion issues. Having said that, it could be as simple as a problem with the boat beside you. You'd be surprised at how quickly a problem here can cause a boat to sink.

[bud37]

QR_BBPOST Ido cathodic protection tests at work for underground tanks....I wonder if this is the same....it's definatly similar!

Here is a quick read to explain further.......Do you use a reference electrode at work to test.

http://www.pcmarinesurveys.com/AC%20DC% ... olysis.htm

[bud37]

QR_BBPOST

QR_BBPOST Ido cathodic protection tests at work for underground tanks....I wonder if this is the same....it's definatly similar!

Here is a quick read to explain further.......Do you use a reference electrode at work to test.

http://www.pcmarinesurveys.com/AC%20DC% ... olysis.htm

https://www.youtube.com/watch?v=TV6SvBQShgA

[bud37]

QR_BBPOST

QR_BBPOST

QR_BBPOST Ido cathodic protection tests at work for underground tanks....I wonder if this is the same....it's definatly similar!

Here is a quick read to explain further.......Do you use a reference electrode at work to test. Now all this could be just from your impact, but it was the bolt shearing like it had rusted like you said that set some alarm bells off....the testing and correcting the anodes and bonding system is a necessity in any case and a good check for anyone.

Also check your fuel fill for proper grounding.

http://www.pcmarinesurveys.com/AC%20DC% ... olysis.htm

https://www.youtube.com/watch?v=TV6SvBQShgA

[CptnCrunch44]

I am a member of a small private club. we try to do as much ourselves as we can. the is no "marina" staff
. just fellow boaters.
the cathodic test I do at work consists of checking the electrical potential between a steel tank and a Magnesium sacrificial anode. oh and there is a bond wire on the strut bolts....( dont know how well its working...but its there)