Propshaft bonding brushes

[Nonchalant1]

I went under yesterday to check my zincs and 4 of my 6 propshaft zincs needed replacing after only 10 weeks in salt water. They were 3 years old in fresh water, but they still looked perfect a year ago and we have only been on salt water since November, The engine zincs, raw water pump zincs and rudder aincs still look excellent.

Even though I got a beep from a continuity tone test of the shafts and props last winter on the hard, I wonder if I need to add bonding wire brushes that contact the propshafts directly. WHat do others have for this? Is there a good commercial contact spring type brush or do I just make wire brushes out of 10 ga. wire and mount them with gentle pressure against a sanded clean area of the shafts?

Also, should I look for reasons the shaft zincs would go? This boat has no isolation trans or dalvanic isolators. All the other zincs are still fine, so it makes me wonder if the problem is bonding.

Thanks,

Doug Shuman

[SKYCHENEY]

Why would you think the shafts aren't bonded well? They are bolted to the trans, which is bolted to the engine, which has a big ground wire back to the batteries. Am I missing something here?

[Beckytek]

According to Nigel Caldor the coupling is not good enough to make a good connection. He suggests a jumper wire connection across the coupling joint and a spring loaded bronze brush against the shaft connected to the bonding system. Ron

[yachtsmanbill]

I learned a lot of relevant things over the years doing maintenance at the generating station. One critical issue was when ever any welding was being done on rotating equipment, the welding ground was never placed on the base; always on the rotor.You NEVER want to ground through a bearing. PERIOD. One small arc burn is as bad as a chip in the bearing, ultimately causing a catastrophic failure.
If you suspect ANY voltage leaking through the shafts, I would ground them with a carbon brush / spring holder to the bonding system.
The first generation of Dodge OMNIs had a major problem with front wheel drive transmission bearings. It was discovered that Chrysler, in their infinite wisdom had grounded the DC system through the shock tower.The ground was good, but as the unit turned arcing was occurring and burning the bearings.
ANOTHER PERIOD!!
As I mentioned here before, I also learned that a prop / shaft spinning in water is in fact a generator. Even 1Mv can cause a burn. THAT, IMHO is what is eating the zincs.
Mount a temporary brush and go for a ride. While underway, lift the rig and check it with a volt meter.That is simple enough to do. The brush will also protect against any AC leaks from traveling through the trans bearings also. The zincs will still atrophy, but at least not through the gears.
According to NIGEL C. , a given size of zinc should be in the water stream and bonded while underway as a non running gear sacrificial anode. If you do the test with the silver chloride half cell the amount of zinc can be determined by the readings. I believe that my Roamer generated 11 Mvs and required 2lbs of zinc on the transom chine in the stream.
You really need to study the info from Yacht Corrosion Contol Consultants. They also sell the "zinc saver" unit that bonds the zincs, bonding system and neutral on the A.C. end as well. Please invest a little time and investigate this. ITS NO BS. ws

[SKYCHENEY]

I do know not to weld where the ground is on the opposite side of a bearing. I can see your point on bonding across the bearing as well. I can also see where the bearing would be insulated to some extent by the oil that surrounds it and therefore the shafts may not be grounded very well at all. I guess it wouldn't take much to try to get a better bond to the shafts and see if it improves. I'm not sure this will help, but it may be worth a try. Another question is "are they really zinc?" Did you install them or did someone else and did they use magnesium since you were in fresh water?

[yachtsmanbill]

Actually, I did the job long before the zinc / magnesium controversy happened.
I am pretty sure they are zinc. I have 4 across the transom at 22 lbs each for stationary protection plus the running gear stuff, plus the "in stream" unit for underway, for a total of around 100 lbs. I needed to generate something like 25Mv and some small amount of MAs to counter what my boat was producing.
I bought them from Jamestown and they are CAMP weld on type that I had to bolt on to the aluminum hull.
Every zinc, fitting, shaft, rudder, engies, generator, and AC system is bonded through the YCCC zinc saver system. It seems to correct the problems I used to have. Its been clean for 15 years now.(no corrosion) and I have used less than 10% of the zinc. Beginners luck?
Also, you cant count on an oil film to protect from grounding through bearings.
Sometimes this grounding is an issue, and on some boats its not. Just another FM ws

[surfdancer45]

I had to use the spring zinc on my shafts next to the trans coupling. I have enclosed shafts under the boat thus no shaft zincs. Worst marine sells the zincs you are lookoing for, a 12'' flat arm with zinc and wire attachment points. Bob

[yachtsmanbill]

Watched a discovery channel show last nite about raising a B25 from Murray Lake SC (?) Been there since 1943. There wasnt a lot left of the skin. Aluminum on steel frames... Steel rivets etc. Thats bad! The plane was covered in 1-2 feet of silt, which probably contributed to the condition.
In Sturgeon Bay, we put in a dock made from sections of a steel smokestack from a ship, filled with bottom rocks with a 32 foot Aluminum scaffold for the deck. Even in '63, my grandad, an old tin knocker, made heavy rubber insulating pads for mounting the two dis-similar metals. Worked perfectly. The killing factor was the ice. Lasted about 10 years though.
The coolest part was transporting the 5 foot dia. X 4 foot long sections from Bay Ship to the cottage in the backseat of a '26 Model T Ford. They probably weighed more that the flivver. Had to drive through downtown SB to get them home.
These days youd need a million permits, EPA certs, and a colonoscopy or they'd have the S.W.A.T. team down on ya for being a threat to homeland security. Go figure (?)! Something is lacking these days! ws

[Nonchalant1]

I do know not to weld where the ground is on the opposite side of a bearing. I can see your point on bonding across the bearing as well. I can also see where the bearing would be insulated to some extent by the oil that surrounds it and therefore the shafts may not be grounded very well at all. I guess it wouldn't take much to try to get a better bond to the shafts and see if it improves. I'm not sure this will help, but it may be worth a try. Another question is "are they really zinc?" Did you install them or did someone else and did they use magnesium since you were in fresh water?

Sky,

Yes, they were standard "Camp" shaft zincs. I replaced them with the identical type.

Doug

[SeaEric]

6 shaft zincs sounds like a lot. Too much zinc is not a good thing. We have had this discussion here before. I'm going to go take a look at previous posts on this subject. Karl? This sounds like your area of expertise.