Installation Frustration!

[Scott T-Bird]

That confuses me just a bit … Casey says a few things about anodes:
"most common casualty is bronze or aluminum propeller on stainless steel shaft"
"electrical contact is essential" "metal to metal" "anode must be in contact with the protected metal"

http://www.boatus.com/boattech/casey/sacrificial-zincs.asp

Yet we attach the anode to the stainless steel shaft and the anode is close but not in contact with the bronze propeller. So what is that all about?
This website shows 2 forms of stainless. steel http://www.kastenmarine.com/metalparts.htm There is the more noble (than bronze) "passive" stainless steel and the far less noble "active" stainless steel.
This website https://performancemetals.com/pages/sacrificial-anodes-faqs explains that when protecting both the shaft and the propeller, we need to add a third metal - obviously the far less noble zinc or aluminum anode. But the diagram indicates that the anode should be in contact with both metals. We don't do that, do we? The anode is usually in contact with the shaft, which is obviously connected to the prop. But does that count?

I'm assuming that the prop shafts are usually Monel or the "passive" stainless steel, which is more noble than the prop. Are we really protecting the prop when we attach the anode to the shaft?

 

[Davidasailor26]

That confuses me just a bit … Casey says a few things about anodes:
"most common casualty is bronze or aluminum propeller on stainless steel shaft"
"electrical contact is essential" "metal to metal" "anode must be in contact with the protected metal"

http://www.boatus.com/boattech/casey/sacrificial-zincs.asp

Yet we attach the anode to the stainless steel shaft and the anode is close but not in contact with the bronze propeller. So what is that all about?
This website shows 2 forms of stainless. steel http://www.kastenmarine.com/metalparts.htm There is the more noble (than bronze) "passive" stainless steel and the far less noble "active" stainless steel.
This website https://performancemetals.com/pages/sacrificial-anodes-faqs explains that when protecting both the shaft and the propeller, we need to add a third metal - obviously the far less noble zinc or aluminum anode. But the diagram indicates that the anode should be in contact with both metals. We don't do that, do we? The anode is usually in contact with the shaft, which is obviously connected to the prop. But does that count?

I'm assuming that the prop shafts are usually Monel or the "passive" stainless steel, which is more noble than the prop. Are we really protecting the prop when we attach the anode to the shaft?

Yes, the anode is electrically in contact with the prop, which provides the protection. It's the same way those fish zincs can work just by being connected to the rigging or anything else connected to the prop.

 

[dlochner]

This website https://performancemetals.com/pages/sacrificial-anodes-faqs explains that when protecting both the shaft and the propeller, we need to add a third metal - obviously the far less noble zinc or aluminum anode. But the diagram indicates that the anode should be in contact with both metals. We don't do that, do we? The anode is usually in contact with the shaft, which is obviously connected to the prop. But does that count?

This in part depends on the prop. Some props require anodes, my MaxProp for one, others are protected by the shaft anode which should be placed close to an unprotected prop.

 

[Scott T-Bird]

My wish list includes a folding prop! Could be why I'm always looking for signs of prop corrosion!

 

[Gunni]

To be most protective to your prop, the anodes should have a conductive attachment to the prop. The prop will be eaten by galvanic corrosion before it gets a start on the aquamet prop shaft. I use two, one on the prop, one on the shaft.
With fresh anodes, bolted to a polished propeller and shaft, that was then masked and painted with zinc chromate paint.
After a season in the water, showing corrosion erosion of anodes, and loss of zinc on the prop blades.

 

[dlochner]

My wish list includes a folding prop! Could be why I'm always looking for signs of prop corrosion!

Well in that case, disregard all the advice you have been given. Just don't tell Sue.

 

[DougM]

It seems that magnesium anodes are recommended in fresh water. The problem for me has been the inability to find a source. The Boat Zincs website was the only place I could even locate a zinc anode that fit. I need a shaft collar that will fit between the prop and the shaft skeg which has very little clearance. I have kept a zinc anode on the shaft since I changed to a folding prop knowing that it probably does no good as witnessed by the fact that the anode still looks as new as the day it was attached.

I am willing to wager that there are not many boat owners around me that even have a clue as to the purpose of a sacrificial anode. If they did, they still wouldn’t know which metal was best in fresh water.

 

[Ward H]

My wish list includes a folding prop! Could be why I'm always looking for signs of prop corrosion!

Scott, I was going to mention to you that the last time I was at the marina I noticed your prop looking a bit pinkish. I think you need to change it.

 

[dlochner]

I am willing to wager that there are not many boat owners around me that even have a clue as to the purpose of a sacrificial anode. If they did, they still wouldn’t know which metal was best in fresh water.

Absolutely! I'm involved in the restoration of a 65' steel schooner. Over the course of its life it has had significant hull corrosion issues. The first time I saw it out of the water, I sadly amazed, there was one good sized zinc at the bow and a couple of small zincs on the rudder. It's no wonder the boat was corroding.

Boatzincs.com is a good source for all kinds of anodes. If you can't find a magnesium anode that fits, an aluminum will work just about as well.

 

[Ward H]

Are the grounding studs insulated from the case? Do they have a plastic bushing?

Since I have the same GI I’ll be installing this spring, I tried to open up my GI to see what Scott was talking about.
The end caps where the studs are located are plastic so they are insulated from the case.
After removing the 5 screws on one end cap, the end cap wouldn’t come off. It appeared the stud was holding the end cap in place. I would have to remove the nuts on the stud in order to remove the end cap. The nuts and studs seemed to be tight so I didn’t go any further in disassembly.

@Scott T-Bird
I’ve only heard of one boat, over by the travel lift, having corrosion problems. The prop lost a blade due to severe corrosion despite having good anodes. Mike was going to move over near that slip and Dick warned him not too.
I agree that our odds of having problems due to other boats are probably very slim for the reasons you mentioned. If the marinas AC electrical system can contribute to our boats having electrical corrosion, then I’ll be worried.
Since I’m planning to leave my boat plugged in more often, I’m going ahead with the GI when I install the Smart Plug this spring. My take from reading Maine Sail’s comments was the safest thing to do is not plug in but if you do, use a GI as a minimum for corrosion protection from poorly wired boats.

The ProSafe GI was recommended by Maine Sail and others so I’m comfortable using it.

 

[Scott T-Bird]

I’ve only heard of one boat, over by the travel lift, having corrosion problems. The prop lost a blade due to severe corrosion despite having good anodes. Mike was going to move over near that slip and Dick warned him not too.
I agree that our odds of having problems due to other boats are probably very slim for the reasons you mentioned. If the marinas AC electrical system can contribute to our boats having electrical corrosion, then I’ll be worried.

You're talking about that Beneteau, I assume. It is odd, that the other boats in that area didn't seem to have those issues. Dick seemed to indicate that particular boat has had numerous odd issues that have not been completely resolved - issues that the other Beneteaus, Catalinas and O'Days in that area have not had.

 

[Ward H]

That’s the one. At the time my impression was Dick thought it was slip related. It does seem strange that that one boat has issues while others do not. Owner related?

 

[Scott T-Bird]

Since I have the same GI I’ll be installing this spring, I tried to open up my GI to see what Scott was talking about.
The end caps where the studs are located are plastic so they are insulated from the case.
After removing the 5 screws on one end cap, the end cap wouldn’t come off. It appeared the stud was holding the end cap in place. I would have to remove the nuts on the stud in order to remove the end cap. The nuts and studs seemed to be tight so I didn’t go any further in disassembly.

Really? I must have had too much blood racing to my head (and I lost a bunch of blood through my hands and fingers ) when I was trying to thread the screws under the platform. I seem to recall that the end cover simply came apart from the case, with the stud and all, after I removed the 5 screws. I might have taken the two outer nuts off - I don't really recall. That end cover didn't seem like plastic to me. We will have to compare!

 

[dlochner]

The prop lost a blade due to severe corrosion despite having good anodes.

The only stories I've heard about corrosion that bad the cause was nothing an anode would protect against. The cause was always traced back to a faulty DC circuit that was allowed DC current to flow through the prop shaft. It doesn't take much DC current to erode the prop.

(@Scott T-Bird just tell Sue that the red wire from the battery to the prop shaft is part of a new and better bonding system you heard about from some guy on the internet. )

AC current is not nearly as potent as DC when it comes to causing corrosion.

 

[Ward H]

The only stories I've heard about corrosion that bad the cause was nothing an anode would protect against. The cause was always traced back to a faulty DC circuit that was allowed DC current to flow through the prop shaft. It doesn't take much DC current to erode the prop.

The story was the owner backed out of the slip, felt a severe vibration and put the boat right back into the slip. I saw it hanging in the travel lift. The break where the blade broke off was pink clean through the thickness, not the normal looking part old metal and part fresh metal like a stress crack that finally broke.
I had never seen an example of corrosion that turned the bronze pink like that, in person. Mechanic said without the zinc the bronze was brittle so the blade just broke off.

@Scott T-Bird Yep, definitely not metal and while I could flex the end cap slightly around all edges, I couldn't pull it off.

 

[NYSail]

When I installed my prosafe 60 I use two wrenches to tighten..... one on each nut so as not to stress the threaded studs. Also I would address the water issue..... water and electric are not friends. Go to the rear of He receptical and see what’s going on. Also when I installed it I remember correctly they indicated to have the GI as close to the receptical as possible.

Good luck!
Greg

 

[Scott T-Bird]

@Scott T-Bird Yep, definitely not metal and while I could flex the end cap slightly around all edges, I couldn't pull it off.

I'll definitely take another look now!

When I installed my prosafe 60 I use two wrenches to tighten..... one on each nut so as not to stress the threaded studs. Also I would address the water issue..... water and electric are not friends. Go to the rear of He receptical and see what’s going on. Also when I installed it I remember correctly they indicated to have the GI as close to the receptical as possible.

Good luck!
Greg

Putting it closer to the shore power plug would be a whole nuther project! I'd have to take my water heater installation completely apart! I hate the thought of that! I'm pretty sure the water gets in at the cover. That can be fixed. Next time I go back, I'll see if water is weeping from the same location. If not, I think I'll leave it alone. But it is a concern.

 

[Scott T-Bird]

Well, I'll be a monkey's uncle! That end cover really is made with plastic (so the aluminum case isn't grounded by the stud). I took it apart again yesterday and when I first looked at it I could swear it was aluminum. I must have been too frustrated before to take note of the details. I'm getting better at clasping the nuts in the dark recesses (please don't go there ) so I took it apart one more time.

Where I mentioned that the stud is not linked to anything, I was, again, wrong. It is actually threaded to a bar that is linked in the interior. That wire is also electrically connected to the bar. What it does inside the case, I haven't a clue! But, at least I have new found respect for it!

 

[jssailem]

at least I have new found respect for it!

"R-E-S-P-E-C-T"

Free now to move forward protecting your boat....

 

[Scott T-Bird]

Maxwell Street! The ultimate city adventure for an adolescent from the Chicago suburbs in the 60's & 70's. Old Town (Wells Street) was another one. Accessible via CTA!

http://www.chicagotribune.com/news/ct-maxwell-street-flashback-per-0831-20140830-story.html