GB 32 shaft problem...

Just had my new-to-me 1990 Grand Banks 32 hauled. Prop had to be replaced due to electrolysis corrosion. The yard said the 1 1/2-inch shaft has "unknown" threads which would not fit any known zinc! Boat is now back in the water with no prop protection so I need to move quickly to solve this problem.

Anybody have any experience with a GB shaft with non-standard threads??

The yard said I should install a brush on the shaft, connected to the transom zinc, but those are prone to failure. I would rather find a better solution.

I'm considering having a diver temporarily remove one of the existing shaft nuts, determining exactly what the thread is, and having a new nut tapped to the right threads. The new nut would be sized correctly to accept a shaft zinc, of course.

Any actual experience, or thoughts, on the best way to handle this?

Thanks in advance.
Oldersalt

My Zincs clamp to the shaft just forward of the prop. Standard 1.5" and $15 or so available anywhere. Not enough room for that style?? I would have thought the yard would have figured that out..

There is often insufficient threading for the style you describe....Depending on the shaft design of course.

We've had brushes on the shafts in the bilge for nine years. No problem so far. As far as I can determine, with a set up like ours, there is no need for external shaft zincs. We have plenty of room between the transmissions and stuffing boxes.

My 32 had a shaft brush that connected to a bus bar which was connected to the transom zinc, as well as a shaft zinc. It had a galvanic isolator in the circuit and no damage from galvanic corrosion when I owned her.

Stainless steel is a VERY poor conductor so you need to constantly check that the brushes are making continuity with the shaft. A good digital meter will tell you that.

Grand Banks used copper straps to bond everything and many of mine were corroded or not possible to tell if they were effective so I replaced all of it with 8 gauge green tinned wire and terminated everything at bus bars so no stacking of connections.

Oldersalt said:

The yard said I should install a brush on the shaft, connected to the transom zinc, but those are prone to failure. I would rather find a better solution.


Any actual experience, or thoughts, on the best way to handle this?

Thanks in advance.
Oldersalt

Click to expand...

Hi; here is my actual experience. I have spent a lot of time at boat yards, and what I see is a lot of shafts that loose their zincs before they get hauled. So, lots of shaft zinc "failures".
I went to shaft brushes and never looked back. Being a southern boater, I didn't have to worry with pre-haulout zincs getting loose on the shaft or even rotting off. I installed the shaft brushes myself, and bonded them to the ships ground, which did include a transom zinc. It took care of the shafts, and props. The rudders are not directly bonded, so I still used zincs on those. I never did wear out a shaft brush. Went maybe 10 years or so, and that was on a high speed shaft, turning about 2000 rpm at cruise.

I used an overboard zinc on a wire that had a clamp on the end. Like an alligator clamp and attached it to the prop shaft while anchored or underway. Worked well.

Now I use a zinc nut. You won't find a blank zinc nut to machine in a store I don't think. Where do you plan on finding a blank nut? Could make square nuts fairly easily from bar stock. I'd go w the diver to remove a nut plan.

Actually a better long term idea is to take your shaft out and get a "shaft saver" (orange) and cut/machine your prop shaft shorter on the prop end the same length of the shaft saver. Of course you'd cut the threads on the new shaft end to match whatever thread you wanted. A common shaft nut thread would be best.

Sometimes the Aisian and Euro shafts come with goofball threads and tapers. Can be a PITA.

Shaft brush should do fine. Just do a good job and get a dedicated high quality lead to the transom zinc.

Oldersalt said:

The yard said I should install a brush on the shaft, connected to the transom zinc, but those are prone to failure. I would rather find a better solution.

Oldersalt

Click to expand...

I don't know why you would think shaft brushes (or straps) are "prone to failure"; my experience is that they are not. And they are easily inspected, unlike zincs which are not seen until the boat is hauled or dived. I think you should take the yard's advice ( & I see most of the posts above are +ve on shaft brushes too)

I read that shaft brush can reduce "singing" noise cause by shaft rotation, is that true?
I find that these brush are a nice solution, how hard are they to install? Any advice?

Reduce singing? I doubt it.

After this thread I may go back to the brush. My bullet shaped prop zinc is usually wasted when I haul out. And I hate putting it on and taking it off. I still have the double nuts.

For the OP (at your next haulout) a short section of shaft probably available at ant machine shop that does shafts could cost next to nothing and a coupling. Figure out where to make the splice and have at it. A splice/coupling would probably be best close to the trans flange. I like the tubular two piece coupling.

OP, Oldersalt,

I notice that you're in the San Francisco Bay Area. Contact Malcolm Morgan. He is with Johnson Hicks Marine Electronics in Sausalito.

Malcolm is, in my opinion, the most knowledgeable person on the planet regarding marine electrolysis. He will recommend shaft brushes and a good galvanic isolator for your system.

His information is:

Malcolm Morgan
Johnson Hicks Marine Electronics
298 Harbor Drive
Sausalito, CA 94965
(415) 331-3166

Willy- if you do a shaft brush, keep the bullet zinc, it will probably last four times as long. And it will take over if shaft brush circuit fails. Which they do.

Lou_tribal said:

I read that shaft brush can reduce "singing" noise cause by shaft rotation, is that true?
I find that these brush are a nice solution, how hard are they to install? Any advice?

Click to expand...

Where did you read that?

So it took 27 years for the prop to go bad?

Not sure you have much to worry about.

Capt.Bill11 said:

Where did you read that?

Click to expand...

From promariner shaft brush description:

Can eliminate radio frequency noise from rotating shaft.

But now I think I misread it and I guess they are not talking about singing noise but noise on RF.

I installed a shaft brush 8-10 years ago and no failure yet. Of course I do check a couple times a year.

Ski in NC said:

Willy- if you do a shaft brush, keep the bullet zinc, it will probably last four times as long. And it will take over if shaft brush circuit fails. Which they do.

Click to expand...

Great thought Ski,
But then I'd still need to fight w the zinc nut. The adjustment point always seems to be between the slots. Spoze I could go with the not so tight slot and use blue lock tight. Don't like taking the hammer to the shaft to get the prop off. I use a torch and just the puller. Never have to use the hammer.
But now I know the drill and it's not as much stress as it used to be.
Thanks

Oldersalt my 74 has a whitworth thread and nuts on the shaft I also have the shaft strapped. I could not find a shaft nut with whitworth threads so I used the size F shaft nut. Propeller Nut With Zinc Anode - Specifications It will be a little loose going on because of thread pitch. I used the smaller original prop nut first. Hope that helps and if anyone knows where to get a 1 1/2 whitworth threaded zinc prop nut let us know?

I think you guys are vastly over-analyzing this. Use a shaft brush. They are not cheap but they last for years, which is more than you can say for prop zincs. You don't need a prop zinc. You could add a belt to your suspenders and use a shaft zinc but that is not essential either. Just keep the transom zinc free of growth and be very sure the electrical connections to the very poor-conducting stainless bolts is as good as you can get. I had zero galvanic corrosion with my 'glass 32.

You could use "regular" prop nuts and cast the anode over
them. Would need to melt it off to change prop.
See picture:

That prop has been on a long time, still good.

A PO (2nd back) said they didn't change the prop when they
changed the engine in 1988. Seemed to indicate that it's the same
prop when he saw it last summer. Don't know if it has been off
in the mean time or not. Don't think anyone will pull it if not
absolutely necessary as it's 53 inch diameter. I think it would
weigh about one and a half or two hernias.

Ted

Xsbank said:

I think you guys are vastly over-analyzing this. Use a shaft brush. They are not cheap but they last for years, which is more than you can say for prop zincs. You don't need a prop zinc. You could add a belt to your suspenders and use a shaft zinc but that is not essential either. Just keep the transom zinc free of growth and be very sure the electrical connections to the very poor-conducting stainless bolts is as good as you can get. I had zero galvanic corrosion with my 'glass 32.

Click to expand...

This made me think about going the shaft brush route on my boat. Found one on Defender Marine site for less than $20 sound reasonable to me.

I have a prop nut zinc sizeF lasts 2 or more years but if the shaft brush transom zinc setup will make it last longer I am game. JohnP

I admit to being confused...

I have always used shaft zincs on my boat and have never had one go missing. The only time I have used a prop zinc is for my sailboats Autoprop. To me, shaft zincs seem simple, effective, foolproof (the fool in question being me), and relatively inexpensive.

Hey Ted, I noticed that your rudder zincs are right in the propwash. So were mine until I moved them to the bottom of the rudder. I now get way less vibration in the rudder and I'm sure it will make the rudder bearings and the bushings in the steering ram last longer. Try moving them to the bottom of the rudder next time you haul.
Okisollo was my favourite from way back in my teens? She used to be berthed at the West Van Yacht Club in Fisherman's Cove - I still can't decide if she looked better with a flying bridge (not that my opinion matters!). I don't have an f.b. either.

Hi Xsbank,

Rudder anodes are matched on the other side too.
I don't notice any vibration in the steering, maybe due to the
low prop rpm? Cruise at 850 to 0875 rpm with a 3:1 reduction,
also have an angle iron, about 1 1/2, welded down the trailing
edge.
Will look into relocating the mounting bolts next time.
I like the looks without the dodger, there are still a set of
controls up there but I haven't used them yet.

Ted

Mine is only 36"... but it does only turn pretty slow. I've forgotten the ratio, I'll have to take a look. Those two in your photo look pretty shot anyway, try putting one larger one above or below the stream from the wheel and see if it makes your maneuvering any easier? Where do you haul out? O.P?
Did I send you that ancient black and white I've got of O.?

Those anodes are new, just distorted by water, visually.

She is quite responsive to the rudder, just a bit too responsive
to a 3 to 5 knot cross current at the floats in Browns Bay, have
to wait for slack water and judge back eddies.

I hauled out at Tarkanen Marine Ways in Sointula.
They were hoping to have one of the ways operating again
last month.

Yes, thanks, you did send me the photo.

Ted

"We have plenty of room between the transmissions and stuffing boxes."

Plenty of room is good as some few trannys move the shaft back and forth when shifting.

dhays said:

I admit to being confused...

I have always used shaft zincs on my boat and have never had one go missing. .

Click to expand...

of course, there are variables in the equation. Shaft rpm, engine time between haulings (mechanical/erosion life), time between haulings (electrical life), and any issues with ac grounding stray currents.
There is another advantage of shaft zincs over shaft brush and that is one more item that can keep the shaft on the boat if the coupler lets go!; (if ahead of the strut)

diver dave said:

of course, there are variables in the equation. Shaft rpm, engine time between haulings (mechanical/erosion life), time between haulings (electrical life), and any issues with ac grounding stray currents.
There is another advantage of shaft zincs over shaft brush and that is one more item that can keep the shaft on the boat if the coupler lets go!; (if ahead of the strut)

Click to expand...

Just put a collar zinc in front of the stuffing box.

Then the shaft can't even back out of the coupler if it gets loose.

dhays said:

I admit to being confused...

I have always used shaft zincs on my boat and have never had one go missing. The only time I have used a prop zinc is for my sailboats Autoprop. To me, shaft zincs seem simple, effective, foolproof (the fool in question being me), and relatively inexpensive.

Click to expand...

Capt.Bill11 said:

Just put a collar zinc in front of the stuffing box.

Then the shaft can't even back out of the coupler if it gets loose.

Click to expand...

THat's a good idea.
I almost lost a boat once, when the shaft moved forward an inch. It had dripless shaft logs and the seal went forward with the shaft, the bellows/seal surface lost contact, and man was there water coming in!