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Old 26-07-2010, 19:48   #1
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I Zinc I Have a Problem

So I went to change out the zincs on my today. Come to find out I don't have any?

Attached to this post are pictures of my prop and of the available space between prop and rudder. With about 1mm of clearance, I can fit a zinc onto my shaft. However, no zinc has ever been there before..

So I have a few questions....
1.) Should I be adding a zinc to the shaft, given the tight clearances? Or is there some other option?
2.) why does my propellor still exist without having a zinc for the past eight month?
3.) Is that tiny worn washer between the nuts and the prop a zinc?

My suspicion is that the answer to all of these questions is that perhaps my shaft was previously isolated from the DC system on the boat. I don't know if that will be the case in the future as I am currently in the process of installing new propulsion....
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Old 26-07-2010, 19:58   #2
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"why does my propellor still exist without having a zinc for the past eight month?"

Depends what your hull is and what other metal structures nearby your shaft and prop are "bonded" to. In a marina, you could even be sacrificing metal off the boat next door.

" Should I be adding a zinc to the shaft, given the tight clearances? Or is there some other option?"

You could put a grounding stap internally on your prop shaft, then mount the zincs on the hull.

"Is that tiny worn washer between the nuts and the prop a zinc?"

Yep.
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Old 26-07-2010, 20:53   #3
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Cutlass bearing looks a little far out.....Sand off about an 1/8 inch on either side of zic and install.
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Old 26-07-2010, 22:28   #4
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If your engine starter is grounded to the block, your shaft is not isolated.

I would take enough off the zinc to allow for thrust on the shaft when engaged. Might get into issues with marine growth between the zinc and the cutless, depriving the bearing of water.

I think all boats should have a shaft ground. I use the end bell from a Delco 24 volt starter, split in two parts and mounted on the shaft. Both brushes connect to ships ground.

If the zinc on the shaft is being eaten, then the current is going through the engine or transmission bearings. I have seen bad ball bearings that I believe failed because of electrical current.

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Old 26-07-2010, 23:36   #5
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Quote:
Originally Posted by Chief Engineer View Post
Cutlass bearing looks a little far out.....Sand off about an 1/8 inch on either side of zic and install.
Agreed. I looks like the cutless is proud.

I was told the rule of thumb for cutless to zinc distance...to provide enough clearance to allow the passage of water...is 1/2 the diameter of the shaft.
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Old 27-07-2010, 06:19   #6
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Quote:
Originally Posted by wadda View Post
... I was told the rule of thumb for cutless to zinc distance...to provide enough clearance to allow the passage of water...is 1/2 the diameter of the shaft.
Quote:
Originally Posted by um saudade View Post
... I think all boats should have a shaft ground...
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Originally Posted by billwa View Post
... You could put a grounding stap internally on your prop shaft, then mount the zincs on the hull...
Is there room to install a Prop Nut (or cone) Anode:

Martyr Anodes – Zinc, Aluminum, Magnesium Anodes for Pleasurecraft and Commercial Craft

Or a Limited Clearance anode:

Martyr Anodes – Zinc, Aluminum, Magnesium Anodes for Pleasurecraft and Commercial Craft
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Old 27-07-2010, 06:26   #7
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Quote:
Originally Posted by billwa View Post
"

"Is that tiny worn washer between the nuts and the prop a zinc?"

Yep.
Really? I've never seen a zinc like that.
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Old 27-07-2010, 06:27   #8
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Quote:
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"

"Is that tiny worn washer between the nuts and the prop a zinc?"

Yep.
Really? I've never seen a zinc like that. How long would a zinc that size last?
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Old 27-07-2010, 06:49   #9
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See also:
Bonding the Prop Shaft

And:
Zincs and the 'Hot' Marina
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Old 27-07-2010, 07:07   #10
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I could be wrong, but I think you will find:

The flat washer is the remnants of the anode, but is not zinc. It is a less reactive metal that has been cast into the anode. The same is true of the 1-2 inch spacing collar between the propeller and the nut.

The original anode would have been a tapered cone, the base of which was the "washer", the tip of which was just behind the nut.

Looks like the reason this has not been changed, from the photo, the rudder is too close to change this anode without removing it.
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Old 27-07-2010, 08:35   #11
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Probably should trim the cutless bearing down, but in the meantime there are some very thin shaft collars such as

Beneteau Donut Collar Zinc Anodes

Also there could have been a Perry propeller nut zinc behind the prop.

Michael

Edit: second look, probably not a Perry nut there before...
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Old 27-07-2010, 14:24   #12
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Thanks for all of the suggestions. One update is that I've discovered that the on the new motor the prop shaft is isolated from the electrical system. Therefore it doesn't need a terribly large sacrificial anode?

I should also add that that tiny washer was the only zinc on the boat from October (when surveyed) of last year until present in a Marina with hundreds of boats.... I have pictures from the survey, but they are not of adequate quality for scanning and posting. (FYI a survey with photos is a wonderful thing for figuring out how things have changed on the boat over time....)

My current plan is to purchase the beneteau anode (thanks for the suggestion, svcambria!), which looks like it should fit with adequate clearance on both the rudder and the cutlass bearing.
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Old 27-07-2010, 16:05   #13
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Why don't you just observe for a while without the anode and see what happens? We have been 25 yrs without one no problems.
Regards, Richard.
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Old 30-07-2010, 08:13   #14
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Why don't you just observe for a while without the anode and see what happens? We have been 25 yrs without one no problems.
Regards, Richard.

HEY!!! I LIKE THAT!!!!

I also went without anodes when I owned my 30' Hunter. In fact for the same 25 years or so as Borden did. I saw no problems what so ever.

But assume there are reasons to add anodes, one should consider using a shaft brush to bond the shaft along with the prop to the boat's ground. There would be no reason for shaft anodes IF THE SHAFT WAS BONDED TO THE OTHER METALS ON THE BOAT and of course with anode attached to the same bonding system if needed.

The need for anodes reminds me of the old tale of the boy banging a drum on the streets of New York. Asked why the drums, the boy answered "to keep the lions away!" See??? No lions therefore the drums work.

There is one and only one way to determine correct anode requirements. Voltages to various grounded points such as shafts must be measured to a reference cell such as a silver-silver chloride half cell.
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