Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 31-12-2013, 16:05   #1
Registered User
 
cwyckham's Avatar

Join Date: Apr 2011
Location: Vancouver, BC
Boat: Niagara 35
Posts: 1,870
Loose shaft zinc

I'm going through shaft zincs like they're going out of style. Every few months, they seem to need replacement. I do it at anchor with a snorkel. I don't really like diving in the marina due to concerns about water quality. I have an isolation transformer and fiberglass boat. I think I must be picking up stray current from those around me? They're live-aboards on somewhat sketchy boats. I move slips soon, so will see if things improve.

Anyways, I had a zinc slide up the shaft while in reverse a few months ago. It came to rest against the hull and wore a bit of a groove. Seems like this has just happened again (sudden rattling sound that started while idling in reverse at dock to warm up). Seems when I'm about 30% done the zincs, they get loose and can slide around. Presumably they also have poor electrical contact at that point.

I was thinking of just installing a hose clamp above the upper shaft zinc (I always install 2 zincs) to prevent it sliding up and damaging the hull. I'm a bit concerned about galvanic corrosion under the hose clamp but could clamp onto a bit of rubber to isolate it.

Any advice on this idea or on why I'm going through so many zincs so quickly? Last ones were installed in late October.
__________________

__________________
cwyckham is offline   Reply With Quote
Old 31-12-2013, 16:15   #2
Senior Cruiser
 
FSMike's Avatar

Cruisers Forum Supporter

Join Date: Aug 2009
Location: Bahamas/Florida
Boat: Solaris Sunstar 36' catamaran
Posts: 2,654
Images: 5
Re: Loose shaft zinc

When you install the zincs, make sure the bolt heads are facing in the direction of rotation when in forward gear.
Tighten the bolts well, bang on the zinc all over with a hammer, then tighten the bolts again.
I trust you have not painted the shaft in the area where the zinc goes?
You and your neighbors do not have power cords dangling in the water?
If you are located in an area where electrolysis is a severe problem, I don't know what to suggest other than a move.
How often do other boats in your area have to replace their zincs?
__________________

__________________
Sail Fast Live Slow
FSMike is offline   Reply With Quote
Old 31-12-2013, 16:20   #3
Senior Cruiser
 
Blue Stocking's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: St. Georges, Bda
Boat: Rhodes Reliant 41ft
Posts: 4,114
Re: Loose shaft zinc

Maybe metric zinc on Imperial shaft, or vice versa. Correct size zinc should require a hammer tap to seat it on the shaft before pulling up fasteners.
__________________
so many projects--so little time !!
Blue Stocking is offline   Reply With Quote
Old 31-12-2013, 16:51   #4
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 3,592
Re: Loose shaft zinc

Rapid zinc depletion is most likely due to an issue aboard your own boat. Look there first.

What brand zincs are you using?
__________________
fstbttms is offline   Reply With Quote
Old 31-12-2013, 18:22   #5
Registered User
 
cwyckham's Avatar

Join Date: Apr 2011
Location: Vancouver, BC
Boat: Niagara 35
Posts: 1,870
Re: Loose shaft zinc

Quote:
Originally Posted by FSMike View Post
When you install the zincs, make sure the bolt heads are facing in the direction of rotation when in forward gear.
Tighten the bolts well, bang on the zinc all over with a hammer, then tighten the bolts again.
I trust you have not painted the shaft in the area where the zinc goes?
You and your neighbors do not have power cords dangling in the water?
If you are located in an area where electrolysis is a severe problem, I don't know what to suggest other than a move.
How often do other boats in your area have to replace their zincs?
I'm not sure what you mean about bolt heads in direction of rotation. There are two hex screws and I'm pretty sure they're on the same size. The hammer thing is interesting, but I'm not sure how to do that under water by snorkel.

The shaft isn't painted and there aren't any cords in the water. I'll have to ask my neighbours about zincs.
__________________
cwyckham is offline   Reply With Quote
Old 31-12-2013, 18:24   #6
Registered User
 
cwyckham's Avatar

Join Date: Apr 2011
Location: Vancouver, BC
Boat: Niagara 35
Posts: 1,870
Re: Loose shaft zinc

Quote:
Originally Posted by fstbttms View Post
Rapid zinc depletion is most likely due to an issue aboard your own boat. Look there first.

What brand zincs are you using?
Hmmm... Maybe I've had my head in the sand in that one. Would a clamp on ammeter be sufficient to see the currents involved? I'll have to research how to do that.

Not sure the brand, they're just in a bin at the local chandelry. I'll check next time I'm at the boat in a couple days.

Is it possible to overtighten the screws? Or should I just be bearing down as hard as possible on them.
__________________
cwyckham is offline   Reply With Quote
Old 31-12-2013, 19:11   #7
Registered User

Join Date: Dec 2010
Location: Wilmington, N.C.
Boat: Marine Trader, Sedan, 40', Donnchaidh
Posts: 21
Re: Loose shaft zinc

Could be the boat next to you or an improper (failed) marina pedistal ground now using your boat as a ground. I had a problem like yours once, I was on a dock and right behind me was an old (really) sport fishing boat. I noticed bubbles coming from my rear zink, looked over at the sport fisher and there was an extension cord running over the side and down into the bilge and looked in and it was hooked to a CAR battery charger, which does not filter out the a/c going to the batteries. I unpluged the extension cord and the bubbles stopped. So I turned my boat around which put the aft far enough away.
Another story, a coworked was telling me that her dads boat's props were getting pitted. On a hunch I told her to tell her dad to take the car battery charger out of his boat and get a real boat charger. The next day she said her dad wanted to know how I knew he was using a car charger.
And still another story, a fellew left a car charger on his run about and it ate the outboards lower unit off even with the water. I had never seen anything like that, must have been 50 years ago.
Getting old is not for sissys but it sure gives you a lot of experiences.
__________________
awpptdt is offline   Reply With Quote
Old 31-12-2013, 19:25   #8
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 3,592
Re: Loose shaft zinc

Quote:
Originally Posted by cwyckham View Post
Is it possible to overtighten the screws?
Not likely. You absolutely need to set the zincs with a hammer, however.
__________________
fstbttms is offline   Reply With Quote
Old 31-12-2013, 19:33   #9
Registered User
 
cwyckham's Avatar

Join Date: Apr 2011
Location: Vancouver, BC
Boat: Niagara 35
Posts: 1,870
Re: Loose shaft zinc

Quote:
Originally Posted by fstbttms View Post
Not likely. You absolutely need to set the zincs with a hammer, however.
OK, I'd never heard of that. So I go down, tighten them on as normal, whack with a hammer on each side a few times (guess I need a pretty heavy hammer to do that under water?) and then re-tighten?
__________________
cwyckham is offline   Reply With Quote
Old 31-12-2013, 20:15   #10
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 3,592
Re: Loose shaft zinc

Correct. A 16oz. claw hammer will do the job.
__________________
fstbttms is offline   Reply With Quote
Old 01-01-2014, 03:06   #11
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Re: Loose shaft zinc

They now sell precise fit zincs that don't need hammering anymore. Used them for the first time this year and like them.

You must check if the isolation transformer really blocks the shore ground wire. When I did that, I was shocked to find they wired it wrong and isolation had been defeated with a jumper.
__________________
s/v Jedi is offline   Reply With Quote
Old 01-01-2014, 03:13   #12
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Quote:
Originally Posted by s/v Jedi
They now sell precise fit zincs that don't need hammering anymore. Used them for the first time this year and like them.

You must check if the isolation transformer really blocks the shore ground wire. When I did that, I was shocked to find they wired it wrong and isolation had been defeated with a jumper.
That was on your Victron isolation transformer? Wow. Need to check mine then. When I installed mine, I noticed precisely zero difference in zinc consumption. That could be the explanation.
__________________
"Parce que je suis heureux en mer, et peut-ętre pour sauver mon ame. . . "
Dockhead is online now   Reply With Quote
Old 01-01-2014, 03:18   #13
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Re: Loose shaft zinc

Quote:
Originally Posted by Dockhead View Post
That was on your Victron isolation transformer? Wow. Need to check mine then. When I installed mine, I noticed precisely zero difference in zinc consumption. That could be the explanation.
No, it was the one I replaced with the Victron. The Victron actually comes with a jumper which you're supposed to use when hauled out. Not that I do that, but it is well documented. Make sure you don't have it installed
__________________
s/v Jedi is offline   Reply With Quote
Old 01-01-2014, 09:21   #14
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 3,592
Re: Loose shaft zinc

Quote:
Originally Posted by s/v Jedi View Post
They now sell precise fit zincs that don't need hammering anymore. Used them for the first time this year and like them.
This is news to me. Who is "they"?
__________________
fstbttms is offline   Reply With Quote
Old 01-01-2014, 09:38   #15
Registered User
 
zippy's Avatar

Join Date: Sep 2005
Location: Halifax, Nova Scotia
Posts: 90
Re: Loose shaft zinc

Originally Posted by cwyckham
Is it possible to overtighten the screws?

Depends on what you are using to tighten the bolts. It is very easy to shear the bolts if you use a ratchet or angled hex key wrench. If using a screwdriver handle it is more difficult.
__________________

__________________
zippy is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 13:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.