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17-07-2011, 13:31
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#1
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Registered User
Join Date: Feb 2011
Location: Sanford, FL
Boat: 1977 S2 8.0
Posts: 310
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Sacrificial Zinc ?
Do we need a sacrificial zinc? We live aboard in a marina in fresh water...have a traditional zinc on the hull and one on the prop shaft. Get conflicting answers here on the dock...some say yes absolutely others say not needed?
__________________
Joe & Tori
"Knot Looking Back" 1977 S2 8.0
Clara , Ducky, Miranda and Nalla the Critters
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17-07-2011, 13:34
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#2
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Registered User
Join Date: Aug 2010
Location: Smithfield Va.
Boat: '72 Tanzer 28 "Her Idea"
Posts: 320
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Well...yes and no...since you have them, might as well keep them...there is really no such thing as a boat in pure water..there are always impurities enough to cause some galvanic corrosion....but do you need them..not really....
__________________
1972 Tanzer 28 "Her Idea"
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17-07-2011, 13:36
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#3
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Registered User
Join Date: Aug 2003
Boat: Dragonfly 1000 trimaran
Posts: 7,145
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Re: Sacraficial zinc?
Anytime you have dissimilar metals under water, you need them.
Fresh water is not as active as salt, but it's still good policy to have zinc anodes.
Fresh water might need a different type though.
Some stern drives use magnesium anodes.
__________________
The question is not, "Who will let me?"
The question is,"Who is going to stop me?"
Ayn Rand
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17-07-2011, 13:39
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#4
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Registered User
Join Date: Dec 2008
Location: ontario canada
Boat: grampian 26
Posts: 1,743
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Re: Sacraficial zinc?
Zinc is for salt water and magnesium for fresh.
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17-07-2011, 21:51
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#5
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Registered User
Join Date: Aug 2007
Location: Clear Lake Marine Services - Seabrook, Texas
Boat: Gulfstar, Mark II Ketch, 43'
Posts: 2,359
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Re: Sacrificial Zinc?
And stray electricity will also eat the metals under water. Stray 110V at the dock is worse than normal galvanic action.
They are cheap so why not spend a couple of $$$. Aquick dive under the boat to change them..
__________________
Formerly Santana
The winds blow true,The skies stay blue,
Everyday is a good day for SAILING!!!!
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18-07-2011, 04:48
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#6
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Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,140
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Re: Sacrificial Zinc?
Yes, you need a sacrificial anode.
The chart below summarizes the anode choices, based on type of boat, and water type.
As you can see, the only anode type that is recommended for all water types is aluminum (or aluminum/zinc/indium alloy).
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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18-07-2011, 09:33
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#7
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 20,420
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Re: Sacrificial Zinc?
Quote:
Originally Posted by GordMay
Yes, you need a sacrificial anode.
The chart below summarizes the anode choices, based on type of boat, and water type.
As you can see, the only anode type that is recommended for all water types is aluminum (or aluminum/zinc/indium alloy).
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So ... can I make an anode by cutting off a thick slab of aluminum and placing it where we normally have the zincs?
???
barnie
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18-07-2011, 10:23
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#8
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Registered User
Join Date: Oct 2008
Location: Northern British Columbia, part of the time in Prince Rupert and part of the time on Moresby Island.
Boat: 50-ft steel Ketch
Posts: 1,884
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Re: Sacrificial Zinc ?
You may make your own anodes in a pinch, but they should be made of an alloy in which catalysts have been added to make sure they do their job (activated alloys), or at least very pure zinc or aluminium. Some alloys are corrosion resistant and you would not want those as they will not be sufficiently sacrificial.
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'Tis evening on the moorland free,The starlit wave is still: Home is the sailor from the sea, The hunter from the hill.
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18-07-2011, 12:37
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#9
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Moderator Emeritus
Join Date: Sep 2006
Posts: 4,663
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Re: Sacrificial Zinc ?
Remember, the sacrificial anode needs to be electrically connected to the metal you're trying to protect -- you can't just hang it in the water without a connection.
If you're not keen on replacing / maintaining your anodes, you might look into something like the zinc "fish" that has a cable and alligator clip. You can clip it to a grounded backstay (or anything that's grounded) and hang it over the side. It will protect any nearby metal on your boat (as long as it's also grounded), and should keep any existing anodes from eroding as quickly as they otherwise might.
I've only seen the zinc fish, but there may be Al or Mg ones as well.
Also, it's possible to "over-zinc" a boat -- perhaps someone here can advise us on that problem?
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
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18-07-2011, 12:44
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#10
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Registered User
Join Date: Feb 2011
Location: Sanford, FL
Boat: 1977 S2 8.0
Posts: 310
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I am in fresh water and have seen the zinc"fish" was considering getting one sounds as if magnesium or aluminum is better suited.
Any aluminum "fish"?
__________________
Joe & Tori
"Knot Looking Back" 1977 S2 8.0
Clara , Ducky, Miranda and Nalla the Critters
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18-07-2011, 13:25
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#11
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Registered User
Join Date: Apr 2004
Location: Toronto
Boat: CS36Merlin, "La Belle Aurore"
Posts: 7,557
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Re: Sacrificial Zinc ?
I have a boat in fresh water. It has a zinc sacrificial anode on the shaft. Never have to change it. In salt water a zinc usually lasts me about four months and that's with little time (a day or two at the most) in a marina.
__________________
Rick I
Toronto in summer, Bahamas in winter.
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18-07-2011, 13:31
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#12
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Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,140
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Re: Sacrificial Zinc ?
Quote:
Originally Posted by Vasco
I have a boat in fresh water. It has a zinc sacrificial anode on the shaft. Never have to change it. In salt water a zinc usually lasts me about four months ...
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A sacrificial anode, that never erodes, is doing nothing to protect your immersed metals.
Perhaps you don't need protection, but perhaps you do.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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18-07-2011, 13:40
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#13
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Registered User
Join Date: Oct 2010
Location: Abaco, Bahamas/ Western NC
Boat: Nothing large at the moment
Posts: 1,037
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Re: Sacrificial Zinc ?
Remember; things can change in a hurry in a marina. If a improperly wired boat pulls in next to you and plugs in to shorepower you become a link in the battery chain. Not nearly as bad as salt water but "fresh" water is never really pure!
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18-07-2011, 13:46
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#14
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Registered User
Join Date: Apr 2004
Location: Toronto
Boat: CS36Merlin, "La Belle Aurore"
Posts: 7,557
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Re: Sacrificial Zinc ?
Quote:
Originally Posted by GordMay
A sacrificial anode, that never erodes, is doing nothing to protect your immersed metals.
Perhaps you don't need protection, but perhaps you do.
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Props still there, Gord. Been seven years since the boats was in salt water, no pitting, nothing.
__________________
Rick I
Toronto in summer, Bahamas in winter.
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18-07-2011, 17:49
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#15
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Registered User
Join Date: Mar 2010
Location: Seattle
Boat: Krogen 58' Xiao Xiu
Posts: 276
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Re: Sacrificial Zinc ?
Go to Passagemaker.com. Steve D'Antonio just did piece on sacrificial anodes, zinc and other metals. He mentioned specifically fresh water issues. It was a pretty interesting piece.
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