Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 02-09-2017, 14:25   #1
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2014
Location: Astoria, NY
Boat: Sabre 38
Posts: 492
Eating through zincs - Need some ideas

I chew through a set of prop and shaft zincs in about 20 hours of motoring.

At first I blamed this on other boats in the marina, but I have come to the conclusion that it is me. I purchased a silver-chorine anode, and have used it to test every electrical component on my boat across various anchorages over the past month.

After flipping on and off every breaker and running each electrical component individually, the only thing that causes a voltage drop between the submerged anode and the engine block ground is running the engine itself.

With a fresh set of prop and shaft zincs, I read about -700mv with my silver-chlorine anodes, which is well within the "safe" range for my fiberglass boat according to the kit. Running the engine, I drop to -500mv or so, below the safe range for my bronze prop.

My engine is the original Westerbeke 33 from 1983, still with its original, case ground, 55amp alt. I figure the grounding among the alternator, the engine block and the DC system has a lot of corrosion, causing the voltage drop, with the leak through the shaft and prop.

Thinking I need to reduce the electrical resistance, I ran 8 awg wire from the bolt on the tensioner arm to the DC system's grounding point on the block. This grounding point is a tab bolted to the back of the engine block, in between the block and the transmission. (I also ran some 8 awg wire from the positive post on the alt to the positive post on the starter, to lower resistance into the battery bank, but I doubt this was the issue.) I also have new 0/2 awg cable between the block ground and the battery bank.

This additional wire didn't do much to solve my voltage drop issue. The boat is now on the hard till October, and I'm sitting here in my hurricane hole thinking of next steps.

I suppose I can remove the alternation and grounding tab in order to sand/grind it's connection points to lower the electrical resistance.

Anyone have additional ideas? Maybe my jumper wire needs to be attached between the alt and the block, rather than the tensioner arm?
__________________

__________________
Stephen

s/v Carpe Ventum
1983 Sabre 38
My Intro
fallingeggs is offline   Reply With Quote
Old 02-09-2017, 14:55   #2
Registered User

Join Date: Dec 2016
Location: LA/northern Utah/Wisconsin/Chicago
Boat: Hans Christian 38 Mk II
Posts: 25
Images: 1
Re: Eating through zincs - Need some ideas

The forum suggested similar topics include "Eating fish", "Mussel eating mackerel" and "wood eating insects aboard".
Possibly there might be ideas in those threads that don't include the obvious first things to do - clean up corroded connection points.
Dribble hot sauce on wiring?
Spray insecticide on connections?
__________________

__________________
AndyEss is offline   Reply With Quote
Old 02-09-2017, 14:58   #3
Head in a locker
 
Cavalier's Avatar

Cruisers Forum Supporter

Join Date: Dec 2010
Location: Houston, TX
Boat: Beneteau 461 47'
Posts: 858
Images: 1
Re: Eating through zincs - Need some ideas

Quote:
Originally Posted by fallingeggs View Post
I chew through a set of prop and shaft zincs in about 20 hours of motoring.



At first I blamed this on other boats in the marina, but I have come to the conclusion that it is me. I purchased a silver-chorine anode, and have used it to test every electrical component on my boat across various anchorages over the past month.



After flipping on and off every breaker and running each electrical component individually, the only thing that causes a voltage drop between the submerged anode and the engine block ground is running the engine itself.



With a fresh set of prop and shaft zincs, I read about -700mv with my silver-chlorine anodes, which is well within the "safe" range for my fiberglass boat according to the kit. Running the engine, I drop to -500mv or so, below the safe range for my bronze prop.



My engine is the original Westerbeke 33 from 1983, still with its original, case ground, 55amp alt. I figure the grounding among the alternator, the engine block and the DC system has a lot of corrosion, causing the voltage drop, with the leak through the shaft and prop.



Thinking I need to reduce the electrical resistance, I ran 8 awg wire from the bolt on the tensioner arm to the DC system's grounding point on the block. This grounding point is a tab bolted to the back of the engine block, in between the block and the transmission. (I also ran some 8 awg wire from the positive post on the alt to the positive post on the starter, to lower resistance into the battery bank, but I doubt this was the issue.) I also have new 0/2 awg cable between the block ground and the battery bank.



This additional wire didn't do much to solve my voltage drop issue. The boat is now on the hard till October, and I'm sitting here in my hurricane hole thinking of next steps.



I suppose I can remove the alternation and grounding tab in order to sand/grind it's connection points to lower the electrical resistance.



Anyone have additional ideas? Maybe my jumper wire needs to be attached between the alt and the block, rather than the tensioner arm?


Does the value change if you temporarily close the raw water intake for the engine? I.e. Does the introduction of constantly replenished electrolytes into the engine cooler alter the local potential.. Westerbeke 33 has zinc anodes in the heat exchanger (correct me if I'm mistaken), maybe be worth taking a look at their condition if the seawater cooling on/off changes the electrical values against the silver chloride anode.

Sent from mTalk
__________________
"By day the hot sun fermented us; and we were dizzied by the beating wind. At night we were stained by dew, and shamed into pettiness by the innumerable silences of stars."
Cavalier is online now   Reply With Quote
Old 02-09-2017, 15:26   #4
Registered User
 
S/V Illusion's Avatar

Join Date: Oct 2007
Location: Lakewood Ranch, FLORIDA
Boat: Alden 50, Sarasota, Florida
Posts: 1,680
Re: Eating through zincs - Need some ideas

Sounds like you have multiple grounds exacerbated by having power to the engine/shaft. It's hard to imagine a different cause of what you describe.

Are all grounds at the same potential or have a common point?
__________________
S/V Illusion is offline   Reply With Quote
Old 02-09-2017, 23:16   #5
Registered User

Join Date: Jun 2013
Location: canada
Posts: 1,656
Re: Eating through zincs - Need some ideas

Is that 500mv reading with the props spinning? Likly if they are spinning. The zincs are no longer making contact with the engine / rest of boat. Due to the gear fluid.

This wouldn't eat your zincs. It would make them last longer if they were no longer protecting the boat. But the boat would have issues.
__________________
smac999 is offline   Reply With Quote
Old 03-09-2017, 00:25   #6
Registered User
 
SailingFan's Avatar

Join Date: Aug 2016
Location: Florida
Boat: Hunter 27, 1978
Posts: 456
Re: Eating through zincs - Need some ideas

__________________
SailingFan
1978 Hunter 27
Learning by the day!
SailingFan is offline   Reply With Quote
Old 03-09-2017, 00:58   #7
Registered User

Join Date: Jun 2017
Location: Subic Bay Philippines
Posts: 537
Re: Eating through zincs - Need some ideas

I would be looking firstly at the INSIDE condition of your Alternator especially for corrosion and or the winding's them selves and the varnish coatings etc, More than likely there's a situation here!!

On my steel built vessels we actually isolate the alternator all together with the use of fiber bearing sleeves and washers, but on GRP this would be extreme and basically never done- So - look for the cause in side first

Cheers Steve
__________________
Captsteve53 is offline   Reply With Quote
Old 03-09-2017, 05:53   #8
Senior Cruiser
 
bletso's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Louisville, KY
Boat: Globe, cutter/ketch,38
Posts: 534
Re: Eating through zincs - Need some ideas

With the speed they are consumed it is obviously stray current. Further, as it seems to only happen whilst the engine is on it will be in a circuit energised with the ignition. You most probably have leakage from a positive wire through wet or moist conditions. This can be from frayed or broken insulation. It is very common with bilge pump wiring. (Not your case)

Very carefully check the condition of your charge circuitry wiring from the alternator / regulator to the battery.
__________________
www.sailboatvigah.com Boats don't like being neglected, but then neither do significant others!
bletso is offline   Reply With Quote
Old 03-09-2017, 10:06   #9
Registered User

Join Date: Dec 2013
Location: Salt Lake City
Boat: Gulfstar 50
Posts: 29
Re: Eating through zincs - Need some ideas

Try adding a shaft wiper, bonded to the ships bonding system
__________________
Mojadito is offline   Reply With Quote
Old 03-09-2017, 11:35   #10
Registered User
 
Panacea2183's Avatar

Join Date: May 2016
Location: Cape Cora, Fl
Boat: 2002 Novatec 42 Sundeck Trawler
Posts: 97
Images: 1
Re: Eating through zincs - Need some ideas

Possibly a bad diode in the alternator itself?
Put a load on your batteries and check alt output with a clamp meter?
Just thinking out loud
__________________
Panacea2183 is offline   Reply With Quote
Old 03-09-2017, 12:23   #11
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,002
Re: Eating through zincs - Need some ideas

Quote:
Originally Posted by AndyEss View Post
The forum suggested similar topics include "Eating fish", "Mussel eating mackerel" and "wood eating insects aboard".
Possibly there might be ideas in those threads that don't include the obvious first things to do - clean up corroded connection points.
Dribble hot sauce on wiring?
Spray insecticide on connections?
Clean up corroded connection points. it's the place to start.
__________________
Cadence is offline   Reply With Quote
Old 03-09-2017, 12:39   #12
Registered User

Join Date: Dec 2011
Posts: 410
Re: Eating through zincs - Need some ideas

Try a spring contact that rides on the prop shaft with a direct connection to the engine block ground point? Maybe?
__________________
jmschmidt is offline   Reply With Quote
Old 03-09-2017, 14:16   #13
Registered User
 
buzzstar's Avatar

Join Date: Apr 2012
Location: ashore in So Calif.
Boat: No more boat (my medical, not the boat's)
Posts: 1,257
Re: Eating through zincs - Need some ideas

Are you motoring in place or going somewhere as your zincs are eaten?
__________________
"Old California"
buzzstar is offline   Reply With Quote
Old 03-09-2017, 15:35   #14
Registered User

Join Date: Jan 2011
Location: Sydney
Boat: Farr 1020
Posts: 221
Re: Eating through zincs - Need some ideas

Try running the engine with the alternator drive belt disconnected. See if the same issue applies. If not, then you at least know it is the alternator. Easy step may reduce the problem, or you may solve it first step!
Roger
__________________
Djarraluda is offline   Reply With Quote
Old 03-09-2017, 17:56   #15
Registered User

Join Date: Apr 2017
Location: Temecula CA
Boat: Still not big enough..!!!
Posts: 24
Re: Eating through zincs - Need some ideas

RE: "Stray Electrical Currents vs. Corrosion".... Vessels and other structures (oil platforms, pipelines, powerline/antenna towers, etc.) sitting in salt water have significant corrosion caused by stray electrical currents. In the extreme, using active electronic devices to 'buck' this, some of this electrical 'difference' can be offset, if not totally 'nulled out' and then, electrically induced corrosion is slowed significantly, if not stopped totally. I would suggest "you have more unaccounted for metal objects in the water" that are aiding in this corrosion process. Is your rudder post &/or the rudder itself a metal (electrically conductive) material..? Or, how about any through-hull fittings under the water, typically naval bronze or Monel, somehow electrically interconnected with the internal metal objects & wiring system. The head may be an example; lots of metal there, connected on thru the hull. Is there a metal strip running the length of your keel..? Is your ballast iron or lead and somehow tied into the electrical system..? Sometimes this is intentionally done to create a 'radio ground plane' and/or lightening protection for metal masts. If not well isolated from seawater contact by hull coatings, which may have been intentionally removed on purpose to enhance seawater contact, you have a connection between that mass and your metal shaft/prop for example. In the simplest terms, electrically induced corrosion, which is a natural chemical/electrical process of two or more 'dissimilar' metals immersed in an electrolyte (...of which sea water is a very-very strong electrolyte....) can eat away an amazing amount of surface metal in short order, as you have seen. Throw in the charging (or battery bank) system 'stray' voltages, which can be very significant during recharging batteries, and this corrosion can really take off. Also, some vessels (steel/aluminum) may be surface preserved in such a way that no hull metal contacts the seawater. But heeled-over & wet, now a 'circuit' exists. some hull designs have steel underwater, yet all above deck structures are aluminum to reduce tip over moments...very tough to protect these designs from literally eating themselves to death. So thoroughly survey for ALL metal objects, including metal anchor chains & anchor immersed in the sea. Any and all can 'complete the circuit' needed to cause this corrosion in the first place....which may only occur "at anchor' for example. Ironically, interconnecting all these metal objects can literally be the very source of your problem(s). More is not necessarily better in this case. Sometimes 'isolation' is the simplest cure.....
__________________

__________________
bluewatervet 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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Eating Fish beau Provisioning: Food & Drink 43 20-07-2010 08:09
Mussel-Eating Mackerel unbusted67 Off Topic Forum 4 23-06-2010 10:03
Wood Eating Insects Aboard rover88 Construction, Maintenance & Refit 6 01-01-2009 13:08
Charleston, SC area eating.. scgilligan General Sailing Forum 8 01-09-2007 06:18
Benefits of eating Fish... GordMay Provisioning: Food & Drink 6 05-12-2004 13:26



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:29.


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.