I also am of the convention of none of the overboards that have
plastic/rubber inboard should be grounded. When I first got the boat in
1980 we were eating zincs, one every other month. I read an article at
the time that basically said that if you have a copper base paint you
were setting up eddy currents between the overboards and the prop zinc.
I remove all the grounds from the overboards and have had the zinc last
the whole season (May-Oct), since then. My two cents
Don Kern
/Fireball /12708
C&C 35 MK2//(1974)/
/
On 8/14/2018 2:43 PM, Bill Coleman via CnC-List wrote:
Well, Joe, you have just thrown some weight to a very weighty question
in my head.
I have read where these thru hulls are to be grounded, and then I read
where you shouldn’t , so I think over the years some I have re-done
some grounds, then I read the other way, and I don’t connect them, so
half mine are grounded, and the other half are not, just because I
don’t know what to do!
Are a couple drinks a day good for you, or bad for you?
Depends on the latest study you read!
So, I am going with you, no grounds on any thru-hulls!
Thanks for clearing my head. (At least until I read another article.)
Bill Coleman
C&C 39 Erie, PAanimated_favicon1
*From:*CnC-List [mailto:[email protected]] *On Behalf Of
*Della Barba, Joe via CnC-List
*Sent:* Tuesday, August 14, 2018 2:08 PM
*To:* [email protected]
*Cc:* Della Barba, Joe
*Subject:* Re: Stus-List [EXTERNAL] Re: Galvanic corrosion (Della
Barba, Joe)
I am still not clear on how the voltage is being measured and between
what points.
I have bronze thru-hulls that are not wired to anything. If I measured
between them and the lead keel or the engine with the stainless shaft,
I am sure I would read a voltage, they are dissimilar metals in salt
water. Absent me wiring up the voltmeter, the thru-hulls have no
connection to anything else and would not corrode. If you do have all
these thru-hulls wired to ground, as is done on some boats, you now
have a battery. You need to be sure there is a zinc involved in there
somewhere and it had better have a good connection so that the zinc is
the part of the battery corroding.
IMHO and also the article referenced in another post, I like to make
sure my seacocks and thru-hulls are NOT grounded. This eliminates the
issue of poor contact to zincs and prevents the boat wiring from being
a path for leakage between boats on one side of you and boats on the
other, which is something a zinc will have a hard time saving you from.
Joe
Coquina
*From:*CnC-List [mailto:[email protected]] *On Behalf Of
*Michael Brown via CnC-List
*Sent:* Tuesday, August 14, 2018 1:53 PM
*To:* [email protected]
*Cc:* Michael Brown <[email protected]>
*Subject:* [EXTERNAL] Re: Stus-List Galvanic corrosion (Della Barba, Joe)
You could try reading current with your multimeter instead of voltage.
Small stray voltages
likely exist when measuring between lead and SS even in fresh water
but I doubt they will
sustain much current.
Just as an example of magnitude very roughly if there was a current of
1 amp continuously
in normal soil it would corrode about 20 lbs of steel in a year.
If you are reading less than 0.5 milliamp I would say those two
surfaces are not going to have
much corrosion between them. If you are seeing over a milliamp then
there is an issue.
The circuit requires two paths, the dissimilar metals in water and
then something on the boat
connecting them together. Some advice has been to connect the mast,
standing rigging and
keel together but do not ground them to the boats electrical system.
That may be difficult
if items like the VHF antenna is mounted to a metal bracket on the
mast. You can test for
this by measuring the resistance between the mast and ship's ground.
Anything under
10 ohms would indicate a connection.
Michael Brown
Windburn
C&C 30-1
Date: Tue, 14 Aug 2018 13:41:43 +0000
From: "Della Barba, Joe" <[email protected]
<mailto:[email protected]>>
Voltage readings between what and what?
Joe Della Barba
Coquina
Sent: Monday, August 13, 2018 7:25 PM
Hi Alan
The readings I posted are at anchor in the Thousand Island area.
I almost never plug in during the cruising season. I only use
shore power to charge the batteries during winter layup when the
solar and wind are removed, every 6 to 8 weeks
So today I did more testing. I disconnected the positive cable
for the start battery and I still saw 0.02V at the prop shaft. So
I ruled out that as an issue. I disconnected the battery charger
and still saw voltage. Next I took the wind generator out of the
equation and the results were the same. Next I disconnected the
windlass, same results. Next I moved inside and checked for
voltage on the tube for the centre board pendant. Saw 0.25 V. I
removed the positive cable to the house electrical panel. Still
saw voltage.
Am I doing this right. My memory tells me that the way I?m
testing might be creating some kind of battery but my memory might
be tricking me.
Could really use some help from any electricians or corrosions
specialist out there.
Mike
C&C 37 K/CB Shoal draft
Persuasion
Stormont Yacht Club
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