|
|
|
|
|||||
|
||||||
From: mike senko (no email)
Date: Mon Oct 01 2001 - 19:02:40 EDT
Eric,
First, Arild is correct in that AC currents when leaked into salt water from
a marina or from another source, will cause rapid galvanic corrosion or
cause you to go through a lot of zinc's in a short period of time. I know of
a Baba 30 that had $10,000 worth of damage and nearly sunk because of it. I
also found the source of the problem.
Second, in reading almost all of the posts, I understand your boat, or the
boat in question, is in fact bonded, ie, all of the through-hulls, engine,
fuel tanks, etc, are all connected together.
You will want to look to see if you DC and AC grounds are connected. If they
are, you can disconnect them, things will continue to work properly, but you
will be outside of the bounds called for by ABYC which states that you must
have them connected. . I know some manufacturers directly connect DC and AC
grounds. I have lived aboard boats for 15 years like this and never
encountered a problem nor failed any surveys because of it.
Next, the GFCI is your friend. If you do not have one installed, you might
consider installing one on your first AC receptacle in the boat. THEN if you
EVER plug any electrical tools into your boat, you will be protected from
any ground faults. Mine have always worked and I have only had to install
one in any boat I owned, contrary to Norm's experience. On one installation
I installed it inside a cockpit coaming and I took every precaution to keep
the water out of the unit by using an outdoor box and coating the wires to
the GFCI. They are also cheap. If you do not know how to install one, find a
trusted electrical contractor and have them do it. GFCI's when wired
properly, protect themselves and all downstream receptacles. Make sure to
test it after it is installed.
Next, you might consider buying a simple AC wiring tester. This will tell
you if your boat is wired correctly, and that no one has swapped neutral and
ground which happens more often than you might think, and may be the problem
you are facing. Then, any marina you transit, just plug in your tester and
you will know if the marina has wired your receptacle properly.
You may have a bad ground someplace, or somewhere in the marina.
With your newly acquired AC wiring tester, plug it into any AC socket in
your boat. It should come up all green LED's. If not, the trouble chart
printed on the plug will tell you what the problem is.
Two things may be going on here, your boat is wired wrong or the marina is
wired wrong. It may be possible that another boat is wired wrong that is on
your circuit. The way I have seen circuits in marinas wired is with 3 phase
120 where each phase is used, for example, 7 boats at a time. It could be
that one of the 7 boats is wired wrong, ie, neutral and ground is swapped.
Battery chargers/Inverters:
Battery chargers can also be a problem of AC leakage into the water through
a boats bonding system. This is because a battery charger is taking AC and
making DC and is a common point for both.
So disconnect the battery charger and see what you get when you try to
measure for ground currents again.
Depending on the make and sophistication of your battery charger, you can
have some transistors or diode bridges that are inadequately insulated
(shorted) to ground, opening a current path from AC to DC.
Isolation transformers are large and expensive. If this is a permanent long
term residence and you have the money to spend or are lucky enough to find
one at a fire-sale someplace, by all means go for it. The way they are wired
is your safety ground stops at the case of the transformer. The transformer
supplies power to all of your AC receptacles without the safety ground. You
would also plug in your battery charger here which would eliminate the DC to
AC connection.
Another question is, if you are not into ham radio, do you want to bond your
boat or not? There are extensive schools of thought on either subject. If
you are a member of Boat US, you may want to look there and see what they
have to say on the subject. They have documents on boats that have been
struck by lightning that were both bonded and not bonded. Also, ABYC might
have some useful information too. My current boat is not bonded, and it is
the first one that I have owned that isn't. Both of my last 2 boats were, as
I had a ham radio installed and required as good of a ground connection to
sea water as I could get. The reason I bring up bonding is that in the above
mentioned incident with the Baba 30, the nearby unbonded boats were not
badly damaged by the AC leakage.
I refer you to "Living on 12 volts with Ample Power", and "Wiring 12 volts
for Ample Power", plus any information you can get from ABYC. Maybe they
have a web site?
Hope this helps,
Mike
----- Original Message -----
From: "Eric Thompson" <>
To: "LIVE_ABOARD" <>
Sent: Monday, October 01, 2001 8:00 AM
Subject: lv-ab: Galvanic currents
> Dick,
> I don't know for sure but I WOULD BET that the original
> atoms from your prop would be gone on the one half cycle and
> then replaced by whatever atoms were most mobile in the
> surrounding seawater during the other half cycle.
> Oh by the way, bronze is an alloy so there are bronze
> molecules not atoms. There are copper atoms and iron atoms
> and whatever the copper is mixed with to make it bronze, but
> no bronze atoms.
> Picky, picky,ain't I?
>
> Eric Thompson
> S/V Procrastinator
> South San Francisco
>
> Dick wrote,
>
> From the point of view of electroplating, or more to the
> point
> unplating, it would certainly seem like AC would not be as
> harmful as
> DC. On one half cycle some bronze atoms from your prop
> might become
> dissociated from the prop, but then on the other half cycle,
> wouldn't
> they just go right back where they came from?
>
>
>
>
___________________________________________________________________________
> || The Live-Aboard List : send a "subscribe" or "unsubscribe" request
||
> || in body of message to:
||
>
___________________________________________________________________________
|| The Live-Aboard List : send a "subscribe" or "unsubscribe" request ||
|| in body of message to: ||
|