[C38] FW: Re: why not unplug when leaving boat?

[Tom T.]

If zincs are eating up faster than one per year, someone at your dock
probably has a "hot" neutral.  Once I took a small power cabin cruiser (aka
stinkpot) to Bimini with a brand new stainless prop and zinc on the
outdrive.  One day in Bimini and my zinc was dissolved and my brand new
stainless prop was coated with a coating of zinc like it had been spray
painted with cold galvanizing paint.  Not much harm done other than eating
up my zinc but it sure showed us how badly a stray current can be.

I now carry a receptacle checker in both of my boats and my motorhome.  In
Key West, a boat next to us had a hot neutral. We got in after dark and the
marina was closed but we had permission to dock.  There was no available
dock power outlet and it was to hot to sleep without the air conditioner so
the boat next to us offered for us to run an extension cord to an outlet in
his cockpit of his boat for the night so we could at least run the air
conditioner.

His found that neutral was hot when I tested our end of the extension cord.
We managed to correct his boat in the morning but for the night, I had to
rewire our plug end on the extension cord so I could get a proper power for
the night.

Stray hot neutrals can dissolve everything metal pretty quickly in salt
water.  They can also be dangerous if you have appliances with a neutral
ground on them.

By the way, earlier this year we had a wiring failure too, and this one was
also at the shore power plug.  If we had known to remove the receptacle and
examine the connections to the wires it would have saved me a lot of work
because after the wire burned, I had to re-route the wires to get enough
slack to provide clean ends for the new shore receptacle insert.  A few
minutes to remove the old receptacle and clean it would have saved me
several hours of work and a new $33 receptacle insert, not to mention the
connection failure could have caused a fire.

Tom T.



> [Original Message]
> From: <mncameron at att.net>
> To: <drstrong at ucdavis.edu>; Catalina 38 Listserve
<listserve at catalina38.org>
> Date: 12/5/2009 1:33:15 PM
> Subject: Re: [C38] why not unplug when leaving boat?
>
>
>
>  
>   -------------- Original message from "D. R. Strong"
<drstrong at ucdavis.edu>: --------------
>
>   We are at the large Emery Cove marina in SF Bay. My marina manager
toldme that all of the fires that have started during her 10 year or
sotenure were due to a short at the point that the shore power cord
wasplugged into the boat. 
>     Another reason to unplug when leaving the boat is that the zink ina
bronze prop can act as a sacrificial anode. In our first year ofownership,
the key to the prop sheared and we lost an expensiveFlex-o-Fold prop while
backing. Not knowing what was going on, Icontinued to leave the boat
plugged while absent from the dock. Threeyears later, the prop key sheared
while motoring. We didn't lose theprop this time because it was driving
forward, not backward. The diverremoved it and showed me that the sheared
key had deep pits, presumablywhere the zink had dissolved. The prop was
also pitted. Since thatepisode, when we were lucky not to have shelled out
another boat unit(=1k) for a new prop, I have had zinks changed every 3
months and haveendeavored to unplug every time when leaving the boat. Since
the newpolicy of unplugging, the zinks look good after 3 months. Before
Istarted to unplug, they would be ravaged and not serving. I assume thatat
the point that the zinks failed, the bronze would take over andbegin to
dissolve. 
>     When my kids forget to unplug after one of their big party days onthe
Bay, lots of zink is now left to take the current for the week orso before
I come back to the boat. We do not know where the current iscoming from. A
doc friend who is an engineer suggests that when pluggedin, stray currents
from other boats could arc through our boat and backto the cord, but he
says that this is just and iffy idea. He measuredsome stray current at the
plug when the boat was plugged in with everyelectrical switch on boat at
off. The marina has recently upgraded theelectricity, and this might reduce
stray current; who knows. Apparentlythere are isolation devices that I
could install just downstream fromthe plug, but if I unplug when leaving I
don't need to do that. What Ineed to do is watch both male and female
components of the plug devicesfor corrosion and or evident of excess heat.
>     All suggestions appreciated.
> Regards, Don
>
>
> Don,
>
> I think its time for a galvanic isolator.  Your marina has problems with
stray current.  If they have their stuff together they could come to your
boat and your neighbors and do some measurements.  You should be able to
leave the boat plugged in all the time and still have your zincs last
several months with no damage to prop or other metals.
>
> The Guest model 2530-P  is what I use and am happy with it.
>
> michael

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