[C38] why not unplug when leaving boat?

[mncameron at att.net]

  -------------- 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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