From: mmp@mmp.UUCP (Lou McIntosh)
Newsgroups: rec.boats
Subject: Zincs on boats
Date: Sun, 13 Dec 92 12:55:39 GMT
Distribution: world
Organization: Maine Meeting Place * 207-324-5310 * Maine's Disabilities Network


In article <1992Dec11.162955.17672@progress.com> gerard@progress.COM writes:

 > 
 > There is a diversity of opinion on the value of bonding, both for lightning
 > protection and for the prevention of electrolysis.  My opinion is that, >  properly
 > done, it can do both.  Done poorly, it is likely to do more harm than good.
 > Further, "properly done" seems to vary with the situation.  This is hardly
 > a black or white type issue.
 > I cannot even find universal agreement on whether a lightning ground from
 > the mast increases or decreases the odds of being struck.  It is pretty clear
 > though that once struck, a good ground path can save your day, your boat, and
 > your life.
 
        I entirely agree with all of the above.  As to the lightning ground 
 from the mast, my experience has been that the best protection is conferred
 by large external chainplates that reach to the waterline ... whereas if you
 force several hundred thousand amps through a bonding conductor, the odds of
 having it find its own fortuitous path out through the hull are high enough
 to be plenty scary.
 
 > Practical experience demonstrates that bonding to good zincs will decrease or
 > prevent electrolysis.  In order for this to work, the zinc has to be 
 >  electrically
 > bonded, through a low resistance path, to the thing(s) it's supposed to 
 >  protect.
 
        Yes; I would add only that since bonding conductors are typically 
 run through the bilge, and are made off to metallic parts using crimp 
 connectors at best, the chances are that over a period of a year or two the
 electrical path at one or more metal fittings will "open" or become high-
 resistance because of the formation of oxides.  The metal fitting may now be
 in good electrical contact with other metal fittings downstream of it, but 
 in poor contact with the zinc.  

        My practice in recent years has been to make up all the bonding 
 connections using one of the antioxidant compounds -- depending on the 
 metals involved, I use either the commercial goo which is spec'd for CU/ALR
 joints in shoreside wiring (which I believe consists of a zinc compound in
 a mineral oil suspension) or a similar goo made of copper particles in an
 oil suspension.  I use the former on stainless, the latter when only copper
 and brass and bronze and lead are involved (including battery terminals, by
 the way -- it's WONDERFUL for battery terminal protection).  It excludes 
 oxygen and salt, and assures electrical continuity -- and it seems to last
 very nicely even if it's occasionally immersed in bilgewater.  This strategy
 has at least made the electrolytic environments much more predictable!

 > Tying all your underwater fittings together and then not having enough anode
 > is a recipe for worse electrolysis.  A positive cure for electrolysis is the
 > use of Marelon type through hulls.  Some surveyors love them, other look 
 >  askance.
 > You decide.  For my money, Marelon is fine as long as it's protected from
 > hard knocks.  In most modern pleasure craft this is a non-issue.
  
        I don't see anything wrong with Marelon, as long as not only the 
 fitting but the attached hoses are mechanically isolated (and, at least for
 the smaller sizes, protected from being stepped on in the course of one's 
 descent into the machinery spaces ...) -- one of the advantages of Marelon
 in wooden hulls is that because it doesn't transmit heat as well as metal, 
 it doesn't tend to condense moisture out of the humid interior air of the 
 boat and deposit it on the adjacent hull -- which in my experience is one of
 the more frequent causes of rot near through-hulls.  (I suspect that the 
 notorious "electrolytic rot" is mostly rot from condensate -- any other 
 thoughts out there on this question?)
Newsgroups: rec.boats