From: gerard@progress.COM (Gerard Bras)
Subject: Re: Zincs on boats
Organization: Progress Software Corp.
Date: Mon, 14 Dec 1992 19:16:24 GMT

mmp@mmp.UUCP (Lou McIntosh) writes:

>        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.

I'll go along with this.  Anything that's expected to carry a lightning 
strike to earth had better have good conductance, thermal mass, and high melting
point.    I've read where chain was recommended for this purpose.  Another 
possibility would be some large guage welding lead.

There are some other considerations.  Lightning strikes like to follow 
straight lines.  Therfore sharp bends in the ground conductor should be 
avoided.  I've also heard of cases where the lightning ran down the mast
and then just punched it's way through a non conductive hull.  In most of these
cases the boat went to the bottom in *seconds*.


>        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.  

Again, this is right on. Part of anual inspection of a bonding system 
might well be to measure the conductance.
 
>        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!

Another winner.  Articles like this really make the group for me.  Another
strategy might be to solder bonding wires into the connectors.  This 
still leaves the joint between the connector and the fitting though.
I really like the idea of this conductive goo.

>  
>        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?)

I've no real experience with wooden boats but I have heard over and over 
that anywhere metal contacts wood is a prime rot spot.  In addition I've
read that the by products of electrolysis can chemically digest wood.
I'll look this up though so I get the story straight.

It's claimed that Marelon is pretty near as mechanically strong as bronze.
Forespar claims you can beat it with a hammer all day and not damage it.
This may be a fun thing to verify on one of those cabin fever days of
winter.

cheers,
gerard

Newsgroups: rec.boats