Phil, I appreciate your engineering expertise. I once had to research lightning heavily in order to serve as an expert witness (my party did NOT settle; opposing counsel probably thought I WAS flappable, but he was wrong, and my client won) so at least I understand the concepts. I'm relying heavily on a book about marine electrical systems (at home, so I can't get the author & title right now). My primary intent for bonding is to dissipate the charges BEFORE they build to enough potential to provide the conductive path. In order to facilitate this, I want a sharp tip atop my mast to leak static potential harmlessly off to the atmosphere, and I want the best conductive path I can get to the ground (although in this case the ground is awfully darned wet!).
While I'm in dissipation mode, I'm dealing with high voltage DC static charges, so I'm going to primarily worry about their behavior more so than the RF effects of an actual lightning stroke. My book recommends standards that were set by the ABYC which wants stranded copper wire, at least 8 AWG, from all shrouds, and a main trunk of 4 AWG (I'm giving all this from memory--may be faulty) with no individual strand smaller than 17 AWG. This is going to be hard to find... I may roll my own from 16 AWG bare copper. I'm not keen on the copper foil in the event of a strike, because it seems to me that the sharp edges of the foil would promote radiation of RF energy and just make the effects inside the cabin worse. But you're absolutely right about lightning--it writes its own rules and is very unpredictable. I wish Tesla were still alive...
My bigger concerns with using the keel as a ground are related to it being solid lead. I don't know enough about lead oxides--are they conductive? Damaging to the environment? Horribly ugly? Will I be growing lead salt formations on my bare-bottomed keel, or find it's been eaten away by the neighbor's leaky inboard/shore power connection? Obviously I need some more research. But that's why I've asked this group. I also plan to check in with the engineering staff at the local anodizing plant--the leader of the group there owns a Pearson.
Thanks for any help!
David Shaddock
----- Original Message -----
From: Phil Agur <[EMAIL PROTECTED]>
Date: Friday, July 14, 2006 21:17
Subject: RE: catalina27-talk: Lead keel question
To: [email protected]
> Due to the high frequency nature of lightning it always hard to
> give advice
> because it doesn't have to behave like DC once it lights up. The
> interestingthing is it doesn't no the nature of the path it
> strikes until the
> ionization path is established. What I mean is it selects a
> target based on
> greatest point of attraction (potential - charge) then follows
> the rules of
> RF conduction once going.
>
>
>
> It doesn't know a wet kite string won't handle the energy of the
> main bolt
> but it looks like a much closer point to strike so it does.
> After that the
> air along the string ionizes (becomes conductive) to provide the real
> conduction path. Researchers use to shoot little rockets into
> storms with
> salts mixed in the solid rocket fuel so it would leave a trail
> of ionized
> gas so they could draw a strike.
>
>
>
> So a relatively small bronze contact point could be used to
> light it off and
> after that it would punch through you bottom paint. The question
> is can you
> keep the ionization path focused on the keel bolts. I've toured
> one factory
> bonding boats right as they come out of the mold and they were
> using a wide
> ribbons of heavy copper foil just like you would expect for RF.
> The battery
> cable approach doesn't offer a good path to RF, which only runs
> on a
> conductor's surface, since a battery cable has a heavy cross
> section but
> minimal surface area it's not the best choice. RF also hates
> bends so even
> the ribbon conductors do broad curves, no creased corners.
>
>
>
> Phil
> Agur s/v Wing Tip
>
> Commodore, Call Sign WCW3485
>
> IC27/270A MMSI 366901790
>
> <http://www.catalina27.org>
> www.catalina27.org Vessel Doc# 1039809
>
> -----Original Message-----
> From: [email protected]
> [mailto:[EMAIL PROTECTED] On Behalf Of
> [EMAIL PROTECTED]: Friday, July 14, 2006 2:16 PM
> To: [email protected]
> Subject: catalina27-talk: Lead keel question
>
>
>
>
> Since Phil is worried that we're too quiet, I have a question
> for the group:
>
>
>
> I'm finally convinced I should bond my mast and shrouds to an
> exposed metal
> plate below the waterline in order to dissipate electrical
> charges and
> minimize the risks of lightning damage to my precious
> electronics. But
> rather than adding more weight and drag, I'm considering leaving
> a section
> of my lead keel exposed, and bonding to the keel bolts in the
> bilge. I have
> concerns: electrolysis, fouling, and legal
> ramifications/pollution... What
> else am I missing? What suggestions do you all have,
> especially addressing
> my concerns?
>
>
>
> Thanks for any advice!
>
> David Shaddock
>
> 1977 C27 Pixie, Rockford IL
>
>
----- Original Message -----
From: Phil Agur <[EMAIL PROTECTED]>
Date: Friday, July 14, 2006 21:17
Subject: RE: catalina27-talk: Lead keel question
To: [email protected]
> Due to the high frequency nature of lightning it always hard to
> give advice
> because it doesn't have to behave like DC once it lights up. The
> interestingthing is it doesn't no the nature of the path it
> strikes until the
> ionization path is established. What I mean is it selects a
> target based on
> greatest point of attraction (potential - charge) then follows
> the rules of
> RF conduction once going.
>
>
>
> It doesn't know a wet kite string won't handle the energy of the
> main bolt
> but it looks like a much closer point to strike so it does.
> After that the
> air along the string ionizes (becomes conductive) to provide the real
> conduction path. Researchers use to shoot little rockets into
> storms with
> salts mixed in the solid rocket fuel so it would leave a trail
> of ionized
> gas so they could draw a strike.
>
>
>
> So a relatively small bronze contact point could be used to
> light it off and
> after that it would punch through you bottom paint. The question
> is can you
> keep the ionization path focused on the keel bolts. I've toured
> one factory
> bonding boats right as they come out of the mold and they were
> using a wide
> ribbons of heavy copper foil just like you would expect for RF.
> The battery
> cable approach doesn't offer a good path to RF, which only runs
> on a
> conductor's surface, since a battery cable has a heavy cross
> section but
> minimal surface area it's not the best choice. RF also hates
> bends so even
> the ribbon conductors do broad curves, no creased corners.
>
>
>
> Phil
> Agur s/v Wing Tip
>
> Commodore, Call Sign WCW3485
>
> IC27/270A MMSI 366901790
>
> <http://www.catalina27.org>
> www.catalina27.org Vessel Doc# 1039809
>
> -----Original Message-----
> From: [email protected]
> [mailto:[EMAIL PROTECTED] On Behalf Of
> [EMAIL PROTECTED]: Friday, July 14, 2006 2:16 PM
> To: [email protected]
> Subject: catalina27-talk: Lead keel question
>
>
>
>
> Since Phil is worried that we're too quiet, I have a question
> for the group:
>
>
>
> I'm finally convinced I should bond my mast and shrouds to an
> exposed metal
> plate below the waterline in order to dissipate electrical
> charges and
> minimize the risks of lightning damage to my precious
> electronics. But
> rather than adding more weight and drag, I'm considering leaving
> a section
> of my lead keel exposed, and bonding to the keel bolts in the
> bilge. I have
> concerns: electrolysis, fouling, and legal
> ramifications/pollution... What
> else am I missing? What suggestions do you all have,
> especially addressing
> my concerns?
>
>
>
> Thanks for any advice!
>
> David Shaddock
>
> 1977 C27 Pixie, Rockford IL
>
>
