Capt. JG wrote:
"IanM" wrote in message
...
Roger Long wrote:

I don't know why my first Google search missed this site:

http://www.marinelightning.com/

but it calls into question the whole idea of the central main conductor.

I'm fortunate in having one of those aluminum toe rails that go bow to
stern on each side. It seems that I might be better off running the
heaviest wire I can between the port and starboard toe rails inside at
bow and stern and then bonding each chainplate to the toe rail and
running 4 ga conductors to each piece of underwater metal I can. I have
a number of unused through hulls that are capped. The chainplates on my
boat all end very close to the toe rail so charge coming down the stays
would likely jump that way even without bonding.

As I said earlier, If you let the lighting get below deck, you are screwed
and if down to bilge level ****ed unless its got somewhere to go. For a
powerboat or a sailboat with a non-conductive mast support post, its
probably practical to *NOT* have a central lightning conductor, but where
do you think the bulk of the lightning current is going to go? Down a nice
thick piece of low resistance aluminium bolted inline to a heavy fairly
low resistance steel pipe leading to the bilge or down fairly high
resistance shrouds and stays with rather dodgy electrical contact at the
top and bottom ends?

There is going to be *some* current down the stays so it would appear
prudent to bond the toerail to the shrouds, stays and mast foot, and cross
bond bow and stern, but then the problem is where do you encourage the
inevitable flashover from the toerail to the water surface to go? A strap
down the stem and each transom corner would be a good start but few
owners are going to tolerate external straps down from the chainplates. I
suppose you could trail a chain from each shroud while berthed and if
caught out in a thunderstorm.


From my manual:
22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS

All Sabre yachts are equipped with a heavy duty lightening ground and
bonding system connecting all essential equipment to the keel using #8 gauge
stranded copper wire.

22:01 BONDING SYSTEM: The bonding system provides low resistance to
electrical connections of all underwater fittings, fuel fill, fuel tank and
engine to the keel. This keeps all fittings at the same electrical
potential to minimize the effects of any galvanic or electrical corrosion
which may occur.

Any additional underwater hardware installed on the boat must be tied in to
the bonding system to maintain proper operation and protection from
corrosion.

The integrity and operation of the system should be checked each year at
launching and hauling times.

Refer to the lightening protection and bonding system diagrams in the back
of the Owners Manual for the wiring details of your boat.

22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system
provides a "cone" of protection around the boat in the even of a lightening
storm. Grounding wires of #8 gauge copper connect all chain plates and the
mast step to the keel.


#8? Ha, Jon, I've seen the inside of an underground vault with the
walls spattered with copper after a 75KA short vaporized copper bus bars
1/2'" thick by 4" wide. That's one hell of lot of #8 wires in parallel.
Imagine what happens with surge that may exceed 200KA?

I go along with others that have suggested that lightning protection for
a plastic boat is probably an exercise in futility.

Cheers
Martin