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.

--
Roger Long