I've read a number of first-hand reports as well as the 'theory' that the
books all say.
The books say if your mast and rigging is grounded to the water there's a
'cone of protection' around the mast and within it you will be ok. This
makes some electrical sense too because your rigging and mast become like a
'faraday cage'. Hanging a heavy chain off your backstay into the water would
probably help and is the advice I've read.
Despite all this, i get the sense from all the reading I've done on the
subject that nobody is really all that sure how to protect from lightning.
There's an awful lot of what I'll call 'juice' running in a bolt of
lightning.
The first-hand accounts I've read (some of which were on this list, one was
in 48 North, and a few others) is that typically the sailors' reaction is
"Wow, that bolt was really close" and only after finding that the onboard
electronics were fried is it realized the lightning actually hit the boat.
This is one situation where I hope I never become too experienced.
FWIW I've never heard of a fatality on a sailboat directly from lightning,
but I suppose it has happened.