Mary,
Last 4th of July I had my two young sons and my wife aboard our N6.0, headed for a gathering of friends about 4 miles away. We had rigged the boat at a ramp that faced east and we were surrounded by lots of tree so we couldn't see the weather approaching from the west. As we sailed out of the harbor and the view opened up, we could see the nasty weather building quickly in the west. We decided to head back to shore. Then, the wind died - completely. My wife was sitting beside me on the hull, holding onto a trapeze wire. Next thing I knew, she yelled, "I've been hit!" The shock caused her to nearly fall in alongside the boat.
A few breaths of air pushed us ashore, alongside a 15 foot vertical bluff with a stairway to a floating dock. Michele and the boys quickly jumped onto the dock as we sailed by it. (I had decided to run the boat solo back into the cove with the ramp. Given all the electricity in the air, it was probably a dumb move on my part, but I couldn't stand the thought of sitting and watching my boat get bashed against that cliff while waiting for the storm to pass.)
The hit that Michele took was not from a direct strike, but rather the result of the air being charged enough to conduct a shock down the wire to her arm.It was enough to make her arm go numb for the entire day.
The incident kind of freaked us out. I, too, am curious about the statistics for folks that have been hit while sailing a beach cat. Often we're sailing four or five miles from shore and coming ashore quickly is not an option. Thunderstorms can build rapidly, and to stay at home whenever they're forecast would cut into a lot of sailing time. Am I taking too big of a risk?
Reference Chapman's Seamanship (I didn't write it...) for information on lightning and the cone of protection. The idea is related what is called the Farraday Cage - surrounding yourself with conducting stuff to attract and direct the hit away from you. What apparently has been realized with boats is that doing this also seems to help bleed off potential, making the boat less attractive to hits in the first place (same thing with other tall structures properly grounded). Boats still get hit, but I'll go out on a limb and say it must be effective to some degree - there are acres of keelboats around, and rarely do I hear of one being hit. I've heard of a powerboat getting hit while underway - strike hit the ungrounded VHF antenna and blew apart the console, nobody killed but it ruined the day.
A powerboater was hit on Biscayne Bay. Unfortunately, he must not have had an antenna -- his head was the highest point, and that is what was hit. He did not survive.
This was enough to convince me that the rule of the Geneva Sailing Club (a cat club on Lake Erie in Ohio) that members must turtle their boats if caught out in a lightning storm is not necessarily a good rule.
Mary-
Last time I was out in that situation I decided the safest thing to do was pull the boat (my Taipan) over on it's side - leaving the beams ~7 feet in the air but well "grounded" in the water while I swam alongside the boat on the hull (opposite the mast side) side until the lightning passed then righted the boat. This just made sense to me at the time 
but I would like to hear what more knowledgeable people think of that idea (obviously it worked that time 
).
Kirt
Hmmm, I had always heard that the worst place to be is in the water. Isn't that why the lifeguards make everybody get out of the swimming pool when there is lightning in the area? .....and why you don't use electrical appliances when you are in the bathtub?
Mary,
This post just shows how litle people know about lightning.
"Grounding" a boat DOES NOT prevent lightning.
On the contrary, it helps to attract it.
Lightning usually hits grounded objects like buildings, trees, antennas, LIGHTNING RODS, etc.
DUH!!!
If done correctly, grounding conducts the lightning strike to a harmless location. See: LIGHTNING RODS
As the man in the power boat found out, it isn't a matter of how high you are,
it is a matter of being the highest object in an area with a lightning strike imminent.
Lightning is certainly one of nature's most awesome forces. It is also surrounded by lots of myth and misunderstandings. With that in mind, it's good to see the interest and discussion in this thread.
Here's a source that I've used as a resource for learning about lightning safety.
National Lightning Safety Institute
Here are some stats from the National Lightning Safety Institute page. Men who hang out in Florida on summer afternoons, take note. 
[color]35 YEARS OF LIGHTNING DEATHS & INJURIES
In October 1997, the National Oceanic and Atmospheric Administration published findings of some 35 years of USA lightning statistics. Fatalities, injuries, and damage were compiled for the years 1959-1994. We summarize the Report (1) as below:
1. Location of Incident:
40% Unreported.
27% Open fields & recreation areas (not golf).
14% Under trees (not golf).
8% Water-related (boating, fishing, swimming…).
5% Golf/golf under trees.
3% Heavy equipment and machinery-related.
2.4% Telephone-related.
0.7% Radio, transmitter & antenna-related.
2. Gender of victims = 84% male; 16% female.
3. Months of most incidents = June 21%, July 30%, Aug 22%.
4. Days of week of most incidents = Sun./Wed./Sat.
5. Time of day of most incidents = 2 PM to 6 PM.
6. Number of victims = One (91%), two or more (9%).
7. Deaths by State, Top Five = FL, MI, TX, NY, TN.
8. Injuries by State, Top Five = FL, MI, PA, NC, NY.
As Sam said, grounding works if it is done right. But if it is not done right, it wreaks havoc with your boat and can be deadly. And you don't know whether it is done right until you have actually suffered a direct strike. Personally, I would rather take a chance with the "Farraday Cage" theory.
Once upon a long time ago, Rick and I were delivering a Seawind 24 (catamaran) from Miami to Nassau. We had to sail straight through because we had a deadline for getting there. We were crossing the Bahama Bank during the night. It was my shift on the helm, and Rick was below sleeping. We had the boat grounded with an alligator clip on the shroud and some cable dragging in the water.
Overhead was clear, starry sky. But several miles ahead, directly in our path, was a black hole, no stars. And then the lightning began, like a picket fence across the horizon, with continual, multiple strikes from cloud to water. It was my worst nightmare.
I woke Rick and asked him if we could anchor and wait until the storm went away. Mr. Punctuality responded, "Nope, we have to stay on schedule." And he went back to sleep.
I continued sailing straight toward the electrical fence, praying the storm would dissipate before I got there.
Finally, I woke Rick again and asked, "Could we at least sail around the end of it, where there isn't any lightning?"
"Nope," said the captain. "Don't worry about it. Maintain your compass heading." Yeah, right. And he went back to sleep.
So there I was, all alone in the night, sailing toward the monster, trying to find a hole to get through where the lightning might be a little less frequent. And the whole time I was agonizing about the alligator clip, knowing that it was going to make it easier for the lightning to find me. I just wanted to make myself and the boat as invisible as possible.
So right before I got to the black hole and the picket fence, I took off the alligator clip. The stars disappeared as I sailed beneath the storm clouds. I braced myself for what I thought was certain death, while Rick slept peacefully. And then, miraculously, stars again appeared above me, and I looked back to see the black hole and picket fence now behind me.
This, of course, proves nothing. All I know is that I removed the grounding device and I did not get hit by lightning. I have always been curious about what would have happened if I had left the alligator clip on.....but not curious enough to go out and play in lightning to experiment.
The wonderful thing about lightning is it will hit anything, grounded or not. The real attraction for it is the difference in charge. Lightning can go cloud-to-cloud, or form a flash when it hits nothing particular. It can hit airplanes and rockets. One of my favorite pictures I've seen is of lightning doing a loop while going from cloud to cloud - it apparently "changed its mind", due to change in potential in the area. The only real way to not get hit is to bleed off or eliminate the difference in potential. The only other alternative is to provide it a likely path to follow if you are hit.
On big/cruising boats, ALL the big metal pieces are tied together via copper strap, and grounded to the keel or a metal plate on the hull. This makes the mast the tallest thing with the same electrical potential as the rest of the conducting bits and the surrounding water, making it the target in case of a hit - this is what gives the "cone of protection" - meaning the hit will be attracted to and follow this path instead of hitting you on deck. Again, according to Chapman's (if I remember right), there seems to be some effect of helping to bleed off some of the charge in the area, making the area less attractive. That's less attractive, not immune. If the connecting straps are not done right, the risk is higher that the strike will not follow the intended path. So, on a beach cat, unless you tie the cross beams and other metal bits together to the mast and to a sufficient grounding setup you may not be achieving what you hope to.
If you're in the water, and the water takes a hit, you'll feel it for sure - the reason to get out of the pool. One reason that they say not be in the shower during a storm.
While this did not happen to my I-20, I have witnessed carbon fiber masts and their interaction with lightning. Had a windsurfing mast rigged as an extension of a CB antennae in the Bahamas and it was hit by a bolt one afternoon. Yes, the antennae and cable did act as a lightning rod, but the middle part of the carbon fiber mast exploded into a large number of splinters. I would guess that this same effect would occur on a larger and thicker CF mast (windsurfing masts are only about 12-15' high). It would probably be due to the extreme heating experienced during the lightning strike.
In the CF mast on a cat, if you were sailing in a storm, I would figure that the film of water on the mast would act more as the conductor than the mast itself. Due to the heat of the lightning, I would suspect some major heat damage in the form of splintering/fractures.
If I recall correctly, they conducted tests on helicopter rotor blades and airplane wings to determine what would happen in the event of a lightning strike (**safety tip**, chopper blades create a bunch of static electricity while hovering, so never grab a rescue cable from a chopper until it hits the ground first!). The aluminum skinned wings/blades emerged relatively unscathed, while the carbon/composite types suffered severe damage. There are even some USAF freaks who PURPOSELY fly jets through lightning. You should see the video!
In our area there's a well-known racing monohull named "DonneyBrooke", which I believe is a custom/modified Santa Cruz 52. All carbon mast, lots of carbon in the boat itself. She took a substantial hit on the mast while lying in her slip. The crew working on board were unscathed, but at last account the mast was a write-off due to structural damage, as were all the electronics. There were indications that the hull itself had suffered damage as well. Big repair bill, including trying to get in the schedule to have a new monster carbon spar built. I think they figured she'd be out action for at least the year.
I have a bit of a tough time with that one. Aluminum is used for household wiring. I think that it is less used nowadays for reasons I am not certain of but it is nonetheless a good conductor.
Carbon fibre is also an excellent conductor as I remember from my hang gliding days there was a guy outside Salt Lake City at a place called "Point Of The Mountain Utah" (I get excited just remembering the excellent flying conditions there) who accidentally managed to sink out and land on some powerlines which were on the perimeter of the "South side".
His carbon fibre glider burned and cooked for quite awhile and knocked out the power to wherever it was going.
Fortunately the webbing which was used to suspend him was conconductive and he managed to only suffer injuries from the fall from the wires.
It was actually kind of bizarre that he was that low in the area of the wires.