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.