I live and work on a boat, a carbon boat with a 60 meter carbon mast on it in fact and the lightning conversation comes up alot!
As a wee lad in the 70's,I had a number of personal experiences with lightning and sailboats. My family had a sailboat business.
1) I just happened to be looking out a window during a storm when lightning struck a nearby boat. The lightning struck the 45 foot tall aluminum mast. For several seconds afterwards, there was a puff of green smoke in the exact shape of a fiberglass radio antenna which had been a part of the mast, until the lightning converted it to smoke. The people on board the boat were not affected, nor were their electronics. The boat had a copper plate under water which was electrically connected to the rig with heavy gauge wires.
2) Not long after, I encountered another boat, where the owner had not opted to purchase the "lightning ground option." This boat had also been struck by lightning while unoccupied. When we saw the boat, it looked like it was sitting a little low in the water. We decided to investigate and found evidence that a fire had been in the boat, and that it was slowly filling with water. Further investigation revealed something like 3,000 little pin-holes thru the fiberglass hull where the lightning had exited. I think the boat was declared a total loss by the owner's insurance company.
Ground the rig. Lightning's going to go where it wants. You might want to offer it a path that helps it to find the ground.