Your first thought of not being on the water during lightning is the best; a lightning strike is very bad news and I've been struck in a carbon fiber yacht, so I know from which I speak.
First, lightning always takes the path of least resistance to ground. In some circumstances, being in a metal boat can be a great advantage in a lightning storm. If you have a tall metal (aluminum) mast to act as a lightning conductor and a metal hull, the lightning will travel down your mast, around the hull and to the water (ground). According to the "Faraday's Cage" principle, if you are inside the cabin and not touching the aluminum hull or deck, i.e. sitting on the wooden interior, the current will pass around the hull to the water and you will remain perfectly safe. In the case of a fiberglass boat, the rig should always be grounded to the keel with heavy gauge wire, to give lightning a path to ground should the boat be struck. Often the guard rails will be grounded too, as these also act as good conductors. But again, inside on a wooden bench you should be safe.
In the case of your friend's 19-foot fishing boat, if it has a cabin then inside there would be the safest place to be, BUT not in direct contact with the hull or any other metal component. For example, make sure you are sitting on a wooden bench or a plastic ice box. If the boat in question is a simple bare aluminum hulled "open" style boat, unfortunately your chances of escaping injury are greatly reduced in the event of a direct hit. The reason is in a 19-foot boat you are at best 9.5 feet away from the point of contact, and if your are sitting on an aluminum bench seat, you are now part of the path to ground. Not good!
If you do find yourself caught out in an electrical storm, your best bet is to head for home as quickly as possible, or if possible get close to a land mass with higher elevation, or better yet high buildings/structures on that land mass. As a last resort, make sure you have a molded plastic ice chest to serve as a non-metallic seat.
Hope this helps.
Captain Ian Fagg "