Protection against lightning is basically to stay neutrally charged. If your mast is aluminum and highly conductive, not a problem as long as it does not emit a "leader" or positive electrostatic charge up into a negatively charged storm cloud. There are two things you do about this: firstly ground out your mast to something substantial and conductive in the water. If the keel is encased in an insulating (electrically speaking) material, grounding to it may not be the best. Note that a lightning strike with poor ground will overcharge all metal in contact and disperse everywhere: this is how the chainplate bolts get popped out of sidestays. The point of contact gets very hot very fast, something sacrificial above the masthead is advised, but not copper or aluminum, they melt easily: try painted ferrous iron. The second part of this is to arrange the boat to have as little static charge as possible: main offender here is going to be wind ripping past sailcloth just before the rains come, creating an ionic charge that is often stored in the mast and boom. Take down all sails when a lightning storm is apparent and check your electrial grounds. The boat should then be close to neutral as the surrounds--or at least as good as it gets. Unplug things electric and sit away from metallic objects. A strike will be proportionate to the attraction of the mast and the negativity of the stormcloud. The strike needs a route from the masthead to saltwater in the shortest path with the least resistance.