I assume you mean you are drilling pilot holes and then tapping them for a machine screw?

Roll tapping does make a better and stronger thread, but the pilot hole size is much more critical (and they are harder to start straight) and that is going to be very hard to do with a hand drill in a boat yard. If you can get the mast onto a drill press and properly jigged, then roll tap. With a cutting type tap, you can use a slightly smaller pilot drill and still get a good thread, if you use a long tapered hand tap.

If you are talking about using self-tapping screws, then hey - it isn't something I would do so you are on your own.

However if it were up to me I would probably use Cherry structural blind rivets. Those aren't the ones you get at the hardware store (or West Marine). More like the link below. You would have to decide whether you want to use aluminum (and let the stainless steps eat the fasteners over time) or stainless (and let the fasteners eat the mast over time). You will need a real rivet puller for these, the one you find a Sears or Home Depot won't do it.