All good info so far. I will add that you should not rely on a self tailing winch when hoisting someone up a mast. See the warning below.
When there are only two of us we use two halyards both running through locked clutches. One to the hoisting winch and the other nearby to take up slack every 5 or so ft. Our halyards are led to the cockpit. We use climbing harness for short trips and bosuns chairs and harness for longer trips. We also use one of our jack line tethers wrapped around the mast a few times with both ends hooked to the harness. If both halyards fail the tether tightens and stops the fall. It also keeps you near the mast should it be rolly. The person going up will try to climb to help the winching person.
Lewmar issues safety warning on self-tailing winches - Ocean Navigator - March/April 2011