Had to go up the mast a year or so ago to install some fittings, and looked at the commercial halyard climbers. They looked impressive, but overpriced. So, I first bought a rock climbing harness (about $40) and started playing with that with a rope up to a tree branch in my yard. Played a bit with prussick knots, but enough wraps to be secure were also very difficult to loosen and slide up/down the rope. Finally bit the bullet and bought a pair of Petzl ascenders for about $90. One goes to the foot strap (home made) and the other to the harness. Worked fine! When you start looking into rock climbing, you're going to learn a bunch of new knots. It's nice to be able to go up the mast without relying on a second party on a winch, who's going to tell you at the wrong time that 'Oops, I've got an override..'