One other thing I wanted to add: never use any hardware on the end of the halyard to attach yourself. Always tie a figure 8 knot that leaves a bight on the end of the line. You can leave the hardware on the bitter end, just down attach to it. Use a locking carabiner meant for climbing to attach the bight to your harness/bosuns chair.
Using the hardware on the end of a halyard leaves too many failure points, the shackle, the knot attaching the shackle, and there may be wear in the line where the line bears on the shackle. Use a figure 8 tied in a bight instead.
There are many videos on Youtube showing how to tie a figure 8 in a bight for climbing.
