When our main halyard parted, we took a spinnaker sheet and ran it through the vang blocks (which provide a 4:1 mechanical advantage). We then attached a cunningham hook to the upper block. The crew was hoisted up in a bosun's chair to the hounds carrying a boathook and the block and tackle. He used the extended boathook to hook the upper block over the masthead crane and then used the block and tackle to hoist himself the last few feet. Once at the masthead, he used another shorter line to provide a safety line to the bosun's chair. NB - this worked for us, but anyone who tries it does so at their own risk. If I were to do it over, I would have had him mount a small cheek block on the side of the mast at the masthead and then run a small messenger line back down to the base. Then a much stronger line could be run when needed for work at the masthead ... or even for an emergency main halyard.
