Ancient Chinese method.
At Cherubini Boat we had a system for reeving halyards through new spars that will work for replacing them as well. It's fast and simple and reliable-- we'd have no time for whipping lines or anything like that. In typical boat-shop lunacy this system got known reverently as the 'ancient Chinese method', even including mandatory dialogue and sight gags.Of course we did this on new boats with the spar lying down, and it came with a twine or carpenter's-string lead for reeving halyards. But you have a line in yours too-- it's the old halyard. Cut off the shackle. Take black electrical tape (use 3M; cheap stuff cannot be trusted) and start about 12 inches from the end, wrapping tightly around about 5 or 6 times at 90 degrees. Then simply BUTT the other line into the end and wrap the tape on a long diagonal till the whole 24 inches is completely covered to the same place on the other line. Then finish off with another 90-degree wrap and snip off the tape. It has to be an unbroken run of tape-- you will have used about a million feet of it (at $5 a roll). Then you do the same thing from the other end going on the opposite diagonal, to guard against the wrap twisting open. The final touch: the 'ancient Chinese' method of rolling the whole thing very quickly between your palms, back and forth, with some kind of ridiculous teeth-clenching grin on your face. (It feels funny but gets the wrinkled tape all seated against the line as tightly as possible.) Make sure you explain to anyone nearby, 'This is the ancient Chinese method.' Voila.Now DO NOT attempt to pull this mess UP inside the mast to the halyard sheaves. Rather, go up the mast on the other halyard and feed it back down. Be gentle-- but if the 'ancient' (LOL) method is done right, you will be surprised how well electrical tape alone will hold and flex, especially if you are there to 'help' it up and over the sheave. Then it's back up on your new halyard to do the same thing for the other one.JC 2