My boat is sitting on the trailer mast down in my back yard. I thought I would do the simple job of replacing my main halyard this afternoon. I bought 65' non stretch & 50'
of dacron 1/8 pull cord. I attached the pull cord to the old rope with electrical tape. It pulled thru with no problem. Then I attached the pull cord to the new rope with electrical tape and started at the bottom of the mast. but when I got to the top it seperated. The tight turn at the top pull was not possible. I was able to get the pull rope back thru with wire. I have tried starting at the top with no luck making the tight turn. #@!!$#. So I have the pull cord in place. What is the trick to this????
Doug Ramsey
Take a paperclip an open it up(bend one loop out), Stick one end thru the halyard, one thru the pull rope then a little bit of tape around all. This is hopw we replace halyards on big boats without dropping the stick. Its never failed me.
David
www.powergroovesailing.com
Doug,
I did this last year with not much trouble. I started at the top end and twisted the rope as I pushed in (as if you were screwing it in). I only had a little trouble getting through a section of the lower mast (around where the luff is inserted), but by helping it through with a very thin screwdriver it finally made it through. At the bottom,the area you are having trouble with, again I used the screw driver to poke the end of the rope and pull it out.
Good luck.
Hobie 18? Can't you just take out the sheave that's causing the problem, route the line, and reinstall the sheave? Pardon me - because I can't recall how that was configured on the Hobie 18.
I use a ice or seal pick. Start with the mast track facing up. Get it started at the top, reach in the track with the pick and stick the line with it, add a little angle to the pick and walk.
Butt the two ends of the lines together. Using nylon thread and a needle sew them together. Real simple sewing. Tie a knot in the end of the thread stick the needle through the line a 1/4" from the end and then through the other line 1/4" from the end. Keep doing this until you have worked your way around the line. The stitches should be loose enough so the ends don't touch (so it can bend around the sheave)
If the mast is down in your backyard 4-5 stitches is enough. If you are going to have to climb a mast if it breaks 20-25 is better, 50 if it's a tall mast
I always did what Mike did; just sew it. It takes only a few minutes and never fails.
Wyatt 
Put a reaving splice into the rope and then just tie a small peice of line (read: little bitty) and then rerun the line through the mast. A reaving splice is incredibly simple, and I'm sure you can find instructions online.
Or, just use duct tape...if you can't duck it, *&%$ it.
Trey
N20 314
Layline Rigging
www.velocitysailing.com