go to masthead with a length of bicycle chain attached to a light line..fish out the chain at the lower exit point..attach new halyard to light line(sewing together works well)..pull

Roland,

I was trying to fish a line down the mast last year and was having a hard time getting the line down the inside of the mast. It kept hanging up on stuff. A friend that was spotting me grabbed a small drill bit, I think it was a either a 1/2" or 3/8" bit, and sent it up. The bit was heavy enough to give me the weight and the line I was using fit inside of the drill bit flute making it clean to lower past the stuff inside of my mast. A few wraps of electrical tape around the bit with the messenger line inside of the flute allowed it to pass thought the mast without hanging up. I used a bent hanger to fish out the bit and small line.

Whatever method you use I would suggest before you pull the halyard sew the messenger line and halyard together and use a Hasty whip to insure you don't have a disconnect. I'd even put a few wraps of tape around the connection to prevent any possible way the line/halyard could hang up. You might find it's a few well spent minutes just in case you have to give the messenger line a good tug...

Chris

I'm curious about one thing: If the boat is in the water, what stops the halyard you are lowering down the inside of the mast from going around one or more of the other halyards that are already in the mast, as the mast sways back and forth?

Do they each go down their own inner tubes or something? (I've never had my mast off the boat to look down it.)

The halyards might possibly wrap around each other but it wouldn't matter. Might even reduce the internal halyard 'slap' :)
There are no separate tubes on our boat.