James,
I don't remember the exact figure as I had the line on hand but it was probably in the neighborhood of 200 to 250 feet. I used a small diameter three strand nylon of about 3/8". It is the same line I use for the reefing gaskets on the main. The long control line is belayed on a belaying pin and the three jack lines are belayed to the center grab rail abeam the mast by looping them around and securing with the carabiners. I had them on stowed on the lifelines, but the way I am docked now, they were being used as assists when visitors were boarding which made for a very unsecure handhold so I removed the temptation, so to speak.
I have to remove the jack lines from the boom in order to put the sail cover on so they remain stowed until it is time to lower the main. I can attach them to the boom after I raise the main and sail with them on and have them ready for lowering but normally don't do that due to chafe and wear and tear on the mainsail and jack lines. Since I have to go on deck to lower the main anyway it is just as easy to deploy them then. If you decide to rig this system, you can make the control line extra long so that you can coil it nicely around the belaying pins and it will give you enough to determine the best length since this line will determine how well the main falls into the jack lines. I tied the system together with bowline knots and experimented until the main fell nicely onto the boom and my wife (then girlfriend) did the eyesplices.
The real truth is that after watching me for about 6 tries, she figured it out using trigonometry, gave me the measurements for the padeye locations on the boom, and it worked perfectly!!! Needless to say I was impressed and married her immediately.
I will be returning to Florida tonight and will try to post some pictures and measurements in the next day or so. In case you missed the link to the diagram with explanations in the hubub of the previous posts, here it is again. This is where I will post the pictures.
http://www.my-flashcards.com/rhapsody/index.html
Werner