Thanks to all for the helpful information. A follow up question. On a boat set up for single handed sailing how does one secure the mainsail to the boom when reefing the sail. Do you have to leave the cockpit and to secure the main to the boom or can a winch handle that?
Rusty: assuming you don't have in-mast or in-boom mainsail reefing, reefing the main is a fairly simple process. You slack the mainsail halyard to allow the sail to come down a certain amount (the amount you lower the sail is generally preset or understood from practice at the dock or in calm conditions), but you don't lower the sail completely. This action is done in the same manner in which you lower or raise the sail normally. Once the sail is partially lowered, you must affix the newly shorted sail to the boom. In the old days, this was done by tying the reef points (short pieces of line that run through the sail at regular intervals parallel to the to the boom) around the boom. Many sails still have reef points, but they are rarely functional, and are only used to cosmetically tuck the now-folded up extra sail snug so it doesn't look sloppy.
The reefed portion of the sail is affixed to the boom these days with a "slab" or "jiffy" reefing system. You now have one or two lines that run along or in the boom, through blocks, up through grommets in the sail at its after-most and fore-most ends, back down the other side of the sail, and then affixed to a strong point. One pull on the reefing line(s), and the entire sail is brought down to the boom in a big slab. Affixing the end of the reefing line to a cleat on the boom then completes the action. If you have reefing points, you can then tie them off, neatening the look of the sail. You then rehoist the halyard taut. Reefing done.
Here's a link to a slab reefing diagram:
Reefing the Mainsail - How to Reef the Mainsail - Slab Reefing for the Mainsail
I have never seen reefing lines that weren't cockpit accessable, and if your mainsail halyard winch is on the coach roof or if the lines are lead back to the cockpit, then you don't have to leave the cockpit to reef. On my boat, I have two reefing lines, both accessable from the cockpit, but my halyard winch is on the mast, so I do have to leave the cockpit to reef. Consequently, I reef before I leave the dock whenever possible. One of these days, I will change over to a single line system like the drawing. One of these days....