AllThumbs: adding reef points and jiffy reefing is one of the easiest sail-modification jobs, and with a bit of endeavor you can do it at home for about $40 total. Really useful if you have an older main to practice on and convince yourself it's not so hard.
First, you want to figure out how deep a reef and how many. For boats our size, I like one medium-deep reef. When a small boat needs de-powering, it tends to need it BAD. And if it needs a super-deep reef, you're prolly in big trouble for other reasons. So a 25-30% reduction is sail area is a good target; I like 34" or so.
Second, keep in mind only the head and clew grommets should be taking force; the middle reef points are there for keeping the bunt tidy, not for constraining the sail. So I put in the head and clew grommets first, each 32"above the boom measured perpendicular to it
. If there's a seam there or thereabouts, adjust your level accordingly.
You'll want two or more layers of reinforcing patches; shape is not critical, but the larger should be good-sized, maybe the area of a dinner plate. Remember -- you only reef when it's blowing stink, so don't skimp. You can get remnants of sailcloth from a loft or from Sailrite, or just buy a yard of 36" wide stuff. A nice weight is 5.5-6.5 oz. I like to put the smaller patch under the bigger one; cuts down one edge to fray.
I use a spray adhesive (3M Super 77 is best) to affix the patches, then zig-zag stitch all around the edges, plus a couple gratuitous stitching lines. You may need to drive the balance wheel by hand when punching thru four or five layers near the leech or bolt rope. You can baste these on by hand, too, but a machine is better. Good, heavy polyester thread.
For grommets, the classic solution is sewn ring-plus-eyelet; a big spur grommet might work on a small boat. Both require expensive setting tools, unless you can bum them. Don't try hardware store grommets! I'm really keen on Sailrite's jiffy grommets
; add a short strip of polyester webbing or two, and they are very strong.
After those are installed, you'll need to stretch out the sail tightly (or better, hoist it on the boat) and snap a line between the fore and aft reefing grommets. Your mid-point ties will need to go BELOW this line, so they don't pull on the sail when reefed. Add 3-4 single reinforcing patches neatly spaced, and either stitch on reefing ties or add spur grommets (#2 work well).
Then you install a cheek block on the boom so it pulls the clew reef down AND back (I like the Harken mini-Carbo
) and a cleat of some sort; then a padeye and cleat on the mast (or use existing) so the tack reef is pulled down and forward. Done. It's actually easier than it sounds, should take an hour or two.
I'll be putting reef points on the new main I'm sewing this week; I'll try to take photos and post them.