There are two major advantages of reefing. The first is that it makes it easier to get under the boom during tacks when the mast is raked back. We generally put the reef in when we rake to 2 5'2 " or more. But now that Howie and I are getting a bit older 25'3" might become our new number. The other advantage is that it helps keep the boom from dragging in the water as you heel over while overpowered tight reaching.

I suppose that there might be a third advantage of reducing sail area, but we think that the reduction is so small that it does not make a big difference. Even when it is windy it is beneficial to be able to ease the outhaul downwind. This system allows you to do that even when the reef is in.

So how does it work? 
I have made a simple diagram below, to show how to rig one up. On the inboard end of the boom the control line [1] goes through a cleat [2] then through a hole in the boom [3]. Once inside the boom it goes around one sheave of a pair of linked blocks [4] (Ronstan Part# RF20284) and then dead-ends through another hole in the boom [5]. On the outboard end the reef line [6] inside the boom ties onto the end of the outhaul wire [7] that attaches onto the clew. I have not shown the rest of the outhaul mechanism in the diagram.

It is important that the outhaul wire attaches directly to the clew like most U.S. boats are rigged and does NOT go through the clew and dead end on the boom like some European boats are rigged. From the outhaul wire the reef line goes through the other sheave of the linked block [4] and then exits the boom through another hole [8]. Once outside the boom the reef line goes through the clew grommet [9], around the leach of the sail [10] and then through the reef grommet. From here it simply ties onto the slide that goes in the boom track [11].

Once rigged, simply pull on the control line to put the reef in, the outhaul will still function as normal. Uncleat the control line to shake out the reef. Good luck and I hope you have enough wind to use it.