After purchasing a used H18, I've replaced a fitting which did't come with the boat -the boom wishbone. Can anyone provide hints for rigging and use?

-a confused laser sailor

It is for mast rotation control. There should be a cleat 8-10 inches back on the boom. Attach a line to the top of the cleat and run it forward to the eye in the end of the wishbone and back to the cleat portion of the jam cleat. Going to windward the rotation control should be set so that the leading edge of the mast is almost dead into the wind. Going downwind set the control at 90 degrees so the flat side of the mast will catch the wind as well. If the mast is 30 feet by 6 inches you have just added approx 15 sq feet to your sail area.