Catboat Sail Trim  © Sailing Magazine, January 2007  How ‘deep throat’ can give better  performance in a single-sail, gaff-rigged boat  n many areas of the country, the traditional  gaff-rigged catboat is seeing a comeback. They  are stable, easy to sail and fun to race, with  fleets sailing strong in Barnegat Bay, Cape Cod  and in Florida. In a classic gaff-rig the sail  controls are simple, but the essentials of sail  shape remain the same as in contemporary  three-sided racing sails. A properly managed  four-sided gaff mainsail is very responsive to sail  shape efforts, and the resulting increase in  performance is astounding. I  It is important to approach the problem of sail  shape by focusing on the end result: The shape of  the sail. All of the controls effect changes in the  three components of shape: angle of attack, draft  and twist. With a four-sided gaff rig, there are  limited controls, so compromises have to be  made. First we will discuss the three components  of sail shape, then speak to specific trim  suggestions for various points of sail and wind  condition. The mainsheet is the only sail control for  bringing the mainsail to the proper angle of  attack with the apparent wind. This is the  familiar easing out or bringing in of the boom to  attach airflow to the sail’s surface. With time in  the boat you will develop a feel for when the boat  is performing well, however, you will need  telltales to actually see the wind on the sail.  Telltales should be mounted on both sides of the  main well back from the mast as well as on the  leech. Usually four sets of telltales are sufficient;  two above the throat and two below the throat,  while only two are needed on the leech. Be sure  to offset the starboard and port telltales from  each other so you can tell them apart when the  sun is behind the sail. Color-coding is also  helpful.  The gaff-rigged catboat sail is very forgiving and generally has a wide groove upwind and down, making it very easy to  sail. However, to get the best performance close-hauled, you need to sail on the edge of the groove closest to the wind. This  is a very narrow part of the groove where the windward telltales should be lifting 50 to 80 percent of the time. It takes a  lot of concentration and practice to stay in this narrow slot of performance through the constant changes in wind direction  and strength.  Angle of attack  Draft  Draft is the curvature of the sail, described as both the position of maximal depth along the length of the sail and how  deep the curve is relative to the length of the sail. 19 A look at the parts of a four -sided gaff-rig sail reveal similarities to the more  familiar three-sided sail, with a few additional points. The reef points divide the  sail lengthwise, and can be used tomeasure the position of the draft.