Radio Control of Twist: Here is an interesting quote from Graham Bantock, Radio Yachting News: No 1, June 93: "In my view the kicking strap and sheet are two independent means of sail trim and any 'kicker' effect the sheet has on the main trim is largely nuisance factor and best avoided where possible."
With apologies to Graham, whose sailing record is vastly superior to ours, we will present a different view. The previous section dealt with twist adjustments that are made on shore and are not controlled by the transmitter. This section will consider how you can control twist during a race. First, let's consider what can't be adjusted. Unless you have a jib sheet traveller, the jib twist cannot be changed significantly via radio. Likewise, since the vang can't be radio controlled the main twist can not be changed when reaching or running. Nonetheless, it is possible to offset the vang pivot axis from the gooseneck axis so that the vang gets tighter as the main is eased. We suppose this could be considered an indirect control by radio. We understand that Bob Sterne has experimented with this and found that in light air the main would not go out all the way. Larry found a similar problem when he tried it on one of his smaller boats. If you really want to try this approach you will have to make sure that the fitting is easily adjustable between races. We don't think it's worth the bother.
This leaves adjusting the main twist with the main sheet while on the wind as the only practical twist control open to the skipper while racing. Jerry Brower calls this "sheet vanging" as opposed to the full size practice of vang sheeting where the vang takes over the twist control from the mainsheet. By the way, the modeling equivalent of vang sheeting occurs when the mainsheet exits up on a post just under the boom. This does not allow much twist control with the mainsheet. We are not sure why there is such an interest in this practice, but we are told that it prevents hooking the main in light air. We suspect the mainsheet post became popular because the winch setup did not allow sufficiently fine control of the mainsheet when fully sheeted on the wind.
In order to sheet vang as described here you must have fine and precise control of the mainsheet when fully trimmed. A 1/8-inch trim is a big adjustment. If you use a drum winch, a step-down drum (originally conceived by Bob Sterne and made locally by Maury Thoresen) is mandatory. For those of us who still use swing arm winches, the mainsheet arm should be set to about 15 degrees off the centerline of the boat when the transmitter stick is full down and the trim lever is full down too. (See Figure 7.12 in Chapter 8.)
A good visual clue to how the air is flowing over sail is also needed if you want to sheet vang without hooking the main or stalling out its upper panels. We especially like the bright pink silk leech telltales described in Chapter 10. They are extremely sensitive and will give you an early warning when the main is mis-trimmed. "Don't try this without them." You also have to know how to read leech flies. See a standard sailing text such as "The North U. Fast Course" for an explanation.
Unless you have a mainsheet traveller, the angle that the main boom makes with respect to the centerline of the boat ("MSA") will have to be quite low, in order to significantly change the main twist. It probably will be under two to three degrees. This may cause the lower part of the main to be over trimmed. To solve this problem Amen and Sterne mainsails have a twist-foot seam just above the foot. This seam helps the lower portion of the sail twist off to the proper angle of attack while the main boom is still quite close to the centerline of the boat. Sounds good, but we have found that you don't really need a twist-foot to sheet vang-you just have to do it carefully.
Why are not all mains made with a twist-foot? We understand that many full size sail makers feel that the vertical curvature of the sail is as important or even more important than the horizontal curvature. Visualize vertical curvature as a draft stripe extending from head to mid-foot. In the 1987 and 1992 America's Cup campaigns, North's sail makers proved to themselves that less vertical curvature was better. With a lot of vertical curvature there is a mountain in the middle of the sail, causing air to flow around instead of over it. We believe this principle can be applied to EC-12's, but both types of sails can be made to work well, so take your choice. See Tom Whidden's The Art and Science of Sails for more on the subject. Unless you have a mainsheet traveller, the angle that the main boom makes with respect to the centerline of the boat ("MSA") will have to be quite low, in order to significantly change the main twist. It probably will be under two to three degrees. This may cause the lower part of the main to be over trimmed. To solve this problem Amen and Sterne mainsails have a twist-foot seam just above the foot. This seam helps the lower portion of the sail twist off to the proper angle of attack while the main boom is still quite close to the centerline of the boat. Sounds good, but we have found that you don't really need a twist-foot to sheet vang-you just have to do it carefully.
So how do you sheet vang? Ask Jerry Brower, but here is an approximation of the technique. When setting up, adjust the mainsheet so that the sail winch trim lever on the transmitter is full down when the main twist is a little under the minimum twist setting as described in the previous section. This gives you a little extra control to play with if the wind increases or you need to gas a competitor. Now raise the trim lever until the main boom makes a five-degree angle with respect to the centerline. Note the trim lever position. As mentioned before, we call this the main sheeting angle (MSA) and we put little marks on the deck so that it can be quickly estimated. Be sure to note the position of the trim lever for reference during racing. Jerry, Bob and Larry have sail tested different sheeting angles and currently feel that about five degrees is optimal for what is to follow. Our sails do not have a twist-foot. Decrease the recommended MSA values (given later in this chapter) by about two degrees if your sail does have a twist-foot. Adjust the vang to give a moderate to high twist depending on the conditions. Kelly's 15-degree recommendation is a good place to start. Smooth Juanita Bay conditions require less twist while variable winds, gusts, and waves will require more. Fine-tune the vang setting with the MSA at five degrees when sail testing before the race. Be sure to watch the main leech telltales carefully. The upper ones should not stall at this vang setting. Expect to have to reset the vang between races as conditions change. Now you are set to try sheet vanging.
At the start, at a leeward mark rounding or after a tack you must accelerate. Set the trim lever to get a five to seven degree main sheeting angle (MSA). Did you remember where that was? Make sure that the upper leech telltales are not stalled; if they are, ease the sail until they stream. This is very important, as you can lose three or four boat lengths very quickly while the main is mis-trimmed. If conditions are appropriate (smooth water, even undisturbed wind, no need to accelerate, etc.), begin to slowly pull the trim lever down while you begin to point up. Watch the upper main leech telltale and keep sheeting in and coming up until the telltale is on the verge of stalling. At this point it will often start to twirl or act erratically, telling you to come up some more or stop trimming. You also watch the inboard jib telltales which will tell you how far up you can come. When they begin to lift, pull the main in until the top leech rag is on the verge of stall. Keep an eye on the upper main leech telltale and continually readjust the main as you sail, but don't come up any higher than the jib rags will let you.
Photo 1 [not included] shows Jerry Brower, #26, and Bob Wells, #52, using their wind rags in a typical windward leeward match-up. White is trying to pinch off black, while staying bow ahead, and black is trying not to fall into white's bad air. At the instant this photo was taken, black has both upper main leech telltales streaming, indicating proper airflow at the top of the main. White's top leech telltale is curled back, indicating that the top of the main has stalled. Jerry will instantly react to this by either pointing up some more if the weather jib telltales will let him or by easing the main a little. Learning to use your telltales in this manner can give you a big advantage on the race course.
Using these techniques may allow you to point as much as five degrees higher, and with appropriate sails, go faster than some of the competition. This method is similar to what Frank Bethwaite calls winding up. It works best in smooth water and even winds. Beware of "falling off the cliff" when you encounter waves, bad air, etc. When you do fall off, immediately bear away a little and ease the main back to the five-degree MSA setting. Then start winding up all over again. This is not an easy technique to learn because you have to watch so many things as well as pay attention to the race, but with practice it will become almost automatic. Is it worth it? If you are willing to put in the time as Jerry has, sheet vanging can give you a very big edge on the competition. In 1995, Bob Wells finally got tired of being burned by Jerry going to weather and, with Jerry's assistance, successfully adopted this technique.