For many of us skippers it is much easier to see what is happening with that big sail in front of our faces than the little one at the front of the boat. However, we know from computer flow programs, that the jib provides 80 percent of any sailplan’s driving force. That being the case, it seems to make sense to give some careful consideration to the person in the front of the boat who trims the jib. But what does this person look for, in order to trim the jib to best affect?
The easiest way to get the correct settings for the jib is simply to look at your sailmaker’s tuning guide. Set the jib lead to his measured position from the headstay, usually in the 96-100” range. Then simply pull the jib in until the top batten lines up with the spreader tip or a little inside, whatever the trim guide for that particular jib suggests. This is usually good enough to get close to the ideal trim for most conditions. But what are some of the finer points we are considering when we come up with these numbers?
Here are some things that go through my mind. First of all let’s think about how it works. The jib luff is the furthest forward of the boat’s center of lateral resistance, while the leech of the main is the furthest aft. The lift contributed by these two parts of the sailplan, must be in balance or the boat will want to turn rather than going straight. These forces must be balanced about the centerboard. If they are not, the helmsman can feel it in the form of excessive weather helm or a lack of any helm when the boat is heeled to the optimum angle for the conditions. We want to trim the sails so there is only enough weather helm to make the boat easy to steer. When we go out for our prerace tune-up, we sail up-wind initially and see how the boat feels. If the helm is too heavy we may be trimming the jib too eased, or the main may be trimmed too hard. So we make that necessary correction. Frequently people refer to the criteria that the luff should break equally, top to bottom, as you head up. This is a good starting point, but the Lightning often performs best with the jib trimmed so the top breaks a little early, particularly in rough water.
The helmsman and jib trimmer need to work together to maintain the best windward performance. We always use the luff tell-tales as a guide. The leeward one should be flowing all the time. The weather one can be allowed to lift intermittently, or in heavy conditions and smooth water, continually. In lighter conditions, the jib trimmer should always have the sheet in his or her hand.
Whenever the boat feels slow, or the leeward telltale starts to stall out, the sheet is eased slightly to keep flow over the leeward side of the jib, as indicated by a steady leeward telltale. Then, whenever there is a puff, the sheet can be trimmed to facilitate higher pointing through the puff. In full hiking conditions the sheet isn’t adjusted as much and the forward crew hikes. However, it is important to get the boat set up with jib trim that properly balances the helm. If the lead is too far forward, the lower part of the jib becomes too full. This situation is recognizable because the bottom of the jib will tend to luff, and the helm will be excessively heavy. This can also mean the main is overtrimmed.
When the lead is too far aft, the bottom of the jib is too flat. If this is the case, to keep the leeward telltale flowing, you have to push on the tiller or if you ease the sheet out until it is easier to keep the leeward telltale flowing, the top of the jib is continually luffing. Once again, I feel that it is bad if the leeward telltale ceases to flow, but the weather telltale should be flying slightly up about 50% of the time in anything but light air with flat water.
Just a word about the angle of the top batten. I’ve usually had the best performance, when the top batten is nearly parallel to the boats centerline or just slightly open from the position. The jibs that are flatter in the head like to be more open so the top batten points more to leeward.
This touches on the basics of lead position and sheet tension. In the finer tuning category we can get into headstay sag and luff tension, but that is a subject for another time.