The
mainsheet is the last of the five basic controls.
Unlike the jib sheet, the mainsheet only moves the clew of the main in two directions, in and down. That is because the clew is attached to the boom and the tension in the foot of the sail is controlled by the
outhaul. The outhaul is another control that is adjusted on a U curve: tight for very light and heavy air, looser in-between and loosest for moderately light airs, or when you want extra power against chop. Flattening the sail depowers it, good for heavy winds, but also allows the flow over the sail to remain attached more easily, good for very light airs.
Sheeting in the main pulls the end of the boom in, changing the angle of attack of the main. At the same time, it also pulls the end of the boom down, tightening the leech of the sail. As for the jib, less tension in the leech means more twist. Because the jib changes the airflow, we can sheet in the main further than we sheet in the jib. To know how far, we use the
telltales at the leech of the mast: if they all stream aft, but the uppermost flicks behind the sail every once in a while, the main is trimmed to the correct angle.
- The Mainsheet
- Mainsheet.GIF (13.93 KiB) Viewed 22203 times
For the jib, we are able to change the position of the fairlead to affect the relative strength of the pull in the fore-and-aft and down directions, for the main, we can use the
traveler or the
vang to change how much leech tension we get when sheeting in the main.
The traveler allows the angle of pull of the mainsheet to change from sideways to down, by allowing the mainsheet block to move from side to side. Not every DS has a traveler, and some that do, don’t have a traveler that is adjustable. If you are a beginner, you might start out with centering an adjustable traveler until you are ready to try to set the sheeting angle and twist of sail independently. When you do, remember that the traveler adjusts the sheeting angle and the mainsheet tension adjusts the twist.
A traveler is active only for a small range of angles when sailing upwind, basically only as long as the boom is inboards. In contrast, a vang acts over the entire range of angles. When sailing downwind, it is used to pull the boom down to maximize the area projected to the wind. If your DaySailer has a stock 3:1 vang, it is intended for that use. Some boats have a much stronger vang (12:1 or even 20:1) which can be used to directly control leech tension (or twist) even when sailing upwind. When used this way, the main sheet mainly controls the angle of attack for the sail. This technique is called
vang sheeting.
As a beginner, you can leave the vang off (loose) except when sailing downwind, or when sailing upwind in stronger winds. If you tighten the vang, it will keep the sail flat so it doesn't power up when you let out the main sheet to respond to a gust. At all other points of sail, you can ignore it until you have sorted out the basic controls first.
If you don't cleat your main, but hold it in your hand, you will be able to respond faster to any gusts, a definite safety feature. This is made easier, if you install a ratchet block, which will help you hold the mainsheet while not cleated. (Ratchet blocks can also be used with the jib sheets). Ratchet blocks and a vang are useful improvements that make your boat more controllable.
Another safety improvement would be to add
reef points to your main and to install jiffy or slab reefing. However, that's a topic of its own.