Wind
speed and
directionWind usually oscillates with regular variations both in speed and direction and in direction. An increase in wind speed is called a puff and a decrease in wind speed is a lull. The wind is said to veer when its direction shifts clockwise on the counterclockwise. A wind that moves more forward, toward the bow, is called a header and the boat is said to be headed. A wind that moves aft gives a lift and the boat is lifted. Getting headed while beating can signal a good time to tack, since a header on one tack becomes a lift on the other.
True and
apparent
windThere is true wind—the speed and direction of the wind—and there is apparent wind, which is the apparent combined effect of true wind and boat motion. Apparent wind is what moves the boat, not true wind. Forward motion of the boat shifts the apparent wind forward of the true wind. An increase in true wind speed, called a puff, shifts the apparent wind aft. A decrease, called a lull, shifts it forward. The speed of apparent wind is measured in knots, as for true wind, and its direction is indicated by the corresponding state of sail trim using terms defined every 30 degrees of arc:
- Points
of sail - Upwind (into the wind or “in irons”)
- Close hauled (or beating, 30 degrees off the wind)
- Close reach (60 degrees off, etc)
- Beam reach
- Broad reach
- Run
- Downwind
These points of sail are identical on either port or starboard tack. Changing direction by moving down the list, or off the wind, is called falling off. into the wind is called heading up.
Running
before
the windEveryone knows that boats cannot sail upwind but fewer appreciate that most boats cannot sail well downwind, either. A boat sailing directly downwind will quickly find itself by the lee, meaning that the wind has shifted around behind the stern onto the same side as the boom, the headsail has emptied and begun to luff, and the boat is about to gybe. Downwind is generally the slowest point of sail, besides, because only the aft faces of the sails are working; the forward sail surfaces are stalled and give no lift then. Also, the apparent wind that moves the boat is least when sailing downwind and it rises steadily as you head up into the wind. What makes reaching faster, even though the apparent wind is less than when beating, is that both surfaces of the sail are working on a reach, while the leeward surface does not contribute much when close hauled.
ReachingA beam reach or a broad reach is the fastest point of sail for most boats. Beating while close hauled might feel faster because this point of sail has the most apparent wind. The apparent wind speed while beating is nearly the sum of true wind speed and boat speed. Apparent wind while reaching has only a little more speed than true wind, and boat motion only moves it somewhat forward of true wind in direction without adding much to its speed.
Sail
twistTrue wind at the top of the mast has higher speed than true wind at the deck, water surface slows the wind. Apparent wind, which is the sum of true wind and boat motion, thus has higher speed at the top of a sail than at the bottom. Boat motion is the same at every height, of course. Apparent wind therefore also shifts aft in direction, higher up on the sail, as a consequence of its rise in speed. Another way to think of this change in apparent wind speed and direction, as you move up the sail, is that the top of the sail is in a puff (higher wind speed) and being lifted (more aft wind direction), relative to the bottom, while the bottom of the sail is in a lull, and being headed, relative to the top. This means that the bottom of the sail must be trimmed differently than the top. That difference in sail trim at the top versus the bottom is called sail twist. Primary sail controls that affect twist are the jib sheet turning block and the main sheet traveler. Many sails have a certain amount of twist sewn into the cloth.
When moving upwind, while apparent wind speed is greatest, the puff (higher wind speed) at the top of a sail dominates the lift (farther aft direction) up there, and we want to add twist, by hardening up the top of the sail while easing the bottom, thereby trimming for the puff aloft. As we fall off, and apparent wind speed drops, the lift at the top of the sail increasingly dominates the puff up there, and we want to remove twist by easing the top of the sail while hardening up the bottom, thereby trimming for the lift aloft.
Our explanation of twist has implied that, although true wind velocity rises as we move up the mast, the true wind direction remains constant at every height. This is not always the components that change its direction at various heights. If so, the amount of twist needed might differ on port and starboard tack.
If there seems to be too much twist, check first to ensure that you have eased the topping lift.
ReefingThe force of the wind increases as the square of its velocity, making it vital to reduce sail, or reef, well before a rising wind makes it difficult or impossible to do so. The three basic rules of reefing are to reef early; reef as if beating even when running; and when in doubt, take a double reef. A rising wind tends to keep on rising. Reef before water washes over the toe rail and before you have more than about 10° of weather helm while properly trimmed. To use the most common mainsail slab or jiffy reefing:
1. Head up directly into the wind.
2. Ease the boom vang and mainsheet, then harden up the topping lift to raise the boom.
3. Lower the sail until the next reef cringle can slip over the hook on the boom, then harden up the main halyard quite firmly with the winch.
4. Haul or winch in the appropriate reefing line to draw the leech cringle down to the boom, ensuring always that the boom can rise so you do not strain the leech.
5. Ease the topping lift, then harden up the sheet and the vang.
6. Fall off and resume course.
7. Tie up the loose bunt of sail only if you can pass the ties above the boom (ie, there is no boltrope on the foot, or the foot is slotted)).