Wind

Summarize

The direction the wind is coming from—upwind—is called windward and the opposite direction—downwind—is leeward (rhymes with “clue word”). 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 sailing upwind can signal a good time to tack, since a header on one tack becomes a lift on the other.

Points
of sail

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. Changing direction by moving up the list and into the wind is called heading up. After heading up, while sailing into the wind, you are said to be beating. After falling off, while sailing downwind, you are running.

Air pressure is thus less on the windward surface, causing lift, and greater on the leeward surface, giving it a push. The combined force of air pressure on the sail—the lift and the push—is perpendicular to the wind. Combining that force with the wind force moves the boat forward at an angle to the wind. Most sailboats can point within 30° to 45° off the wind on either tack, creating a no-go zone of 60° to 90° directly upwind where the boat cannot go because it would then be in irons.

This means that when you come off of a run and head up into the wind, boat speed and apparent wind will both increase as you move from a broad reach through a reach. Then the boat will slow down while the apparent wind continues to rise as you move through a close reach to close hauled. What you are getting close to is the wind, which is why you slowed down.

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.

Going downwind, again it is best to tack in most boats. A downwind tack, where the stern passes through the wind, is called a gybe. As when beating, the boom will cross the cockpit, but because the mainsheet is now loose, it will travel much farther and faster than when tacking upwind and can crash across, damaging the gooseneck at the mast, the traveler, and other parts of the rig.

When gybing in all but the lightest air, first harden up the mainsheet to center the boom and then ease it after the boom comes across. Avoid sailing by the lee, when the wind crosses the boat astern and blows from the leeward side, lest you gybe acci­den­tally without having time to center the boom.

When running, be always alert for signs that the boat is about to gybe. As it turns directly downwind, the boat will stop heeling and stand upright. The jib will empty and flutter as the mainsail begins to block its wind. It is by then probably too late to harden up the main sheet and you would be wise to duck as the boom crashes across.

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 case. Sometimes the wind has eddy or shear 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.

• Reef early.
• Reef as if beating even when running.
• 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).