ILCA Sailing Tips: Keeping Speed Up in Light Air
In light air, protect speed and flow before chasing height. Apparent wind, stall, puffs, and lulls matter more than a fixed trimming rule.
The best advice I remember being given when trying to sail fast in light winds was: when in doubt, speed up in light air.
How do you know when to pull your sail in block-to-block? I do not think there is a rule of thumb for this in any condition, and in tricky light wind it is even less predictable. Take your attention away from when and turn it to why.
Apparent wind and stall
The ILCA sail has a very closed leech, which means the curve from luff to leech is similar from top to bottom. The wind has a lot of distance to travel to keep attachment and proper flow from luff to leech on both sides of the sail. To trim the sail, consider the speed at which the wind is flowing over your sail and the angle at which it is hitting it.
Apparent wind direction is the combined angle of true wind and the artificial wind created by the forward movement of your boat. Like any boat, the ILCA sails by apparent wind angle rather than true wind. Because of sail curvature and speed range, it is easy to become stalled. Stalled means you lose flow around the leeward side of the sail. To recover flow, you can head up, sheet out, or both.
Changing gears
As boatspeed increases, apparent wind shifts forward and you can begin bringing the sail in to match the entry angle. If chop hits the bow and slows the boat, apparent wind moves aft toward the dominant true wind direction. The entry angle moves back and flow over the back of the sail decreases, sometimes lifting the leeward telltale, though not always.
This is often confused with pinching, which is the opposite: an increase of flow over the leeward side of the sail, commonly noticed with backwinding or the windward telltale flipping up. In the case of stalling, speed up in light air. In the case of pinching, bear away.
We are constantly changing gears to keep the boat balanced and quick. Every time a wave or set of waves slows the boat even slightly, adjust by sheeting out to maintain flow over the leeward side of the sail.
Velocity headers and lifts
If you bear away with a stalled sail, you become increasingly stalled, which often results in loss of pressure, windward heel, and leeway.
A velocity header is a sudden drop in wind speed, a lull, that temporarily shifts apparent wind forward toward the bow. This can give the appearance that you are pinching. Remain calm. As boatspeed slows, apparent wind moves aft again and there should be little change to balance. Release the cunningham to open up the entry, and maintain speed and pointing.
A velocity lift is a sudden increase in wind speed, a puff, that temporarily shifts apparent wind away from the bow. This usually gives the appearance that the wind has shifted aft and you can head up. Your best course of action is to sheet out, get the boat up to speed as soon as possible, bring apparent wind forward, then sheet back in to stay flat.
Summary
Every time waves slow the boat, sheet out with the mainsheet to maintain flow over the leeward side of the sail. As speed increases in light air, trim back in to match apparent wind moving forward. Every time wind velocity increases, sheet out to match your boatspeed instead of heading up right away.
