When a trailing opponent camps on your air during a downwind leg, knowing whether to hold and or fold is the key to maintaining your lead. "Tactics" from our June 2011 issue.
Unless you’re a graduate of the Buddy Melges School of Racing, where you start first and then extend, sooner or later you will be looking down the wrong end of the barrel when it comes to maintaining clear air on the run. While it’s important to keep your air clean downwind in any type of boat, not doing so in a boat with a sprit-mounted asymmetric spinnaker can be especially costly. And that goes double for a-sail boats with the ability to plane.
To determine the best way to escape a windshadow on the run, you first must be able to figure out the windshadow’s location. This requires understanding the apparent wind angles for the boat you’re sailing and the boat you’re sailing against. On boats with asymmetric spinnakers, the true and apparent wind angles are ofen widely divergent when sailing downwind.
On lightweight, planing keelboats, such as the Melges 32, and lightweight dinghies, such as the 49er, the tremendous downwind boatspeed moves the apparent wind well forward of the true wind. These boats go much faster at hotter (i.e. closer to the wind) angles. In fact, in the Melges 32 class, few people sail with full-size spinnakers. A slightly smaller kite, with less drag, will be faster at a slightly higher angle and result in better progess (velocity made good or VMG) toward the leeward mark. In planing boats, just a few more degrees of height can create a significant difference in speed.
At the opposite end of the spectrum are heavier, non-planing sprit boats, such as the J/120. The speed differential between a J/120 that’s sailing a low angle and one that’s sailing slightly higher is usually quite small. These boats carry large asymmetric spinnakers. By easing off the tack line, heeling the boat to windward, and rotating the kite from behind the mainsail, you can sail quite deep without losing much speed. The true and apparent wind angles will be further apart than on a boat with a symmetric spinnaker, but not by a lot.
The other factor to consider is the general range of a windshadow. A good rule of thumb is that a windshadow will extend as far as 10 boatlengths to leeward of a boat in light air and as little as six boatlengths when it’s windy. The most accurate guide to the location of your opponent’s windshadow is the Windex on the top of his mast. However, that can be hard to see, or he may not have one. It’s often easier to use your Windex (or shroud tell tales). And your Windex provides the key information to how you should react.
Sight off your Windex and see where it points relative to your opponent’s sail plan. If your Windex is pointing close to the center of your opponent’s sail plan, then you can safely assume he has you in his sights.
If your Windex is pointing in front of the luff of your opponent’s spinnaker, you’ll be in clear air. Since your breeze is coming from ahead of the other boat, this situation is referred to as “air ahead.” If your Windex is pointing well aft of the leech of your opponent’s mainsail, you’ll be in clear air as well. Conversely, this is known as “air behind.” Knowing whether you’re covered, have air clear behind, or have air clear ahead will help you determine your next move.