But we had waited; the new wind had appeared; it was obvious, a strong dark line only a mile ahead. And we were still wrong; the advantaged side had been to the left, away from the new wind.

Conditions in which one side is obviously advantaged are the least common of the three typical wind scenarios in a race, but it seems to be the one most used. In professional match racing (with the aid of a team meteorologist, a tactician, and a strategist) a deliberate choice is typical: "They seem to want the right." The implication is that there is something on the right that is better than on the left, and that they know about it. The average sailor mimics this behavior, presumes that an advantage exists, and acts as if he knows what it is. Although one side often turns out to have been advantaged, predicting during the next 25 to 30 minutes which side that will be is actually quite difficult.

The development of a new wind is a particularly unreliable reason for an immediate move to one or the other side of a beat. The most reliable reasons, in order of certainty (and none are certain), are as follows:

➤ A persistent shift or an alteration in velocity due to channeling
If local knowledge includes the presumption that the existing wind will shift or alter in velocity as it bends around or passes near a shoreline feature (particularly if the airflow is cold and the feature prominent), presume that it will create an advantage on one side of the course and head for it.

➤ Divergence and veering in a parallel-to-shore wind
In a parallel-to-shore flow with water on the wind's right, acceleration and veering of the overwater segment takes place in a near shore band as it diverges from the slowed overland segment. This results in a near certain advantage on the right side of the beat, is only slightly less common than reason No. 1. Whenever a racecourse is set so that a significant portion of the starboard layline lies within one-quarter mile of a shore to the right, head for that shore.
➤ A major difference in the current velocity between the two sides of the course
Management of this condition (tacking immediately to the advantaged side) should be limited to circumstances in which you have measured the difference in velocity with a current stick and in which, short of the laylines, the difference is significant.

➤ A persistent shift due to a velocity veer (or in the Southern Hemisphere, a velocity back)
If, in the early part of the afternoon, the local sea or lake breeze usually increases in velocity, it will veer as it does so. Restrict the presumption that a velocity veer will advantage the right side of the course to sea/lake breezes in early afternoon.

➤ A near-shore veer in an insolating, offshore wind (particularly a sea/lake breeze blowing over and off land)
Thermal turbulence above a sun-warmed surface regularly induces downdrafts of higher velocity, upper-air flow so that overland and near-shore the mixed wind is veered to that farther offshore.

➤ A dying wind replaced by a new wind (and/or two winds simultaneously)
If the wind dies during an around-the-buoys race, one can presume it is about to be replaced by a new wind, usually by a thermal wind, which results, for at least a brief period of time, in two winds simultaneously (see below).

➤ A difference in wind velocity or wave size
Differences in wind velocity (or wave size) are significant in light to moderate winds when boats are sailing at less than their hull speeds (and particularly in very fast boats whose speed continues to increase at boat speeds above their hull/length limits). However, even though such differences often cause one side of the course to be advantaged, in the places that race committees usually select (far from blanketing shores and leeward barriers), that side is rarely predictable. Even the side that in a pre-race inspection appears to have the greater velocity is unlikely to continue to do so during the 20- to 30-minute beat to come.