Anyone who has learned to sail understands at least the basics about why you need to be constantly aware of wind speed and direction when sailing. Sails are trimmed and adjusted for maximum efficiency and speed according to both wind speed and direction.
But experienced sailors learn to read the wind in a more sophisticated manner by paying attention to indicators both on and off the sailboat. Racing sailors become adept at observing changes at a distance and predicting wind shifts. This article provides an overview of what to watch for.
Wind Indicators on the Boat
Many larger sailboats, especially those that race or cruise long distances, have electronic wind instruments, which are coming down in price but still tend to be expensive. Sensors at the masthead measure wind speed and direction, reported on gauges or readouts typically in the cockpit where the helmsperson can easily see them. These precise measurements help sailors determine the best strategies not only for sail trim but also for routing and strategic planning. Changes are easily noticed, allowing for sail changes, reefing, etc. at an appropriate time.
The latest trends in electronic wind instrumentation are wireless sensors (to avoid having to route more wires through the mast) and integration of wind information with other data on a single display such as a plotter or computer screen. Sophisticated routing software integrates wind data in course planning.
The average recreational sailor, however, does not need expensive or sophisticated wind instruments to sail well. Wind direction is not difficult to determine, and with a little experience one can estimate wind speed fairly accurately. A sailor wanting more precise wind speed data can use an inexpensive handheld wind-meter.
After electronics, the best wind direction indicator is a wind vane or masthead fly, such as the Windex. Like an old-fashioned rooftop weather vane, the masthead fly is essentially an arrow pointing into the direction from which the wind is coming. (Remember this is apparent wind, affected by the boat's direction of motion and speed, not true wind direction.) Most masthead flies also have two backswept arms that help the sailor determine how close the boat can come to the wind when close-hauled.
Finally, small sailboats and even medium-sized or larger ones without a masthead fly may simply have telltales on the shrouds to help one judge wind direction. Commercial telltales are available but usually work no better than short lengths of light yarn tied to the shrouds on both sides. Remember to observe the telltales on the windward side, not those on the leeward side which are more affected by the sails.
Wind Indicators Off the Boat
The wind can vary considerably over an area of water, although there usually is an overall flow tendency. Especially when the local wind right around the boat seems variable, it can be useful to observe other wind indicators at a distance. Watch other sailboats to see how they heel when on the wind. Look for flags onshore or in the rigging of moored boats. Smoke from a chimney may indicate the general direction of the wind even while it seems to change moment by moment around your boat. (When cruising, for example, it's often better to set the sails for the average speed and direction rather than constantly trimming in and letting out with every small fluctuation.)
With experience, reading the wind by its effect on the water around you, and at a distance, can provide information about coming changes. Obviously, waves grow larger as the wind grows, and in open water with a constant bottom you can judge something (but not everything) about wind direction by the direction of waves.
Reading the water is usually easier and more important when the wind is fairly light - a skill racers of small sailboats value much. Look around you on a calm day. While calm water is flat (except for residual waves or swells), small increases in wind (puffs) cause ripples ("cat's paws") that often can be seen at some distance. Ripples also often make the water look darker. One part of a race course may have more wind than another, helping racers determine which tack is better and other strategies. Simply seeing a wind increase coming helps you prepare for changes in sail trim. For example, even if the wind does not change in true direction, an increase in wind speed relative to boat speed and direction (apparent wind) will change the wind's apparent direction, requiring a change in sail trim. Racers talk frequently about being "headed" or "lifted" by puffs, and good racers are already trimming their sails as the wind arrives.
Or Use a Handheld Wind Meter
An inexpensive handheld wind meter is a cost-effective compromise for sailors who want accurate wind measurements but don't want to spend the big bucks for a masthead system. The Kestrel 1000 model is a perfect solution.