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Chuck Husick: Techno-Talk, July 2006 from BoatUS Magazine

- updated September 2009

Wind Instruments

Successful politicians always know which way the wind is blowing. Skilled America's Cup tacticians are renowned for their ability to sense even the slightest shifts in the wind and to anticipate changes that have not yet reached the boat. The kids who excel in the junior sailing program at your boating or yacht club quickly develop an acute feeling for the breeze and how it can be used to best advantage.

I frequently sail on the wide-open waters of the Gulf of Mexico and the lower part of Tampa Bay, areas exposed to wind from all directions. It is not unusual to see power boats having what is clearly a tough time powering into the short, steep seas that can very rapidly develop in these relatively shallow waters. (I have experienced the same conditions in the Chesapeake Bay and on the Great Lakes, especially on the very shallow waters of Lake Erie).

Unfortunately the increasingly popular semi-enclosed fly bridges and air-conditioned wheelhouses on many powerboats prevent the helmsman from physically sensing the wind. Secure in a cocoon little different from the environment in a car, they are isolated from and ignorant of how the wind is blowing and may accidentally expose their boat and its occupants to unforeseen and unnecessary risk. These boats should be equipped with remote reading wind-sensing systems, preferably ones that can compute and display true wind velocity.

A mariner unaware of the actual wind condition can expose his vessel to potentially dangerous situations when altering course after a delightful period of running in what appears to be light wind and almost flat seas. A boat moving at 20 knots before a 15-knot breeze is encountering a 5-knot headwind. The seas appear to be almost flat. The "fun" begins when a necessary course change puts the breeze on the beam or perhaps on the bow. If the new course is directly into the wind the helmsman might attempt to maintain minimum planning speed, perhaps 15 knots. The 5-knot zephyr is now a 30-knot moderate gale! The once flat seas are now a nasty chop that has to be pounded into. The passengers and crew are no longer happy. Slowing the typical planing hull boat to displacement speed will help, the headwind will be reduced to perhaps 20-23 knots, however the seas will still be square shaped and the return trip will take a very long time. The pleasure has gone from pleasure boating.

There are a number of solutions to this problem. You can plan all voyages so that they are dead downwind. However, doing so may not be practical, you might wind up far from where you want to be. A better choice is to become as sensitive to and informed about the wind as those guys (sailors) foolish enough to try to go from one place to another using "free energy", the wind. (Of course, although the wind is free, the sails, halyards and sheets needed to use it are NOT!)

A good first step is to install a set of wind instruments, a wind vane and an anemometer. The position of the vane relative to the bow and the rotation speed of the anemometer cups can be shown on a dedicated display on your instrument panel or presented on your chart plotter. However, the "raw" information is relative wind data. The only time the wind speed and direction will be "true" is when the boat is dead in the water (with no current running). You will need some additional information and a bit of computational hardware if you want to know the truth about the wind. Fortunately, the equipment needed to provide a display of true wind is readily available, often as part of the autopilot system or the chart plotter.

Some powerboat owners may be put off by the appearance of sailboat gear, the wind vane and rotating anemometer cups on their sleek craft. Fortunately some new technology is available from Airmar (their WeatherStation) and Maretron. Both of these systems use ultrasonics to determine wind velocity, have no moving parts and look just like a small GPS antenna. These systems can measure wind speed, direction, barometric pressure, temperature, relative humidity, dew point, chill factor and can determine true wind velocity. Complete information on these two advanced technology wind sensors can be found at www.airmartechnology.com and www.maretron.com.

If you use an iPhone you may find the Wind Meter app useful. It uses the phone's microphone as a sensor, converting the sound created by the air moving across the microphone port into a wind speed reading. Speed can be displayed in feet per second, meters per second, Beaufort Scale, km per hour or knots or miles per hour. Data display can be instantaneous speed or average speed.

By Chuck Husick

Chuck Husick is a pilot, engineer, sailor and former president of Chris Craft Boats.

© Copyright BoatUS Magazine 2006
(updated Sept. 2009)

 





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