Hobie Cat 18 User Manual page 13

Apparent Wind
apparent
true
true
wind
true
wind
wind
wind
apparent
wind
boat-speed
wind
Beam Reach
boat-speed
wind
Close Hauled
Head to Wind
apparent
Boat is stopped wind
true
or backing up
wind
boat-speed
wind
apparent Wind
wind
true
Broad Reach
Run
wind
boat-speed
wind
Apparent Wind is the wind that the sailors and the sails feel as the boat moves across the water.
Apparent wind is the product of two forces, first is the True Wind that mother nature provides and sec-
ond is the wind created by the forward motion of the boat (boat speed wind). To sail fast, or to sail at
all in light air, you must set your sails in the correct relationship to the apparent wind. Any change in
the apparent wind will require changes in sail trim or boat direction. A basic understanding of
apparent wind is helpful in dealing with the varying conditions that you will encounter.
As I said, the apparent wind is the product of the true wind and the wind created by the motion of your
boat. Because apparent wind is the product of these two forces, it is affected by changes in either
force. If the true wind's speed increases or decreases, the apparent wind will change in both velocity
and direction. If the true wind's direction changes, the apparent wind will again change. If your boat
accelerates or decelerates, the wind speed your boat creates will change, causing a change in the
apparent wind.
To graphically demonstrate how changes in true wind and boat speed wind effect the apparent wind we
will use vectors (arrows) which show both the speed and direction of each wind. The direction of the
vectors (arrows) show the direction each wind is blowing and the length of each vector indicates its
strength or speed of the wind in MPH.
The boat speed wind always blows from the direction that the boat is traveling, as depicted in the dia-
grams above. The speed or strength of the boat speed wind is equal to the boats speed and thus I have
shown the strongest boat speed wind when the boat is on a beam reach, which is the fastest point of
sail. For simplicity, in the diagrams above, the true wind remains the same in each diagram.
Note, in the diagram, how the sails have been changed as the boat goes from close hauled to beam
reach to broad reach. As the boat and the apparent wind change direction, the sails are changed to keep
the sails leading edge cutting the apparent wind and the rest of the sail gently bending the wind.
Page 8
Hobie University, NAHCA
30 Mar 02