That is why I said it can be a little confusing. Apparent wind is a sailing term that also applies to kiteboarding, even more so beause you can reach higher speeds than in sailing. If you have taken any basic physics maybe you remember vectors?
The apparent wind is the vector sum (the vector is speed WITH a direction) of the true wind and the wind that you would feel if you were somehow riding your kiteboard on a windless day. In other words, If the first vetcor is true wind speed with direction, add to it the second vetor which is board speed with the direction equal to opposite of the diretion you are traveling (think of the wind you feel when you ride a bicycle on a calm day).
When you add the vectors, you need to consider both the speed and the direction. You can visualize a vector by drawing a line with an arrowhead on one end, where the legnth of the line represents the speed and the arrow shows the diretion.
Unless you like to do algerbra (which I don't
) the easiest examples are where the direction components are exactly opposite, this way you do not have to calulate the angles to find the "legnth" and direction apparent wind.
Say you are flying in 20 knot winds and you decide to head straight downwind. Since the direction component of the vectors is exactly opposite you can get the apparent wind by subtracting your board speed from the true wind speed. If you travel straight downwind at 10 knots board speed the apparent wind is 20-10=10 knots. When you travel straight downwind at 20 knots the apparent wind becomes 20-20=0 and your kite falls out of the sky.
This is why you need to sine the kite more when you travel more and more on a downwind course. Flying the kite up and down increases the apparent wind that the kite experiences, because the kite is moving faster across the wind than it would if it were just parked in one spot.
On a course slightly downwind of straight across the wind, the vetor diretions are additive so the apparent windspeed is actually somewhat higher than the true wind speed.
Sorry if my explanation is piss poor. My undertanding of physics and algerbra is not so great so my ability to explain suffers. Try a sailing book or do a google seach on "apparent wind"
Here's a link to an "apparent wind calculator" which calulates apparent wind speed and direction based on your own input of true wind, boat speed, and the angle between them:
http://www.sailingusa.info/true_wind_calculator.htm
The page demonstrates it well. You can enter different angles for the same boat speed and true wind speed and see what the apparent wind will be and it's direction. The angle actually indiates how much the center of the wind window moves from where it would be if you were not moving at all.
Make sure you use the "apparent wind calculator" and not the "true wind calulator" It opens a new page where the results are displayed at the very top of the page.
On 2002-11-12 20:05, supermaned wrote:
Confused about the term 'apparent wind'. Your definition (Anon) seems counterintuitive. Wouldn't edging upwind increase the apparent wind speed, since you are traveling against it?
Speaking from small experience, it seems it is necessary to move the kite more when flying downwind that when edging upwind in the same session.
Would appreciate any clarification about this conundrum.