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Re: [ksurfschool] Apparent wind effect

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• I think it s not so much the size of the kite or board, but rather the efficiency of the gear in light wind, likely due to smoothness of the water surface. In
Message 1 of 8 , Oct 21, 2000
I think it's not so much the size of the kite or board, but rather the
efficiency of the gear in light wind, likely due to smoothness of the water
surface. In other words, since the water is so smooth (in the lighter winds
encountered with larger gear) boardspeed is a higher percentage of windspeed
(compared to in stronger winds). That means the apparent wind is also
higher, relative to the true wind.

To put it yet another way, I'll use two beam reach examples:

With a big kite in 10 knots (meaning smooth water) let's say you can go twice
the true windspeed, or 20 knots, so the apparent windspeed is over 22 knots
(220% of windspeed) from an angle of only about 26 degrees upwind of the bow.
This makes the kite produce much more power at speed (compared to when
you're just getting going) & makes it hard to point upwind (to control speed
& power).

With a smaller kite in 20 knots (meaning rougher water) you can probably only
go about 1.5 times the wind speed, or 30 knots, so the apparent windspeed is
about 36 knots (only 180% of windspeed) from an angle of over 33 degrees
upwind of the bow. This makes the kite not produce that much more power at
speed, & makes it much easier to point upwind.

Mel
• ... OK. So the apparent wind effect is due to light wind and not big kites. How about the second question? However, in real life, it has not been an issue
Message 2 of 8 , Oct 21, 2000
kiteboard@... wrote:
> I think it's not so much the size of the kite or board, but rather the
> efficiency of the gear in light wind, likely due to smoothness of the water
> surface. In other words, since the water is so smooth (in the lighter winds
> encountered with larger gear) boardspeed is a higher percentage of windspeed
> (compared to in stronger winds). That means the apparent wind is also
> higher, relative to the true wind.

OK. So the apparent wind effect is due to light wind and not big kites.

How about the second question?

"
However, in real life, it has not been an issue for me in 5-6 knots
with the XXXL and the FONE 230 board.

Given the fact that I am lighter, but why should the apparent wind
effect only applies for heavier person?
"

Hung.
• Hi, I find the discussion very interesting and i just wanted to try to contribute to it In normal boat sailing apparent wind is the total wind that a sail
Message 3 of 8 , Oct 22, 2000
Hi,

I find the discussion very interesting and i just wanted to try to
contribute to it

In normal boat sailing apparent wind is the total wind that a sail sees,
i.e: the addition of the real or existing wind to the wind effect
produced by the speed of the boat (similar to driving a convertible in a
day of zero wind, if you stick your head above the windscreen you feel
wind in your face proportional to the speed you're going)
Therefore i would agree that in light winds the apparent wind (the wind
that actually propels you) is created mostly by the boards own speed and
the added effect of the movement of the sail,i.e: when moving it in a
sinusoidal (which unfortunately is not a possibility in normal sailing
boats).
However the apparent wind exists always, regardless of the force of the
wind or the gear your using.
The goal would be, i think, to find out what combination of board and
sail will maximize apparent wind given the wind conditions.

Hung Vu wrote:
>
> kiteboard@... wrote:
> > I think it's not so much the size of the kite or board, but rather the
> > efficiency of the gear in light wind, likely due to smoothness of the water
> > surface. In other words, since the water is so smooth (in the lighter winds
> > encountered with larger gear) boardspeed is a higher percentage of windspeed
> > (compared to in stronger winds). That means the apparent wind is also
> > higher, relative to the true wind.
>
> OK. So the apparent wind effect is due to light wind and not big kites.
>
> How about the second question?
>
> "
> However, in real life, it has not been an issue for me in 5-6 knots
> with the XXXL and the FONE 230 board.
>
> Given the fact that I am lighter, but why should the apparent wind
> effect only applies for heavier person?
> "
>
> Hung.
>

--
___________________________________________________________

Eduardo Aldaz Carroll, tel: +41 22 7679153
CERN, PS Division fax: +41 22 7678510
CH-1211 Geneva 23, Switzerland.
___________________________________________________________
• hungvu@netcom.ca (Hung Vu) writes: Keep in mind that skill & a board
Message 4 of 8 , Oct 22, 2000
hungvu@... (Hung Vu) writes:

<< it has not been an issue for me in 5-6 knots
with the XXXL and the FONE 230 board. >>

Keep in mind that skill & a board that rails well will keep the nose from
being pulled off the wind, & allow you to point to control speed. Where you
ride it may be less gusty when it's light too. Assuming you are fully
powered up (once up to speed), the only other thing I can think of is that
the board may be too big, & therefore slowing you down, reducing the apparent
wind.

<< Given the fact that I am lighter, but why should the apparent wind
effect only applies for heavier person? >>

Right now I can't think how rider weight would make a difference (but I may
come up with somthing later!).

AND:Eduardo.Aldaz.Carroll@... (Eduardo ALDAZ CARROLL) writes:

<<However the apparent wind exists always, regardless of the force of the
wind or the gear your using. >>

I know it always exists, & did not mean to imply otherwise, just that since
in lighter wind (flatter water) boat speed is higher (relative to true wind),
apparent wind is also higher (relative to true wind).

Mel
• Let s me try to make a summary to make life simpler (or more complex???) for all of us ;-) There is an effect called apparent wind that is more pronounce in
Message 5 of 8 , Oct 22, 2000
Let's me try to make a summary to make life simpler (or more complex???)
for all of us ;-)

There is an effect called "apparent wind" that is more pronounce in
light wind that makes one be overpowered easily at speed. This means a
smaller wind range for light wind kites (oftenly implies big kites).

Larger boards extend the lower wind range of the kite such that in light
wind it is appropriate to use a larger board and a slightly underpowered
kite (to avoid being overpowered easily at speed). This is my
experience with the XXXL and the FOne 230 at 5-10 knots.

Thinner boards (a smaller board is usually thinner) somewhat extend the
upper wind range of the kite such that in light wind it is appropriate
to use a thinner board and a right powered kite (overpowered situations
can be deal with using the knees and rail). This is my experience with
the XXXL and the Clam Sandwich in 7-11+ knots.

Apparent wind effect is not "currently" related to rider weight and kite
size is directly proportional to rider weight. I am 125 lbs. and the
XXXL project surface is 8.55 m2. Someone 175 lbs or 1.4 my weight would
need a 12 m2 projected surface kite and a board "his size" (very thin,
slightly taller than he is and wider than his shoulder width) to repeat
the same experience that I had with the XXXL and the Clam Sandwich in
7-11+ knots. Someone 200 lbs. would need a 13.68 m2 projected surface
kite. Kite type is also VERY important; the kites used should be
comparable in performance to the open cell XXXL (C-Quad is fine; Stamos
may be too low performance? I am not so sure about the larger
Naish/Wipika AR5+ unless they are inflated by helium?)

P.S. A larger, thinner board would have the widest range (but clumsier
than a smaller, thinner board) ?

P.P.S. A thinner board helps to handle gusts such that one don't need to
use the trim loop much ?

P.P.P.S. We has gone a loooooong way in light air kitesurfing (the
largest kitesurfing kite back in 1998 was the Wipika 8.5 m2 .......)

Hung.

kiteboard@... wrote:
>
> hungvu@... (Hung Vu) writes:
>
> << it has not been an issue for me in 5-6 knots
> with the XXXL and the FONE 230 board. >>
>
> Keep in mind that skill & a board that rails well will keep the nose from
> being pulled off the wind, & allow you to point to control speed. Where you
> ride it may be less gusty when it's light too. Assuming you are fully
> powered up (once up to speed), the only other thing I can think of is that
> the board may be too big, & therefore slowing you down, reducing the apparent
> wind.
>
> << Given the fact that I am lighter, but why should the apparent wind
> effect only applies for heavier person? >>
>
> Right now I can't think how rider weight would make a difference (but I may
> come up with somthing later!).
>
> AND:Eduardo.Aldaz.Carroll@... (Eduardo ALDAZ CARROLL) writes:
>
> <<However the apparent wind exists always, regardless of the force of the
> wind or the gear your using. >>
>
> I know it always exists, & did not mean to imply otherwise, just that since
> in lighter wind (flatter water) boat speed is higher (relative to true wind),
> apparent wind is also higher (relative to true wind).
>
> Mel
>
• In a message dated 10/22/00 4:51:57 PM Pacific Daylight Time, hungvu@netcom.ca writes:
Message 6 of 8 , Oct 22, 2000
In a message dated 10/22/00 4:51:57 PM Pacific Daylight Time,
hungvu@... writes:

<< A thinner board helps to handle gusts such that one don't need to
use the trim loop much ? >>

I agree with everything you wrote, including the above, although to be
perfectly correct I'd change it VERY slightly to say "you don't need to use
the trim loop AS much". I'd say "If it's not very gusty you don't need to
use it much".

Mel
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