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 Post subject: Upwind Angle
PostPosted: Sun May 27, 2012 5:33 am 
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What angle can the best race boards sail upwind to with respect to the apparent wind?

I've seen claims that in 6 knots of wind, the top racers are sailing upwind at over 10 knots. I guess upwind is a relative term, but even if they can sail 25 degrees to the apparent wind, that is only sailing at 70 degrees to the true wind.

I checked my calculation of angle with this website: http://www.sailingusa.info/true_wind_calculator.htm

Calculated angle between heading and apparent wind to be 25 degrees for inputs of hull speed = 10 knots, true wind speed = 6 knots, and angle of hull to true wind = 70 degrees.

I've noticed this on my GPS plots in light winds (<10 knots) my speed is equal to or better than the wind speed, but upwind angle is horrible!

Do the top racers sail at 70 degrees to true wind when racing in 6 knots or do they slow down and point higher?


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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 3:32 am 
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Location: buffalo, ny
Very interesting topic. Obviously kite point much higher towards windward because the distance and subsequent angle the kite(pull force) is relative to the kiter. This is our unique advantage that other wind sports have not been able to incorporate. I'm not a physicist but enjoy the subject. Let's here some input.


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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 5:11 am 
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Location: Mauritius, waterman since 1960
70 degrees cannot be right, or it would take you hours to tack upwind.
Thats just 20degrees better than no upwind at all.
If you've worked out 25degrees on apparent wind then you should be able to do 25degrees to the real wind too as you will not be able to go any hicgher upwind then 0degrees.
however 25degrees does sound a little too efficient upwinding to me, but much closer than the 70degree calculation.
I am basing my comments on 40+ years of practical sailing and no theoretical calculation whatsoever.
Lets hear the theory fundies comments
Nico


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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 9:06 am 
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There was a good article by Callum Edge in Kiteworld #52 about how he uses his GPS to train.

Typical figures he was quoting were 50 degrees off wind on the upwind leg. 15 knots upwind and 25 knots downwind.

He didn't mention windspeed, but I would assume those were fully powered figures.


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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 3:43 pm 
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I'm not sure what the actual angle to apparent wind is. I was thinking 25 degrees is reasonable but on the high side. Let me know if anyone has figured it out.

The easiest situation to think about it is when your board speed = the true wind speed. In that case, the apparent wind direction will be halfway between your heading and the true wind direction.

So if you are going 10 knots in 10 knots of true wind heading at 50 degrees to the true wind, then the apparent wind is at 25 degrees, halfway between true wind (0 degrees) and your heading (50 deg).

As you go faster, the apparent wind shifts more in front of you. If you want to go 10 knots in 6 knots of wind, you aren't going to point very high because the apparent wind angle will be very high.

Nico wrote:
70 degrees cannot be right, or it would take you hours to tack upwind.
Thats just 20degrees better than no upwind at all.


That's true. You have to slow yourself down to point higher though. You can't point very high at all when you are riding upwind at nearly twice the wind speed.


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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 3:54 pm 
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Here's some examples. Riding the same board, Cabrinha Race 183x59 with stock quad fins.

One day in about 15-17 knots of wind with Dyno 10m. Boardspeed of about 12-13 knots going upwind.

Another day in about 9-10 knots of wind with Dyno 18m. Boardspeed of about 10 knots going upwind.

You can see the difference in upwind angle. Is there an easy way to measure angles on a picture?


Attachments:
File comment: Dyno 18m. 9-10 knots of wind.
5-24-2012.png
5-24-2012.png [ 416.35 KIB | Viewed 1837 times ]
File comment: Dyno 10m. 15-17 knots of wind.
OceanRaceboard3-15-12.png
OceanRaceboard3-15-12.png [ 386.02 KIB | Viewed 1837 times ]
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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 5:40 pm 
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I'd just use a protractor and measure the angle 'T' between tacks. Angle to wind = 90 - (T/2)


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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 7:45 pm 
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I measured the angles. On the day with the 18m kite, my angle to the true wind was about 81 degrees. On the windier day with the 10m kite, my angle to the true wind was about 75 degrees.

However, my angle to the apparent wind was pretty much the same on both days on multiple tacks. Angle to apparent wind was between 36.5 and 37.5 degrees. That makes sense, angle to the apparent wind should be pretty consistent.

Both of these days included working against the current as I was going upwind, so my actual upwind angles were higher than shown on the GPS track. I'll have to try this again on a day with no current.


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 Post subject: Re: Upwind Angle
PostPosted: Mon May 28, 2012 8:38 pm 
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Davesails, just download GPSActionReplay free version (Gpsar333). It is Java so it should run on most computers

http://gpsactionreplay.free.fr/index.php?menu=6

Just click wind gauge to correct direction (or allow software automatically to determine it) and estimate wind strength and you can have all sailing statistics you are asking for.


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