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Post your polar and VMG

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alexrider
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Post your polar and VMG

Postby alexrider » Sun Apr 09, 2017 11:07 pm

In order to compare more objectively the performance of kite/hydrofoil/rider combo than test reviews, may I suggest you guys to show your day's polar and VMG. You obviously need a waterproof GPS device in order to achive that.
The program I use on PC under Windows is the excellent GPS Action Replay. I don't know of any other ones; if you are aware of any, please let me/us know. BTW, the program does a lot more than just show the polar graph. Check it out there:
http://gpsactionreplay.com/
For those who are not familiar with the use of the polar diagram, VMG, and their meaning... I've described the procedure in one of my blogs, "On the use of GPS watches to analyse tracks":
http://www.nautikites.net/blog/index.ph ... 905-145635

My session yesterday as an example:
- Wind averaging 10 knots, ranging 7 to 11
- Hydrofoil: Cabrinha Double Agent 2016
- Kite: Flysurfer Sonic2 13
- Distance covered 32 km in 2 hours, practising jibes
- Top speed: 13 knots over 100 meters (you don't need to laugh, the Cab IS slow, but so much fun - like a Piper Cub in another realm)
- Rider HF experience: still consider myself a beginner with 90 hours and 1200 km, having started nearly a year ago

Polar (speed units are knots):
2017-04-09_190904.jpg
And the track (which you can also visualise in Google Earth or whatever app that comes with the GPS watch):
2017-04-10_045951_cr.jpg
Beware: the polar is accurate only if the wind direction isn't shifting. If it is, what is shows can be very optimistic. In that case, cut your track in smaller ones in which you consider the wind steady in direction.

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Re: Post your polar and VMG

Postby gmb13 » Mon Apr 10, 2017 12:36 am

Hi Alex,

That sounds like a good Idea.

Here is my polar from todays little training session.

- Wind 12-15 Knots
- Hydrofoil: Banga
- Kite: Ozone R1v1 15m
- Lines: 14.5m
- Top speed: 31 Knots (500m)
- Distance: 21km
- Rider HF experience: 7 years
Screen Shot 2017-04-10 at 00.30.45.jpg
--
Gunnar

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alexrider
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Re: Post your polar and VMG

Postby alexrider » Mon Apr 10, 2017 1:36 am

Hi Gunnar,
Wow, R1V1/Banga/Gunnar looks like a pretty good combo. :clap:
Top speed 31 knots and 17 knots net gain in the direction of a 12-15 knots wind. Looks fabulous.
Does it mean you maintained 31 knots over 500 meters?
Also looks like you avoid going 75 degrees to true wind. :D
Can you give the specs of the Banga foil? Mast length, wing area and span...
In 12-15 knots I use 8 or 6 FS Speed. I don't like to get scared and out of control, and that's why I'm not yet using my more advanced hydrofoil.
Maybe we could add in the parameters the watch used, not that it matters much. Mine is Polar (sic!) M400 which I prefer to my Suunto Ambit3 and Garmin watches which give me spurious results with a messed up polar. Still trying to find out the reason.
BTW advice for new users: set the GPS fix frequency to shortest possible, usually 1 second.
gmb13 wrote:
Mon Apr 10, 2017 12:36 am
Hi Alex,

That sounds like a good Idea.

Here is my polar from todays little training session.

- Wind 12-15 Knots
- Hydrofoil: Banga
- Kite: Ozone R1v1 15m
- Lines: 14.5m
- Top speed: 31 Knots (500m)
- Distance: 21km
- Rider HF experience: 7 years

Screen Shot 2017-04-10 at 00.30.45.jpg

--
Gunnar

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Re: Post your polar and VMG

Postby evan » Mon Apr 10, 2017 8:26 am

My polar of last week

- Wind: 16-20kn
- Hydrofoil: Levitaz Bionic with small proto wing and 110cm mast
- Kite: 11+14m Peter Lynn Aero UL
- Lines: 13 and 14m (measured from bar to end of pigtails)
- Top speed: 30.5kn
- Best speed over 500m: 27kn
- Distance: 70km
- HF experience: 3 years

As I remebered correctly the wingspan is around 58cm and the area roughly 350-400cm^2

2017-04-05-3.JPG
Was testing a bit shorter lines this time, on the 14m it was ok-ish but on the 11m it filte like the wind was extremely turbulent and the chop was higher. Was almost calling it a day when my friend told me the wind was perfect so switched back to my trusted 14m lines and everything was super smooth again. Suprising one meter of line would make such a big difference!

Also some of the best up- and downwind runs including a tack and gybe below, this way you get a better idea of the angles as the wind shifts always a bit during a session and give you way better angles on the polar that are not possible on the water. Compared to Gunnar i need to work on my top speeds!
Attachments
2017-04-05-4 downwind.JPG
2017-04-05-4 downwind.JPG (50.03 KiB) Viewed 1399 times
2017-04-05-2 upwind.JPG
2017-04-05-2 upwind.JPG (34.52 KiB) Viewed 1399 times

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gmb13
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Re: Post your polar and VMG

Postby gmb13 » Mon Apr 10, 2017 9:22 am

alexrider wrote:
Mon Apr 10, 2017 1:36 am
Hi Gunnar,
Wow, R1V1/Banga/Gunnar looks like a pretty good combo. :clap:
Top speed 31 knots and 17 knots net gain in the direction of a 12-15 knots wind. Looks fabulous.
Does it mean you maintained 31 knots over 500 meters?
Also looks like you avoid going 75 degrees to true wind. :D
Can you give the specs of the Banga foil? Mast length, wing area and span...
In 12-15 knots I use 8 or 6 FS Speed. I don't like to get scared and out of control, and that's why I'm not yet using my more advanced hydrofoil.
Maybe we could add in the parameters the watch used, not that it matters much. Mine is Polar (sic!) M400 which I prefer to my Suunto Ambit3 and Garmin watches which give me spurious results with a messed up polar. Still trying to find out the reason.
BTW advice for new users: set the GPS fix frequency to shortest possible, usually 1 second.

Hi Alex,

You can find all the info on the Banga on my Video Review of it:

phpBB [video]


I use the Suunto Ambit 3. It does a 1point per second frequency. Work good for me.

--
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gmb13
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Re: Post your polar and VMG

Postby gmb13 » Mon Apr 10, 2017 9:23 am

2

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alexrider
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Re: Post your polar and VMG

Postby alexrider » Mon Apr 10, 2017 2:03 pm

A bit off topic (but I'm allowed because I'm the OP :P ): what's the advantage of shorter lines wrt performance? Seems that racers all opt for that.

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Re: Post your polar and VMG

Postby Mossy 757 » Mon Apr 10, 2017 2:28 pm

alexrider wrote:
Mon Apr 10, 2017 2:03 pm
A bit off topic (but I'm allowed because I'm the OP :P ): what's the advantage of shorter lines wrt performance? Seems that racers all opt for that.
Hold more power, more direct feeling during maneuvers and the timing works a bit better for going at max VMG upwind/downwind.

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Re: Post your polar and VMG

Postby tegirinenashi » Mon Apr 10, 2017 4:21 pm

Beginner question here: how is it possible to go almost 30 kn downwind in 12-15 kn conditions? I understand there might be lateral apparent wind component, but how is it possible to go > 15 kn along (not across) the wind direction? To be more concrete, Gunnar diagram shows 17-18 kn dead downwind, and jumps to almost 30 kn at around 150 degrees. Therefore it is actually two questions:
1. How can he go 17-18 kn downwind in 12-15 kn.
2. How can it be almost 30 kn at 150 degrees? Please note that 30 kn at 150 degrees is about 25 knots at 180 degrees true wind direction!

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Re: Post your polar and VMG

Postby Lokihel » Mon Apr 10, 2017 5:56 pm

It is all about apparent wind speed.

I am a bit lazy to do the math to show it right now, but basically the faster you go, the more wind you create, so the faster you go.
Essentially, you're still sailing 'upwind', although you are actually travelling downwind.

I am not sure what the limit is on a hydrofoil, but on a high performance sailboat you want the apparent wind to remain a 90°.
As you gain speed, the apparent wind will shift 'forward', allowing you to bear a little downwind. You can then very easily be 150° off the true wind.
You have to start by again speed though. If you start by pointing 150° off the true wind you will struggle to build speed.


Because of that magic, performance sailors can have a VMG downwind greater than the true wind speed.
This means they can get downwind faster than the wind that is powering them.


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