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Vmg

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socommk23
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Vmg

Postby socommk23 » Tue Jan 10, 2017 8:37 am

Ok. So as i understand it. Vmg is the best angle/speed to get to a turn point. Im assuming this generally in racing is only really important when a few turns are needed to make it upwind, otherwise direct to each turn will always be better (other than directly down wind where a series of chained together suiside turns at speed are best) 

While on the move, how do we know what is the best angle/speed to use to get to that upwind turn point? 

Is there a real science to it? 

More importantly could a device be made to how you should be traveling?

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Re: Vmg

Postby Mossy 757 » Tue Jan 10, 2017 11:25 pm

The wiki is really comprehensive: https://en.wikipedia.org/wiki/Velocity_made_good

The way you train to this for hydrofoil racing is to have a good GPS watch that allows you to "mark" an upwind mark and a downwind mark, then you sail various speeds to calculate best VMG. For example:

Upwind you're looking at your watch and notice you're going 18 knots. You foot off a little to go faster until you're running around 21 knots. Even though you're not pointing as high, you might have just increased VMG because your speed through the water allows you to reach the laylines faster and therefore reach the top mark before someone who was going 17 knots but pointing a lot higher.

Conversely, you might be going upwind at 23 knots and then after the session calculate that your VMG actually decreased because you footed off too far and weren't pointing enough to optimize VMG.

Once you do some practice runs at various speeds/angles and run the VMG calculations for that foil and kite (and believe me, it's going to work out differently for EVERY kite) you'll essentially have a "target speed" that you'll try to hit on each leg. So if your target speed based on your VMG calculations is 22 knots and you're only going 20, you know you should either foot off a bit to build speed OR tack because you're in a header and you're already footed way off but still too slow.

Without a good GPS watch that can place a mark upwind and downwind and then run lap times around the course as you collect data logs, you're not going to be able to sail to VMG.

I've personally not done these calculations but I know a few guys are working on Apps for Garmin and Fenix watches that will do this specifically with hydrofoil racing in mind.

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Re: Vmg

Postby matth » Wed Jan 11, 2017 4:57 am

socommk23 wrote:Ok. So as i understand it. Vmg is the best angle/speed to get to a turn point. Im assuming this generally in racing is only really important when a few turns are needed to make it upwind, otherwise direct to each turn will always be better (other than directly down wind where a series of chained together suiside turns at speed are best) 

While on the move, how do we know what is the best angle/speed to use to get to that upwind turn point? 

Is there a real science to it? 

More importantly could a device be made to how you should be traveling?
I use to race sailboats on a recreational level and know a little about VMG. Its definitely a science, and serious racers are very into the science of it.
I had a computer sailing simulator at one time that really helped me with the concept, I'm am sure they are still around

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Re: Vmg

Postby aendorphin » Fri Apr 16, 2021 9:01 am

Do we know what VMG racers reach? I'm interested in SOG (Speed Over Ground) and VMG pairs.
For example for me on an 11m Sonic 3 with 17m lines just a couple of "moments from my session":
  • 17.1 SOG -12.7 VMG
  • 19.6 SOG - 11.5 VMG
  • 20.8 SOG - 15.5 VMG (this is maybe just a calculation error)
(Based on this: https://raceqs.com/tv-beta/tv.htm#userI ... eading=360)
A may do something wrong

I'm interested in what can the pro racers reach.

I'm talking about upwind VMG but also interested in downwind.

I found this:
Kitefoil racing being the fastest sailing class after the ACs is very different than a classic dinghy racing. A kitefoil racer can go around a 1.2 miles windward-leeward course twice in less than 10 minutes, thanks to an average VMG of 20+ knots.
but I guess that the average 10+ is thanks to a high downwind VMG

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Re: Vmg

Postby Flyingseb » Fri Apr 16, 2021 8:57 pm

What about that kind of thing?
D5DEC05B-5726-4C73-B8F4-0387B7E1F371.png

aendorphin
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Re: Vmg

Postby aendorphin » Sun Apr 18, 2021 7:37 pm

Flyingseb wrote:
Fri Apr 16, 2021 8:57 pm
What about that kind of thing?
D5DEC05B-5726-4C73-B8F4-0387B7E1F371.png
Look like a nice tool but unfortunately, I couldn't use this when the wind was very changing (I'm not sure how it calculates the wind direction but see my polar diagram from this session: http://regepe.com/showmap/f7013744d7f37)
best-vmg.png
I don't think that my VMG was ~19 knots. Or is this the downwind part? How can I see only the upwind part then?


But my question is:
What about PROs???

Here are a couple of other sessions of mine in better winds, but still not believing what I see:
http://regepe.com/showmap/f7013b5ac72fb
http://regepe.com/showmap/f7013d2fdcdbd

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Re: Vmg

Postby evan » Mon Apr 19, 2021 6:20 am

From what I can see is that the wind is shifting around 20deg between different Upwind runs. This makes a polar based on the average wind direction utterly useless, especially if it only shows the maximum values like on this website.

You want to look at average vmg on a stable wind or you need to pick sections and adjust the wind direction / Upwind angle yourself to calculate the vmg.
Current racers are doing roughly 15-17kn vmg Upwind and 25-30kn vmg Downwind

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Re: Vmg

Postby Peter_Frank » Mon Apr 19, 2021 7:14 am

evan wrote:
Mon Apr 19, 2021 6:20 am
From what I can see is that the wind is shifting around 20deg between different Upwind runs. This makes a polar based on the average wind direction utterly useless, especially if it only shows the maximum values like on this website.

You want to look at average vmg on a stable wind or you need to pick sections and adjust the wind direction / Upwind angle yourself to calculate the vmg.
Current racers are doing roughly 15-17kn vmg Upwind and 25-30kn vmg Downwind

Exactly, so you can take a given section on two tacks and measure the VMG, or the angle to the wind which can be interesting but a different subject.
Then do it on a few other tacks also (if the wind has shifted slightly, which it will), and use the average value.

In my experience by far the best way, in fact the only way.

Polars gives a wrong picture IMO, as every little or big windshift makes them waaaaaay too good, both upwind and downwind.

Whereas if you take the average for limited upwind paths instead, averaging these, windshifts will usually out-compensate and you still got a quite correct value.

8) Peter

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Re: Vmg

Postby aendorphin » Mon Apr 19, 2021 11:46 am

evan wrote:
Mon Apr 19, 2021 6:20 am
From what I can see is that the wind is shifting around 20deg between different Upwind runs. This makes a polar based on the average wind direction utterly useless, especially if it only shows the maximum values like on this website.

You want to look at average vmg on a stable wind or you need to pick sections and adjust the wind direction / Upwind angle yourself to calculate the vmg.
Thanks for the idea, all clear. I'll do some experiments.
evan wrote:
Mon Apr 19, 2021 6:20 am
Current racers are doing roughly 15-17kn vmg Upwind and 25-30kn vmg Downwind
How do you know this? What is your source? Can you share some .gpx files of current racers?

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Re: Vmg

Postby knot_moving » Mon Apr 19, 2021 4:37 pm

If you pick a good sea breeze day then you will see 10-20 deg shifts about ever 2-4 minutes. You should be able to see these very clearly when riding upwind.
- they should also be very clear in your data.

There are lots of smaller shifts happening but they will average out.

It’s usually lots harder to pick out shifts downwind, But you might be going fast enough that they become visible in your data.

In other winds the shifts are much more random and will be really hard to look at your data and figure out what segments to use.

When racing sailboats recreationally, but competitively we do the following to keep good vmg:
1) before the start, figure out if the wind is blowing from the left or right of the upwind mark. The best VMG will be to go on port tack if wind is to left of Mark.
— then while racing, every time a wind shift (more than 10 deg) happens, tack to keep pointing closest to Mark.

Point of this is that if you are training to improve VMG then you should be training to understand polar to your apparent wind angle, since that is all you can feel when riding. Easiest to do in sea breeze riding upwind

... you prob know all this - guess I will change my username to CaptObvious284
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