It is possible to do swift alphas with out doing super smooth, first rate gybes. A lot depends on entry speed and how fast you get back up to speed.

I am wondering if there would be a way to use the GPS data we already collect to indicate better how well you are actually maintaining speed through the arc of your turn.

What if we had a Gybe Efficiency Metric where we divided the session's best alpha result by either the 2sec, or 5 x 10 speed? The result would indicate how close your alpha was to your top speed.

For example:
20.5 kts (alpha) / 31.5 (2 sec) = 0.65

Or

18.5 kt (alpha) / 24.3 kt (2sec) = 0.76

The second example had a lower alpha speed but it was closer to the 2 sec indicating better speed maintained through the turn because the speeds are closer together. Chasing the ultimate gybe efficiency number of 1.0 could be an interesting exercise. It would also give sailors in rougher waters something to aim for as they are never going to get top speeds.

What do you think?

Here is my best alpha (Aus record) divided by the 2sec peak during the alpha 500.

28.78alpha 500 / 33.3 2 sec=0.86 edit

There was a discussion in a topic in the GPS forum, with another method to get a percentage to what your alpha was, or something like that. That was quite interesting too.

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izaak said...

Here is my best alpha (Aus record) divided by the 2sec peak during the alpha 500.

28.78alpha 500 / 33.3 2 sec=1.15

There was a discussion in a topic in the GPS forum, with another method to get a percentage to what your alpha was, or something like that. That was quite interesting too.

In your case 28.78 /33.3 = .86 which shows a close correlation between your top speed and your gybe (well done - getting close to 1.0).

A metric like this would enable sailors of varying speed potential but equivalent gybing skill to compete or compare against each other, or provide a new way of measuring their improvement in gybing that is more meaningful that just the standard alpha measure alone.

Opps,post fixed now Anyway yes i agree. I bet i have a 1.0 somewhere, but going threw 100's and 100's and 100's of track sessions is probably not worth it. Now i have a goal to get a 1.0 now

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izaak said...

Opps,post fixed now Anyway yes i agree. I bet i have a 1.0 somewhere, but going threw 100's and 100's and 100's of track sessions is probably not worth it. Now i have a goal to get a 1.0 now

OK izaak's on board. Any other's find this an interesting concept? I suspect the GPSTC website or KA72 could easily make the calculation and add a new column in the results (easier said that done?). There would also be the matter of choosing which speed to calculate against: 2sec or 5x10 average - whichever sailors felt gave the best indication of their speed on the water.

I think it should be calculated by your 2sec from the alpha done.

If we are thinking of using Gybe Efficiency as a measure of how good you are at being a generally good sailor and maintaining speed through your turns there might be a case for 5x10 because it's a better indication of how generally fast you have been in the course of the session. The 2sec, for many sailors, is a quick burst not closely related to the rest of their sessions.

You can tweak the numbers around to produce any result you want imo
A true measure of gybe efficientcy is...if you plane through a gybe and dont fall in
Then its a 100per cent perfect in my opinion.
Gybing in strong winds and flat water is a piece of piss,gybing in light winds and staying on the plane is the real challenge.
Gps action replay has a built in rating system for gybes and tacks.

Don't see how you could ever get a "1", min gybe speed can never be the same as the max speed.

I like the "G force" read out in gpsar, if you can pull >.5g through the gybe, you're not doing too bad.

No, it's not possible to get a "1". Realistically 0.8 something is probably as high as you could go. To get a 0.9 you'd have to do a 27kt alpha on a 30kt 2sec. Tough ask?

Jman in the other thread had a 20klt alpha and a top speed of 23.3 which is an efficiency score of 0.85 which compares favorably against isaak's effort even though the speeds were not at all close. So you can see how you could get a great efficiency score which demonstrates you gybing skill even though you've only had a slow day on the water.

Here's a quick spreadsheet of my last four sessions with Gybe efficiency calculated. They are consistent numbers but they do show that I gybed a little bit better on the first two days than the last two which is roughly what I remember of those days. This is a very small sample, certainly, but over time you could easily pick up trends in your sailing and see whether you were improving or not.

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ikw777 said...

Jman in the other thread had a 20klt alpha and a top speed of 23.3 which is an efficiency score of 0.85 which compares favorably against isaak's effort even though the speeds were not at all close. So you can see how you could get a great efficiency score which demonstrates you gybing skill even though you've only had a slow day on the water.

If that's his overall top speed and not the max alpha speed, probably just means he isn't going downwind enough for his 2sec score.

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decrepit said...

ikw777 said...

Jman in the other thread had a 20klt alpha and a top speed of 23.3 which is an efficiency score of 0.85 which compares favorably against isaak's effort even though the speeds were not at all close. So you can see how you could get a great efficiency score which demonstrates you gybing skill even though you've only had a slow day on the water.

If that's his overall top speed and not the max alpha speed, probably just means he isn't going downwind enough for his 2sec score.

Yes, but it if that were the case (an correct my logic if it's wrong), he's hardly belting into the turns then either (as he's not coming off big bear-offs), so his gybing skill must be great, as indicated by the efficiency score.

You can't do a good alpha by doing big bear offs, the gybe is too wide and you have to go upwind to make the 50m proximity.
square to the wind in each direction is probably the best unless you can gybe real tight.
I guess that may be the case in lighter winds, but then you're more likely to fall off the plane.

I agree with Izaak, forget about 2sec and 5X10, if they're the result of a proper downwind run, they'll be much higher than the alpha max speed, and could make the alpha look bad.
Where as if you're only going for alphas and not going downwind, that will give a better result.
A comparison of alpha max speed with alpha speed is a better indication of how consistent the alpha is, but is affected just as much by the straight legs as the turn.
Wouldn't a better measure of the gybe be, a comparison of alpha max and min speeds?
But that still doesn't tell the whole story.
As discussed on another thread, alpha results can still be good with a low minimum speed. It's how long you're at the minimum speed that counts.

I agree that if you are going to create a ratio then it must be compared to the peak while in the alpha run, not your 5x10 or 2 sec as those are completely different disciplines.

It is a good idea for those who like to analyse a lot. Of course if you have a low min and a good alpha then you must have had a high peak, which will give a lower result to a good constant speed all the way through. It is going to be a factor of water state, location, wind direction etc more than skill I think. But if you do sail the same spot regularly it gives a good target to improve on without a doubt, which in turn will improve your alphas. Mine are still low (21.2 is my best) with usually around a 28knot peak and a 10-12knot minimum, but they are getting a lot more consistent, this time last year I only had the very occasional alpha over 17!

These are interesting and important points and I think I do understand what you are saying. If I may elaborate on my goal here though, the idea was for a simple metric to compare your gybe against general sailing speed (yes I know - they are rubbery concepts in themselves, but it's what we've got). So in broad terms a sailor might say to himself, "hmm I did only 24 knots today, but got an alpha of 20. That's pretty good, I wonder how that compares with last week?". Divide the one by the other and you'll get an idea.

It's the idea of working to bring your alpha close to your general speed that interests me. Particularly for people who (like me) sail at light wind, rough water spots. We'll never reach 30kts but could use our GPS to help improve our sailing and compare ourselves with the others we sail with. It could only ever be a broad indication of improvement/performance but might bring a sailor satisfaction to see it occurring over time.

I can see the problems with 5x10 and 2sec, because serious speed sailors achieve their speeds on big bear-offs. That's fine but not everyone has the conditions to enable them to do so.

Comparing the alpha max and alpha is only available to those who use GPSResults or some other GPS program. I don't, and I know that more than a few people on our team just rely on KA72. I'm sure there are lots of others too (we all vary I guess).

I might be I am going up a dead end with this and that's fine, I'm just trying out an idea I've had for a little while to see if it floats.

If you could set the software to do the two second average either side of five seconds prior to the gybe and then contrast this with the exit speed... then a lot of people who don't speed sail would be interested.

I can see it working on a personal individual level, after all you should be aware of how much you went downwind for your 2sec result, and apply a compensating factor. (although in my case I'm sometimes surprised by just where I've gone, sieve memory syndrome)
But you can't compare that with anybody else's result as you don't know how they achieved their 2sec.

Hmm, well here's a thought, but it's a bit messy.

It involves a separate file for alphas, intentionally keeping max speeds confined to alpha attempts.
Would mean turning the gps on and off at the start and end of the alpha session, so the alphas can be calculated separately to the other divisions.
Would mean you couldn't do an automatic upload from ka72, and you'd have to add a note to say that it's an alpha "gybe index" and give the result.
Then anybody interested could do comparisons with each other.
Maybe Dylan could be persuaded to facilitate in some way?

If you're keen on analysing this kind of stuff, GPS action replay gives you all the data you need to check how efficient your alphas are.
I've been checking this regularly and I check the alpha speed Vs top speed in the alpha 500 distance....easy with GPSAR.
I've noticed that the most efficient ones are in light wind with big sails.
I guess it's the flat water that does it.

25.25 max with 22.17 alpha ....0.87 ratio
15-18kts of wind for this.
Min speed was 11.24kts
95 litre Slalom board, 7.0 Maui TR3, Techtonic 40cm Spitfire fin

GPSAR also has a 'Jibes analysis' function which gives enough data to get your head spinning......Max centrifugal force, 4 sec centrif, 4 sec radius etc, etc.

But keep in mind that we are only at 1 Hz sampling and all these numbers will look very different (particularly around the slow point) when the sampling speed eventually improves.

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ikw777 said...

izaak said...

Opps,post fixed now Anyway yes i agree. I bet i have a 1.0 somewhere, but going threw 100's and 100's and 100's of track sessions is probably not worth it. Now i have a goal to get a 1.0 now

OK izaak's on board. Any other's find this an interesting concept? I suspect the GPSTC website or KA72 could easily make the calculation and add a new column in the results (easier said that done?). There would also be the matter of choosing which speed to calculate against: 2sec or 5x10 average - whichever sailors felt gave the best indication of their speed on the water.

Yes I like the concept it would give us guys that sail mostly on open water a division that we can compete with.

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decrepit said...

ikw777 said...

Jman in the other thread had a 20klt alpha and a top speed of 23.3 which is an efficiency score of 0.85 which compares favorably against isaak's effort even though the speeds were not at all close. So you can see how you could get a great efficiency score which demonstrates you gybing skill even though you've only had a slow day on the water.

If that's his overall top speed and not the max alpha speed, probably just means he isn't going downwind enough for his 2sec score.

That was the max speed in my alpha

I think it's a great concept, and one that I've thought about a fair bit.
- but it's important to keep it simple.

I'd be happy to use the 2 sec or 10 sec as the denominator, as this number represents the potential speed that was out there for that sailor, on that gear in that particular session.

- the problem with using the alpha divided by the 2 sec peak, or 10 sec (on that individual run) is that on a windy day, a good sailor could back-off the power for the 250 m each way (eg hang around 20kts), but power up through the turn (keeping around 20kts) thus producing a near score of "1.0", but in reality it was contrived.

For me, if I've got an 18.5 alpha, I like to compare it to what was my best speed on the day. The smaller the gap, the more satisfaction I get.

You'd probably find that people on speed gear like Izaac may not get as close to "1.0" as guys on wave or FSW gear, who are going as fast as they can on that gear, then jibing on a wave face.

It'd be interesting. Good topic.

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Bondalucci said...

I think it's a great concept, and one that I've thought about a fair bit.
- but it's important to keep it simple.

I'd be happy to use the 2 sec or 10 sec as the denominator, as this number represents the potential speed that was out there for that sailor, on that gear in that particular session.

- the problem with using the alpha divided by the 2 sec peak, or 10 sec (on that individual run) is that on a windy day, a good sailor could back-off the power for the 250 m each way (eg hang around 20kts), but power up through the turn (keeping around 20kts) thus producing a near score of "1.0", but in reality it was contrived.

For me, if I've got an 18.5 alpha, I like to compare it to what was my best speed on the day. The smaller the gap, the more satisfaction I get.

You'd probably find that people on speed gear like Izaac may not get as close to "1.0" as guys on wave or FSW gear, who are going as fast as they can on that gear, then jibing on a wave face.

It'd be interesting. Good topic.

I think you're right, it won't be speedys doing the biz because their top speed is too high.....wave boards will be in the lead specially if you use the max 2 sec of the session rather than of the alpha run.

PS....when you get bored with it, try tack alpha 500's...even better

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Bondalucci said...

I think it's a great concept, and one that I've thought about a fair bit.
- but it's important to keep it simple.

I'd be happy to use the 2 sec or 10 sec as the denominator, as this number represents the potential speed that was out there for that sailor, on that gear in that particular session.

This is a good perspective, I hadn't thought of that.

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- the problem with using the alpha divided by the 2 sec peak, or 10 sec (on that individual run) is that on a windy day, a good sailor could back-off the power for the 250 m each way (eg hang around 20kts), but power up through the turn (keeping around 20kts) thus producing a near score of "1.0", but in reality it was contrived.

This is a risk I suppose but it's hard imagine who would back off like that for a whole gps session.

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For me, if I've got an 18.5 alpha, I like to compare it to what was my best speed on the day. The smaller the gap, the more satisfaction I get.

It's good to know i'm not alone!

It's possibble that scores from a metric like this would be best not contributing to overall scores in the competition but rather be a general interest category?

Call me simple, but I can't for the life of me figure out what the hell this thread is about!

As far as I can see, the best measure of a good Alpha is........well.....the Alpha speed!

If you really want to get anal about it, how about some measure of Alpha speed V's average wind speed. Good luck finding a way of measuring that though.

Or what about Alpha speed V's body weight and height? (taller and heavier guys can go faster square to the wind - but you still have to do a good gybe! )

Yeah, I'd agree with sailquik. It looks interesting but I'd rather go sailing than sit around doing maths.

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Te Hau said...
I think you're right, it won't be speedys doing the biz because their top speed is too high.....wave boards will be in the lead specially if you use the max 2 sec of the session rather than of the alpha run.

Not even close.... think long boards. Go into the gybe in 20kn of wind, go in to the gybe at 3kn, slam that gybe around, stall the exit. I'm tipping something around 1.5...

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sailquik said...

Call me simple, but I can't for the life of me figure out what the hell this thread is about!

As far as I can see, the best measure of a good Alpha is........well.....the Alpha speed!

If you really want to get anal about it, how about some measure of Alpha speed V's average wind speed. Good luck finding a way of measuring that though.

Or what about Alpha speed V's body weight and height? (taller and heavier guys can go faster square to the wind - but you still have to do a good gybe! )

I think the basis of this thread can be expressed with the following eg.

2 guys clock an alpha of 22.5 kts.
-the first guy gets his by sailing really fast (maybe 35 kts), does a dodgy gybe, but eventually regains composure and gets back up to a similar high speed sometime over the remaining 250 metres.

-the second guy (maybe sailing in crappier conditions, or on slower gear) gets his, by sailing in at 25kts, completing a near flawless gybe and getting back up to his max speed asap.

Both guys get an alpha of 22.5kts (knowledge of results), but their knowledge of performance is quite different.

This thread is looking at a way of measuring that.