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Board » Technical Discussion » Performance loss

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Posted by
Rod


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2010-06-24 22:30:48
2013-10-11 21:46:48 - Re: Performance loss
I have been exploring the rate of recovery of "perf" after a gybe of 270 degrees at a speed of 25-26 knots. The rate of recovery is linear, but has two components. It required 20 minutes to recover, but for the first 16 minutes the rate of recovery was 0.4% per minute. For the last 4min, the rate was0.74% / minute.
After a gybe of 180deg, at the same speed, it required 23 minute, at a rate of 0.52% per min for the first 15.5 min, and then a rate of 0.90% / min for the last 7 minutes.
I can see no reason for either the greater loss for the lesser turn, or for the changes in recovery rate that were observed.
I will continue to collect data.
As Alice said, "This is getting curiouser and curiouser!"
p.s. I think it was Alice (of Wonderland fame,) but I'm not certain....

--- Last Edited by Rod at 2013-10-11 21:48:54 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
kroppyer


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2010-02-05 15:25:55
2013-10-11 21:59:21 - Re: Performance loss
This peace of code does not include performance recovery.

As far as I can tell from this code, it doesn't matter if you gybe from twa=155 to twa=-155, or from twa=175 to twa=-175. performance is in boat gybe half you boat speed.

What is possible (what I believe hmm did) is to change course to twa=179 (slow) then gybe to best VMG (low performance loss because low boat speed.

With the tall ships you might be able to tack with almost no performance loss: you're sailing with twa=70, change course to twa=(about)50, so that you boat speed is (almost) 0. Then tack to twa=-70 (no extra performance loss). I'm not sure whether 10 seconds with speed=0 is better than a little more performance loss.

This makes me think... tall ships can sail backwards.. tacking when you're speed is negative should increase performance according to this code. In the most extreme case you could sail with -0.373 kts backwards, tack an have a performance of 100.19%. It's quite possible that there's something in the performance recovery code that prevents the performance from exceeding 100%.

EDIT: Currently trying these things.. I'm wrong on at least one point: it the boatspeed *after* the tack/gybe that determines performance loss.

EDIT:
There are still weird things going on. In the tall ships race, there's not enough wind to go "fast" backwards. I was not able to get performance above 100% It might be possible to speed up de performance recovery (with the negative speed trick), but I can't measure that now (I can only do a 0.02% increment).
I noticed something weird with speeds <= 0. Somehow, if you tack, and your speed after the tack is smaller of equal to 0, your performance is 100% immediately. When you change course (don't tack or gybe) to an angle with a boatspeed smaller or equal to 0, your performance recovers very fast. Has boatspeed something to do with performance recovery? That would explain why fast boats have slow recovery.

--
It's not that one of these things would make you any faster, but while discovering how SOL works, we might find some things that do make you faster. These performance things might be very interesting for practice racers (like me) :)

--- Last Edited by kroppyer at 2013-10-11 22:10:37 ---

--- Last Edited by kroppyer at 2013-10-11 22:27:13 ---
Posted by
A2


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2009-10-26 00:39:42
2013-10-11 22:41:35 - Re: Performance loss
Ok so if its the speed after the G/T then could the flat turn gybe that hmm did at Digby be 1st to just do a change sign at 179.99 then go to VMG ?
None so blind
Posted by
kroppyer


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2013-10-11 22:59:14 - Re: Performance loss
Yes, at this point I think something like this happened:
twa=145
twa=-179.99 (speed: 17.3 kts, perf.: 91.35%)
twa=-145 (no additional perf. loss because perf<93%)

===(edit)===
Let me add a "translation" for those not familiar with programming.

Now e is a percentage (0-100%), boatspeed is in knots, dTWA is positive difference in course, in degrees (I believe dTWA was in radians in the original code).

---
If (tack or gybe (twa changes sign))
then
e = 100 - boatspeed/2
else
e = 100 - dTWA*180/(25*PI)
end

perf = perf*(e/100).
---

There is something with the recovery though, sometimes the performance loss is very low or not even noticeable. I think this is because recovery is very fast when boat speed is low.

--- Last Edited by kroppyer at 2013-10-12 08:09:20 ---

--- Last Edited by kroppyer at 2013-10-12 08:11:23 ---
Posted by
Rod


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2013-10-12 13:49:52 - Re: Performance loss
What is " PI "????
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
hmm


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2011-11-03 13:35:22
2013-10-12 14:00:08 - Re: Performance loss
Rod said @ 2013-10-12 13:49:52:
What is " PI "????
PI = 3.141592...

Probably that is because dTWA is in radians.
Posted by
Rod


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2013-10-12 15:35:10 - Re: Performance loss
Complicateder and complicateder---"Radians"?
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
A2


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2009-10-26 00:39:42
2013-10-12 15:41:15 - Re: Performance loss
I found this graphic that I snagged in the past that was posted here in the Forum. Unfortunately I don't know who provided it but it does relate to Boat Speed recovery.

The url where it was linked from is no longer valid but this is the defunct location.

http://farm3.staticflicker.com
(space added)
/2357/2063504228_33f768fe40.jpg

By looking at the graph axis labels 'e' stands for efficiency in the formulas that are under discussion.

This is not definitive but it is a start
None so blind
Attachments
Posted by
hmm


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2013-10-12 15:44:54 - Re: Performance loss
Rod, you know you have a computer in front of you which has the ability for search for information?

Whether you like it or not, simulating the performance requires mathematics. And if you want to understand that, you should be aware of some basic mathematical terms like "pi" and "radian".

The answer is the first hit google gives you for "radians".


Posted by
Rod


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2013-10-12 21:44:29 - Re: Performance loss
I know Pi and radians, but is it necessary for the calculation? It's a long time since I did a lot of math, and I'm sure many SOLers don't even remember as little as I do about how to manipulate radians in an equation. I will persist......
If it breaks, it's not strong enough--if it doesn't, it's too heavy.

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