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Board » Technical Discussion » Performance loss

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Posted by
A2


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2013-10-12 22:09:07 - Re: Performance loss
Yes it is necessary if thats the way the formula is written & as most spreadsheets use radians so that degrees must first be converted for those calculations to work.

Please desist . . .
None so blind
Posted by
kroppyer


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2010-02-05 15:25:55
2013-10-13 13:02:06 - Re: Performance loss
The image A2R found would suggest the performance recovery formula to be linear, with 9/boatspeed% recovery per minute. (boatspeed in knots)

Obviously something is preventing a negative recovery, so it might be 9/abs(boatspeed)% per minute...

So... little question for those that can do a little maths: is it beneficial to sail a slower course while performance is still recovering? Possibly not, but what if sailing VMG/VMC? (because cog might be much slower, recovering faster, while vmg/vmc isn't that much slower)

I'll do some of the maths later.

All of this is assuming the image A2R found shows correct data. Which might not be true, since Rod found that the rate of recovery changes over time.

Thanks again, A2R for finding this next bit of information.

--
The PI is indeed the PI that is half of TAU, and it is indeed because dTWA is in radians (which is much easier to use than degrees, if you're doing maths).

--- Last Edited by kroppyer at 2013-10-13 13:10:05 ---
Posted by
captjack1942


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2013-10-13 17:03:11 - Re: Performance loss
The performance chart comes from Kalle's Flickr page. The link was given by kalle (or maybe Jakob) in chat back in 2008. The link:
recover.png

It was from the early days of SOL. It still seems to me to accurately reflect the loss/recovery of performance on a gybe or tack. There is more to the actual code that relates to smaller course changes, but when course changes across the wind, the loss kicks in.

--- Last Edited by Jack Watson at 2013-10-13 17:07:30 ---
Posted by
kroppyer


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2013-10-13 19:05:17 - Re: Performance loss
I made a little spreadsheet that calculates things with performance loss and recovery.

All according to these, unverified formulas. I did part of tonight's practice race on DCs, I included performance loss in the calculations, and my DCs turned out pretty well. Though, they fired a little later than I expected, so maybe performance recovery is faster than these formulas predict.

And of course there is a huge possibility I miscalculated something, or the spreadsheet has an error.
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Posted by
Rod


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2010-06-24 22:30:48
2013-10-14 14:49:13 - Re: Performance loss
There are two basic ways in which this problem can be attacked and solved. The first is to try out the equations that have been provided and determine if the boat responds as it is supposed to. (Kroppyer's approach). The second is to carry out a series of tacks, gybes and course changes, and observe the Perf% and the rate of recovery. This does not assume that the equations are correct. I will try the second approach. I have completed only two 'runs' so far, but they suggest that the recovery rate is linear, but not constant. The rate is faster as it approaches 100%. When I have more data, I will present a graph.
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
javakeda


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2013-03-01 03:18:22
2013-10-14 15:59:59 - Re: Performance loss
What a great thread!

1) Thanks to HMM for sharing the role of BtSpd in tacks and gybes.
2) I'm with Rod on this being a time to gather data.

I am gathering data on
-- tacks
-- gybes
-- reaching off
-- hardening up

The obvious questions are:
a) What will the PERF hit be as a result of this maneuver?
b) What is the expected rate of recovery?

I am using three open windows to gather the data:
#1 is the SOL client
#2 is an Excel worksheet to record the data
#3 is the Google APP "Stopwatch".

Stopwatch allows me to record 'split' times with a mouse click and then type the data I see into the worksheet.
Usually, the data is simply the PERF reading. However, I work in TWS, TWA, and BtSpd every minute or so in the ~15sec window between PERF updates.
After the data gathering run is over, I can cut and paste the split times into the worksheet.
Finally, I can plot PERF values [or the PERF 'delta' values] against time to show the recovery rate graphically.

I pledge to share all my data in this thread. I encourage others to gather and share data as well.

--- Last Edited by javakeda at 2013-10-14 16:02:52 ---
Posted by
javakeda


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2013-03-01 03:18:22
2013-10-14 16:27:17 - Verisimilitude
A major asset for SOL is its high degree of 'verisimilitude' -- the degree to which any model [game or not] resembles reality.

In real life, we learn about the performance of our boats by actually sailing our boats.

With tacks, we learn that we need to get the boat speed up before we can point at maxVMG.

With gybes, we learn we have to get the kite flying before we can trim it to the optimal course.

Both of these facts illustrate real life examples of multi-step tacks and gybes.
Is the analogy perfect?
No.
But I submit that having a '93%' rule actually adds verisimilitude to the SOL game space.
Posted by
javakeda


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2013-03-01 03:18:22
2013-10-14 17:17:35 - Sail Management
Sailing my SOLTP52 in ~17kts TWS earlier today, I reached off from a TWA of -36 to a TWA of -153.
I was greeted with an initial PERF hit down to 91.83%
The polar says I can expect a BtSpd of ~11kts at that TWA and TWS.
That boat speed implies a PERF hit down to 94.5% in a tack or gybe.
Oooops!
Clearly something else is going on.

Before suggesting what that might be, let me call your attention to the following website:
http://team-yacht-treff.de/polars/

Note:
#1 This site is a precursor to Brainaid's Toolbox.
#2 The links to SOL and the Toolbox at the top of the page still work.
#3 Scrolling down, you can see graphic polars beautifully rendered in 3D.
#4 Scrolling down further, you can see 3D-graphic polars with color highlights that appear to depict the best head-sails to use with various TWAs and TWSs.

Well, ain't that special? [with apologies to SNL]

So, my working hypothesis is that the 'half-the-boatspeed' rule works in tacks and gybes where there is no change of sail. Where a change of sail is implied, an additional PERF penalty applies as well.

Time to gather some more data to check out that hypothesis. I'll focus on the area around TWA=110. From the 2D-graphic polar, that sure looks like the point at which the boat flies the kite.
Posted by
A2


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2013-10-14 17:45:31 - Re: Performance loss
example cited is consistent with the formula



--- Last Edited by A2R at 2013-10-15 11:22:12 ---
None so blind
Posted by
kroppyer


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2013-10-14 18:56:18 - Re: Performance loss
Right now, I'm sailing a practice race, and I wrote a PHP script that logs my TWA, SOG, and PERF every 15 seconds. The script only ran for a couple of minutes, then I restarted it with other settings, and it's still running now.
I have a (very accurate) small dataset for those first couple of minutes, for the other two hour we still have to wait.

Here a picture of those first couple of minutes :D
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