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Board » Technical Discussion » Performance loss

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Posted by
hmm


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2011-11-03 13:35:22
2013-10-10 10:59:18 - Performance loss
Post annotated by RainbowChaser :
This thread was moved from the category General Discussion.
I think most of this is quite general knowledge by the more active solers but to clarify things, I want this to be general knowledge:

1. Performance loss percentage when tacking/gybing is half of your boat speed after the tack/gybe. I.e. if you gybe to an angle where the boatspeed would be 20kts, the perf loss would be 10% and boat performance will be 90%.

2. When not changing tacks, the performance loss is much less and depends on the amount of turn + the boat speed after the turn.

3. The performance loss is cumulative, however if your performance is less than 93% the additional turns or tacks will not cause more loss.

4. The performance gain is logarithmical, i.e. gain from 90->91 is much faster than 99->100.

In my opinion, as this facts have been mentioned many times in chats, so they are sort of general knowledge. They probably should be in the manual as well.

And, during my latest run in Kerguelen Timed race, knowing rules 1. and 3. during my gybe near Cap Digby was important.
Posted by
Go4iT


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2011-03-14 23:58:15
2013-10-10 15:40:00 - Re: Performance loss
If I understand you correctly, you gybed to a square run (minimising Boat Speed after the gybe) so as to reduce your performance loss (Rule 1). With the performance loss then >93% you hardened up to optimum negative VMG without incurring any additional penalty (rule 3).
I am lucky to be within a minute of you as I slammed my boat into the gybe with a penalty I carried most of the way down the East Coast of the island.
Thanks for the education.

--- Last Edited by Go4iT at 2013-10-12 07:12:16 ---
Posted by
Rod


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2013-10-10 18:52:42 - Re: Performance loss
In view of some comments on the chat regarding this discussion of the Perf Loss problem, I would like to clarify my position. I did not know about the "93% Rule" before now, although I have both inquired and commented upon the problem several times over the last 2-3 yrs.
'hmm' obviously did know, as he has stated it here. But I do ask--"How did he know?" ---unless he had read the code or been told by someone who HAD read the programming code. How many others had such private knowledge? I know that I 'sail' here as precisely as I can, yet find others achieving speeds of which I seem incapable.
Yours, for a level playing field,
Rod.
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
RainbowChaser


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2013-10-10 19:03:19 - Re: Performance loss
Rod - most people find things out by practising themselves and testing the polars to see how they perform. The person who taught me to do this, NZL Spindrift, isn't often SOLing these days but he would spend ages in pre-race practice to-ing and froing and working it out. He also taught me the concept of "averaging" when calculating DCs.

Sadly, most of the hints/tips I have acquired I have forgotten through lack of use as I now spend all my time doing Admin type stuff.

Aaron, for example, made copious notes on each race - that is why his "new" GUI has a notes function associated with it.

A lot of finding out about SOL isn't stuff that anyone is acquiring secretly, most of it is in plain sight and, you are right, it would be great to have tips/hints all listed.... maybe you would do this.. act as a scribe here for any/all the hints/tips you have acquired through being on SOL and asking questions?

As for the perf loss "thing"? I didn't know it either and, if I hadn't arrived in chat when I did, I still wouldn't!!

That's why I would like to see info shared in the Forums...

PLUS

I'd also really like folks to read the Manual... there's a LOT of information there and most think "I know how to SOL I don't need to read it"... <eyeroll>
Posted by
Rod


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2013-10-10 19:37:04 - Re: Performance loss
I had never heard of "averaging" as any part of setting DCs. My DC setting experience has suggested:-
1. Never trust the next Wx---set your alarm clock and get out of bed.
2. Never set a DC that that includes a tight turn around a headland---you will always turn short, and spend several hours on the rocks, until you obey point (1.) above...
3. Never trust a TWA course beyond the Wx change time--again, get out of bed.
4.Get yourself a kitchen timer and set it a minute or so BEFORE anything is supposed to happen, and be there to supervise.
5. No matter how long the race is, sit constantly in front of your computer and adjust your course every few minutes--when you do, you will ALWAYS find that you are going slightly slower than you could be, and are therefore LOSING.
6. Sleep, Work, Meals, Errands, medical emergencies, etc.etc. are not conducive to fast SOLing, so don't do them......
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
RainbowChaser


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2013-10-10 19:46:59 - Re: Performance loss
I'll try and find my handwritten notes that I made back in 2009 when Spindrift told me how to calculate reasonable "longhand" DCs.

Gist is using the wx slider, take readings of wind speed and direction over DC-able period.. then average them, from this you will derive likely BS and on time/distance you can set reasonable DCs.

But you are probably doing that already?

I just sail my own boat here on SOL... probably because I don't have time to look at what others are doing. If someone makes a massive leap in performance or results, i am interested to learn why/how it might be, but otherwise accept that if I only change course a few times a day and miss wx updates then I get the results I deserve.

But I also accept that while bright in my own way, I don't have a lifetime of sailing experience, I don't have time to spend even working out best-average DCs, I am probably not as smart as many sailing here, esp the top performers, so I don't expect to sail as well as any one particular other person.

As an individual I am competitive, have always been, so it is quite galling to perform so badly, but set in context of my health, my SOL Admin current workload and the complete lack of spare "brain", I just have to accept my results are mediocre at best.

One day, when the new organisation is in place, and I have little in teh way of workload, I may have to accept that my results are because I am not that good!! hehehe Until then, I am wishfully thinking that they will and can improve :-)

BUT

you didn't say anything about being our scribe for tips/hints? picking up ideas where you see them in chat etc? What say you?

_____________

--- Last Edited by RainbowChaser at 2013-10-10 19:50:07 ---
Posted by
hmm


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2013-10-10 20:24:48 - Re: Performance loss
Rod, my point on this posting is to share knowledge so that SOL would be a level playing field. I could have of course just chosen to be silent but I happen to believe in fair game.

I obviously have access to the code but to learn about the 93% rule you don't need to have access to it. You just have to turn your boat when having less than 93% performance to notice that the performance won't drop any further. I believe many people knew at least that there is a limit of more loss near 90% so I found it fair to share the information here to everyone.


Posted by
Rod


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2013-10-10 21:02:50 - Re: Performance loss
I fully accept your explanation, and had no intention of accusing anyone of 'intentional unfairness'.
It is a fact that I had never heard of 93%, and do not think that any normal experimentation would have derived that situation. I did experiment with 'stepping' around a turn in small increments, but found that the perf loss was, as expected, cumulative. I once tried running down the English Channel while staying in the center where the wind speed was greatest, and the perf loss caused me to lose ground steadily.
In radio sailing, we all know that "tacking is slow", (our small boats do not have much momentum), but gybing is quick and results in only small loss of speed.
It would have required a rather sophisticated research program to test tacks and gybes in two 'steps' of varying angles to derive the 93% rule. This would, I think, be something more than the average SOLer would think to set up himself---unless he suspected that such a phenomenon existed.
I think you will agree that there is nothing obvious in sail boat performance that would even suggest that a 'two-step' tack or gybe should be faster overall than any 'single step' turn.
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
K3 (Bernd)


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2013-10-10 22:31:34 - Re: Performance loss
I have no access to the code and it would be useless for me if I have :)
The limit of performance loss is easily to see, when you ping-pong narrow channels by DCs. You will stay near 93% all the time and you will be 7%+bbq-time behind the leaders at the finish.
I want a performance loss limit for my IRL-boat and for my personal human performance loss too :)
Ciao
Bernd (K3)


Posted by
kroppyer


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2010-02-05 15:25:55
2013-10-10 22:46:33 - Re: Performance loss
It's doable to find these rules just by trying, however it's a huge help to have a little head start like this.

I always thought performance loss depends on the boat-type, and possibly on the wind speed. But the boat-type doesn't matter, and it's not windspeed, but boatspeed that determines performance loss. It would've taken a long time to figure that out.

I think I would've found the 93% rule if I was trying to figure out how performance worked. I've noted before that, when I was tacking and gybing once or twice a minute, performance was always 92%/93% or a little lower. It never got as far down as I expected.

I want to put performance loss and recovery into spinnacer, and maybe there's gonna be more I will be putting into this program. As I'm doing that, I'm trying to find the exact formulas SOL uses. I have no problem sharing these formulas, so following RC ("it would be great to have tips/hints all listed"), should I prepare to make a list of these formulas? With possible ways to use/misuse them? Should I aim to describe them so that everyone understands, or so that they're exact, correct and unambiguous?

Be aware, admins, I've heard you don't want the entire working of SOL open for public? Then at what point should I stop publishing the formulas behind SOL? (RC/hmm, this might overlap with the mail I will send you)

Anyway, thanks for sharing this hmm!

EDIT, after reading k3's post, I wondered, what exactly happens with performance if beached (how much does it drop)? It's easy to find out, but easier if someone just tells it.

--- Last Edited by kroppyer at 2013-10-10 22:48:59 ---

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