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Board » Technical Discussion » Performance loss

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Posted by
javakeda


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2013-03-01 03:18:22
2013-12-20 12:55:52 - Re: Performance loss
Kroppy,

Thank you for your work.

How are we to read the X-axis in the tack/gybe graph?
In particular, is this the initial BtSpd?
And, if so, don't we need to walk up the BtSpd value to the PERF curve to determine distance lost?

Need just a little more help here.


--- Last Edited by javakeda at 2013-12-20 13:17:58 ---
Posted by
A2


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2009-10-26 00:39:42
2013-12-20 14:32:53 - Re: Performance loss
Really nice work with these new graphs. Could you also include one with Time as an Axis to show how long until full recovery for a range of boat speeds as well ?

--- Last Edited by A2R at 2013-12-20 14:35:47 ---
None so blind
Posted by
Rod


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2010-06-24 22:30:48
2013-12-20 15:31:11 - Re: Performance loss
One thing worries me about this current work on Performance Loss----The original calculation was apparently included in the programming to prevent unlimited and frequent tacking or gybing, which would be unrealistic.
However, the equations chosen set an equally unrealistic scenario, in which a yacht could be tacked or gybed with the speed falling by MORE than 7%, without the speed decreasing for additional turns. Yet if the speed fell by less than 7% in the first turn, an additional turn would cause an additional speed decrease.
This is not reasonable. If a yacht is tacked or gybed back-and-forth repeatedly, IRL, the speed will drop almost to zero.
The recovery from the performance loss depends more upon the weight of the boat in relation to its sail area, rather than to the ultimate speed that the hull can attain.
I mention these things because some people are obviously expending a lot of time and energy to clarify the existing Perf Loss calculations, when perhaps the original equations should instead be modified to reflect a more realistic model of IRL yacht performance.
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
2013-12-20 19:42:24 - Re: Performance loss
Rod

The performance model is not realistic, I agree.

HOWEVER, the model effectively prevents tacking, gybing and hopping with an unrealistic frequency.

Something that is realistic: people that put time and effort in analysing the manoeuvres are able to execute the manoeuvres slightly better in some cases. The difference might be even bigger in reality than in SOL.

As far as I'm concerned, a better (more realistic) performance model does not have a high priority, there are a lot of other improvements that contribute to a more realistic experience.

This brings us to the unanswered question of Klyvarn: what can we do in designing a new performance model? And how will SOL (and it's community) react to a proposition for a new model?

I think we can brainstorm what we want about a new model, but the current model is good enough not to have any hurry.

--- Last Edited by kroppyer at 2013-12-20 19:43:00 ---
Posted by
A2


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2013-12-20 20:18:19 - Re: Performance loss
I agree that the programming resources required to implement any change is not a simple undertaking.

Transparency in how the inherent behavior of your boat is affected by this penalty is what we should strive for to put us all on an equal footing.

Realism is a high minded Ideal but practical considerations will be the final arbiter.

Should that day arrive when these issues are addressed I propose that instead of Performance Loss we should call this a "Momentum Module" such that when pointing up performance can go higher than 100% for an appropriate length of time as well.
None so blind
Posted by
javakeda


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2013-03-01 03:18:22
2013-12-20 22:12:22 - Re: Performance loss
I remember PERF values >100%. That was the approach that VORG used. VORG was my first virtual sailing environment.

My gut feel is that PERF values >100% help the SOTP skipper and the mobile skipper by penalizing the skipper who is making frequent course "corrections" -- often software-generated.

I like the concept, but am concerned about its application when there is a significant and protracted wind shift.

This should be a great topic for on-going discussion.
Posted by
A2


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2013-12-21 02:26:34 - Re: Performance loss
IRL I neither sail boats nor write software so please excuse my naïveté.

My concept is a transition based model determined by 2 variable coefficients that reside with each boat's polar csv file.

I imagine that boats take time to get up to speed as well as coast down when changing TWAs so one function would be momentum & the other time.

A Momentum coefficient of 1.0 would represent a linear transition & Time its duration. Momentum greater than 1 would be slightly convex & less than 1 concave along with its duration either of which could be defined by the type of maneuver undertaken.

Initially all boats could use identical coefficients, no different than it is now, but would allow for future development thereby giving each boat distinctive characteristics.

Even small nuances would cause influential separation of our fleet over the course of a race using existing composite polars.



--- Last Edited by A2R at 2013-12-21 06:38:01 ---
None so blind
Posted by
Rod


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2013-12-21 15:26:34 - Re: Performance loss
There seems to be some worry that I am overly concerned with realism, and that this, in some way, interferes with successful racing. While SOL is definitely a "game", nevertheless it also acts as instruction in "Introductory Ocean Navigation for Sailing Yachts".
As a long time educator, I am always very aware that I shouldn't teach some concept that is wrong merely because it is convenient, easy or fashionable.
Even in this "game", therefore, I think that the performance of a yacht while changing course, tacking or gybing, should be represented as accurately as possible, just as much as it is in it's normal performance as represented by the many different Polar Diagrams that we use in each race.
One standard Polar Diagram for all yachts would be as wrong as one standard Perf Loss equation.
While a clipper ship and an 18 ft Australian skiff may both attain speeds of 15 knots, their perf loss and recovery would be very different.
I would suggest therefore that the "Dev Dudes" be requested to re-think this part of the SOL program. "IF" they do so, much of this effort to clarify the existing 'Perf Loss' problem would be wasted.

--- Last Edited by Rod at 2013-12-21 15:36:42 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
Klyvarn


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2013-12-21 16:33:47 - Re: Performance loss
I can see there are a few SOLers really engaged in the performance model.

In SOL of today, there are obviously a lot of matters, more unrealistic than the performance model. What can it be ?

Is it an improvement of realism to let the SOLers do high numbers of turnings?
Erasing lines of programming code might also make an improvement.


Posted by
Rod


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2013-12-21 18:45:36 - Re: Performance loss
On the contrary! I would suggest a perf loss equation based upon the weight of the boat and it's speed. A light boat will obviously slow more quickly than a heavy boat, but will recover its speed (Accelerate) more quickly too. A heavy boat will take much longer to slow down, so will lose less speed during a turn/tack/gybe, but will also regain speed much more slowly.
On further consideration of the overall problem of the perf loss calculation, I have come to the conclusion that the fault lies with that 93%/7% divider. It is that divider that is un-realistic, and the main cause of the problem. If that 93/7 divider was eliminated, repeated turns in a short time would reduce boat speed close to zero---which is, after all, the ONLY purpose in having the perf loss calculation at all!!
If it breaks, it's not strong enough--if it doesn't, it's too heavy.

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