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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
2016-11-24 19:41:00 - Re: Performance loss
I hate to play the ignorant here, but at the level of my SOLing, I do not particularly care about the distance lost by tacking or gybing--they are inevitable!!!
What I need is a quick 'graphical' method of determining the perf loss I will suffer when I round a mark that I am approaching. I want to know what perf loss I will have--and if it is greater than 7% (which will reduce my perf below 93%)---what angle do I need to turn to make the first part of a two-part turn give me a perf loss of slightly less than 7%? I can then complete my turn without incurring further perf loss. This works directly as stated, only for gybes...???
You state that, when tacking, the perf loss is equal to half of the new boat speed. This is not helpful, as I do not know what my new boat speed will be until I know the perf loss. (This is a circular argument!)
What I need to know as I approach a position or a mark, at which I will tack, is a way to determine quickly if my perf loss will be more than the 7% level, and if it is, to what angle should I make the first part of my tack, so that I may complete the rest of the tack with no further increase in loss.
I realise, that whatever my total perf loss from my tack, I will pay the penalty of 'distance and time lost'--there is nothing I can do about that!!!

--- Last Edited by Rod at 2016-11-24 20:03:36 ---

--- Last Edited by Rod at 2016-11-24 20:04:25 ---
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
2016-11-24 20:22:45 - Re: Performance loss
The boatspeed that is used to calculate the performance loss after a change of tack is the boatspeed on the new course with 100% performance (this might not be clear from the document).

You want to know how much you loose when you have a choice. For example "gybe directly" vs "gybe with an extra command", or "tack every 2 minutes along the shoreline" vs "tack every 30 seconds along the shoreline". Distance lost or time lost can help with a rough estimate of how much you gain/loose with either option.

The more exact option is to look at the average VMC during the manoeuvre (as long as the time interval are the same). To use this, you need to fully understand sailing with VMC, as outlaw explains in his solfans posts.

The main purpose of having performance loss is to make skippers decide between things like "tack every 2 minutes along the shoreline" vs "tack every 30 seconds along the shoreline" and choose the realistic option because it's fastest. We've seen that the current performance model fails in this regard when the boats are on the extreme ends of the scale (AC72, DN, Square Rigger).
The current performance model has as a (in my opinion, unwanted) side-effect that the way we tack/gybe our boats can have a large influence on performance loss.

Anyway, I hope I cleared up the circular reasoning (which can actually be solved with some math, but why bother, it's not necessary anyway) and I hope you understand (to the extend you want to) the importance of "distance lost" and/or other metrics to quantify the losses the are the result of particular manoeuvres.

--- Last Edited by kroppyer at 2016-11-26 01:00:26 ---
Posted by
Rod


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2016-11-25 21:53:53 - Re: Performance loss
I am starting to follow your reasoning about the Perf loss while tacking or gybing. However, at this point in my practice, you are one step ahead of me still. So far, I am still at the stage of trying to keep my perf loss to a minimum. At lower boat speeds most of these manoevers can be carried out while still keeping the loss to 7% or less. It is only at higher speeds that a course change can result in a loss greater than 7%. My concern then becomes my efforts to reduce this loss to as close to 7% as possible by tacking or gybing in a double action, so that the second part of the action will result in no further increase in loss.
I have not yet reached the degree of sophistication where I start to worry about a choice of how much I am able to minimise the losses in a series of tacks or gybes in quick succession.
I will attempt to extend my thinking to such operations as multiple tacks along a shoreline (which I have observed being done without clearly understanding "why").

--- Last Edited by Rod at 2016-11-25 21:56:32 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
kroppyer


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2016-11-26 01:00:09 - Re: Performance loss
A series of tacks (along a shoreline) is not to minimise performance loss.

In a right shift, you are best of being the rightmost boat (within the laylines*). Sometimes a landmass is in the way of being the rightmost boat and you have to tack to keep clear. Question is, how long do you keep on sailing in the wrong direction before tacking back to the right? For this you need to know two things:
- how much am I losing by sailing in the wrong direction?
- how much am I losing by tacking?

The second one requires an understanding of the performance loss model, even when you are in no way trying to "cheat" the model with fancy manoeuvres/tricks.

One simple tactic: when your performance is enough below 93% (after beaching for example), you don't lose anything with two additional tacks to bring you more to the right: you are free to tack very quickly along the shoreline until your performance is over 93% again. The tricky thing here is to avoid another bbq, and you're usually not wining much anyway.

(* typically just outside the laylines actually, but that's besides the point here)
Posted by
Schlumpi


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2016-07-22 08:14:22
2017-01-16 05:03:49 - Re: Performance loss
Kroppyer (and others). This is a very important thread, about a topic often poorly understood by newbies - I still consider myself one of them.

Is there any timeline being proposed for the changes to PL (and recovery)? It does seem well overdue. I will not add my 2c to the "way to change" argument.

A thought I would like to add is to add some light info to the Manual in Section 1.9 - a brief explanation of what happens and how to minimise it. Perhaps a link to a page with more info. The piece Yohann wrote in his post in this thread on 2016-05-06 16:01:13 is perhaps the most elegant I have come across.

A quick "Thank you" to all in the SOL community who work so hard to maintain and improve this simulator :)

Posted by
PresentTense


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2017-05-03 02:18:44
2017-05-04 01:12:27 - Re: Performance loss
I'm new to SOL and quite frankly, this thread makes me not want to be involved. Along with another aspect that I believe exists, which is account sharing?

I understand the idea of performance being lost through a tack or gybe, but does it really make a difference to who wins or loses a real ocean race?

The fact that it is being used in the way described in this thread makes me think the whole game is broken. IMO it would be better to have no Performance Loss at all than to have people gaining a competitive advantage from abusing it. And the answer is "well, anyone can work it out and use it for themselves, so that means its okay..."
No, it's not. It's Cheating.
Posted by
kroppyer


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2017-05-04 10:39:21 - Re: Performance loss
Hi PresentTense,
Welcome to sailonline! You have very quickly discovered what I think is the worst aspect of sailonline. Performance loss usually does not really play a role in race on sailonline, but some of the shorter races (sprints/timed races), or those with special circumstances (sailing with tallships, weather that gives a large advantage to hugging the coast, etc.) sometimes bring out the worst of the current implementation of performance loss. In those cases people with a full understanding of how performance loss works in sailonline can leverage their knowledge to gain an advantage over the competition. Of course people with more knowledge and experience should have an advantage over the competition, but this type of knowledge has nothing to do with sailing, so it shouldn't give an advantage. I think everyone would agree. We need to change this.

So yes, for most of the races (esp. the ocean races) it doesn't really make a different whether or not we have performance loss. But by disabling it, there will be a small number of cases where the fastest route includes tacking/gybing every 10 seconds. Performance loss takes solves almost all of this small number of cases, but as a side effect introduces a smaller number of cases where performance loss itself has an undesirable effect on racing.

I think the current performance loss is better than no performance loss, but it could definitely do with some improvement. I'm convinced we can make performance loss better, meaning: it prevents tacking/gybing every 10 seconds in all cases and it has less side effects.

I really hope the current performance loss implementation doesn't affect your enjoyment of the game/simulation. In normal ocean racing is only very rarely that people with a full understanding of performance loss can use it to their advantage (to gain 10 or 20 seconds).

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