Facebook

Login

Support Sailonline

If you haven't already - join the SAILONLINE YACHT CLUB!

Please also consider making a donation - all amounts are greatly appreciated!

Board » General Discussion » Wrong Speed VMG

Page: Previous 1 2 3 4 Next

There is no such thing as 105% performance :)
I have read Jakob ask if anyone has ideas on how to implement the performance loss on manouvers. How do you currently implement it? If you could provide something like a pseudo algorithm would be good. I do have some ideas on this, but it could simply be a variation on what you already have in place.
I help develop the client interface for the best online ocean racing sim there is... __/)/)_/)__
Well, the current model determines if the maneouver is a tack or a gybe or just a minor change in twa (dTWA is the twa change).If (tack or gybe) {e = 1.0-self.bs/200.0} else {e = 1-abs(dTWA)/25.0}. perf = perf*e. However if perf<0.93 no further maneouver loss is done. something like that.
...one of the guys behind the game...
OK firstly, I do not sail large boats so I am unsure if any of this is realistic but...
From what you wrote Jakob, the faster your bs, the greater perf loss, whereas I would have thought the opposite would be the case, that perf loss is inverse to bs?
And I asssume you also use abs(e), in cases where dTWA > 25? This part seems a bit off, as a dTWA of 50 would result in 0 loss and 25 in maximum performance loss. Also a bear away takes time reach full bs, whereas pointing up doesn't...

What determines the rate at which performance is re-establised, as this seems to be the issue that concerns people.
In my sailing experience gybes usually return to full bs quicker than tacks?
Perhaps making it a function of TWS would work? Or a function of bs and TWS as that would simulate acceleration?

Maybe I will play with some code and try some different algorithms for all this.
How simple do you wish to keep it? ie, should a manouver that changes from headsail to spinnaker (and back) be penalised more than simple course change or tack/gybe? Obviously you need a quick algorithm for this...

As I said above... I have had little experience on large yachts, so all of this could be completely unrealistic!

also, to StuArt: As far as I know, racing rules prohibit techniques where you gain performance advantage from tack/gybe manouvers... In dinghies for example, it is sometimes possible to gain speed through a tack (but very hard to do) and this is prohibited [although very hard to prove in protest ;-)]...
I help develop the client interface for the best online ocean racing sim there is... __/)/)_/)__
Hi. You are very welcome to try some new algorithm for speed recovery. The current models are designed by myself and Magnus Woxén, a very experienced yachtsman with 3 laps around the globe and a place on the Ericson 3 from Qindao. So some thought is put into this. :-)
...one of the guys behind the game...
Maybe a different view on the performance loss effect helps to be less scared. What you are interested in is not the % performance or the duration of recovery, but the overall loss against the other boats.

In the example above I will use worse case numbers I have seen sailing here.

Assume we tack at a BS of 10kn and experience a performance drop to 90% with a recovery time of 20minutes. In almost all cases I have seen the loss is less and the recovery faster.

I use the term e for performance below, so with 90% performance e = 0.9 and the term t_r for recovery time in hours so with 20 minute recovery time t_r ~ 0.333

The distance you travel with the boat is s = v * t. The distance you loose when assuming linear recovery is s_l = v * (1 - e) * t_r / 2
which is s_l = 10 * (1 - 0.1) * 0.333 / 2 = 0.167

The overall loss in this extreme example is 0.167nm or with t_l = s_l / v this is 60 seconds.

These figures sound very reasonable, as we are not sailing in calm waters and stearing up to the new wave pattern and optimizing trim on the new tack takes its time.

Also the loss of 60 seconds or 0.167 nm does not introduce a penalty as high as "felt" by the 90% and 20 minutes recovery. It will only hurt in very tight racing situations where your opponent does not have to tack anymore. But then again you made some mistake earlier by not covering your opponent. ;)

All in all I think the algorithm is reasonable and I hope I could take away some of the fear caused by looking at the performance figure or the recovery time alone. I have attached a quick drawing showing the amount of loss.
_/)_/)_/)
The sea is lovely, dark, and deep, But I have promises to keep, And miles to sail before I sleep, And miles to sail before I sleep.
Attachments
I use the term e for performance below, so with 90% performance e = 0.9 and the term t_r for recovery time in hours so with 20 minute recovery time t_r ~ 0.333

The distance you travel with the boat is s = v * t. The distance you loose when assuming linear recovery is s_l = v * (1 - e) * t_r / 2
which is s_l = 10 * (1 - 0.1) * 0.333 / 2 = 0.167

The overall loss in this extreme example is 0.167nm or with t_l = s_l / v this is 60 seconds.

And here I was thinking I could just wing it. ;-)

Philip
I made some experiments with performance loss during the last practice session. I edited 10 gybes with a delta-twa of 178 deg in steps 0,05 h. The crew didn't liked me afterwards.
The minimum performance after the gybes was about 92 %. The effect on boatspeed was only about 9 %. So nothing to worry about, my own mistakes have always bigger effects.
We introduced this performance loss not to punish normal sailing maneouvers but to prevent boats to tack e.g. once every minute during hours just to ride on a tws that optimizes vmg. The prformance loss implementation succeeded in preventing that behavior and is as stated above not a problem for normal maneouvers. Thanks all for caring!! :-)))
...one of the guys behind the game...
And here I was thinking I could just wing it.

Philip
...........................
Just a bit of physics: s = 1/2*a*t^2 (s = distance, a = acceleration, t = time) and differential calculus... Yeah... brainaid has an appropriate name :-)

...........................
Jakob: I wasnt actually complaining myself about the way things are with the loss, just responding to others posts. And I certainly didnt mean to imply that thought had not gone into how it is implemented, you have obviously been developing this simulation for quite a while, just pointing out things that seem to *me* not quite right, based on the algorithm you posted. As I said, I dont sail ocean racing boats, so have no real idea how they perform... I was simply extrapolating from my own sailing experience. I was also unaware that it was implemented such as to discourage abuse as you say...
Having said that:
a) any performance loss should prevent abuse, yes?
b) do Ocean Racing Yachts really loose upt0 .15nm on a single tack in 10knots? I am asking seriously... I dont sail them... I suppose you dont do alot of leebow manouvuers! :-)
I help develop the client interface for the best online ocean racing sim there is... __/)/)_/)__

Page: Previous 1 2 3 4 Next

Please login to post a reply.

Races

Next Race: 00d 00h 00m


Current Races:

Galveston to Galway 2022
For the second time, we will be able to test our navigational skills in this massive ocean race across the Gulf of Mexico and the Atlantic Ocean! You can navigate the 4980 NM to Galway, Ireland in any direction, of course within the designated race boundary area. Your only task is to reach the finish line in the best place, preferably at the highest podium. Prepare your C2R 74 well for the race and take advantage of all its opportunities. Good luck!
PRIZE: SMPF
Race #1592
INFO by brainaid.de
C2R 74 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
OCQ3 - OCCH - SUPSOL - SYC
Race starts: Jul 09th 18:00 Registration Open!

▶ Flash
GO TO RACE

Sines to Bermuda 2022
Another race with the finish line in Bermuda. This time we will start from Sines in Portugal. There is 3213nm ahead of us across the Atlantic Ocean. Previously, this race was one of the stages of the Rendez-Vous 2017 Tall Ships Regatta. This time we will use this route in the race played as part of the SOL All Round Championships and we will use our Orange 125 fast catamarans to cover it. We invite you to participate.
Race #1591
INFO by brainaid.de
Orange 125 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ3 - ARCH - SUPSOL - SYC
Race starts: Jul 04th 04:00 Registration Open!

▶ Flash
GO TO RACE

PIC Insurance 2022 - Race 1
Welcome to Auckland, New Zealand! Sailonline is happy to provide our SOLers with the virtual version of the brilliant three-race SSANZ two-handed series which will be sponsored by PIC Insurance Brokers this year. We will be racing around the beautiful waters of the Hauraki Gulf off New Zealand’s North Island. Our first race of the Series is a 50-miler out to Motuora Island and back. Our direct competitors as always in our Young 88s will be the real racers of the Young 88 Association who will be participating in the Railblaza fleet in the real life race!
Race #1598
INFO by brainaid.de
Young 88 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SPRCH - SPRQ3 - SUPERSOL - SSANZ - SYC
RACE CLOSE: Wednesday,
July 6 at 2300 UTC.
Race starts: Jul 01st 21:15 Registration Closed

▶ Flash
GO TO RACE

Geraldton to Cape Town 2022
A race in the Southern Indian Ocean is always entertaining, especially in a Riptide 50. Traditionally the course would be West to East, to take advantage of the prevailing winds, but this time the SRC is challenging us to an E-W course, from Geraldton in Western Australia to Cape Town in South Africa. A brief 4800nm!
PRIZE: SMPF
Race #1575
INFO by brainaid.de
Riptide 50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
OCQ2 - OCCH - SUPSOL - SYC
RACE CLOSE: Thursday,
July 14 at 2300 UTC.
Race starts: Jun 12th 05:00 Registration Closed

▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member WRmirekd
  2. Sailonline Yacht Club Member rafa
  3. Sailonline Yacht Club Member Pit8008
  4. Sailonline Yacht Club Member GREATSKUA
  5. Sailonline Yacht Club Member FreyjaUSA
  6. Sailonline Yacht Club Member Sax747
  7. Sailonline Yacht Club Member Satori
  8. Sailonline Yacht Club Member HappyHour
  9. Sailonline Yacht Club Member Vida_Maldita
  10. Sailonline Yacht Club Member TarassBoulba

View full list

Series

Mobile Client

SYC members have the benefit of access to our mobile/lightweight web client!

The mobile client