Sailonline.org - Online Sailing

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!

Tweets by @sailonline

Board » General Discussion » Wrong Speed VMG

Posted by kalle Posts 413 Registered at 2007-06-01 09:58:04	2009-02-04 17:55:13 - Re: Wrong Speed VMG
	There is no such thing as 105% performance
Posted by AGage Posts 411 Registered at 2008-12-27 10:31:57	2009-02-09 04:44:56 - Re: Wrong Speed VMG
	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... __/)/)_/)__
Posted by jakob Posts 364 Registered at 2007-09-04 10:05:30	2009-02-09 07:10:33 - Re: Wrong Speed VMG
	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...
Posted by AGage Posts 411 Registered at 2008-12-27 10:31:57	2009-02-12 03:32:36 - Re: Wrong Speed VMG
	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... __/)/)_/)__
Posted by jakob Posts 364 Registered at 2007-09-04 10:05:30	2009-02-12 06:20:56 - Re: Wrong Speed VMG
	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...
Posted by Eddie C. Dost Posts 57 Registered at 2008-08-23 11:40:29	2009-02-12 09:51:39 - Re: Wrong Speed VMG
	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 perf.gif (3.6 KB)
Posted by Schakel Posts 183 Registered at 2008-12-19 09:19:00	2009-02-12 09:58:41 - Re: Wrong Speed VMG
	Eddie C. Dost said @ 2009-02-12 09:51:39: 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
Posted by K3 (Bernd) Posts 130 Registered at 2008-08-25 12:34:07	2009-02-12 09:59:31 - Re: Wrong Speed VMG
	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.
Posted by jakob Posts 364 Registered at 2007-09-04 10:05:30	2009-02-12 10:36:39 - Re: Wrong Speed VMG
	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...
Posted by AGage Posts 411 Registered at 2008-12-27 10:31:57	2009-02-12 13:12:18 - Re: Wrong Speed VMG
	Schakel said @ 2009-02-12 09:58:41: And here I was thinking I could just wing it. Philip ........................... Just a bit of physics: s = 1/2at^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:

Kapiti Chetwodes Race 2024

For only the second time in SOL history, we have the pleasure of inviting you to the Kapiti Chetwodes Race, held in the Cook Strait region. Organised IRL by the Royal Port Nicholson Yacht Club from Wellington in New Zealand. The approximately 160nm long route, full of turning points, will take us from the bay at RPNYC around the islands of Somes, Kapiti and Chetwodes and back to the finish line at RPNYC. We have only a 26 ft Albin 79 yacht at our disposal. All this means that we will have a lot of fun, so fair winds!
Race #1864
INFO by brainaid.de
Albin 79 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ4 - ARCH - SUPSOL - SYC
Race starts: Nov 25th 17:00 Registration Open!

▶ Flash

GO TO RACE

Raja Muda Selangor 2024 - Penang to Langkawi

Welcome to the third and last online race of the Raja Muda Selangor International offshore series – a 70nm final trip further north again up the Malacca Strait from Penang to the exotic island of Langkawi, and again in Ker 40s.
Race #1871
INFO by brainaid.de
Ker 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: RMS - SYC
RACE CLOSE: Monday,
November 25 at 2300 UTC.
Race starts: Nov 21st 04:00 Registration Open!

▶ Flash

GO TO RACE

Raja Muda Selangor 2024 - Pangkor to Penang

Welcome to our second online offshore race in cooperation with Raja Muda Selangor International – an 80nm trip from Pangkor north to Penang up the Malacca Strait, again in Ker 40s.
Race #1870
INFO by brainaid.de
Ker 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: RMS - SYC
RACE CLOSE: Saturday,
November 23 at 2300 UTC.
Race starts: Nov 18th 04:00 Registration Open!

▶ Flash

GO TO RACE

Two Oceans Doublecross TIMED Race 2024

Our November Timed race takes us to Cape Town near where the Atlantic and Indian oceans meet. Our ride is a beautiful ketch, the Archer 78. Starting at Cape Town, we’ll round Robben Island, then head south to round Cape Point, up around Seal Island before heading north to round Dassen Island before returning to Cape Town. This is a TIMED race, so you may RE-REGISTER HERE to try again, after finishing a run. You will have 13 days and 11 hours to test your skill and decision making after the race opens.
Race #1872
INFO by brainaid.de
Archer 78 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ4 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
30 November at 23:00 UTC
Race starts: Nov 17th 12:00 Registration Open!

▶ Flash

GO TO RACE

Nassau to Bodo 2024

Prepare for the grand finale - the 6th and concluding leg of the RTW challenge, an odyssey from Nassau in the Caribbean to Bodø in Norway. Embracing a journey of 4000 nautical miles, this leg promises an exhilarating 18-day voyage. It also heralds the November installment of our prestigious Ocean Race Championship. Embark on a voyage of a lifetime, where prowess, tactics, and camaraderie unite in the pursuit of triumph. We eagerly await your presence at the starting line! May the winds be ever in your favor.
PRIZE: SMPF
Race# 1866
INFO from brainaid.de
Swan 65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ4 - OCCH - RTW - SUPSOL - SYC
Race starts: Nov 11th 11:00 Registration Closed

▶ Flash

GO TO RACE

Go to race archive

SYC Ranking

View full list

Series

Mobile Client

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

The mobile client