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:

Comoros Cruise TIMED Race 2024

It’s time to sail our Lagoon 55 luxury catamarans approximately 232 nm in a figure 8 around the Comoros Islands in the Indian Ocean. We start in the capital Moroni, round the islands of Mohéli and Nzwani and then return to Moroni. 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 #1861
INFO by brainaid.de
Lagoon 55 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ4 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
26 October at 23:00 UTC
Race starts: Oct 13th 12:00 Registration will open soon

▶ Flash

GO TO RACE

Paros to Naxos Sprint 2024

This month’s first sprint race sees us head to the Greek Isles as we complete a 30nm PYOC to Naxos Island in our Class 40’s.
Race #1849
Chart from brainaid.de
Class 40 POLAR
WX Updates: 0430 / 1030 / 1630 / 2230
Ranking:
SPRQ4 - SPRCH - SUPSOL – SYC
Race starts: Oct 12th 21:00 Registration Open!

▶ Flash

GO TO RACE

Ushuaia to Nassau 2024

We extend a warm welcome to the 5th leg of the RTW challenge, a thrilling journey from Ushuaia in the Land of Fire to Nassau in the Caribbean. It also marks the October edition of our esteemed Ocean Race Championship. Covering a distance of 6300 nautical miles, this leg is anticipated to span approximately 29 days. Join us for an unforgettable adventure on the high seas, where skill, strategy, and camaraderie converge in the pursuit of victory. We look forward to seeing you at the starting line! Fair winds and following seas.
PRIZE: SMPF
Race# 1842
INFO from brainaid.de
Swan 65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ4 - OCCH - RTW - SUPSOL - SYC
Race starts: Oct 07th 11:00 Registration Open!

▶ Flash

GO TO RACE

Halifax to Hooper Bay 2024

And now it’s Autumn in the Arctic, the sun is permanently below the horizon, but during the day, from c 0900 to c 1700 local time, there is some twilight – nautical twilight, not to be confused with civil twilight which is brighter. Having receded all summer, ice is starting to return to the numerous straits and bays of Canada’s North West Passage. High time then to set off on our last leg of the High Latitudes Series from Halifax in Nova Scotia to Alaska’s Hooper Bay. It’s 3850nm and we need to hurry, so we’ll take the Pelagic 77!
Race #1781
INFOby brainaid.de
Pelagic 77 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: HLAT - SYC
Race starts: Oct 02nd 19:00 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