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 » Technical Support » wrong VMG

Page: 1 2 3 Next

Posted by
dunbur


Users avatar

Posts
9
Registered at
2009-02-18 06:03:58
2009-04-20 23:30:37 - wrong VMG
I think that has been mentioned before: the VMG is still showing wrong. At least for me (firefox 3.0.8 on linux). I think it is wrong since I rounded the mark at Fernando de Noronha. Before that I had the impression it was show the VMG directly to Boston (also not quite appropriate), but now the VMG is calculated as if the next mark would be directly upwind rather than towards Boston. See the attached screen shot. I am sailing with a TWA of 90° and the VMG is 0.00knts though I am pointing roughly to Boston (and the boat speed is not 0knts).
Attachments
Posted by
kalle


Users avatar

Posts
413
Registered at
2007-06-01 09:58:04
2009-04-20 23:50:47 - Re: wrong VMG
As said before, VMG is velocity made good *against the wind*. Waypoints has got nothing to do with VMG in ocean racing.
Posted by
dunbur


Users avatar

Posts
9
Registered at
2009-02-18 06:03:58
2009-04-20 23:56:57 - Re: wrong VMG
Thanks for the quick answer. And sorry that I missed the answer earlier.

May I turn that into a feature request, then. I see that VMG to way points is of limited usability, if you have to navigate around weather systems, but it would still be nice to have and very useful in shorter in-shore races.
Posted by
Chappo


Users avatar

Posts
53
Registered at
2009-04-17 12:00:35
2009-04-21 01:27:29 - Re: wrong VMG
So VMG is only relevant when trying to find the best course when sailing upwind. Once reaching and running, SOL's VMG is not relevant and you need to calculate VMG with reference to the next mark or turn point. This is done by a calculation using BS and the cosine of the difference between your CC and direct course to the next mark.
Posted by
jakob


Users avatar

Posts
364
Registered at
2007-09-04 10:05:30
2009-04-21 05:08:31 - Re: wrong VMG
Well, SOLs definition of Vmg is relevant both for upwind and downwind conditions e.g. whenever you want to maximize your speed component against or along the wind direction. A negative Vmg indicates you have a speed component downwind.
...one of the guys behind the game...
Posted by
Chappo


Users avatar

Posts
53
Registered at
2009-04-17 12:00:35
2009-04-21 05:53:47 - Re: wrong VMG
Yes I agree a -ve VMG shows a downwind component and I can see that if your -ve VMG matches your BS, then you are dead square downwind. How would you use that to maximise speed once close or broad reaching and heading for a turn point or finish. It seems to me you have to incorporate the bearing to the buoy or finish in your calculation to get the best VMG. I have a simple Excel worksheet that does that for me.
Posted by
jakob


Users avatar

Posts
364
Registered at
2007-09-04 10:05:30
2009-04-21 06:19:58 - Re: wrong VMG
You are right, the Vmg does not help you in all situations. We will most likely not implement any other form of Vmg/Vmc e.g. since it will be unclear what it means. Consider the example when you are approaching the finish-line. Shall Vmc be the speed to closest part of line, to mid point of line or maybe the part of the line that you can reach in minimum time? The latter would require route optimization...
...one of the guys behind the game...
Posted by
Chappo


Users avatar

Posts
53
Registered at
2009-04-17 12:00:35
2009-04-21 06:45:01 - Re: wrong VMG
Yes I agree Jakob, you would need to input a bearing. SOL should leave some work for the sailors and not make it too mechanical like some aspects of Virtual Regatta when assisted by VR routing software. SOL weather is far more realistic as is the invisibility of the competitor's performance.
Posted by
dunbur


Users avatar

Posts
9
Registered at
2009-02-18 06:03:58
2009-04-21 06:56:32 - VMG to waypoint
I don't quite agree. Of course one need a bearing. The bearing is quite easy to get. To the next way point. The argument with the finish line is rather weak. If you are far away, the exact point on the line does not matter. Just default to the midpoint as it is on the red line which connects all the way points. Then the VMG get useful. Currently, I fing the VMG not useful at all. When is the course really upwind? And then the VMG upwind is easily estimated. Just add horizontal lines to the polar and you have it.
Posted by
kalle


Users avatar

Posts
413
Registered at
2007-06-01 09:58:04
2009-04-21 08:05:54 - Re: wrong VMG
It must be added that VMC, while being the instantaneously best speed against a waypoint, is almost never the best course. The best course is determined by intelligent routing w.r.t the weather forecast.

Page: 1 2 3 Next

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Tasman Double 2025 - Hobart to Sydney

With Hobart astern and celebrations behind them, the fleet turns north for Leg 2 of our Tasman Double Series. Over 625 nautical miles, our SOLers aboard their mighty Super Maxi 100v2s return to the Tasman Sea, where shifting weather, demanding seas, and nonstop decisions shape every mile. The race back to Sydney rewards those who read the conditions best, manage their speed wisely, and stay focused until the final approach.
Race #2000
INFO by brainaid.de
Super Maxi 100v2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: TD - SYC
Race starts: Jan 02nd 02:00 Registration Open!
▶ Flash
GO TO RACE

Cape Town to Rio 2026

Welcome to South Africa and RCYC's classic transatlantic Cape2Rio Race from Cape Town, South Africa, to Rio de Janeiro, Brazil. First run in 1971, this run is buddied with the IRL, Cape2Rio 2025 arranged by the Royal Cape Yacht Club with the cooperation of the
Iate Clube do Rio de Janeiro Despite this being announced the 2025 race (starting dec. 27) it is the 2026 SOL championship kickoff. This virtual version, will be raced once again in Mark Mills' 74ft speedster, the stunning C2R74.
Race #1996 INFO
by brainaid.de
C2R74 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
OCQ1 - OCCH - SUPBUD - SYC
Race starts: Dec 27th 12:00 Registration Open!

▶ Flash
GO TO RACE

ORCV Melbourne to Hobart 2025

Welcome to the legendary Westcoaster, a true test of endurance and seamanship that’s challenged sailors for over 50 years! Spanning 435 nautical miles, this iconic race takes the fleet from Melbourne, across the wild Bass Strait, and around Tasmania’s rugged west coast to Hobart. Organized by the Ocean Racing Club of Victoria, this year our SOLers will be racing the sleek and powerful Dehler 46—a fast, elegant regatta cruiser built for both speed and adventure. Get ready for an unforgettable offshore classic!
Race #1952
INFO by brainaid.de
Dehler 46 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Dec 27th 02:30 Registration Open!
▶ Flash
GO TO RACE

Tasman Double 2025 - Sydney to Hobart

Christmas in Summer? Indeed! Kick off the first leg of our two-leg Tasman Double series in the classic 625nm Sydney to Hobart race, this year in the upgraded SuperMaxi 100v2. Inspired by Neville Crichton’s legendary Alfa Romeo II and her near-sister Wild Oats XI, these yachts blaze across online and real-world waters alike. Feel the thrill even in storm-force winds as you tackle the Tasman Sea—dock in Hobart victorious, or at least in time for a well-earned post-Christmas drink!
Race #1953
INFO by brainaid.de
Super Maxi 100v2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: TD - SYC
Race starts: Dec 26th 02:00 Registration Open!
▶ Flash
GO TO RACE

Valletta Sprint 2025


We invite you once again to this SOL classic around the Middle Sea, departing from and returning to historic Valletta. Loseley modelled on an IRL classic often sponsored by a luxury wristwatch purveyor, our c 600nm course takes us north as far as Stromboli, then west of Sicily and south to Lampedusa and back to Valletta probably via the strait between Malta and Gozo. This year we will race it all in very Meddy Dufour 40’s!
Race #1949
INFO by brainaid.de
Dufour 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
RACE CLOSE: Monday,
December 29 at 2300 UTC.
Race starts: Dec 20th 11:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member KaSToR
  2. Sailonline Yacht Club Member WRmirekd
  3. Sailonline Yacht Club Member CriticalHippo
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member bonknhoot
  6. Sailonline Yacht Club Member vida
  7. Sailonline Yacht Club Member CollegeFund
  8. Sailonline Yacht Club Member Sax747
  9. Sailonline Yacht Club Member sassy63
  10. Sailonline Yacht Club Member Adlaem

View full list

Series

Mobile Client

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

The mobile client