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:

Chesapeake and Potomac TIMED Race 2026

Welcome to the Chesapeake Bay, the sailing capital of the United States. Feast on Maryland crab cakes or crabs seasoned with Old Bay spice before sailing down the Bay aboard a Formula 18 catamaran on a 128 nm course that will take you up the Potomac River finishing at Quantico, Virginia. This is a TIMEDrace so you may RE-REGISTER HEREto try again after finishing a run. You will have two weeks to test your skill and decision making after the race opens.
Race #2032
INFOby brainaid.de
Formula 18 catamaran Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ2 - TRCH - SYC
RACE CLOSE: Saturday,
23 May at 23:00 UTC
Race starts: May 10th 12:00 Registration will open soon
▶ Flash
GO TO RACE

Tobruk to Iskenderun 2026

Welcome to the fourth of our nine races across the length and breadth of the Magical Mediterranean Sea, and the second that is not in partnership with a real-life event, this time for good reason, which we won’t get into here. From Tobruk to Iskenderun it’s 670nm in length, with the added complication that the island of Cyprus will be in your way. Hoping, possibly forlornly, for plenty of downwind sailing, we’ll take the Lagoon 55 for the voyage!
Race #1976
INFO by brainaid.de
Lagoon 55 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: MED - SYC
Race starts: May 05th 15:00 Registration Open!

▶ Flash
GO TO RACE

Tasmania to Kamchatka 2026

Welcome to yet another all-new route. Tasmania to Kamchatka, part of our Ocean Championship and also the third leg of the ROW (Round the Old World) series. Be aware of the obstacles on the way, likely to split the fleet. It's like X:mas to X:mas, crossing the same waters, navigating the same archipelagos. This second race of OCQ2 2026 will be sailed in our revised 'version 2' Imoca 60 Foil. Race #2031
INFO by brainaid.de
Imoca 60 Foil v2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - ROW - OCCH - SYC
Race starts: May 04th 11:00 Registration Open!
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

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

View full list

Series

Mobile Client

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

The mobile client