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:

Rommel by Balloon 2026 - Through the Sahara


Generalfeldmarschall Johannes Erwin Eugen Rommel may have been that chivalrous, gallant tank commander of legend, led astray by the Prussian military traditions of loyalty and chain of command, but one thing he wasn’t, was mad. So, let’s do it anyway – not stick to the coast and the battle for logistical superiority – but depart the oases of Siwa south west into the desert for Agadez and its uranium. And let’s go by balloon, it’s only 2500km (1250nm)!
Race #1973
INFOby brainaid.de
SOL Balloon PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: BOL - SYC
Race starts: Apr 07th 13:00 Registration will open soon
▶ Flash
GO TO RACE

Falklands to Tasmania 2026

Welcome to yet another all-new route. This next race is part of our Ocean Championship as well as the ROW series. Falklands to Tasmania, is like last year's island to island. It’s one of the longer ones 6400nm, more than half way around the world (and the Antarctica). It starts the 2026 OCQ2, and will be sailed in our Steinlager 2, contrary to prior notice.
Race #2021
INFO by brainaid.de
Steinlager 2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - ROW - OCCH - SYC
Race starts: Apr 06th 11:00 Registration Open!
▶ Flash
GO TO RACE

Gladstone Ports Corporation Brisbane to Gladstone Yacht Race 2026


Sailonline is thrilled to partner with the Queensland Cruising Yacht Club for the 2026 Gladstone Ports Corporation Brisbane to Gladstone Yacht Race! This 308 nautical mile offshore challenge follows Australia’s stunning east coast from Brisbane to Gladstone. Racing the fast and tactical Farr 40, sailors will need precision, strategy, and focus as shifting conditions test every decision from start to finish!
Race #2027
INFO by brainaid.de
Farr 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SUPBUD - SYC
Race starts: Apr 03rd 01:00 Registration Open!
▶ Flash
GO TO RACE

Rapallo to Nador 2026


Welcome to Liguria’s Rapallo, there where Zarathustra spoke - at length - to Nietzsche, for our first race of nine to celebrate all things Mediterranean - fickle winds, history and olive oil. A number of our races in this new Magical Mediterranean series will be partnership with famous real-life races, but this first race is pure fiction - 780nm in refurbed IMOCA 60s, past or through the Balearic Isles and on into the Alboran Sea, to a finish off Nador on the Maroc Mediterranean coast.
Race #1975
INFOby brainaid.de
IMOCA 60v2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: MED - SYC
Race starts: Mar 30th 15:00 Registration Open!
▶ Flash
GO TO RACE

Cross the Convergence 2026 - Guam to Ouvéa


The third race of our series of ocean voyages across the World’s convergence zones takes us southeastward now down the Pacific, from Guam’s Apra Harbour at 13.5 degrees North, back across the Equator to the glorious New Caledonian resort island of Ouvéa, on the edge of the Tropic of Capricorn at 20.5 degrees South. It’s 2400nm, and there’s more than a few other islands in the way, so mind where you go in your Ocean 50s. Race #1981
INFOby brainaid.de
Ocean 50PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: CCZ - SYC
RACE CLOSE: Tuesday,
April 7 at 2300 UTC.
Race starts: Mar 20th 18:00 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 rafa
  4. Sailonline Yacht Club Member rumskib
  5. Sailonline Yacht Club Member CollegeFund
  6. Sailonline Yacht Club Member Panpyc
  7. Sailonline Yacht Club Member Sax747
  8. Sailonline Yacht Club Member CriticalHippo
  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