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:

Silverrudder 2025


Ahoy, SOLers! Get ready for the epic Silver Rudder – Challenge of the Sea! This 125nm single-handed race around Denmark’s island of Funen is back—shallow waters, narrow straits, and shifting winds await. This year, we trade up to our single-handed X-99s—can you master their power where precision counts most? It’s the world’s largest solo regatta, and your virtual helm is calling! Chart your course, trust your instincts, and race for glory in this ultimate test of seamanship!

It is imperative that you read AND understand these special Starting Conditions for SILVERRUDDER 2025:
Starting Conditions!!
Race #1948
INFO by brainaid.de
X-99 Single-handed PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Sep 19th 09:00 Registration Open!

▶ Flash
GO TO RACE

Rome to Tripoli 2025


The next race in the ARCH series will take us almost straight from Rome to Tripoli. But don't expect this 550nm race to be an easy one. The Mediterranean always offers some surprises. So let's prepare your Lagoon 55 with due care and... Fair Winds.
Race #1943
INFO from brainaid.de
Lagoon 55 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ3 - ARCH - SUPSOL – SYC
Race starts: Sep 15th 17:00 Registration Open!
▶ Flash
GO TO RACE

Carib Rum Run 2025

Welcome to the Caribbean and Sailonline’s legendary Carib Rum Run! This year we trade tall ships for pure speed as we race our sleek Santa Cruz 70s on a 1759nm slalom through the rum islands. Yer mission: plunder barrels from the region’s finest distilleries and deliver ‘em to the rum-thirsty sands of Cancun, Mexico. Finish on or before International Talk Like a Pirate Day, 19 September, to etch yer name in legend! Join SYC before race end and ye scallywags can disguise yer boat with a pirate name for this race only! Hoist the sails, sharpen yer cutlasses—the rum run awaits!
Race #1944
INFO by brainaid.de
Santa Cruz 70 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Sep 15th 00:00 Registration Open!
▶ Flash
GO TO RACE

Roslagen TIMED Sea Race

Welcome to quite possibly the most challenging TIMED race of the year. This month finds us in Sweden with lots of islands and narrow passages when we sail our Seacart 30 trimaran over the 86nm from Lidingö outside Stockholm to the beautiful coastal village of Öregrund. Consider yourself a winner if you complete the course nonstop! This is a TIMEDrace so you may RE-REGISTER HEREto 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 #1945
INFO by brainaid.de
Seacart 30 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ3 - TRCH - SUPSOL - SYC
Race starts: Sep 07th 12:00 Registration Open!
▶ Flash
GO TO RACE

Great Nicobar to Marion Island 2025

The Adventure Continues – Leg #6 of the RWW Series.
We’re setting sail on the next stage of the RWW Series: a 4,400-nautical-mile passage from Great Nicobar to Marion Island. This demanding leg will test endurance, strategy, and seamanship at the highest level. As part of the 2025 Ocean Championship, this marks the ninth legendary challenge in the series — and one of the most exhilarating yet. The race will be contested aboard the Archer 78’ ketch, a vessel built to push sailors to their limits across the vast Indian Ocean.
PRIZE: SMPF
Race #1942
INFO by brainaid.de
Archer 78 PARTICULARS    
WX Updates:
0430 / 1030 / 1630 / 2230    
Ranking: OCQ3 - RWW - OCCH - SUPSOL - SYC
Race starts: Sep 01st 11:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member vida
  2. Sailonline Yacht Club Member WRmirekd
  3. Sailonline Yacht Club Member CriticalHippo
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member KaSToR
  6. Sailonline Yacht Club Member Kipper1258
  7. Sailonline Yacht Club Member BRENTGRAY
  8. Sailonline Yacht Club Member Sax747
  9. Sailonline Yacht Club Member Panpyc
  10. Sailonline Yacht Club Member CollegeFund

View full list

Series

Mobile Client

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

The mobile client