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 » General Discussion » VMG

Page: 1 2 Next

Posted by
larx


Users avatar

Posts
1
Registered at
2008-08-31 21:38:48
2008-11-30 10:56:05 - VMG
the VMG you can see (under Boat speed) in polar diagram, is that generated against last destination or which waypoint?

Pls explain how this VMG is calculated.

--- Last Edited by larx at 2008-11-30 10:59:49 ---
Posted by
Pergite


Users avatar

Posts
15
Registered at
2008-10-07 12:19:07
2008-11-30 13:21:35 - Re: VMG
The VMG value is the boat speed in relation to the direction of the wind.

Its calculated with this formula:
"speed*(cos(twa))"

//Göran
Posted by
NOR184


Users avatar

Posts
2
Registered at
2008-09-07 20:28:31
2008-11-30 14:58:41 - Re: VMG
Yes, ok. But to which point? Next waypoint to follow?. I mean in order to calculate VMG you need two points to calculate to and from. One is my currnt position, but the second?
Posted by
Pergite


Users avatar

Posts
15
Registered at
2008-10-07 12:19:07
2008-11-30 15:07:58 - Re: VMG
As I understand it and according to the formula, you don't. VMG is "way made good" in relation to the wind direction or the angle to the wind, twa. So you don't need two positions, only boat speed and twa.

Though I guess you need two positions or a course to calculate VMC, "way made good to course" or something like that, but I don't know the formula for it.

//Göran
Posted by
NOR184


Users avatar

Posts
2
Registered at
2008-09-07 20:28:31
2008-11-30 15:16:57 - Re: VMG
OK. What I (and maybe larx) don`t understand is if the VMG is 2kn and my boat speed could be 4kn (if different course). Then I mean this has to refer to a certain waypoint.
Posted by
kalle


Users avatar

Posts
413
Registered at
2007-06-01 09:58:04
2008-11-30 15:41:03 - Re: VMG
VMG is velocity made good _against_ _the_ _wind_.
Posted by
6times7


Users avatar

Posts
10
Registered at
2008-10-11 16:26:11
2008-12-05 19:12:36 - Re: VMG
kalle said @ 2008-11-30 15:41:03:
VMG is velocity made good _against_ _the_ _wind_.
.
.
.
Think that clears it up... but if you really want, imagine a mark in the direction of the wind at your current location, VMG is speed towards that mark. -ve VMG is towards a mark downwind, +ve VMG towards a mark upwind.

--- Last Edited by 6times7 at 2008-12-05 19:13:05 ---

--- Last Edited by 6times7 at 2008-12-05 19:13:26 ---
Posted by
HolidayTours


Users avatar

Posts
3
Registered at
2007-08-12 16:24:04
2008-12-09 13:19:31 - Re: VMG
Do any have the formula for VMC? Or could you calk. it by change the TWA to the dir. to mark.

Rolf

EDIT: I found it. Its COS(angel of your boats directions) * Speed
or COS(60) * 5 = 2.50 knots made north (vmg)
if mark is N (360) and you sail 60 deg. in 5 kn.

And BTW VMG is "Velocity made good"

--- Last Edited by HolidayTours at 2008-12-09 13:44:57 ---

--- Last Edited by HolidayTours at 2008-12-09 13:47:36 ---
Posted by
jakob


Users avatar

Posts
364
Registered at
2007-09-04 10:05:30
2008-12-09 14:08:33 - Re: VMG
Hi
If you want to calculate your speed component parallell to the wind direction, here called VMG you simply use VMG=boat_speed*cos(TWA). Yes, you need the cosinus and you need to make sure that you and your calculator use the same units, e.g. degrees for the TWA. You can test that by verifying that cos(90)=1.

The boat speed relative to course VMC is somewhat more difficult to calculate. However, if one simplifies things and assume that YOU know what Course from boat To Target (CTT) you are interested in life is easy again. You can e.g. get CTT by using the ruler-tool in the game.

Now you need only to calculate your speed component parallell to CTT, lets call it VMC, which is almost as simple as VMG. If we define the boat course as CC you simply calculate VMC= boat_speed*cos(CTT-CC). Piece of cake :-) ... as long as you remember that the precision of these calculations decay with increades distance between boat and target. Also, negative VMG & VMC means that you are heading away from target.

Note:
The advanced reader might observe that the VMG-calculation is nothing but a special case of the more general VMC-calculation, where CTT=-TWD and thus the TWA=-TWD-CC.

/Jakob
...one of the guys behind the game...
Posted by
HolidayTours


Users avatar

Posts
3
Registered at
2007-08-12 16:24:04
2008-12-09 22:02:34 - Re: VMG
Thanks Jacob

Now we know ho to calculate the VMC. But to find out the best one you need to do a lot of calculatens in different directons (or). As your boatspeed is different (as the polar shows)at differents angel. I.e if you do 5kn with 55 deg to mark or you do 6.5 kn at 60 deg you had to calc both to find hos is fastest VMC.

Any easy way to do that?
/Rolf

--- Last Edited by HolidayTours at 2008-12-09 22:08:09 ---

Page: 1 2 Next

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

West Papua to Oregon 2026

Our next race in our Ocean Championships is the first of a series of great natural migrations we will track in 2026. The leatherback turtle is the most widely distributed marine reptile on planet Earth, and chooses to breed in warm tropical waters, but prefers to forage in more temperate habitats, travelling thousands and thousands of miles effortlessly annually to maintain this way of life. Our race will follow one of the typical trips of this turtle, from breeding grounds in the seas off West Papua to the coast of Oregon. It’s only 5900nm, so to keep up, but in comfort, we’ll follow in our Gunboat 90.
Race #2006
INFO by brainaid.de
GB 90 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ1 - OCCH - MIG - SYC
Race starts: Feb 02nd 11:00 Registration will open soon
▶ Flash
GO TO RACE

Race to Up Helly Aa 2026

A-OI!!! The fiery spirit of Shetland’s legendary Up Helly Aa returns, and Sailonline’s annual race to Lerwick is once again upon us. Covering 383 nautical miles from Aberdeen, SOLers will tackle winter waters steeped in Viking tradition. This year, we race the classic Frers 33, a proven cruiser-racer born from the golden era of offshore racing and still a sturdy performer both on the virtual and real water. Can you master the course and reach Lerwick in time for the flames?

SAILING NOTE: Gruney may be approached from any direction but must be passed for rounding purposes as indicated on the chart.
Race #2005
INFO by brainaid.de
Frers 33 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
SYC
Race starts: Jan 30th 17:00 Registration Open!
▶ Flash
GO TO RACE

Red Eye - Hobart Convict Run 2026

Back in 2010, one of our SOLers of the first hour, AUS_Scott76, came up with this ‘Convict Run’ out from Hobart, past Cape Raoul and the penal colony of Port Arthur, round Tasman Island, up and back down the east coast of Tasmania, to finish with a tight technical run – so Scott called it – up the picturesque D'entrecasteaux Channel, home to Hobart once again. It’s 250nm, ideal for a bit of ‘Red Eye’ in comfortable Finngulf 43’s, and if the original idea was to pick up some convicts on the way for a bit of R&R and sea air, you may always drop’m back before returning to Hobart!
Race #2002
INFOby brainaid.de
FG 43 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: RED - SYC
Race starts: Jan 27th 12:00 Registration Open!
▶ Flash
GO TO RACE

New Ice Age 2026 - Longyearbyen to Browerville


Although we have by no means exhausted the possibilities of ice boating on lakes at high latitudes or high altitudes, it was noticeable that as our 2025 Series progressed, there were calls from time to time for longer-distance challenges, and so in response to these calls we will pretend that global warming has reversed and as a result the coastal waters of Antarctica and Russia and Canada have fully (and smoothly!) frozen over offering us the possibility of a 4-race New Ice Age series in our trusted no-PL DN machines. Our first leg takes us 2600nm from Svalbard’s Longyearbyen east to North Alaska’s Browerville. You’ll be a few days on the ice, so dress warmly and take some provisions; go!
Race #1968
INFOby brainaid.de
DN PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: NIA - SYC
Race starts: Jan 22nd 07:00 Registration Closed
▶ Flash
GO TO RACE

Cross the Convergence 2026 - Robinson Crusoe to Galapagos


Welcome to our first race of a new series of ocean voyages across the World’s convergence zones, this first race taking you north from south of the Tropic of Capricorn to the Equator-straddling Galapagos, home of magical iguanas and other exotic fauna (but no mythical kings, Dory) Departing from the island where in 1704 adventurer Alexander Selkirk inspired Daniel Defoe to write the best-seller "The Life and Adventures of Robinson Crusoe", by debarking off the unsound "HMS Cinque Ports", four months before she foundered off the coast of present-day Colombia, we will sail the 2200nm in our decidedly sounder and faster than the " Cinque Ports",
Ocean 50 !
Race #1983
INFOby brainaid.de
Ocean 50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: CCZ - SYC
RACE CLOSE: Friday,
January 30 at 2300 UTC.
Race starts: Jan 16th 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 CriticalHippo
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member Sax747
  6. Sailonline Yacht Club Member rumskib
  7. Sailonline Yacht Club Member bonknhoot
  8. Sailonline Yacht Club Member vida
  9. Sailonline Yacht Club Member Panpyc
  10. Sailonline Yacht Club Member Kipper1258

View full list

Series

Mobile Client

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

The mobile client