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: Previous 1 2 3 Next

Posted by
NZL_PaulR


Users avatar

Posts
311
Registered at
2008-07-22 12:21:30
2009-04-21 10:53:40 - Re: wrong VMG
I use the VMG all the time.

SOL is ocean racing, not harbour racing.

Certainly there are times when VMG is not critical, but on broad reaching it is critical as well as when close hauled beating.

If sailing dead downwind, then you are naturally very slow, and at TWA=180, BS will equal -VMG, but who would ever sail that slow?

At TWA=90, there VMG=0.0 as you are sailing exac6tly across the wind, neither upwind nor downwind.

Try setting your TWA=0.0 and see how fast you can go!


--- Last Edited by Paul Rosser at 2009-04-21 11:01:09 ---
If it breaks, it's not strong enough!
Posted by
Chappo


Users avatar

Posts
53
Registered at
2009-04-17 12:00:35
2009-04-21 12:46:32 - Re: wrong VMG
I am curious how you use - VMG when close and broad reaching, can you please explain. Doesn't the polar give you the best course to sail when reaching when the - VMG is just a -ve number that is neither a maximum or a minimum.
Posted by
dunbur


Users avatar

Posts
9
Registered at
2009-02-18 06:03:58
2009-04-21 16:22:41 - vmc
That's for sure. Looking at the weather is essential. And that's why SOL would not be mechanical with VMC as a previous poster claimed. But showing the VMC would help to judge losses and gains on detours due to weather.


--- Last Edited by dunbur at 2009-04-21 16:24:48 ---
Posted by
jakob


Users avatar

Posts
364
Registered at
2007-09-04 10:05:30
2009-04-21 17:52:33 - Re: wrong VMG
Great discussion. SOL listens carefully and follows the debait but are not yet convinced to implement vmc. :-) We want to be unambiguous, fair and not too detailed in the info since we want sailor skills to be vital.
...one of the guys behind the game...
Posted by
NZL_PaulR


Users avatar

Posts
311
Registered at
2008-07-22 12:21:30
2009-04-21 20:14:11 - Re: wrong VMG
Before developing any VMC, I would prefer development of the predicted course indicator to include any DELAYED COMMANDS. Currently the predicted course "bends" when a TWA is being steered, which is a great first step. However once you enter a delayed command, the course predictor indicator becomes useless because it does NOT show that planned change and its effect.

Showing planned changes is very important if tacking or gybing betwwen islands, rounding marks etc.

I would be happy to limit the course prediction indicator to Delayed Commands that exist for the next 6 hours, as per existing course predictor indicator limitation.

This I see as far more useful and important for "ALL" sailors.

VMC will not be used much, but if used, it will be used only by a few. Once you move off a planned course, the old course becomes irrelevant and is of historical and limited use.

Racing Navigation is always about where you are NOW and that "NEW" best course to the next mark. Who cares where you planned to be yesterday? That's gone forever. Your "here" now and what is your next plan? How are you going to get to the next mark faster is all that matters.

Last weeks meals are of little importance if you are hungry today!!!!

The wind is the most important factor, follows by planned course. Thus boat speed and VMG to the "wind" is MOST critical.

--- Last Edited by Paul Rosser at 2009-04-21 20:22:40 ---
If it breaks, it's not strong enough!
Posted by
jakob


Users avatar

Posts
364
Registered at
2007-09-04 10:05:30
2009-04-21 20:39:44 - VMG
I hear you Paul and add the request to the list.
...one of the guys behind the game...
Posted by
NZL_PaulR


Users avatar

Posts
311
Registered at
2008-07-22 12:21:30
2009-04-21 20:53:01 - Re: wrong VMG
Chappo said @ 2009-04-21 12:46:32:
I am curious how you use - VMG when close and broad reaching, can you please explain. Doesn't the polar give you the best course to sail when reaching when the - VMG is just a -ve number that is neither a maximum or a minimum.
REPLY:
The polar is a great diagram but it is hard to be accurate, given the small scale, when trying to read off resultant speed prediction.

Press the "wheel" icon and as you move the course, the polar diagram shows the Boat Speed and VMG to 2 decimal places, far more accurately.

I am quite happy to beat you by sailing x.01knots faster, as long as I'm faster!!LOL (My current leaderboard position is not necessarily my planned one!! LOL)

When reaching, Boat Speed and VMGs are a trade off, with VMG becomming progressively less important as TWA approaches 90 degrees. Therefore where VMG is maximised is generally at about 45 degrees upwind and 135 degrees downwind. BUT, and it is always a big "BUT", this does not apply in all wind strengths and IRL with different wave patterns. VMG to windward maximises between 30 to 50+ degrees dependant upon wind stength and boat design, weight and trim. In SOL waves, weight and trim are not factored in.

Planning a course needs to consider both bearing and VMG speed. Hence gybing down wind to maintain "hot" (faster) angles is very important e.g. Americas Cup or any match racing shows this up critically. 2nd is still "LAST". Fleet racing clouds the effect a lot as you may be trying to cover several boats at once. It's all down to trigometry and how accurate your wind forecast and hence boat speed forecast on the other leg will be.

When to tack or gybe or adjust course, especially with wind shifts, is what is the difference between 1st and ALL other positions.

--- Last Edited by Paul Rosser at 2009-04-21 20:54:49 ---
If it breaks, it's not strong enough!
Posted by
dunbur


Users avatar

Posts
9
Registered at
2009-02-18 06:03:58
2009-04-21 21:43:50 - Re: wrong VMG
NZL_PaulR said @ 2009-04-21 20:14:11:
Before developing any VMC, I would prefer development of the predicted course indicator to include any DELAYED COMMANDS.
Oh yes, I second that. I also would wish for the course predictor to extend to e.g. 12 hrs rather than six. But I would give the inclusion of delayed commands higher priority. Then an extension of the course predictor and last but not least I would rather have VMC than VMG.
Posted by
Jeroen


Users avatar

Posts
245
Registered at
2007-08-15 09:17:47
2009-04-22 06:49:46 - Re: wrong VMG
HI Paul, great discussion going on here.

I like he idea of including the delayed commands in the course predictor. But this might give people the impression that its fail safe. Then the course predictor plots out their exact course and they start thinking less about the course. (not the veterans of course).

I think this is the same by extending the course prediction to 12h, now its a clear indicator of the 6h blocks the weather comes in. Showing more might lead to the illusion that the course shown will always be true.

--- Last Edited by Jeroen Tiel at 2009-04-22 06:52:11 ---
I am a ex-admin of SOL who joins in from time to time.
Posted by
NZL_PaulR


Users avatar

Posts
311
Registered at
2008-07-22 12:21:30
2009-04-22 10:24:24 - Re: wrong VMG
If the courses are all "COMPASS" courses, then the predictor is very accurate and the margin of error is indeed small.

If "any" of the commnads (current or delayed) are TWA based, then with wind shifts, increases and decreases the accuracy of prediction decreases.

In that case a wavy line (lke a current arrow on a chart) should be used to indicate a widening course of probability with the hourly circles getting larger in area. Perhaps a widening arrow but this could obscure some boats. So a wavy line that widens further out will show greater uncertainity of future course.

So with combinations of CC & TWA delayed commands, the course predictor could have a most interesting look. Would you like a diagram example?


However with most SOL Racing, it is very rare to have lots of different commands with many tacks and gybes within any 6 hour period. Certainly I have used many commands (say up to 10 if one is using Sail Planner) but these DC's are generally minor course alterations on the same basic course / tack. Just minor and slow increments in changing the TWA to suit a weather front or major wind shift as it passed by. Three or four DC's if sailing between islands.

--- Last Edited by Paul Rosser at 2009-04-22 10:27:07 ---
If it breaks, it's not strong enough!

Page: Previous 1 2 3 Next

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Beketov by Balloon 2026 - In Siberia


Way-back-when France and England, and Spain as well, were squabbling about who should control what of North America, only to lose the most of it to their own insurging colonists, their eastern European neighbour empire, Russia, was quietly assimilating vast, thinly nomadically populated territory of its own – Siberia! Amongst the many explorers and adventurers that served Russia so well in these conquests was the Cossack hetman Pyotr Beketov. Let’s pretend we’re he and eschewing horseback, let’s travel by balloon from Yekaterinberg to Krasnoyarsk – just a short 2000km (1100nm) section of the Trans-Siberian Express’ 9289km!
Race #1972
INFOby brainaid.de
SOL Balloon PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: BOL - SYC
Race starts: Feb 03rd 13:00 Registration Open!
▶ Flash
GO TO RACE

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 Open!
▶ 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 CLOSE: Monday,
February 2 at 2300 UTC.
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 CLOSE: Monday,
February 2 at 2300 UTC.
Race starts: Jan 22nd 07:00 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