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 » VMC

Page: Previous 1 2

Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-11-01 12:18:09 - Re: VMC
Viva Rod.

Thank you for your comments and my sincere apologies if I wasn’t clear on statements.

Ideal Polar and the butterfly.

Let me start with your ideal boat and so, the corresponding “ideal” Polar.

It can’t simply be a “circle”, Rod.
Because even in a so called “ideal boat” there are some basic limitations from the physics.

For a quick understanding I’ll give just two:

1 - With TWA = 0,00º the BS is plain zero (forget now any water induced effects).
2 - With TWA = 0,00º or TWA = 180,00º the BS can’t be the maximum (the first one is immediately evident).

Polar’s shapes (generally speaking) are similar to “butterflies” with more “wing” area in the down side of it (we agree that we go faster downwind) - in the attached pdf the “ideal” Polar is in orange color and the general “butterfly” Polar in red color (you can also turn on/off the layers clicking in the "eyes" inside the layers window).

The 3D.

Let’s see if you won’t be more puzzled now.

In reality boat’s Polars are contained inside 3D surfaces. Using 3 axes for representing (TWA; TWS; BS) you get it.
In your ideal Polar, a sphere, in a general view, a 3D shape like the one shown on the attached AVI file (it is part of my initial study for the recent SOL Ker40 Polar).

Still puzzled my dear Rod?
Hope not.

A Big Hug
Sail Fair.
Attachments
Posted by
sol


Users avatar

Posts
298
Registered at
2008-08-14 11:08:14
2016-11-01 16:55:30 - Re: VMC
Viva Rod and all.

The second part of Rod’s reply.

1 - VMG and VMC.

VMG and VMC are equal in the sense that, they are calculated from the same vector (BS vector) in specific directions.

VMG (Velocity Made Good on Wind”) is calculated with:

VMG = BS x Cos (TWA),

VMC (Velocity Made Good on Course) is calculated with:

VMC = BS x Cos (Angle between BS (vector) and boat Course direction),

where:

“Cos” is the Cosine of an angle;
“TWA” is the True Wind Angle.

They can only be the same in value, in two particular occasions: when your boat course direction coincides with the VMG,Up or VMG,Down angles (assuming they are both unique, which normally they aren’t).

2 - VMC calculations with variation on (TWD; TWS) pair.

In a simple course from “A to B” if the pair (TWD; TWS) changes during race time - which is what normally Nature do - to get the most of your boat performance inside the (TWA; TWS) pair, or boat Polar, you probably won’t go for a straight line course. Most probably you will “curve” your boat’s path/course.

Mind you that when I speak about a “curve” in reality it’s not a “curve” but, lots of small straight consecutive lines circumscribed by the so mentioned “curve”.
At each vertice of your projected path, you can calculate the corresponding VMC value.

The best course will be the one that optimizes (minimizes) the SUM (D,i / VMC,i), where:

“SUM” is the math symbol for sum;
“D,i” = Distance of each straight line “i”;
“VMC,i” = Velocity Made Good on Course during the Distance “i”.

If you have in your projected path, for instance, 100 straight lines, “i” goes from 1 to 100 and you have 99 sums.

Translating now to a simple figure: Total course time, which is nothing more than the result of the above SUM. The less the better.

Rod, you can use your graphical expeditious tools. No problem with that but, for short paths is my advice.
The issue is on long paths with several days to do it, which takes us to the router talk.

In relation to your statement: “This has nothing to do with Orthodromic, Loxodromic, Rhumb or Starting lines, and the precision of the calculation is whatever you desire”, I suppose it would be better if you think a little more on it using now the recent input.

A Big Hug.
Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-11-01 16:57:59 - Re: VMC
Sorry all, I was logged in as "SOL".
Sail Fair.
Posted by
Rod


Users avatar

Posts
392
Registered at
2010-06-24 22:30:48
2016-11-03 15:17:08 - Re: VMC
My comment about loxodromic etc courses was made with the assumption that it was dealing with a "featureless" ocean, where any arbitrary "destination point" might be chosen. Where specific points must be chosen that are more than 'six hours' away, then naturally one is dealing with land, wind speed and direction in a much more complex calculation, as in the use of a router. I do not use a router, just the "little grey cells", which does simplify the calculation--(and increases the "finishing position number" at the end of the race!!)
Re-reading the above columns, I feel I should expand slightly on my "ideal boat" and its polar--it can be represented by an Ocean Liner, or a battleship, on a calm, windless ocean, going equally well in any direction. In high winds, it probably goes a little bit slower up wind, and faster downwind.

--- Last Edited by Rod at 2016-11-03 18:02:25 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-11-04 08:54:26 - Re: VMC
Viva Rod.

Good morning.

In general I agree with you, but particularly with your insightful notion of a “futureless” ocean.

At the rate Earth climate is changing, we are all going to be sailors.
I was wondering what will be a global “Venice”.
Sail Fair.
Posted by
Rod


Users avatar

Posts
392
Registered at
2010-06-24 22:30:48
2016-11-13 03:04:11 - Re: VMC
You and I will be long dead, and pushing daisies up from below, before we have a "futureless" ocean, JB!
What I was trying to emphasise was that the 'general' case must be understood by 'everybody' before the 'special' cases make sense. I am not a user of routers, and I suspect the majority of SOLers are not either, but the advice we give to others should not be predicated upon the assumption that they already know more than we do.
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-11-13 14:03:02 - Re: VMC
Viva Rod.

You have a point and it is preety fair your thought.

A BH.
Sail Fair.
Posted by
BER_Baggus


Users avatar

Posts
70
Registered at
2008-12-26 18:46:10
2016-11-28 17:08:29 - Re: VMC
Is anyone having problems downloading Agage's Optimum Angles tool? I get an error message from the link http://agage.sol.hmm.iki.fi/OptimumAngles.html
Posted by
Roddo


Users avatar

Posts
13
Registered at
2014-06-28 00:51:17
2016-11-30 00:57:52 - Re: VMC
Viva everyone who has contributed to this thread. You have managed to both confuse me and educate me at the same time - haha. But I thank you for it. I now have a good understanding of the mechanics of VMC - thanks to all of you but particularly to the SPINNAKER; the visual VMC representation there I think was the final piece of the puzzle.
I appreciate that you have taken them time to educate me with a little fun along the way, I still have a long way to go. Thankyou to Outlaw for your new VMC post, I know the practical answers are in there, I think I'll just have to read it a few more times and do some practical training with Kippers CAT for things to finally drop.

Cheers AND Beers from downunder
Rod

Page: Previous 1 2

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Regata dell’Accademia Navale 2026

Welcome to Sailonline’s partnership with the City of Livorno/a> (Leghorn say the English) in cooperation with the local yacht clubs and the Italian Navy, offering all the online opportunity to race the famous Regata dell’Accademia Navale - 630nm in length. Starting and finishing in Livorno, this year the race takes you the length and breadth of the Tyrrhenian Sea via little Mortorio (Mortoriotto) off Sardinia to Capri and home again to Livorno. This race also counts towards Sailonline’s Magical Mediterranean Series and the SuperBuddy title. Online, you will be sailing a Mini 6.50, to give you a match against several of the real-life entrants, which you will be able to track on-screen!
Race #2020
INFO by brainaid.de
Mini 6.50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: MED - SUPBUD - SYC
Race starts: Apr 25th 16:00 Registration Open!

▶ Flash
GO TO RACE

Guess Gotland TIMED Race 2026

The Guess about Gotland is do we helm our First 27 solo east or west of the island in this 140 nm race. 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 #2030
INFOby brainaid.de
First 27 solo Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ2 - TRCH - SYC
RACE CLOSE: Saturday,
2 May at 23:00 UTC
Race starts: Apr 19th 12:00 Registration Open!
▶ Flash
GO TO RACE

Quiberon Islands 2026


The Quiberon peninsula extends as a submerged granite ridge a further 15nm or so beyond the La Teignouse lighthouse on the rocks off its southern tip, surfacing as two small islands, Houat and Hoedic, the duck and duckling in Breton, 5nm and 10nm beyond the light. Treacherous, tidal waters, but on SOL that daunts us not. Of course, we've raced here before, mostly Timed Runs out of Quiberon around Belle Ile, just south of the islets, and back, but this time it's a sprint from Belle Ile's capital of Port Marie round the foul fowl and back. A triangular course of 22nm, appropriately enough for Moody S38.
Race #2022
INFO by brainaid.de
Moody S38 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
RANKING:
SPQ2-SPCH-SYC
RACE CLOSE: Tuesday,
April 21 at 2300 UTC.
Race starts: Apr 18th 02:00 Registration Closed
▶ Flash
GO TO RACE

The Three Kings Race 2026


The Three Kings Race returns with a demanding 468 nautical mile challenge from Auckland up to the remote Three Kings Islands and back again. This rugged and spectacular course tests both endurance and strategy as our SOLers navigate open ocean and ever-changing conditions. Racing the powerful Riptide 50, our SOLers will need precision, timing, and smart routing to master this iconic out-and-back course and secure a strong result!
Race #2028
INFO by brainaid.de
Riptide 50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SUPBUD - SYC
RACE CLOSE: Friday,
April 24 at 2300 UTC.
Race starts: Apr 16th 22:00 Registration Closed
▶ Flash
GO TO RACE

Roma per Tutti 2026


Sailonline are honoured and delighted to have been asked to partner an online first Roma per Tutti yacht race with organizing yacht club, Circolo Nautico Riva di Traiano . In real life, this will be the 33rd edition of this 540nm offshore race from Rome’s Riva di Traiano to the Aeolian Islands and back. Online, the race will not only be our first partnership with CN Riva di Traiano, but also the second race of our Magical Mediterranean series. A number of Mini 6.50s have been entered for the 33rd edition of the Roma per Tutti; so our own vintage Mini is also our virtual yacht of choice for this one.
Race #2019
INFOby brainaid.de
Mini 6.50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: MED - SUPBUD - SYC
RACE CLOSE: Wednesday,
April 22 at 2300 UTC.
Race starts: Apr 11th 10:00 Registration Closed
▶ Flash
GO TO RACE

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 CLOSE: Sunday,
May 3 at 2300 UTC.
Race starts: Apr 07th 13:00 Registration Closed
▶ 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 Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member WRmirekd
  2. Sailonline Yacht Club Member KaSToR
  3. Sailonline Yacht Club Member CriticalHippo
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member Panpyc
  6. Sailonline Yacht Club Member rumskib
  7. Sailonline Yacht Club Member CollegeFund
  8. Sailonline Yacht Club Member sassy63
  9. Sailonline Yacht Club Member Sax747
  10. Sailonline Yacht Club Member bonknhoot

View full list

Series

Mobile Client

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

The mobile client