Sailonline.org - Online Sailing

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!

Tweets by @sailonline

Board » General Discussion » VMC

Posted by JB 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 Polar_and_the_Circle.pdf (117.1 KB) Ker_40_3D_Polar.avi (1.9 MB)
Posted by sol Posts 296 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 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 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 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 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 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 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 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:

Southampton to Punta del Este 2024

Sailonline is delighted to offer our sailors a 'reversed' Atlantic ocean race. As the RTW championship Atlantic part takes a detour to the Bahamas, we will offer you a reversed course as we will not do the 'usual' leg this year either. It is the July edition of this year's Ocean Championship. Our boat is the OD_65v3.
PRIZE: SMPF
Race# 1820
INFO from brainaid.de
OD65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ3 - OCCH - SUPSOL - SYC
Race starts: Jul 01st 11:00 Registration Open!

▶ Flash

GO TO RACE

Tall Ships Races 2024 - Klaipeda to Helsinki

Welcome to the first of three virtual Tall Ships Races on the Baltic Sea which are being organized in-real-life by Sail Training InternationalThis first race is from Klaipeda, Lithuania to Helsinki, Finland; circa 240nm in Sailonline’s stately fanciful Full Rigger.
NOTE: Starts and Finishes in tall ships racing are always offshore to avoid conflict with shipping and shipping lanes.
Race #1811
INFO by brainaid.de
Full Rigger PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: TS - SYC
RACE CLOSE: Saturday,
July 6 at 2300 UTC.
Race starts: Jun 27th 14:00 Registration Open!

▶ Flash

GO TO RACE

Haida Gwaii 2024

We will end the second quarter of the ARCH competition with a 390nm race around the Haida Gwaii islands (literally "Islands of the Haida people"), also known as the Queen Charlotte Islands. This is an archipelago located on the northern Pacific coast of Canada. In SOL, we last raced on this route in 2012 and few people remember what happened there. Prepare your Riptide 50 well, it's going to be a lot of fun.
Race #1819
INFO from brainaid.de
Riptide 50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ2 - ARCH - SUPSOL - SYC
RACE CLOSE: Wednesday,
July 3 at 2300 UTC.
Race starts: Jun 24th 17:00 Registration Closed

▶ Flash

GO TO RACE

Newport Bermuda Race 2024

The 636-mile biennial Newport Bermuda Race is one of the oldest regularly scheduled ocean races, and with the Fastnet Race and the Sydney to Hobart Race, it is one of the three great classic races of the yachting world. Founded in 1906, this 53rd running of the Bermuda Race can again also be participated in online.
Entries are invited for one of the four divisions:
Double-Handed Division:
Jeanneau Sun Fast 3600
St. David's Lighthouse Division:
Santa Cruz 52
Gibbs Hill Lighthouse Division:
Judel Vrolijk 62
Finisterre Division:
Riptide 50
Details for each yacht are available in the ‘Particulars’ links below. As in real life, you can only sail one boat in one division, so choose your virtual yacht carefully, and because of the unusual (for SOL) 4-division nature of the event, please note results will not count towards any Sailonline rankings.
Race #1808
INFOby brainaid.de
Sun Fast 3600 PARTICULARS
Santa Cruz 52 PARTICULARS
Judel Vrolijk 62 PARTICULARS
Riptide 50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: None
RACE CLOSE: Friday,
July 5 at 2300 UTC.
Race starts: Jun 21st 17:05 Registration Closed

▶ Flash

GO TO RACE

Auckland to San Francisco 2024

Welcome back to Auckland as we continue our Round The World voyage. This 5600 nautical miles race from Auckland to San Francisco, first sailed in 2023, is the third leg of the RTW, proposed by SOLer ita10267. It is also the June edition of this year's Ocean Championship. Our boat is the Swan 65, as in all RTW races this year.
PRIZE: SMPF
Race# 1790
INFO from brainaid.de
Swan 65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - OCCH - RTW - SUPSOL - SYC
RACE CLOSE: Tuesday,
July 9 at 2300 UTC.
Race starts: Jun 03rd 11:00 Registration Closed

▶ Flash

GO TO RACE

Go to race archive

SYC Ranking

View full list

Series

Mobile Client

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

The mobile client