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 » Sailonline Yacht Club » VMC or "by the numbers" in oscillating winds

Page: 1 2 Next

Posted by
WhyNot


Users avatar

Posts
51
Registered at
2011-02-03 18:39:54
2011-04-09 15:12:58 - VMC or "by the numbers" in oscillating winds
I'm finally beginning to understand the concept of VMC, but I gave a question.

I'm familiar with "sailing by the numbers" when tacking/gybing in oscillating winds i.e. not tack-/gybing on the header, but on the "mean". When I sail by the numbers, my TWA is always max VMG.

Will this work if my TWA is VMC?
Posted by
NOR_Jawik


Users avatar

Posts
70
Registered at
2008-08-31 20:55:18
2011-04-09 16:13:50 - Re: VMC or "by the numbers" in oscillating winds
76 Trombone's site

have a nice explanation and by the way VMG = Sped x cos(TWA)

--- Last Edited by RainbowChaser at 2012-02-18 09:50:10 ---
Posted by
Rod


Users avatar

Posts
392
Registered at
2010-06-24 22:30:48
2011-04-09 17:34:12 - Re: VMC or "by the numbers" in oscillating winds
I must admit to being puzzled by the "choice of target destination", when the obvious target will not be reached before the new wx. That is, in a short race the obvious destination is the next turn "Mark". But in a multi-day ocean race, how to I pick an "intermediate destination" unless I use a router?
And if I were to use a router, would not all these decisions be made for me?

--- Last Edited by Rod at 2011-04-09 20:23:08 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
WhyNot


Users avatar

Posts
51
Registered at
2011-02-03 18:39:54
2011-04-09 17:48:15 - Re: VMC or "by the numbers" in oscillating winds
Thanks Jawik, but 76's explanation does not help me with oscillating wind. Or maybe it does, but I don't understand it:)
Posted by
WhyNot


Users avatar

Posts
51
Registered at
2011-02-03 18:39:54
2011-04-09 18:00:07 - Re: VMC or "by the numbers" in oscillating winds
Rod: I don't say this is the answer, but I have the same problem and the following is what I experiment with:

Disregarding the usual persistent shift! I aim at the point on the predictor that is half way through the shift. Again - not saying this is the right answer! If anybody knows that I'm way out in left field - pls let me know.
Posted by
Rod


Users avatar

Posts
392
Registered at
2010-06-24 22:30:48
2011-04-09 21:32:36 - Re: VMC or "by the numbers" in oscillating winds
to Tom Nordal:- Could you diagram what you mean and attach it to your next input? I am much more comfortable with diagrammatic explanations of these situations.
I have been using 76T 's ideas with regards to offsetting my course from the polar to account for the direction to the next clear 'turn point' such as a Mark or a Headland, but I don't understand these interim destination points at all.

--- Last Edited by Rod at 2011-04-09 21:38:53 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
76Trombones


Users avatar

Posts
362
Registered at
2009-08-03 18:04:56
2011-04-10 00:20:26 - Re: VMC or "by the numbers" in oscillating winds
Nope, I haven't covered choosing the target at all yet, and it is almost *never* the mark/headland... The whole idea of using a fixed point for VMC calcs is a result of GPS/computerised nav, ETA math and engines. For sail routing purposes we'll use an angle that we'll adjust over a leg to take advantage of TWS changes as well as TWD.

For sail routing, a good starting point for target angle is based on the average TWD. There are rules of thumb such as "half the magnitude of the shift" that give you a handle on how far to stray from VMG sailing SOTP. Exmeromotu is an expert on such - maybe he'll chime in? ;-)

Important points to remember are that a shift is required, and you usually need a tack/gybe as well to take full advantage. Sailing low and fast only works if you can sail low and fast the opposite direction as well. Try it in steady winds and the VMG crowd will be laughing.

If you work out a VMG track to the next mark, chances are that a VMC breakdown tacks at similar times. You *always* tack when your VMC=VMG so this is a decent way to start your figuring...

Also note (from a pure learning pov mind, we'd never blindly follow) that you can very easily pick the VMC target that the superpowers are sailing by scoping their angles relative to the polar... The steering line and a piece of right-angle card are a pretty sneaky tool, and no math required.
Posted by
Rod


Users avatar

Posts
392
Registered at
2010-06-24 22:30:48
2011-04-10 01:03:11 - Re: VMC or "by the numbers" in oscillating winds
I sincerely hope, 76T, that you have a book on this subject in the 'works'!
I have a Norie,1840, Jeans 1853, W.A.Smith 1973, Walker 1976, Melges and Mason 1983, Turner and Jobson 1979,and Schlereth 1975, in my library, as well as several more books on dinghy racing, and not one of them mentions the ideas you are presenting here. Have you thought of presenting this in a mini-course on SOL as a preliminary to writing your book?
Speed the day!!!
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
ShamrockPirate


Users avatar

Posts
189
Registered at
2010-12-03 17:49:57
2011-04-10 01:15:30 - Re: VMC or "by the numbers" in oscillating winds
How about doing a SOL Webcast?

Get the BlogMeisters (76, AGage, SWE54 and others)to do a Web-based "primer" and advanced seminar? This is a terrific tool to reach out over multiple timezones.
Posted by
WhyNot


Users avatar

Posts
51
Registered at
2011-02-03 18:39:54
2011-04-10 11:22:18 - Re: VMC or "by the numbers" in oscillating winds
Shamrock: Wouldn't that be great if they would?

There would certainly be a brewsky of their favorite choice awaiting (or two or ten) if they stumbel across me somewhere:)

Page: 1 2 Next

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Roma Giraglia Regata 2026

Our eighth race of nine to celebrate all things Mediterranean - fickle winds, history and olive oil – is another buddy-up; this one with the Circolo Nautico Riva di Traiano . Founded in 1984, as the new Traiano yacht Harbour neared completion, the Circola since then has developed into one of the major yachting competition centres in Italy, and next to the 450nm Roma per Tutti (which SOL buddied earlier in the year), the Roma Giraglia Regata is its other headline offshore event. First raced in 2005, the 210nm course takes competitors from Traiano to a rock on the inside of the Ile de la Giraglia off the northern tip of Corsica and back to the Italian mainland for a finish in the bay of Santo Stefano. We’re racing this one in our Class 40!
Race #2058
INFO by brainaid.de
Class 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: MED - SUPBUD - SYC
Race starts: Oct 08th 16:00 Registration Open!

▶ Flash
GO TO RACE

Arctic Tern - Greenland to Antarctica 2025

Welcome to the fifth leg of our MIG series. Now it's time to race the Arctic Terns, on their migration from Greenland to Antarctica, 8300 NM. This is also part of our monthly Ocean Championship, and as such the first race of OCQ4 2026. This race will be sailed in our Maxi Trimaran. Race #2061
INFO by brainaid.de
Maxi Trimaran PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230 Ranking:
OCQ4 - OCCH - SYC - MIG
Race starts: Oct 05th 11:00 Registration Open!
▶ Flash
GO TO RACE

Bornholm PYOC


Welcome to the Baltic Sea, where we are about to hold another sprint race. The course runs from the north to the south of the beautiful Bornholm island. There are only two waypoints, the start and the finish so the choice of which side of the island to sail along is up to you. Our Albin 79s will cover a distance of approximately 23 nautical miles.
Race #2064
INFO by brainaid.de
Albin 79 PARTICULARS
WX Updates:
0245 / 0845 / 1445 / 2045
Ranking: SPQ4 - SPCH - SYC
Race starts: Oct 03rd 06:00 Registration Open!
▶ Flash
GO TO RACE

Cross the Convergence 2026 - Masirah to Chagos


Having crossed, re-crossed and re-re-crossed the Convergence Zones of the Pacific and the Atlantic, we now face our second crossing of the Convergence Zone of the World’s third great equator-spanning sea, the Indian Ocean, taking us from the channel between Masirah Island and the Oman mainland to the Chagos Archipelago. It’s 1900nm and we’ll be sailing our very fine Archer 78, and won’t mention that both locations (of departure and arrival) are heavily militarized and the why’s and what next’s concerning that – mindful as always of SOL Netiquette.
Race #1988
INFOby brainaid.de
Archer 78PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: CCZ - SYC
Race starts: Oct 02nd 18:00 Registration Open!
▶ Flash
GO TO RACE

Carib Rum Run 2026


Ahoy, ye landlubbers and seasoned salts! Welcome back to Sailonline’s legendary Carib Rum Run, perfectly timed to kick off on International Talk Like a Pirate Day, 19 September!

This year, we command the magnificent Falkun—the ultimate high-tech superyacht modeled after the iconic Maltese Falcon. This 1759nm slalom takes us through the Caribbean’s rum islands to plunder barrels from local distilleries and deliver them to the rum-parched sands of Cancun.

Join SYC before the finish to disguise yer boat with a pirate name for this race only. Hoist the sails, sharpen yer cutlasses, and plot your winning course!
Race #2060
INFO by brainaid.de
Falkun PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Sep 19th 05:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member KaSToR
  2. Sailonline Yacht Club Member CriticalHippo
  3. Sailonline Yacht Club Member WRmirekd
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member Panpyc
  6. Sailonline Yacht Club Member cdhinman
  7. Sailonline Yacht Club Member rumskib
  8. Sailonline Yacht Club Member rthinman
  9. Sailonline Yacht Club Member BRENTGRAY
  10. Sailonline Yacht Club Member Sax747

View full list

Series

Mobile Client

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

The mobile client