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

Page: 1 2 Next

Posted by WhyNot 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 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 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 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 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 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 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 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 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 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:

Round Greenland 2024

Just as Skip Novak was embarking for Kamchatsky, Amyr Klink also quietly slipped his Antarctica moorings and by now Paratii 2 has reached Reykjavik, where he invites you to join him on Leg 5 of our High Latitudes Series, a full 3650nm circumnavigation of Greenland. The course is clockwise round, so down the North Atlantic to Cape Farewell, then up the Davis Strait into Baffin Bay and on into the Arctic Ocean proper, where, hopefully and certainly virtually, Paratii 2’s special ice-breaker features will get us thorough the summer ice out onto the Greenland Sea and back to Reykjavik. Stay warm!
Race #1780
INFOby brainaid.de
Paratii 2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: HLAT - SYC
Race starts: Aug 29th 19:00 Registration Open!

▶ Flash

GO TO RACE

Pico Island TIMED Race 2024

900nm due West of Lisbon you’ll find Portugal’s Azores Islands where SOLers have been known to come and go, both IRL and on-line. Marking the junction of two major tectonic fault lines – the North Atlantic Ridge and the zone where the African and Eurasian plates meet – it is a seismically hyper-active place, but warm and verdantly beautiful with one rain-laden depression after another rolling over its ash-fed hillsides. If it wasn’t for the pods of whales mooching about offshore, at sea might be the safer place to be, but let’s go racing anyway – 53nm round Pico, this year in Mini 6.50’s. This is a TIMED race, so you may RE-REGISTER HERE to 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 #1833
INFO by brainaid.de
Mini 6.50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ3 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
31 August at 23:00 UTC
Race starts: Aug 18th 12:00 Registration will open soon

▶ Flash

GO TO RACE

The Beagle in the Galapagos 2024

It took the Beagle a further fifteen months of adventure and exploration to, on September 15, 1835, reach the Galapagos Islands, whose populations of giant tortoises and iguanas and finches and mockingbirds of great variety from island to island were such a significant inspiration to Darwin formulating his Theory of Evolution. It won’t be a retrace of his peregrinations, but here in 2024 an interesting 500nm course will take you by most of the archipelago’s islands, in your very own Beagle, a Class B Tall Ship!
Race #1754
INFOby brainaid.de
Tall Ship Class B PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SVF - SYC
RACE CLOSE: Monday,
August 19 at 2300 UTC.
Race starts: Aug 08th 13:00 Registration Closed

▶ Flash

GO TO RACE

SOL's Balloon Transat 2024

Sailonline offers a huge variety of boats to sail in. One of the more unusual ones has got to be SOL's Balloon, which was polarized by past SOLmaster 76Trombones. Notably, the SOL Balloon will actually ‘sail’ in other directions other than straight downwind, although it will not 'sail' over land or beyond a 'beam reach'. This year we have a new course to challenge all you aeronaut’s and we will be taking the Balloon across the Southern Atlantic from Cape Horn to 'land' it in the Cape of Good Hope. Tips: Wait for favourable winds before launching and set DC aware predictor to maximal length.
Race 1831
INFO by brainaid.de
SOL Balloon PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
None
Race starts: Aug 06th 19:00 Registration Closed

▶ Flash

GO TO RACE

San Francisco to Ushuaia 2024

After a superlong RTW-leg3 (27 days), we have had a month to recover, and maintain our boat, in order to continue our around the world race. Leg 4, even longer than the previous, takes us from California to the world's southernmost city Ushuaia. No waypoints, even "the Ditch" is an option, but maybe a bit too much of a treat. With 6300 nm to go, the estimated duration of this race 29 days. This course is also the August edition of our ocean race championship.
PRIZE: SMPF
Race# 1717
INFO from brainaid.de
Swan 65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ3 - OCCH - RTW - SUPSOL - SYC
Race starts: Aug 05th 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