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 JimGodders Posts 3 Registered at 2011-11-06 17:56:14	2018-09-11 20:30:24 - VMC
	Hi all, I've been reading about a little as I'm looking to improve, and have zeroed in on VMC as an interesting concept. But, for the life of me, I can't seem to get my head round it properly and I have a few questions that I'm sure you fine folks will be able to answer for me. As I understand it, sailing to VMC maximises the boat's speed over the ground in the defined direction. Considering 2 boats, starting at the same point at the same time with both wanting to get as far north as they can, if 1 is sails to VMC, they will be further north than the other sailing due north, though the boat sailing to VMC will also be off to the left or right. What I'm struggling to understand is how this is useful in racing. I know there's little point in sailing VMC direct to a mark if the wind ins't expected to shift as you'll lose whatever time you've gained on the leg trying to get back to the mark. I've seen some suggest that in shifting wind, a reasonable VMC target is to sail to half the shift. I don't understand what this means though. I've tried google but to no avail - this doesn't seem to be a topic that is easily accessable. Could someone please explain what the VMC target would be if trying to get a mark due north, with a wind veering from NW to W over the course of the leg please?
Posted by Bimmer Posts 447 Registered at 2015-02-23 15:38:27	2018-09-12 07:05:40 - Re: VMC
	Hi Jim. This might be helpful: http://solfans.org/blog/sailing-by-the-numbers/vmc-revisited/
Posted by JimGodders Posts 3 Registered at 2011-11-06 17:56:14	2018-09-12 18:50:34 - Re: VMC
	Thanks very much Bimmer. I had seen that article already, and others on the same blog and this is what is leading to my confusion! Let's take this article. Outlaw has chosen to VMC to a bearing of 280. For the given wind conditions, sailing a course over the ground of 307 gets Outlaw furthest down a line drawn from his/her current position on a bearing of 280, though they will be to starboard of a point on a direct 280 bearing from their current position. Nevertheless, sailing a course of 307* gets them farthest up the 280* bearing. Now, I understand that 280* was chosen as this is the TWD that Outlaw will tack at. But this is what I can't quite get my head around. A TWD of 280* seems incorrect - that could happen anywhere along the leg, and not necessarily in the best tacking position. Does he mean he'll tack when the bearing to the mark is 280*? I often see mentioned that a tack/gybe should be done when VMC = VMG. Why is this not a consideration here? I feel like this is a missing piece of the puzzle for me, so I'd love to try and understand it better!
Posted by outlaw Posts 33 Registered at 2012-06-01 13:37:55	2018-09-13 21:48:43 - Re: VMC
	1. I prefer 'his'. Not that I've ever claimed to be human. 2. The only claim is that if I sail a couple hours at a set VMC, and arrive at point A, it is fundamentally impossible to beat me to point A. Bimmer could sail to point B, then have the faster path to the finish. Happens. 3. The causality for picking the target IS confusing. In an ocean race I could decide to go 'west', wade thru bird entrails until I come up with VMC280, and tack at TWD280 because that's how the VMC function works. OTOH in a round the buoys type race I could just do an SOTP estimate where/when I'm going to tack, determine the TWD @tack, and use that as the target. Post tack the boat would just point in the general direction of the mark, bearing ~240, probably.

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Neumayer Station to Biscoe Wharf 2024

It’s Autumn now in Antarctica, the sun is permanently below the horizon, but during the day, from c 0900 to c 1700 local time, there is some twilight – nautical twilight, not to be confused with civil twilight which is brighter. The penguins are starting to huddle together to keep warm and the sea ice is growing. Time to get back to Biscoe Wharf then, before the water becomes impassible. Including a detour past Argentina’s main two Antarctic stations, it’s only 1900nm, so, although we’ll be in a hurry, we will take the bigger, better ice-classed Paratii 2 once more, just to be sure!
Race #1766
INFOby brainaid.de
Paratii 2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: HLAT - SYC
Race starts: May 13th 19:00 Registration will open soon

▶ Flash

GO TO RACE

Mellum to Trischen PYOC 2024

The next installment of the sprint race series sees us paying an all too rare visit to the German coast for a 30nm Pick Your Own Course race in Fox 9.50’s. Along the way enjoy the company of the popular harbour seals that populate the Wadden Sea.
Race #1810
INFO by brainaid.de
Fox 9.5 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SPRQ2 - SPRCH - SUPSOL – SYC
Race starts: May 11th 09:00 Registration Open!

▶ Flash

GO TO RACE

Flight of the Godwit - Hegura to Anchorage 2024

Welcome to the second flight of our bar-tailed Godwit!. This race is the second of three legs reflecting the bird's annual migratory route, and simultaneously the fifth leg of the 2024 Ocean Race Championship. The voyage promises to be not only a test of skill and strategy but an immersive experience in the beauty of the archipelagos of the Aleutian Islands. Join us as we push the boundaries of seafaring prowess on this epic adventure. Let's fly like a godwit!
PRIZE: SMPF
Race #1791
INFOby brainaid.de
Maxi Trimaran PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - GWT - OCCH - SUPSOL - SYC
Race starts: May 06th 11:00 Registration Open!

▶ Flash

GO TO RACE

Melbourne to Osaka Prelude 2024

Welcome once again to what these days is Sailonline’s almost annual virtual Melbourne to Osaka Yacht Race. In real life, this double-handed 5500 nm race between these two sister cities, one deep in the southern hemisphere, the other high in the northern hemisphere, is run every four to five years, and is planned to be held again in 2025, so this race is a Prelude in partnership with the Melbourne Osaka Cup 2025 organising committee collaborating with the Ocean Racing Club of Victoria (ORCV), and the Sandringham (SYC) and Osaka Hokko (OHYC) yacht clubs. On this occasion, we’ll be racing the well-known First 40, a popular size of boat for a long-distance double-handed race. With the doldrums unavoidably lying across the track, you can expect to be at virtual sea for at least a month!
Race #1669
INFO by brainaid.de
First 40 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Apr 20th 00:00 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