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

Posted by
JimGodders


Users avatar

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


Users avatar

Posts
447
Registered at
2015-02-23 15:38:27
2018-09-12 07:05:40 - Re: VMC
Posted by
JimGodders


Users avatar

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


Users avatar

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:

Lake Victoria TIMED Race 2026

This month’s TIMED race takes us inland to Lake Victoria in the heart of Africa. Starting at Rosebery Channel in Uganda sail the AC72v2 on a 196nm course around Bugala Island on the way to the finish line in Tanzania’s Speke Gulf. 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 #2018
INFOby brainaid.de
AC72v2 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ1 - TRCH - SYC
RACE CLOSE: Saturday,
28 March at 23:00 UTC
Race starts: Mar 15th 12:00 Registration Open!
▶ Flash
GO TO RACE

SSANZ Round North Island Race 2026 - Leg 4

The final challenge awaits in Leg Four of the Round North Island Series! From Napier, the fleet sets off on a 354 nautical mile run back to Auckland, completing the full circumnavigation where the journey began. Fatigue may be setting in, but this last leg could decide the overall standings. Sailing the fast and responsive Sun Fast 3600, our skippers will need sharp tactics and steady focus to finish the series strong and claim victory!

The start time for this race may change at short notice to align with the real race. The confirmed start date and time will be announced via an in-race “L” flag message — Please monitor race communications closely.
Race #2014
INFO by brainaid.de
Sun Fast 3600 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: RNI - SUPBUD - SYC
Race starts: Mar 12th 22:00 Registration Open!
▶ Flash
GO TO RACE

SSANZ Round North Island Race 2026 - Leg 3

Leg Three of our Round North Island Series, in partnership with SSANZ, keeps the pressure on! From Cook Strait, the fleet turns north for a 187 nautical mile passage up the east coast to Napier. It may look like a quick overnighter, but shifting coastal winds and the ever-lively Cook Strait demand sharp focus. In our responsive Sun Fast 3600s, a proven short-handed racer and powerful downwind performer, tactical decisions and precise timing will make all the difference!

The start time for this race may change at short notice to align with the real race. The confirmed start date and time will be announced via an in-race “L” flag message — Please monitor race communications closely.
Race #2013
INFO by brainaid.de
Sun Fast 3600 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: RNI - SUPBUD - SYC
Race starts: Mar 08th 22:00 Registration Closed
▶ Flash
GO TO RACE

Iceland to the Falklands 2026

Welcome to an all-new route, the first of three Round the 'Old World' of Europe, Africa, Australia and Asia. To give each leg of the ROW a bit of length we'll try to hug the coasts as little as possible, so starting in Iceland our first leg of the series, which will also be the final leg of our Quarter 1 Ocean Championships takes us 7200nm to the Falklands, the full length of the Atlantic end to end. To make sure we'll get it done within the month we'll be sailing our Maxi Trimaran.
Race #2010
INFO by brainaid.de
Maxi Trimaran PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ1 - ROW - OCCH - SYC
Race starts: Mar 02nd 11:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

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

View full list

Series

Mobile Client

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

The mobile client