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:

Chesapeake and Potomac TIMED Race 2026

Welcome to the Chesapeake Bay, the sailing capital of the United States. Feast on Maryland crab cakes or crabs seasoned with Old Bay spice before sailing down the Bay aboard a Formula 18 catamaran on a 128 nm course that will take you up the Potomac River finishing at Quantico, Virginia. This is a TIMEDrace so you may RE-REGISTER HEREto try again after finishing a run. You will have two weeks to test your skill and decision making after the race opens.
Race #2032
INFOby brainaid.de
Formula 18 catamaran Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ2 - TRCH - SYC
RACE CLOSE: Saturday,
23 May at 23:00 UTC
Race starts: May 10th 12:00 Registration will open soon
▶ Flash
GO TO RACE

Tobruk to Iskenderun 2026

Welcome to the fourth of our nine races across the length and breadth of the Magical Mediterranean Sea, and the second that is not in partnership with a real-life event, this time for good reason, which we won’t get into here. From Tobruk to Iskenderun it’s 670nm in length, with the added complication that the island of Cyprus will be in your way. Hoping, possibly forlornly, for plenty of downwind sailing, we’ll take the Lagoon 55 for the voyage!
Race #1976
INFO by brainaid.de
Lagoon 55 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: MED - SYC
Race starts: May 05th 15:00 Registration Open!

▶ Flash
GO TO RACE

Tasmania to Kamchatka 2026

Welcome to yet another all-new route. Tasmania to Kamchatka, part of our Ocean Championship and also the third leg of the ROW (Round the Old World) series. Be aware of the obstacles on the way, likely to split the fleet. It's like X:mas to X:mas, crossing the same waters, navigating the same archipelagos. This second race of OCQ2 2026 will be sailed in our revised 'version 2' Imoca 60 Foil. Race #2031
INFO by brainaid.de
Imoca 60 Foil v2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - ROW - OCCH - SYC
Race starts: May 04th 11:00 Registration Open!
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

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