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: Previous 1 2

Posted by
AGage


Users avatar

Posts
411
Registered at
2008-12-27 10:31:57
2011-04-11 07:43:01 - Re: VMC or "by the numbers" in oscillating winds
Try these webpages Tom, it is about a technique you describe known as 'wallying the windshifts':
http://www.ockam.com/vmc.html
and
http://wcsailing.blogspot.com/ - near the bottom for this specific issue, but there is also more good stuff....

If you are required to sail the non-favoured tack (ie land forces you to), then you often want to sail higher than VMG - by how much is the magic question, and I cant really give you any general answers. One good way to get a feel though is experimenting with the predictor line.
Set your boat at the max VMG angle, and get to 100% performance. Then point up by 1 degree. After you click 'Send' place the crosshair over the point for 1 hour, and hold it there. When the new course is established and the predictor redraws itself, compare the new 1hr point to the old. For simplicity say you are trying to maximise your course N, and are on Port so want to minimise your Eastward travel (which is further from rhumbline). Well what you want to compare here is the 2 points' latitudes. If the new point is no further S than the original vmg point, then 1 degree higher is better. Now do it again...
Eventually you will find pointing higher slows you too much.
Also using the ruler to record the various points is a good idea, and zoom in so you are measuring as accurately as possible. Also be aware that as you are actually moving N, the points will tend to be more N anyway each time, so factor this in if possible.
And of course you can also do the exact same thing pointing progressively lower than vmg angle, to see visually how sailing a bit faster (but also remember as 76T points out - also further)...

Also download my polar butterfly overlay and experiment using some card as 76T suggest, or a tool I also mention on the blog: MB-Ruler for drawing and moving lines on the screen.
;-)

Regarding books, the best I have ever read is "High Performance Sailing" by Frank Bethewaite - he is a meteorologist and aeronautical engineer, has (IIRC) 5 world championships between his 2 kids and he and his son were largely responsible for the development of the 18" Skiffs here in Aus as well as many other classes. He was also official met for the Aus Olympic sailing team for decades - so while the book is largely detailed toward dinghies, there are also excellent sections on weather reading and waves etc...
When he retired from his job, he and a likeminded group set about trying o understand boats better and to make them sail faster (this was decades ago, before much of what we now know was known), and (one of) the thing i really like about his book is he talks alot about the actual experiments they did to sail faster - and not just 2 boat testing or similar, but actual emperical scientific experiments, like drag tests on foil designs and he even built his own wind tunnels - probably the advance he is most known for inventing/discovering is the wing-mast.
I help develop the client interface for the best online ocean racing sim there is... __/)/)_/)__
Posted by
AGage


Users avatar

Posts
411
Registered at
2008-12-27 10:31:57
2011-04-11 07:55:49 - Re: VMC or "by the numbers" in oscillating winds
BTW, The Ockam site is chock full of great info - when it mentions using 'strip charts' these are available for SOL by using brainaid's NMEA proxy and NavMonPC, which gives you stripcharts for both wind data and boat performance
I help develop the client interface for the best online ocean racing sim there is... __/)/)_/)__
Posted by
sol


Users avatar

Posts
300
Registered at
2008-08-14 11:08:14
2011-04-11 09:54:17 - Re: VMC or "by the numbers" in oscillating winds
Thank a lot Aaron. I have seen "Wallying" mentioned, but have put it on the backburner for the time being. Now I find that I already know what it is:)

Thanks for the links, and the trick with the predictor and markers.

I have your Butterfly, but having been a SOTP sailor for almost 50 years - I havn't really figgered out what to use it for. I just print a paper copy of the polar. I will look more into it though. At my age - I'm a slow learner.
Posted by
WhyNot


Users avatar

Posts
51
Registered at
2011-02-03 18:39:54
2011-04-11 09:57:16 - Re: VMC or "by the numbers" in oscillating winds
Ooopss! That was me answering:). To many instances of SOL running at once.

Sorry
Posted by
76Trombones


Users avatar

Posts
362
Registered at
2009-08-03 18:04:56
2012-02-18 20:15:03 - Re: VMC or "by the numbers" in oscillating winds
I'm not actually sure that this is working properly, but here is a quick spreadsheet that I worked up a while ago, allowing you to compare VMG and VMC courses for different shifts and target angles/mark locations. You want the target that'll get you to the mark the quickest, which depends more-or-less on average wind direction. The amount you can foot varies with the amount of shift.
Attachments
Posted by
76Trombones


Users avatar

Posts
362
Registered at
2009-08-03 18:04:56
2012-02-18 20:23:45 - Re: VMC or "by the numbers" in oscillating winds
Updated to show the effect of sailing VMG on the wrong tack. Footing on the wrong side is even worse, obviously.
Attachments

Page: Previous 1 2

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

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 will open soon
▶ Flash
GO TO RACE

Silverrudder 2026


Ahoy, SOLers! Welcome to the 2026 edition of the Silver Rudder – Challenge of the Sea! This epic 125nm single-handed race around Denmark’s island of Funen is back!

Shallow waters and shifting winds await in the world’s largest solo regatta. This year, we return to the popular First 27 solo. This superlight, water-ballasted planing machine features twin rudders and weighs a full tonne lighter than her older stepsisters. Will you master her power where precision counts most?!

It is imperative that you read AND understand these special Starting Conditions for SILVERRUDDER 2026:
Starting Conditions!!

Race #2059
INFO by brainaid.de
First 27 Solo PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC - SUPBUD - RED
Race starts: Sep 18th 08:30 Registration Open!
▶ Flash
GO TO RACE

Isle of Mull TIMED Race 2026

Welcome to the west coast of Scotland for an 80 nm race around the Isle of Mull. Mull is home to castles, distilleries, and the Highland Games. The race begins just north of Oban in the shadow of Dunstaffnage Castle and after rounding the island finishes down the coast at Crinan. The Twister 28 with its classic long keel is the boat for this race.
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 #2057
INFOby brainaid.de
PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ3 - TRCH - SYC
RACE CLOSE: Saturday,
26 September at 23:00 UTC
Race starts: Sep 13th 12:00 Registration Open!
▶ Flash
GO TO RACE

Cross the Convergence 2026 - Cocos to Sagar Island


Kapil Muni, incarnation of Lord Vishnu, founder of the Samkhya school of philosophy, disturbed from his meditation, in his wrath reduced the 60,000 sons of Sagar to ashes, as they dug the earth to retrieve the sacrificial horse that Lord Indra, the king of the Gods, stole off Sagar, thus creating the Sagara (ocean). Aeons later, Bhagiratha, a descendant of Sagara, asked Ganga to cleanse the ashes of the 60,000 princes, and her resultant torrential fall from heaven created the great river and where it met the ocean, the princes’ souls were washed and raised to heaven and Gangasagar (Sagar Island) was formed. So, let us join the pilgrimages to Kapi Muni’s Temple (see above) and race 2400nm from Cocos Island deep in the Sagara thence, in rather rapid Rapido 60s.
Race #1987
INFOby brainaid.de
Rapido 60PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: CCZ - SYC
Race starts: Sep 11th 18:00 Registration Open!
▶ Flash
GO TO RACE

Shearwater - Rio de la Plata to Irish Sea 2026

Welcome to the fourth leg of our MIG series. This time we're racing the Sooty Shearwater on their migration from the breeding grounds in South America to the northern Atlantic. This is also part of our Ocean Championship, and as such the third race of OCQ3 2026. This race will be sailed in our Gunboat 90. Race #2055
INFO by brainaid.de
GunBoat 90 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
OCQ3 - OCCH - SYC - MIG
Race starts: Sep 02nd 11:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member CriticalHippo
  2. Sailonline Yacht Club Member KaSToR
  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 rthinman
  8. Sailonline Yacht Club Member BRENTGRAY
  9. Sailonline Yacht Club Member Sax747
  10. Sailonline Yacht Club Member vida

View full list

Series

Mobile Client

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

The mobile client