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 » Technical Support » * * * Vic-Maui Malfunction Alert * * *

Posted by A2 Posts 347 Registered at 2009-10-26 00:39:42	2010-06-26 01:46:47 - *** * * Vic-Maui Malfunction Alert * * ***
	Passing the Cape Flattery Waypoint to the North when "Rounded" causes the Boat Ranking to place you at the bottom of the list with a DTG of 2704.1 nm in a race that is 2311.4 nm long. None so blind
Posted by Eddie C. Dost Posts 57 Registered at 2008-08-23 11:40:29	2010-06-26 11:01:07 - Re: * * * Vic-Maui Malfunction Alert * * *
	This is a small problem with the way SOL calculates the distance to go: You need to look at the half angle line from the next waypoint to pass. SOL searches for a great circle passing this line orthogonally and going through the position of your boat. In this case the great circle passes the waypoint Nakalele at some distance, so you get a longer distance to the waypoint and a longer distance from there to the finish. See attached sketch for details. The above algorithm is necessary so the DTG function is continuous and there are no jumps in the ranking during passing of a waypoint. The real bug is in the overall calculation of DTG, the above algorithm is only applied to the next waypoint to pass, if there are more waypoints the distance of the great circle going through these waypoints is used in the calculation. This causes the jump in DTG after passing Cape Flattery. As the ranking issue will sort itself out once the boats are about 400nm offshore, I'd consider this a minor problem, rankings will be fine for the remaining 2000nm of the race. _/)_/)_/) The sea is lovely, dark, and deep, But I have promises to keep, And miles to sail before I sleep, And miles to sail before I sleep. Attachments map.png (42.4 KB)
Posted by RainbowChaser Posts 2656 Registered at 2009-06-14 09:44:50	2010-06-26 11:22:22 - Re: * * * Vic-Maui Malfunction Alert * * *
	Super explanation... even my little grey cells comprehend!! Thank you
Posted by A2 Posts 347 Registered at 2009-10-26 00:39:42	2010-06-26 11:41:36 - Re: * * * Vic-Maui Malfunction Alert * * *
	Thanks for the technical details of the situation. I had not encountered this sort of behavior in any previous races. P.S, Thanks for the graphic & expanded explanation, Standing down from * Alert * status --- Last Edited by Aethereal at 2010-06-26 12:19:06 --- None so blind
Posted by Eddie C. Dost Posts 57 Registered at 2008-08-23 11:40:29	2010-06-26 11:54:16 - Re: * * * Vic-Maui Malfunction Alert * * *
	The half angle line is derived as follows: Take the line (I think it's the loxodrome) from the previous waypoint (or start point) to the waypoint in question and the line from the waypoint in question to the next waypoint (or finish). These two lines of the race track define two angles, a greater "outside" angle and a smaller "inside" angle. The "outside" angle is on that side where the waypoints needs to be passed. The line cuting this angle in two halfs is the "half angle line" I was referring to. When your boat passes this line, the server will mark the waypoint as passed (if passed in the correct direction, of course). _/)_/)_/) The sea is lovely, dark, and deep, But I have promises to keep, And miles to sail before I sleep, And miles to sail before I sleep.
Posted by nacrr Posts 55 Registered at 2010-01-01 15:57:17	2010-11-10 19:34:20 - Re: * * * Vic-Maui Malfunction Alert * * *
	This "small" problem creates a huge mistake in the case of the race "Ron Cazar". Please find a way to solve the problem! nacrr
Posted by A2 Posts 347 Registered at 2009-10-26 00:39:42	2010-11-14 17:06:54 - Suggestion for DTG Anomaly
	Thanks to Eddie's technical description & some subsequent discussions with 76T an idea occurred to me on how to improve the DTG measurement without radically altering the method by which it is derived. I post it here so that my understanding of how things actually work can be evaluated. As it stands now the "Bearing to Mark" splits the difference (Half-Angle) between the incoming Rhumbline and its exit. Crossing this imaginary line is where a rounding is registered and the closest approach to this same imaginary line is how the DTG measurement is calculated. Now if this "Bearing to Mark" was rotated forward in favor of the exiting Rhumbline until it was perpendicular to it, then the closest approach measurement would more closely resemble the actual course distance. My suggestion is to give the Bearing to Mark a forward bias. None so blind

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Kapiti Chetwodes Race 2024

For only the second time in SOL history, we have the pleasure of inviting you to the Kapiti Chetwodes Race, held in the Cook Strait region. Organised IRL by the Royal Port Nicholson Yacht Club from Wellington in New Zealand. The approximately 160nm long route, full of turning points, will take us from the bay at RPNYC around the islands of Somes, Kapiti and Chetwodes and back to the finish line at RPNYC. We have only a 26 ft Albin 79 yacht at our disposal. All this means that we will have a lot of fun, so fair winds!
Race #1864
INFO by brainaid.de
Albin 79 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ4 - ARCH - SUPSOL - SYC
Race starts: Nov 25th 17:00 Registration Open!

▶ Flash

GO TO RACE

Raja Muda Selangor 2024 - Penang to Langkawi

Welcome to the third and last online race of the Raja Muda Selangor International offshore series – a 70nm final trip further north again up the Malacca Strait from Penang to the exotic island of Langkawi, and again in Ker 40s.
Race #1871
INFO by brainaid.de
Ker 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: RMS - SYC
RACE CLOSE: Monday,
November 25 at 2300 UTC.
Race starts: Nov 21st 04:00 Registration Open!

▶ Flash

GO TO RACE

Raja Muda Selangor 2024 - Pangkor to Penang

Welcome to our second online offshore race in cooperation with Raja Muda Selangor International – an 80nm trip from Pangkor north to Penang up the Malacca Strait, again in Ker 40s.
Race #1870
INFO by brainaid.de
Ker 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: RMS - SYC
RACE CLOSE: Saturday,
November 23 at 2300 UTC.
Race starts: Nov 18th 04:00 Registration Open!

▶ Flash

GO TO RACE

Two Oceans Doublecross TIMED Race 2024

Our November Timed race takes us to Cape Town near where the Atlantic and Indian oceans meet. Our ride is a beautiful ketch, the Archer 78. Starting at Cape Town, we’ll round Robben Island, then head south to round Cape Point, up around Seal Island before heading north to round Dassen Island before returning to Cape Town. 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 #1872
INFO by brainaid.de
Archer 78 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ4 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
30 November at 23:00 UTC
Race starts: Nov 17th 12:00 Registration Open!

▶ Flash

GO TO RACE

Nassau to Bodo 2024

Prepare for the grand finale - the 6th and concluding leg of the RTW challenge, an odyssey from Nassau in the Caribbean to Bodø in Norway. Embracing a journey of 4000 nautical miles, this leg promises an exhilarating 18-day voyage. It also heralds the November installment of our prestigious Ocean Race Championship. Embark on a voyage of a lifetime, where prowess, tactics, and camaraderie unite in the pursuit of triumph. We eagerly await your presence at the starting line! May the winds be ever in your favor.
PRIZE: SMPF
Race# 1866
INFO from brainaid.de
Swan 65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ4 - OCCH - RTW - SUPSOL - SYC
Race starts: Nov 11th 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