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 Discussion » When is my command executed?

Posted by kroppyer Posts 346 Registered at 2010-02-05 15:25:55	2016-10-26 16:30:33 - When is my command executed?
	warning: I'll explain how serverjumps, commands and the client refresh rate work, but it's complicated and I cannot tell you yet how to take advantage of this knowledge (when rounding a mark for example) Most of you know about server jumps. For rounding a mark, it's important to turn as early as possible, but absolutely not too early. This is made difficult by the server jumps, and client refresh rate, you rarely see your boat where it actually is. What you see is running a couple of seconds behind, in rare cases it could reach up to about 45 seconds. So what is exactly happening. It's more than just the server jumps and the client update rate, but let's start with them anyway: The server continuously checks all boats. For every boat that has not been moved by the server for at least 10 seconds, the server updates its position. This means, your boat will move every 10-12 seconds (when it's busy, it may take 2 seconds before the server notices it hasn't moved your boat yet). When you haven't issued a command in the last 15 minutes or so, the server may skip you once or twice, and then do one big jump to catch up. This unloads the server a bit from boats that aren't actively steered. useful tip: send a command 5-10 minutes before rounding a mark (setting a delayed command for 5-10 minutes before the mark also works). It'll make sure the server jumps for your boat are short when you reach the mark. For the rest of this post, let's assume server jumps of 11 seconds: your boat is moved by the server every 11 seconds. I'm also assuming you have a fast internet connection. The client polls the server every 15 seconds (roughly). Let's see what can happen with an example: 12:00:00 (jump) server moves your boat 12:00:00 (poll) client polls boat position, you see your boat at its current position (barely any delay!) 12:00:11 (jump) 12:00:15 (poll) your boat moves from its 12:00:00 position to its 12:00:11 position (running 4 second behind) 12:00:22 (jump) 12:00:30 (poll) your boat moves from its 12:00:11 position (19 seconds behind) to its 12:00:22 position (8 seconds behind). 12:00:33 (jump) 12:00:44 (jump) 12:00:45 (poll) your boat moves from its 12:00:22 position (23 seconds behind) to its 12:00:44 position (1 second behind). Note: the 12:00:33 position is not shown, it looks like you made one large jump. A better understanding of how this works may not easily transfer into being able to steer your boat better. One useful tip is: when you see your boat make a large jump, you know two server jumps happened in the last 15 seconds, meaning the last jump happened less then 4 seconds ago. If you see a short jump, you know only 1 server jump happened in the last 15 seconds, meaning the last jump happened between 4 and 11 seconds ago. Commands are executed independently from serverjumps. What does this mean? You might have seen your command execute at the start of a new server jump, or at the end. Both can happen. A command will never execute in the middle of a serverjump. All commands due to be executed (of every boat, in every race) are executed in one go, with 4 or 5 seconds between each go. So your command will generally be executed within 5 seconds after the time you set the command for. BUT your boat may still be at a position from 11 seconds ago. This means, your command will have an effect 11 seconds earlier than it was set to execute. So now there are three things with an interval: the client polls ever 15 seconds, the server moves boats every 11 seconds and turns boats every 4 or 5 seconds. This is complicated, I can't tell you yet how to take advantage of this knowledge. Up to now I've done one of two things for markroundings: - wait until the client shows me clear to round, then send the command. - when I expect a double jump to happen until the next client refresh, and I only need one more jump, I count, to 10. But 11 is probably safer. Now I've researched how commands work, I might come up with a method that results in better roundings, without the risk of missing the mark. That will be something I'll post on solfans
Posted by JimKnopf Posts 24 Registered at 2010-06-10 23:14:48	2016-10-26 21:18:39 - Re: When is my command executed?
	One advantage I take of your very informative explanation is: Don’t tack (gybe) too short for rounding a waypoint/buoy. To set a tack command in advance may have the effect to round too early. Seems to be better to wait for the visible pass by of the waypoint – then tack or gybe or set new course. (Apologies for bad english).
Posted by Kipper1258 Posts 179 Registered at 2015-06-18 22:08:49	2016-10-26 22:36:58 - Re: When is my command executed?
	This is why roundings are missed even though DC Checker shows the mark as clear. DC Checker assumes that the DC is going to fire exactly at that time with no uncertainty. That is not the case in reality.

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

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 Open!

▶ Flash

GO TO RACE

St Nazaire Chasse TIMED Race 2024

Welcome to a "chasse" (hunt) from St. Nazaire to La Baule on the west coast of France! This race was designed by SOLer FR_flouflou in 2010. The KER 40 was introduced to SOL in 2016 by SOLer psail, and the Sol-KER was a welcome addition to SOL’s fleet of 40- footers, as it was to the IRL Ker fleet of eponymous - like KERonimo, KukuKERchu and Ice BreaKER. This is a TIMEDrace, so you may RE-REGISTER HERE to try again, after finishing a run. You will have 13 days and 11 hours to show your skill and decision making after the race opens.
Race #1797
INFOby brainaid.de
Ker 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ2 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
27 April at 23:00 UTC
Race starts: Apr 14th 12:00 Registration Open!

▶ Flash

GO TO RACE

The Beagle in the Straits of Magellan 2024

Both before and after visiting the Falkland Islands, the Beagle extensively explored the south eastern coast of South America, hither and thither, from north of the Rio Plate to the tip of Tierra del Fuego, but it was not till the end of June 1834 that the ship made it into the Pacific Ocean, transiting via the Straits of Magellan. Online in 2024, the choice is yours - passage the strait or round the cape; 400nm or more in your Class B Tall Ship.
Race #1753
INFOby brainaid.de
Tall Ship Class B PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SVF - SYC
Race starts: Apr 09th 13:00 Registration Closed

▶ Flash

GO TO RACE

Cape Town to Auckland 2024

Welcome to the second leg of this Round The World series 2024. It's also the April edition of this year's ocean race championship. The course is the same as the one sailed in 2023, but this year we sail the iconic Swan 65, as suggested in the concluding RTW race last year.
Prepare yourselves for an epic 30-day journey, navigating through the unpredictable waters of the South Seas. It's essential to take care of provisioning to ensure a smooth and enjoyable race experience. With the longer duration, we anticipate plenty of opportunities for camaraderie, competition, and unforgettable memories.
PRIZE: SMPF
Race# 1789
INFO from brainaid.de
Swan 65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - RTW - OCCH - SUPSOL - SYC
Race starts: Apr 01st 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