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 » Technical Discussion » When is my command executed?

Posted by
kroppyer


Users avatar

Posts
347
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


Users avatar

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


Users avatar

Posts
248
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.
Posted by
ForbanduCollet44


Users avatar

Posts
1
Registered at
2024-10-18 23:02:24
2025-03-12 22:33:41 - Re: When is my command executed?
Hi kroppyer

Thanks a lot for your explanation.

This post is quite ancient so, is it still true or had the situation changed ?

At the end, you speak about another post on solfans, I didn't find it.

Thanks
Posted by
kroppyer


Users avatar

Posts
347
Registered at
2010-02-05 15:25:55
2025-03-13 14:32:40 - Re: When is my command executed?
The server-side hasn't changed much in this regard as far as I know. But there's a whole new client by now, so that part of the story may have changed.

I have never written that post on solfans. I think partially because I didn't find easy and reliable ways to get a significant advantage from the knowledge.

By now, I think there is software that tries to sync up with the server jumps. I believe Kipper's AGL does this, and possibly even the HTML5 client. Which makes it easier, and more intuitive to work with the server jumps.

From what I recall, I had some thoughts that could help you navigate around a mark with the server jumps. If you are in sync with the server jumps, you basically have 10 seconds to decide when and how much you want to steer, and it should be fairly obvious when to turn and by how much. What matters a lot here is that you need to get luck with where you end up after each jump. For example: If you jump just short of the mark, you'll have to continue sailing in the same direction for another 11 second, even though you needed only 2 more seconds to reach the mark. Depending on the situation, you can reduce the effect of this by aiming a bit wider, so that when you're less than 10 second from the mark, you can already start part of your turn. Of course, beware of wind direction and performance loss. And finally, I recall that maybe I wanted to figure out and describe a somewhat reliable way to determine where you'd end up multiple jumps ahead so that you know whether you need to steer wider or not.

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Koshiki PYOC Sprint 2025


For the first time since 2017 we return to the islands and shima’s offshore Nagasaki, Japan. This time our crafts of choice are X-35’s. Just 23nm in a straight line but choose your course wisely.
Race 1954
INFO by brainaid.de
X-35 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
SPRQ3 - SPRCH - SUPSOL – SYC
Race starts: Sep 20th 15:00 Registration will open soon
▶ Flash
GO TO RACE

Silverrudder 2025


Ahoy, SOLers! Get ready for the epic Silver Rudder – Challenge of the Sea! This 125nm single-handed race around Denmark’s island of Funen is back—shallow waters, narrow straits, and shifting winds await. This year, we trade up to our single-handed X-99s—can you master their power where precision counts most? It’s the world’s largest solo regatta, and your virtual helm is calling! Chart your course, trust your instincts, and race for glory in this ultimate test of seamanship!

It is imperative that you read AND understand these special Starting Conditions for SILVERRUDDER 2025:
Starting Conditions!!
Race #1948
INFO by brainaid.de
X-99 Single-handed PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Sep 19th 09:00 Registration Open!

▶ Flash
GO TO RACE

Rome to Tripoli 2025


The next race in the ARCH series will take us almost straight from Rome to Tripoli. But don't expect this 550nm race to be an easy one. The Mediterranean always offers some surprises. So let's prepare your Lagoon 55 with due care and... Fair Winds.
Race #1943
INFO from brainaid.de
Lagoon 55 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ3 - ARCH - SUPSOL – SYC
Race starts: Sep 15th 17:00 Registration Open!
▶ Flash
GO TO RACE

Carib Rum Run 2025

Welcome to the Caribbean and Sailonline’s legendary Carib Rum Run! This year we trade tall ships for pure speed as we race our sleek Santa Cruz 70s on a 1759nm slalom through the rum islands. Yer mission: plunder barrels from the region’s finest distilleries and deliver ‘em to the rum-thirsty sands of Cancun, Mexico. Finish on or before International Talk Like a Pirate Day, 19 September, to etch yer name in legend! Join SYC before race end and ye scallywags can disguise yer boat with a pirate name for this race only! Hoist the sails, sharpen yer cutlasses—the rum run awaits!
Race #1944
INFO by brainaid.de
Santa Cruz 70 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Sep 15th 00:00 Registration Open!
▶ Flash
GO TO RACE

Roslagen TIMED Sea Race

Welcome to quite possibly the most challenging TIMED race of the year. This month finds us in Sweden with lots of islands and narrow passages when we sail our Seacart 30 trimaran over the 86nm from Lidingö outside Stockholm to the beautiful coastal village of Öregrund. Consider yourself a winner if you complete the course nonstop! 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 #1945
INFO by brainaid.de
Seacart 30 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ3 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
20 September at 23:00 UTC
Race starts: Sep 07th 12:00 Registration Open!
▶ Flash
GO TO RACE

Great Nicobar to Marion Island 2025

The Adventure Continues – Leg #6 of the RWW Series.
We’re setting sail on the next stage of the RWW Series: a 4,400-nautical-mile passage from Great Nicobar to Marion Island. This demanding leg will test endurance, strategy, and seamanship at the highest level. As part of the 2025 Ocean Championship, this marks the ninth legendary challenge in the series — and one of the most exhilarating yet. The race will be contested aboard the Archer 78’ ketch, a vessel built to push sailors to their limits across the vast Indian Ocean.
PRIZE: SMPF
Race #1942
INFO by brainaid.de
Archer 78 PARTICULARS    
WX Updates:
0430 / 1030 / 1630 / 2230    
Ranking: OCQ3 - RWW - OCCH - SUPSOL - SYC
RACE CLOSE: Thursday,
September 25 at 2300 UTC.
Race starts: Sep 01st 11:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member vida
  2. Sailonline Yacht Club Member WRmirekd
  3. Sailonline Yacht Club Member CriticalHippo
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member KaSToR
  6. Sailonline Yacht Club Member Kipper1258
  7. Sailonline Yacht Club Member BRENTGRAY
  8. Sailonline Yacht Club Member Sax747
  9. Sailonline Yacht Club Member Panpyc
  10. Sailonline Yacht Club Member CollegeFund

View full list

Series

Mobile Client

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

The mobile client