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Board » General Discussion » Timing Course Changes

Posted by
bonknhoot


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2013-08-06 21:35:15
2014-05-04 13:17:52 - Timing Course Changes
Just read Roland Stoerte's report on the B2B2 of last night. As he wrote it was all about 'rounding' and a minor tactical decision for the close-hauled bit to the finish: pinch or put in a tack. Roland writes about 'counting' to know when to press 'send command'. How does that work, anybody?
During my short SOL career I have developed a quite different approach to the dilemma of 'timing'. I found a few VBA UDF's on the net which return course and distance between two lats and lons. So I enter the relevant lats and lons into a spreadsheet before a race (or as I go along) and then copy and paste time of day, speed and position over from BrainAid (ever more frequently) as I close on a buoy or a cape or a shore. If BrainAid's data is fully synced, then my spreadsheet returns me my exact ETA to the next manoeuvre, except of course that speed may change as I progress and that I may be on a TWA curve and not a COG straight line. Editing the pre-set DC then completes the process and with 30 secs to go I just sit back and wait. It continues to surprise how much the calc'd ETA varies from one sample to the next. Even with just two or thee minutes to the mark and no noticeable speed variation (e.g as a result of performance recovery perhaps) the swings are often order of mag 5 to 10 secs. An element of luck and a trade-off risk v reward thus remains. So... does BrainAid provide a wholly accurate sync'd sample of a SOL yacht's data, or... ?
Thoughts anybody?
Clipping along
Posted by
kroppyer


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2010-02-05 15:25:55
2014-05-04 19:34:55 - Re: Timing Course Changes
SOL's normal client updates your own boat position every 15 seconds, and requests its data directly from sailonline.

brainaid's navigation page updates boat data roughly every 10 seconds, and requests its data from brainaid.de (which probably gets its data, without caching, from sailonline).

Sailonline recalculates the position of your boat with a variable interval. My experience is that this interval is usually 10 seconds.

This means that, using sol's client, you will see your boat move every 15 seconds (maybe in a rare case, 30 seconds). If you see you have only one jump left to the mark, you can count to 10, and then turn, assuming the server already jumped, but before the client updates. This can go wrong.

Sometimes I get the feeling that commands are executed in-between two jumps (boat turns less than a single jump-length from my last position). Sometimes, even after 10 seconds, my boat turns at its last position, 5 seconds later the client updates and shows a track that suggests my boat turned 10 seconds earlier than I sent the command.

If you set a good DC, with some margin (and do not adjust it using the DC countdown, unless you are sure your local clock is in sync with sailonline), your boat often does a good rounding.

For now, I think the best method is:
set a reasonably safe DC (like 10 seconds after the mark), then try to beat that manually, using your preferred method (counting, instinct, visual, confidence, praying, persuasion of sol server, telekinesis).

Turning you boat at an exact place is hard, and I think part of a good rounding is not only getting your boat to turn where you want it to turn, but also accepting that you can't do that, and solving it differently: leave some room to the mark (or land), turn about one jump before you're at the mark so that you touch the mark (this needs practise). You will sail past the mark with a better angle: the distance you travel after the mark is not as much in the wrong direction as usual. When you can, of course, complete the turn.


This is how accurate DC roundings can be:


--- Last Edited by kroppyer at 2014-05-04 20:11:18 ---
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Posted by
JB


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2013-03-07 08:54:34
2014-05-05 07:57:38 - Re: Timing Course Changes
Viva Jan and Kroopy.

Not long ago in this forum I’ve put some words about my frustration precisely about this issue.
So, I’m totally in tune with both.
My conclusions were/are simple.
Instead of a precise boat maneuver, trying to turn where you need and want, it’s an act of pure luck and/or faith.
For the same “sail engine” input conditions (TWD/TWA/TWS) the same boat has, sometimes, makes different consecutive jump lengths and, even in the same run, different ones.
So, I discovered also that my boat has free will, challenging logic, laws of kinematics, accuracy and, in last ratio, the patient of the sailor.

In long races, unless you are close to a competitor, it doesn’t make a big difference or, any at all.
In TR’s, where go “cutting the corners”, it can result in loss of several places.

Yes, we have to accept that “luck” is part of the sport, but it shouldn’t be here applicable.

There are two (cumulative, or not) solutions for this problem:

1 - Effective DC’s - function of remaining distance and B.S., the boat changes direction in the precise calculated time, as it should be;
2 - Waypoints - the boat changes direction on previously defined marks, independently of all the prevailing conditions.

The same lack of accuracy can be pointed to the famous “jumps over land”.
I was in shock when it happened to me.
Again, it shouldn’t.

Big Hug from
João
Sail Fair.
Posted by
Rod


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2010-06-24 22:30:48
2014-05-05 16:14:57 - Re: Timing Course Changes
The above entries describe very closely my own experience and complaints about the precise point and time at which course changes are executed. I also have not,(so far?) been able to determine any "formula" which describes the process.
My question here, as a "non-user-of-routers", and observing the superior performance of those who do use them, is whether these routers have SOLVED this problem. Am I merely penalizing myself and my SOLing performance by refraining from their use, just to keep tuned the "old grey cells"?
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Posted by
kroppyer


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2014-05-05 21:20:32 - Re: Timing Course Changes
Rod,

Most* routers are useless in these short races. To speed up the routing process they use "jumps" of much more than 10 or 15 seconds. So they certainly do not help you rounding marks (or at least, not when you can't lose a few minutes).

*) I say "most" because I can't pretend to know "all" routers. Maybe there is a router, specifically made for online sailing, that is able to use very small jumps.
Posted by
Rod


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2014-05-06 02:23:05 - Re: Timing Course Changes
I will continue to exercise the "old grey cells"---in the vague hope that they will become "young" grey cells----if I could just remember 'how' to do it......

--- Last Edited by Rod at 2014-06-27 16:28:18 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.

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