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 Support » #4 simple question to Phillipe/maitai.

Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-05-13 10:49:09 - #4 simple question to Phillipe/maitai.
Viva all.

And the questions are:

1 - Does qT uses Time Steps (TS) (in time units) calculations for the Isochrones calculations?
2 - If yes, is it 1 minute the minimum TS?
3 - If it doesn’t use TS for Isochrones calcs, does qT use Distance Step (DS) (in distance units)?
4 - In that case is 1 nm the minimum DS?

Thank you.
Sail Fair.
Posted by
maitai


Users avatar

Posts
114
Registered at
2016-02-25 08:15:33
2016-05-17 07:01:06 - Re: #4 simple question to Phillipe/maitai.
qtVlm uses a time step (otherwise it won't be called isochrone, would it?). The internal time step is configurable in the general settings. The minimum is 1mn. Routing module uses this internal step to calculate a way from one isochrone to the next, but the minimum time step between two isochrone is 5mn. That is already too small and useless, taking too much cpu, memory and time for nothing at all. 30mn or 1h between iso is a much better choice.
Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-05-17 13:30:52 - Re: #4 simple question to Phillipe/maitai.
Viva Philippe.

Thank you for your reply but it didn’t clear out my doubts. By the contrary.

I knew/know that qT used/uses one of the two processes: “Time” or “Distance” Step for calculating consecutive Isochrones.
Hence my questions on previous points 1 and 3.

As you know, if the process is a “Time Step” one, we have to use “Time” units for it, (seconds, minutes, hours, etc.).
But, if the process is a “Distance Step” one, the units are “Length” (meter, km, nautical miles, etc.).

In your reply you mix the “internal time step” (sic, I assume that it is in “Time” units) with a “minimum” of “1 nm” for the calculations (I assume it is in “Length” units), and “5 nm” for the distances between consecutive Isochrones (idem).

At minimum, it’s not physically congruent, Philippe.
Or you use time or you use distance. Not both at the same time.

Meanwhile I’ve made a small test with qT - pls see attached picture.
In top of a trivial routing I’ve put two marks, the first at the distance made by the boat on 1 minute and a second mark at a distance made in 5 minutes, this one on top of the first shown Isochrone in the routing.
Well, being an Isochrone calculation what you get in the chart plotter is a representation of the consecutive curves that can be reached at at the same time by a boat travelling at a constant speed between them.
But, again, I’m using here only “time” units (minutes), not “nm” (nautical miles), Philippe.

In relation to your opinion that “is already too small and useless”, the 5 minutes, I totally disagree.
There are several reasons for it. I give you two:

- Light winds;
- Fast boats on tight spaces.

Thank you again, Philippe.
Sail Fair.
Attachments
Posted by
maitai


Users avatar

Posts
114
Registered at
2016-02-25 08:15:33
2016-05-17 13:53:33 - Re: #4 simple question to Phillipe/maitai.
The minimum time between 2 routes points in 1 minute. The minimum time between 2 isochrones is 5 minutes. In case these 2 values are set to the minimum, it means it takes 5 steps to qtVlm to generate one isochrone. There is no distance concept there or elsewhere.
Posted by
maitai


Users avatar

Posts
114
Registered at
2016-02-25 08:15:33
2016-05-18 07:19:22 - Re: #4 simple question to Phillipe/maitai.
Plus: the boat does not travel at constant speed between 2 isos, not in real life nor in qtVlm. Wind and currents change constantly between 2 isos, and qtVlm takes that into consideration.

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Tall Ships Races 2025 - Dunkirk to Aberdeen


Welcome to the second of four virtual Tall Ships Races in European waters which are concurrently being organized in-real-life Sail Training International . This second race is from Dunkirk in France up the North Sea to Scotland’s Aberdeen; circa 400nm in Sailonline’s magnificent 90m Barque.
NOTE: Starts and Finishes in tall ships racing are always offshore to avoid conflict with shipping and shipping lanes; online and real-life may not match exactly.
Race #1924
INFO by brainaid.de
Barque 90m PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: TS - SYC
Race starts: Jul 13th 16:00 Registration Open!
▶ Flash
GO TO RACE

Suursaari TIMED Race 2025

The first TIMED race of the northern hemisphere Summer takes us to the Gulf of Finland on a 165nm zig-zagging course beginning and ending in the seacoast village of Haukilahti and circling the island of Suursaari. It’s only appropriate that the boat for this race is Finland’s own Club Swan 50. 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 #1928
INFOby brainaid.de
PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ3 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
26 July at 23:00 UTC
Race starts: Jul 13th 12:00 Registration Open!
▶ Flash
GO TO RACE

Lake Ontario 300 Challenge 2025

Lake Ontario Offshore Racing (LOOR) welcomes Sailonline sailors (SOLers for short) to a second virtual version of a race in their annual series, the LO300. As the name implies, the LO300 is a 300nm offshore race across the length and breadth of Lake Ontario, from and back to Port Credit YC. Once again, as is our wont on Lake Ontario, a fleet of Beneteau First 36.7s is being made available to virtual racers. There is an overall prize for the SOLer who best bosses Lake Ontario over the two races hosted by Sailonline, this 300 and the Susan Hood raced back in May; so, let the competition be fierce!
Race #1931
INFOby brainaid.de
First 36.7 PARTICULARS
NAM_AWIP WX Updates:
0245 / 0845 / 1445 / 2045
Ranking: LOOR - SYC
Race starts: Jul 12th 15:10 Registration Open!

▶ Flash
GO TO RACE

SSANZ Triple Series 2025 - Race 1

Join the excitement as Sailonline partners again with New Zealand's Short-handed Sailing Association for the thrilling SSANZ Triple Series, proudly sponsored by Lewmar Marine. Our SOLers will tackle an exhilarating 47-nautical-mile race, navigating the waters of the beautiful Hauraki Gulf out to Motuora Island via The Haystack and back. Racing virtual Young 88 yachts, our virtual fleet will match skills and strategies with the real-life fleet of the vibrant Young 88 Association. Don't miss this intense, tactical challenge!
Race #1932
INFO by brainaid.de
Young 88 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
SSANZ - SYC
RACE CLOSE: Tuesday,
July 15 at 2300 UTC.
Race starts: Jul 11th 21:15 Registration Open!
▶ Flash
GO TO RACE

Tall Ships Races 2025 - Le Havre to Dunkirk


Welcome to the first of four virtual Tall Ships Races in European waters which are concurrently being organized in-real-life by Sail Training International . The course for this first race is between the French ports of Le Havre and Dunkirk; circa 125nm in Sailonline’s magnificent 90m Barque.
NOTE: Starts and Finishes in tall ships racing are always offshore to avoid conflict with shipping and shipping lanes; online and real-life may not match exactly.
Race #1923
INFO by brainaid.de
Barque 90m PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: TS - SYC
RACE CLOSE: Monday,
July 14 at 2300 UTC.
Race starts: Jul 07th 16:00 Registration Closed
▶ Flash
GO TO RACE

Young Island to Great Nicobar 2025

The adventure continues as we launch this fifth leg of the RWW series, racing from Young Island to Great Nicobar on the edge of the Bay of Bengal. Get ready for a chilling start as we set sail on the seventh leg of the 2025 Ocean Championship Series! A 5200nm journey of endurance, strategy, and pure sailing excitement. This leg will be pursued aboard the Super Maxi 100v2, pushing sailors to their limits. Do you have what it takes to conquer the Indian Ocean? Join us and put your skills to the ultimate test!
PRIZE: SMPF
Race #1929
INFO by brainaid.de
Super Maxi 100 v2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ3 - RWW - OCCH - SUPSOL - SYC
Race starts: Jul 07th 11:00 Registration Open!
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member CriticalHippo
  2. Sailonline Yacht Club Member WRmirekd
  3. Sailonline Yacht Club Member KaSToR
  4. Sailonline Yacht Club Member FreyjaUSA
  5. Sailonline Yacht Club Member rafa
  6. Sailonline Yacht Club Member Kipper1258
  7. Sailonline Yacht Club Member rumskib
  8. Sailonline Yacht Club Member BRENTGRAY
  9. Sailonline Yacht Club Member vida
  10. Sailonline Yacht Club Member YANN

View full list

Series

Mobile Client

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

The mobile client