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:

Doha Basra TIMED Race 2026

Welcome to Kuwait for a short 78 nm TIMED race from the port of Doha (not to be confused with Doha, Qatar) to Basra, Iraq. Jazirat Light on Auha Island is the only mark to observe, leaving it to port. The Beneteau First 40.7v2 racer-cruiser is our ride this month. 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 #2008
INFOby brainaid.de
First 40.7v2 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ1 - TRCH - SYC
RACE CLOSE: Saturday,
28 February at 23:00 UTC
Race starts: Feb 15th 12:00 Registration will open soon
▶ Flash
GO TO RACE

San Diego Islands Race 2026


Sailonline is proud to once again partner with the San Diego Yacht Club for the annual Islands Race! This iconic offshore challenge spans approximately 140 nautical miles, starting in Long Beach, rounding the Catalina Islands, and finishing in San Diego. Shifting coastal winds and tactical island roundings will test every sailor’s judgment and nerve.

This year, our SOLers will race the Ker 40, a proven high-performance design by Jason Ker and built by McConaghy Boats. Fast, responsive, and demanding, the Ker 40 rewards precision and smart strategy. The competition will be tight. Every decision will count. See you on the start line!
Race #2009
INFO by brainaid.de
Ker 40 PARTICULARS
NAM_AWIP WX Updates:
0245 / 0845 / 1445 / 2045
Ranking:
SUPBUD - SYC
Race starts: Feb 13th 20:00 Registration Open!
▶ Flash
GO TO RACE

Cross the Convergence 2026 - Samoa to Hawaii


The second race of our new series of ocean voyages across the World’s convergence zones, takes us northward again up the Pacific Ocean, now from Samoa at 13.5 degrees South, across the Equator to Hawaii, famed for its breaking surf and active volcanoes, on the edge of the Tropic of Cancer at 19.5 degrees North. It’s 2300nm, so we’ll take our very steady Steinlager II. Race #1982
INFOby brainaid.de
Steinlager IIPARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: CCZ - SYC
Race starts: Feb 06th 18:00 Registration Closed
▶ Flash
GO TO RACE

Beketov by Balloon 2026 - In Siberia


Way-back-when France and England, and Spain as well, were squabbling about who should control what of North America, only to lose the most of it to their own insurging colonists, their eastern European neighbour empire, Russia, was quietly assimilating vast, thinly nomadically populated territory of its own – Siberia! Amongst the many explorers and adventurers that served Russia so well in these conquests was the Cossack hetman Pyotr Beketov. Let’s pretend we’re he and eschewing horseback, let’s travel by balloon from Yekaterinberg to Krasnoyarsk – just a short 2000km (1100nm) section of the Trans-Siberian Express’ 9289km!
Race #1972
INFOby brainaid.de
SOL Balloon PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: BOL - SYC
Race starts: Feb 03rd 13:00 Registration Closed
▶ Flash
GO TO RACE

West Papua to Oregon 2026

Our next race in our Ocean Championships is the first of a series of great natural migrations we will track in 2026. The leatherback turtle is the most widely distributed marine reptile on planet Earth, and chooses to breed in warm tropical waters, but prefers to forage in more temperate habitats, travelling thousands and thousands of miles effortlessly annually to maintain this way of life. Our race will follow one of the typical trips of this turtle, from breeding grounds in the seas off West Papua to the coast of Oregon. It’s only 5900nm, so to keep up, but in comfort, we’ll follow in our Gunboat 90.
Race #2006
INFO by brainaid.de
GB 90 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ1 - OCCH - MIG - SYC
Race starts: Feb 02nd 11:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

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

View full list

Series

Mobile Client

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

The mobile client