Expedition Expedition Navigation Software

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7/28/2019 2:23 am  #1


Holding wind constant to study tidal effects?

In the August 2019 issue of Yachting World Libby Greenhalgh's Navigation Briefing column focuses on Fastnet preparation. In it she suggests getting a feel for the tidal gates by running a number of routings with the wind fixed to the course average strength and direction while varying the start times. Is there a simple way to do this in Expedition? Or is the solution to create an artificial grib file with spacial and temporal resolution so low that it covers the entire course for the length of the race?

TIA,
Kass

 

7/28/2019 3:10 am  #2


Re: Holding wind constant to study tidal effects?

Kass,
You can do that using "Instrument" feature on the Optimize tab and readjusting your Settings to "use Instrument winds" 

Another method, I like better, is to find the tide point at the time of your class start of your race.
Say it's '1 hour after flood at Point Rump'
Find that tide point for every day from now until the actual Start
Every day until the race, use the time that corresponds to  '1 hour after flood at Point Rump' as your start; with 'real' wind.

You will get a variety of wind conditions but with close to the actual tides for your race
AND you can run all the fabulous features built into the Expedition Optimize tab; like 'TWS%' and 'TWD+/-'

Good Luck in the Fastnet!
Ernie


“If you don't know where you are going,
you'll end up someplace else.”
Yogi Berra
 

7/28/2019 7:28 am  #3


Re: Holding wind constant to study tidal effects?

Meant to say:
"using "User" or "Instrument" feature on the Optimal tab
E


“If you don't know where you are going,
you'll end up someplace else.”
Yogi Berra
 

7/28/2019 3:03 pm  #4


Re: Holding wind constant to study tidal effects?

The other thing I notice is that people use far too many marks for routings. The fewer the better in general.

 

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