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3/31/2016 3:21 pm  #1


Departure Planning

I'm trying to plan a delivery, and looking at options for departure times, based on current along the route.  This is months away, so there are no GRIB files available.  No issues with the route in Expedition.  And Expedition has the built in tidal streams.  But I can't find a way to have it use a defined speed.  I'd like the use the Optimize Multiple, to establish a few different departure times, then define a speed, say 6kts, and have it run the optimization, taking into account the tidal streams.  But an optimization needs a GRIB file.  I could trick the speed part by making a delivery GRIB that had the same speed for all wind pressure, and angles, but for the tidal streams to be accurate, I'd want to use the actual dates.  Is there any way around not having a GRIB?  Or does someone have a good work around for departure planning?  Am I missing something obvious?

To me, it seems like Expedition is really close to having this.  There is already a "motor if speed is below" function.  It just needs a way to manually input a speed, rather than use (GRIB + Polar).

 

3/31/2016 3:52 pm  #2


Re: Departure Planning

JRG,
The tides pretty much do repeat, so couldn't you pick a tide period when you 'want' to leave and find a corresponding tide currently available i.e. flood starts at 1700 on June 17 corresponds to flood starts at 0400 tomorrow and then use tomorrows wx to do the optimization.  Not gonna be exact but if you pick a day with 'typical' June 17 wx than at least a good guess.
Cheers

 

3/31/2016 10:01 pm  #3


Re: Departure Planning

I have done some routing based around the same requirements (for motorboat) with a fixed speed polar similar to what I think you are trying to achieve - with a simple TWS 0, 15 and 30 kt, and TWA 0, 90 and 180. Something like this:
          A  S  A  S  A   S   
0        0  6  90 6 180 6
15      0  6  90 6 180 6
30      0  6  90 6 180 6

So for any given wind grib you will always have a boatspeed of 6kt.

And using the offset to a day with a similar tide cycle as mentioned by Ernie M you should be able to achieve what you are after.

Hope this helps.


:::Campbell Field::::::www.fieldyachting.com:::
 

4/01/2016 5:40 am  #4


Re: Departure Planning

Thanks Ernie & Campbell.  This is pretty much the conclusion I had come to also.  I guess it just seemed a little more complex than I'd like.  For instance, to see what would happen if you averaged a slightly higher speed, you'd have to copy and edit a new polar.  And always have to do the time correction in your head between the tide of a day inside a 16 day GRIB, and the day the trip is actually taking place.

     Thread Starter
 

4/03/2016 11:01 am  #5


Re: Departure Planning

JRG wrote:

Thanks Ernie & Campbell.  This is pretty much the conclusion I had come to also.  I guess it just seemed a little more complex than I'd like.  For instance, to see what would happen if you averaged a slightly higher speed, you'd have to copy and edit a new polar.  And always have to do the time correction in your head between the tide of a day inside a 16 day GRIB, and the day the trip is actually taking place.

You don't have to create a new polar, you can simply adjust by %


:::Campbell Field::::::www.fieldyachting.com:::
 

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