Expedition Expedition Navigation Software

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7/11/2019 4:06 pm  #1


Routing shows sailing directly upwind?

I have attached an image of the routing table. It show sailing directly upwind?

https://imgur.com/IE2cphL

 

7/11/2019 5:52 pm  #2


Re: Routing shows sailing directly upwind?

Twa values in parentheses indicate tacking or gybing. Also see the comments in the Exp help.

 

7/12/2019 2:36 pm  #3


Re: Routing shows sailing directly upwind?

This is a big question that every user hits after they have stared at routes for a while.  Try explaining it to your yachtmaster the first time.
Nick, the related question I have is about the TWA/TWS and sail usage summary (Results/Filter).  I assume the ? entries in the sail summary are where TWAs are narrower or deeper than the loaded polars and crossover.  How does that reconcile with the TWA/TWS table, which is entirely within the limits of the polars?

 

7/12/2019 4:23 pm  #4


Re: Routing shows sailing directly upwind?

Thanks, I am trying to understand this. Even when you play the route it shows the boat sailing upwind angles that it can't physically achieve?  It does graphically show "tacks" but at very shallow angles. Not the angles on the polars for that wind speed and wind angle.

     Thread Starter
 

7/12/2019 5:03 pm  #5


Re: Routing shows sailing directly upwind?

From the help:

Important note
If any TWA value is in parentheses, for example (-12), then Exp has tacked or gybed for that part of the optimal route.
Sometimes this might be one tack or gybe, but in other cases it might mean staying in a lane of stronger wind for example.
These will also be displayed as dashed lines on the chart.

 

7/12/2019 8:31 pm  #6


Re: Routing shows sailing directly upwind?

This is how I explain it to the crew when they ask .... as they always do. The software is routing you from one internal "waypoint" to  another via a series of short "legs".  The algorithm spits out a TWA for each of these legs derived from TWD and HDG at the time and place.  If the TWD is (say) 180 degrees, and the HDG is also 180, then the TWA is 0 degrees.  In that case, you'll tack on the favourable oscillations to get there quickest.  The software can't allow for those oscillations, and doesn't.  Likewise for TWAs greater than your polar angles downwind.
How'm I doing, Nick?

 

7/12/2019 11:56 pm  #7


Re: Routing shows sailing directly upwind?

Yes, often it can be a good indicator that tacking on the shifts will be rewarding.

 

7/16/2019 6:13 pm  #8


Re: Routing shows sailing directly upwind?

Ok, Bear with me  Seeing the track show the boat going straight upwind without tacks, does the routing include the extra distances and time expend we you have to tack upwind seeing you cannot sail straight to the mark? Do I need to add this time and distance to come up with a valid time and distance?
Sorry if I am missing something.

     Thread Starter
 

7/16/2019 6:32 pm  #9


Re: Routing shows sailing directly upwind?

Expedition allows for that and includes tacking and gybing.

It could be that Exp thinks it is important to get upwind in that location or it could be wanting to stay in a lane of pressure.

As above, assuming the forecast is correct, it can be a good indication to tack or gybe on the shifts.

The other useful information is that a value such as (-12) indicates tacking, with more time on port. That is mentioned in the help.

Will Oxley also mentions it in his ebook.

 

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