Expedition Expedition Navigation Software

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7/24/2017 2:01 am  #1

Optimisation Results - glossary/descriptions

Is there any place I can go, to get detailed descriptions of each of the columns in the optimization results?

The help documentation (including appendix) has a good glossary of numbers boxes, but doesn't go into the detail of optimization results. Eg some question I had: how targ is used/relates to twa, is bearing the same as heading to steer?


7/24/2017 2:50 am  #2

Re: Optimisation Results - glossary/descriptions

Target twa is just the target from the polar used at that wind speed.


7/24/2017 5:47 am  #3

Re: Optimisation Results - glossary/descriptions

Thanks Nick,

Still a bit confused. My understanding: for a given TWS, polars provide boat speeds for various TWA. So how does the optimizer settle on the one TWA to report for the given wind speed? Or am I missing the point entirely and I should look at it as a measure of TWA adjusted for tide and/or boatspeed (which I guess is apparent)

And is bearing the same as heading to steer, or does it make other assumptions about leeway/tide?

Some illustration of how these outputs might be used to help guide the helmsman would be useful.

     Thread Starter

7/24/2017 1:02 pm  #4

Re: Optimisation Results - glossary/descriptions

Exp knows (or has worked out where it is going next in the route optimisation). So it knows what the TWA is and thus polar bsp.

​If there are currents, Exp has to correct the grib winds for them.

​If you look at the paths as well, you can see what Exp is doing.

​The bearing is just the great circle bearing between points on the optimal path. It could have been made to be course to steer, but that would just complicate things in the output.



7/25/2017 12:54 am  #5

Re: Optimisation Results - glossary/descriptions

Thx Nick, almost getting there now, apologies for the newbie deep dive, final followup!

Under what circumstances would you expect the twa and targ (twa) to be different? is it simply that targ twa is twa with tide effect added on?

Bearing now clear thx! Helm should match COG to bearing the follow the route (assuming tide, wind, etc matching)

     Thread Starter

7/25/2017 2:10 am  #6

Re: Optimisation Results - glossary/descriptions

Target twa (and bsp) by definition is the upwind or downwind target.


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