Polars again

[David Knecht]

I lost my polar plots sheet overboard at the end of last season so I was reprinting them to put on the boat in the spring.  I noticed that there are some discrepancies in the various versions that have been posted that I don't understand.  

Looking at 10 knots TW from the spreadsheet:

upwind

TWV=10, BTW= 42, V=6.1

downwind

TWV=10- BTW 173, V=5.1

But the extracted polar plot

upwind

TWV=10 BTW= 42, v=4.8

downwind

TWV=10, BTW=146, V=4.9

Those are quite different in optimum upwind speed and downwind angle.  Am I misreading?  Dave

[Chuck Scheaffer]

I think one table shows "velocity made good" and the other shows boat speed?

Chuck

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David Knecht

S/V Aries

1990 C&C 34+

New London, CT

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[David Knecht]

Hi Chuck- I had the same thought but felt that velocity would be a pretty useless parameter to work toward as an upwind target.  Technically, that would be "speed" not "velocity" since velocity has a directional vector which is why we have VMG where the vector is toward the mark.  I was actually even more concerned about the downwind target.  146 vs. 170 is really different as an optimal target. I will believe the polar plot data since it is pretty clear where the numbers come from and I don't know where the table data comes from.    Dave

  

David Knecht

S/V Aries

1990 C&C 34+

New London, CT

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[Chuck Scheaffer]

Those polars are based on a clean bottom, good sails including spinnaker.  I never know if they involve a spinnaker for reaching.

C

 

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[David Knecht]

And whether downwind targets apply to wing on wing with whisker pole and no spinnaker.  

PS- I am shocked that you might consider racing with a dirty bottom and old sails!

David Knecht

S/V Aries

1990 C&C 34+

New London, CT

On Feb 6, 2026, at 4:46 PM, Chuck Scheaffer <scheaff...@gmail.com> wrote:

Those polars are based on a clean bottom, good sails including spinnaker.  I never know if they involve a spinnaker for reaching.

C

 

On Fri, Feb 6, 2026 at 4:41 PM David Knecht <davida...@gmail.com> wrote:

Hi Chuck- I had the same thought but felt that velocity would be a pretty useless parameter to work toward as an upwind target.  Technically, that would be "speed" not "velocity" since velocity has a directional vector which is why we have VMG where the vector is toward the mark.  I was actually even more concerned about the downwind target.  146 vs. 170 is really different as an optimal target. I will believe the polar plot data since it is pretty clear where the numbers come from and I don't know where the table data comes from.    Dave

David Knecht

S/V Aries

1990 C&C 34+

New London, CT

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[Chuck Scheaffer]

I would never intentionally race with a dirty bottom.  We used to dive before a race using a hookah and scrub the bottom.  Only took 45 minutes and made a big difference.  We suffered one race when my son neglected to clean the prop and shaft of barnacles.  It was frustrating to lose a knot and see other boats get ahead because of it.  I was just commenting before that the speeds on the graph require a clean bottom.  

I'm pretty sure the polars are based on spinnaker downwind, not wing and wing.  On some polars, there is a crossover where genoa and spinnaker cross near the 90 degree sailing angle.

C

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