Stus-List Re: Understanding Polars

[Josh Muckley via CnC-List]

Dennis said exactly what I was thinking.  I can't think of any time when VMG 
shouldn't be the metric.  Most boats have polars that are flat or concave 
between 170 and 190.  As I understand it this is likely because the boat has 
more wetted surface area when it is flat in the water.  Regardless of spin or 
wing you should get crew weight to the leward side and cheat to the wind as 
much as the boat will allow to maximize VMG.  A preventer helps for safety and 
a whisker pole helps keep the headsail open.  With both you can probably come 
up as much as 10 or even 20 degrees - again, as needed to maximize VMG.  All 
things being equal, jibe when your angle to the mark is slightly more than 
double the amount which you're off 180°.  This will also be about the same time 
that your VMG as a percentage of wind speed will start to drop.  My apparent 
wind meter has demarcations between 160 and 200.  I try to stay out of that 
region...it sucks.

Josh Muckley
S/V Sea Hawk
1989 C 37+
Solomons, MD


Apr 5, 2024 17:31:27 Dennis C. via CnC-List :

>   Personally, I think sailing to polars can be challenging.  I prefer to use 
> VMG.  VMG rules for windward/leeward race courses!  Bear with me on this.
> 
> First, a couple of definitions used by Touche's Nexus instrument system.
> 
> Velocity - speed and course
> VMG - velocity made good wind based.  The velocity directly upwind or 
> downwind.
> WCV - waypoint closure velocity.  The velocity made closing on the set 
> waypoint
> 
> Okay, if your instrument calculates VMG (wind based), simply steer the boat 
> to maximize VMG.  Done!
> 
> If your instruments do not calculate VMG (wind based), here's how to get your 
> GPS to closely approximate it.  First, many GPS systems show VMG which is 
> actually WCV when a waypoint is set.  If you set the upwind (or downwind) 
> mark as the waypoint, WCV will incur more error as you approach the layline.  
> Visualize it.  As you approach the layline, your WCV will decrease to zero as 
> you near 90 degrees to your course to the mark.  (If you overstand, WCV will 
> turn negative as you've sailed past your mark.)
> 
> So, set a waypoint 10 miles directly upwind or downwind of the race mark.  
> Now your GPS WCV will closely approximate VMG (wind based).  Steer to 
> maximize WCV and your course(s) to the mark will be optimized.
> 
> --
> Dennis C.
> Touche' 35-1 #83
> Mandeville, LA
> 
Please show your appreciation for this list and the Photo Album site and help 
me pay the associated bills.  Make a contribution at:
https://www.paypal.me/stumurray
Thanks for your help.
Stu

Stus-List Re: Understanding Polars

[Joel Aronson via CnC-List]

That’s pretty amazing!

Joel



On Fri, Apr 5, 2024 at 8:11 PM Dreuge via CnC-List 
wrote:

> Hi,
>
> Just for the fun of it, I entered the text of your email into ChatGPT4.
>
>
> You:
> I have a set of polars for my C 34+ (below), but I am unsure of how to
> interpret the downwind data.  There is no information I have found on how
> the angles were determined.  I am interested in best angles for downwind
> work without a spinnaker going wing on wing with a whisker pole.  I am
> guessing the data is with a spinnaker and I am not sure if that matters.
> The issue is whether to go wing on wing direct to a mark and go a shorter
> distance vs. wing on wing or not on a lesser angle according to the polar
> chart.  I have tried to measure this on my boat and have not found a big
> enough difference to convince myself I should tack downwind.
>
> ChatGPT:
> Interpreting the downwind data from the polar diagrams of your C 34+
> requires understanding a few key points about these diagrams and how they
> relate to sailing without a spinnaker. Polar diagrams are typically
> generated with a spinnaker, especially for downwind angles, so the speeds
> shown might be higher than what you can achieve wing on wing with just a
> mainsail and a jib.
>
> Here’s how you can approach the interpretation and application of this
> data for wing on wing sailing without a spinnaker:
>
> Understand the Polar Diagram: The polar diagram shows boat speed at
> various wind speeds and angles. If the data is indeed with a spinnaker, the
> speeds at downwind angles will likely be optimistic for wing on wing
> sailing.
>
> Determine Best Angle for Wing on Wing: Without a spinnaker, your best
> downwind VMG (Velocity Made Good) might be at a different angle than what's
> optimal with a spinnaker. Wing on wing is most efficient when the wind is
> directly behind, but if the polar diagram suggests a slightly off-wind
> angle is faster, it may be due to the spinnaker's influence.
>
> Experiment and Record: Since you’ve mentioned not finding a significant
> difference in speeds when testing different angles, it’s essential to
> conduct more trials under various wind conditions and record your boat’s
> performance. Accurate and consistent data can help you understand your
> boat's behavior better.
>
> Consider the Course and Conditions: The choice between going straight
> downwind (wing on wing) or jibing downwind at angles suggested by the polar
> diagram also depends on the course and sea conditions. If the direct
> downwind route is shorter and the speed loss is minimal, it might be the
> better choice. However, if off-wind angles significantly increase speed,
> the extra distance might be worth it.
>
> Adjust for Non-Spinnaker Performance: Since the polar diagrams are likely
> based on spinnaker performance, you might need to adjust the expected boat
> speeds downwind. You can do this by reducing the speed values slightly or
> by using performance data from similar boats sailed without spinnakers.
>
> Software and Tools: Consider using sailing software that can adjust polar
> diagrams for different sail configurations. Some programs allow you to
> input your data and conditions to simulate the best course and sail setup.
>
> Ultimately, the decision to go directly downwind or jibe at angles
> according to the polar chart should be based on a combination of empirical
> data from your own experiences, the specifics of the course and conditions,
> and adjusted expectations from the polar diagrams. Continuous recording and
> analysis of your sailing data will help refine your strategy over time.
>
>
> -
> Paul E.
> 1981 C Landfall 38
> S/V Johanna Rose
> Fort Walton Beach, FL
>
> http://svjohannarose.blogspot.com/
>
> On Apr 5, 2024, at 3:18 PM, Bill Coleman via CnC-List <
> cnc-list@cnc-list.com> wrote:
>
>
>
> On Fri, Apr 5, 2024 at 2:44 PM Bill Coleman  wrote:
>
>> I anguish over this nearly every race, and one thing I can tell you is
>> that whichever choice you decide, you will wish you did the other!
>>
>> Bill Coleman
>> Erie, PA
>>
>>
>>
>> On Fri, Apr 5, 2024 at 1:48 PM David Knecht via CnC-List <
>> cnc-list@cnc-list.com> wrote:
>>
>>> I have a set of polars for my C 34+ (below), but I am unsure of how to
>>> interpret the downwind data.  There is no information I have found on how
>>> the angles were determined.  I am interested in best angles for downwind
>>> work without a spinnaker going wing on wing with a whisker pole.  I am
>>> guessing the data is with a spinnaker and I am not sure if that matters.
>>> The issue is whether to go wing on wing direct to a mark and go a shorter
>>> distance vs. wing on wing or not on a lesser angle according to the polar
>>> chart.  I have tried to measure this on my boat and have not found a big
>>> enough difference to convince myself I should tack downwind.  Dave
>>>
>>>
>>> S/V Aries
>>> 1990 C 34+
>>> New London, CT
>>>
>>> Please show your appreciation for this list and the Photo Album site 

Stus-List Re: Understanding Polars

[Dreuge via CnC-List]

Hi,

Just for the fun of it, I entered the text of your email into ChatGPT4.   


You:
I have a set of polars for my C 34+ (below), but I am unsure of how to 
interpret the downwind data.  There is no information I have found on how the 
angles were determined.  I am interested in best angles for downwind work 
without a spinnaker going wing on wing with a whisker pole.  I am guessing the 
data is with a spinnaker and I am not sure if that matters.  The issue is 
whether to go wing on wing direct to a mark and go a shorter distance vs. wing 
on wing or not on a lesser angle according to the polar chart.  I have tried to 
measure this on my boat and have not found a big enough difference to convince 
myself I should tack downwind. 

ChatGPT:
Interpreting the downwind data from the polar diagrams of your C 34+ requires 
understanding a few key points about these diagrams and how they relate to 
sailing without a spinnaker. Polar diagrams are typically generated with a 
spinnaker, especially for downwind angles, so the speeds shown might be higher 
than what you can achieve wing on wing with just a mainsail and a jib.

Here’s how you can approach the interpretation and application of this data for 
wing on wing sailing without a spinnaker:

Understand the Polar Diagram: The polar diagram shows boat speed at various 
wind speeds and angles. If the data is indeed with a spinnaker, the speeds at 
downwind angles will likely be optimistic for wing on wing sailing.

Determine Best Angle for Wing on Wing: Without a spinnaker, your best downwind 
VMG (Velocity Made Good) might be at a different angle than what's optimal with 
a spinnaker. Wing on wing is most efficient when the wind is directly behind, 
but if the polar diagram suggests a slightly off-wind angle is faster, it may 
be due to the spinnaker's influence.

Experiment and Record: Since you’ve mentioned not finding a significant 
difference in speeds when testing different angles, it’s essential to conduct 
more trials under various wind conditions and record your boat’s performance. 
Accurate and consistent data can help you understand your boat's behavior 
better.

Consider the Course and Conditions: The choice between going straight downwind 
(wing on wing) or jibing downwind at angles suggested by the polar diagram also 
depends on the course and sea conditions. If the direct downwind route is 
shorter and the speed loss is minimal, it might be the better choice. However, 
if off-wind angles significantly increase speed, the extra distance might be 
worth it.

Adjust for Non-Spinnaker Performance: Since the polar diagrams are likely based 
on spinnaker performance, you might need to adjust the expected boat speeds 
downwind. You can do this by reducing the speed values slightly or by using 
performance data from similar boats sailed without spinnakers.

Software and Tools: Consider using sailing software that can adjust polar 
diagrams for different sail configurations. Some programs allow you to input 
your data and conditions to simulate the best course and sail setup.

Ultimately, the decision to go directly downwind or jibe at angles according to 
the polar chart should be based on a combination of empirical data from your 
own experiences, the specifics of the course and conditions, and adjusted 
expectations from the polar diagrams. Continuous recording and analysis of your 
sailing data will help refine your strategy over time.


-
Paul E.
1981 C Landfall 38 
S/V Johanna Rose
Fort Walton Beach, FL

http://svjohannarose.blogspot.com/

> On Apr 5, 2024, at 3:18 PM, Bill Coleman via CnC-List  
> wrote:
> 
> 
> 
> On Fri, Apr 5, 2024 at 2:44 PM Bill Coleman  > wrote:
>> I anguish over this nearly every race, and one thing I can tell you is that 
>> whichever choice you decide, you will wish you did the other!
>> 
>> Bill Coleman
>> Erie, PA 
>> 
>> 
>> 
>> On Fri, Apr 5, 2024 at 1:48 PM David Knecht via CnC-List 
>> mailto:cnc-list@cnc-list.com>> wrote:
>>> I have a set of polars for my C 34+ (below), but I am unsure of how to 
>>> interpret the downwind data.  There is no information I have found on how 
>>> the angles were determined.  I am interested in best angles for downwind 
>>> work without a spinnaker going wing on wing with a whisker pole.  I am 
>>> guessing the data is with a spinnaker and I am not sure if that matters.  
>>> The issue is whether to go wing on wing direct to a mark and go a shorter 
>>> distance vs. wing on wing or not on a lesser angle according to the polar 
>>> chart.  I have tried to measure this on my boat and have not found a big 
>>> enough difference to convince myself I should tack downwind.  Dave
>>> 
>>> 
>>> S/V Aries
>>> 1990 C 34+
>>> New London, CT
>>> 
> Please show your appreciation for this list and the Photo Album site and help 
> me pay the associated bills.  Make a contribution at:
> https://www.paypal.me/stumurray
> Thanks for your help.
> Stu

Please show your 

Stus-List Re: Understanding Polars

[Dennis C. via CnC-List]

Actually, 3 miles might be a bit short.  Excuse the tech analysis but if
one assumes you sail 0.5 miles from the rhumb line between the upwind and
downwind marks and the arbitrary waypoint is only 3 miles away, then 0.5/3
is 0.1667 the sine of which equates to an angle of about 9.5 degrees.  That
would mean about a 10 degree error in your course.

Conversely, 10 miles would be 0.5/10 or .05.  That equates to about 3
degrees error.

Dang, my brain hurts.

--
Dennis C.
Touche' 35-1 #83
Mandeville, LA

On Fri, Apr 5, 2024 at 5:11 PM Dennis C.  wrote:

> Purely arbitrary.  3-5 miles would probably work.
>
> --
> Dennis C.
> Touche' 35-1 #83
> Mandeville, LA
>
> On Fri, Apr 5, 2024 at 4:33 PM Matthew Wolford via CnC-List <
> cnc-list@cnc-list.com> wrote:
>
>> Thanks, Dennis.  How did you arrive at 10 miles.
>
>
>>
Please show your appreciation for this list and the Photo Album site and help 
me pay the associated bills.  Make a contribution at:
https://www.paypal.me/stumurray
Thanks for your help.
Stu

Stus-List Re: Understanding Polars

[Dennis C. via CnC-List]

Purely arbitrary.  3-5 miles would probably work.

--
Dennis C.
Touche' 35-1 #83
Mandeville, LA

On Fri, Apr 5, 2024 at 4:33 PM Matthew Wolford via CnC-List <
cnc-list@cnc-list.com> wrote:

> Thanks, Dennis.  How did you arrive at 10 miles.

Sent from my iPhone
>
> > On Apr 5, 2024, at 5:31 PM, Dennis C. via CnC-List <
> cnc-list@cnc-list.com> wrote:
> >
> > 
> >   Personally, I think sailing to polars can be challenging.  I prefer to
> use VMG.  VMG rules for windward/leeward race courses!  Bear with me on
> this.
> >
> > First, a couple of definitions used by Touche's Nexus instrument system.
> >
> > Velocity - speed and course
> > VMG - velocity made good wind based.  The velocity directly upwind or
> downwind.
> > WCV - waypoint closure velocity.  The velocity made closing on the set
> waypoint
> >
> > Okay, if your instrument calculates VMG (wind based), simply steer the
> boat to maximize VMG.  Done!
> >
> > If your instruments do not calculate VMG (wind based), here's how to get
> your GPS to closely approximate it.  First, many GPS systems show VMG which
> is actually WCV when a waypoint is set.  If you set the upwind (or
> downwind) mark as the waypoint, WCV will incur more error as you approach
> the layline.  Visualize it.  As you approach the layline, your WCV will
> decrease to zero as you near 90 degrees to your course to the mark.  (If
> you overstand, WCV will turn negative as you've sailed past your mark.)
> >
> > So, set a waypoint 10 miles directly upwind or downwind of the race
> mark.  Now your GPS WCV will closely approximate VMG (wind based).  Steer
> to maximize WCV and your course(s) to the mark will be optimized.
> >
>
Please show your appreciation for this list and the Photo Album site and help 
me pay the associated bills.  Make a contribution at:
https://www.paypal.me/stumurray
Thanks for your help.
Stu

Stus-List Re: Understanding Polars

[Matthew Wolford via CnC-List]

Thanks, Dennis.  How did you arrive at 10 miles.
Sent from my iPhone

> On Apr 5, 2024, at 5:31 PM, Dennis C. via CnC-List  
> wrote:
> 
> 
>   Personally, I think sailing to polars can be challenging.  I prefer to use 
> VMG.  VMG rules for windward/leeward race courses!  Bear with me on this.
> 
> First, a couple of definitions used by Touche's Nexus instrument system.
> 
> Velocity - speed and course
> VMG - velocity made good wind based.  The velocity directly upwind or 
> downwind.
> WCV - waypoint closure velocity.  The velocity made closing on the set 
> waypoint
> 
> Okay, if your instrument calculates VMG (wind based), simply steer the boat 
> to maximize VMG.  Done!
> 
> If your instruments do not calculate VMG (wind based), here's how to get your 
> GPS to closely approximate it.  First, many GPS systems show VMG which is 
> actually WCV when a waypoint is set.  If you set the upwind (or downwind) 
> mark as the waypoint, WCV will incur more error as you approach the layline.  
> Visualize it.  As you approach the layline, your WCV will decrease to zero as 
> you near 90 degrees to your course to the mark.  (If you overstand, WCV will 
> turn negative as you've sailed past your mark.)
> 
> So, set a waypoint 10 miles directly upwind or downwind of the race mark.  
> Now your GPS WCV will closely approximate VMG (wind based).  Steer to 
> maximize WCV and your course(s) to the mark will be optimized.
> 
> --
> Dennis C.
> Touche' 35-1 #83
> Mandeville, LA
> 
> Please show your appreciation for this list and the Photo Album site and help 
> me pay the associated bills.  Make a contribution at:
> https://www.paypal.me/stumurray
> Thanks for your help.
> Stu
Please show your appreciation for this list and the Photo Album site and help 
me pay the associated bills.  Make a contribution at:
https://www.paypal.me/stumurray
Thanks for your help.
Stu

Stus-List Re: Understanding Polars

[Dennis C. via CnC-List]

  Personally, I think sailing to polars can be challenging.  I prefer to
use VMG.  VMG rules for windward/leeward race courses!  Bear with me on
this.

First, a couple of definitions used by Touche's Nexus instrument system.

Velocity - speed and course
VMG - velocity made good wind based.  The velocity directly upwind or
downwind.
WCV - waypoint closure velocity.  The velocity made closing on the set
waypoint

Okay, if your instrument calculates VMG (wind based), simply steer the boat
to maximize VMG.  Done!

If your instruments do not calculate VMG (wind based), here's how to get
your GPS to closely approximate it.  First, many GPS systems show VMG which
is actually WCV when a waypoint is set.  If you set the upwind (or
downwind) mark as the waypoint, WCV will incur more error as you approach
the layline.  Visualize it.  As you approach the layline, your WCV will
decrease to zero as you near 90 degrees to your course to the mark.  (If
you overstand, WCV will turn negative as you've sailed past your mark.)

So, set a waypoint 10 miles directly upwind or downwind of the race mark.
Now your GPS WCV will closely approximate VMG (wind based).  Steer to
maximize WCV and your course(s) to the mark will be optimized.

--
Dennis C.
Touche' 35-1 #83
Mandeville, LA
Please show your appreciation for this list and the Photo Album site and help 
me pay the associated bills.  Make a contribution at:
https://www.paypal.me/stumurray
Thanks for your help.
Stu

Stus-List Re: Understanding Polars

[Bill Coleman via CnC-List]

On Fri, Apr 5, 2024 at 2:44 PM Bill Coleman  wrote:

> I anguish over this nearly every race, and one thing I can tell you is
> that whichever choice you decide, you will wish you did the other!
>
> Bill Coleman
> Erie, PA
>
>
>
> On Fri, Apr 5, 2024 at 1:48 PM David Knecht via CnC-List <
> cnc-list@cnc-list.com> wrote:
>
>> I have a set of polars for my C 34+ (below), but I am unsure of how to
>> interpret the downwind data.  There is no information I have found on how
>> the angles were determined.  I am interested in best angles for downwind
>> work without a spinnaker going wing on wing with a whisker pole.  I am
>> guessing the data is with a spinnaker and I am not sure if that matters.
>> The issue is whether to go wing on wing direct to a mark and go a shorter
>> distance vs. wing on wing or not on a lesser angle according to the polar
>> chart.  I have tried to measure this on my boat and have not found a big
>> enough difference to convince myself I should tack downwind.  Dave
>>
>>
>> S/V Aries
>> 1990 C 34+
>> New London, CT
>>
>>
Please show your appreciation for this list and the Photo Album site and help 
me pay the associated bills.  Make a contribution at:
https://www.paypal.me/stumurray
Thanks for your help.
Stu