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

Stus-List Re: 36-1 Stuffing Box Access.

[Richard Bush via CnC-List]

Mike, I have 37 and I share your pain in getting to the stuffing box area; I 
went with the PYI and have been happy with it; there are other brands which 
seem to do well also; I just didn't want to crawl down in there on a frequent 
basis, and bit the bullet on the new shaft...; best of luck with your 36!   

Richard
1986 C 37 CB; Ohio River, Mile 596;

Richard N. Bush Law Offices2950 Breckenridge Lane, Suite NineLouisville, 
Kentucky 40220(502) 584-7255
 

On Thursday, April 4, 2024 at 10:33:40 PM EDT, Mike Nicholls via CnC-List 
 wrote:  
 
 
John,

 I replaced my flax packing with Tefpak along with Teflon lubricant. I am 
continually adjusting  the stuffing box to get an appropriate drip rate of 1-2 
drops/min with the shaft rotating. The drip continues when the engine is not 
running. Fortunately my boat is a 35 Mark III with easy access to the stuffing 
box. (Only minimal boat yoga needed to access the stuffing box).  If your 
access is poor my recommendation is to continue with flax. 

Mike Nicholls 

From: John McCrea via CnC-List [mailto:cnc-list@cnc-list.com] 
Sent: April 4, 2024 4:08 PM
To: 'Stus-List'
Cc: johnmcc...@comcast.net
Subject: Stus-List Re: 36-1 Stuffing Box Access.

  

Thanks John.

  

From: John Read via CnC-List  
Sent: Thursday, April 4, 2024 7:06 PM
To: Stus-List 
Cc: John Read 
Subject: Stus-List Re: 36-1 Stuffing Box Access.

  

Hi John. Teflon packing works great.  Check with Brer Rabbit.  Their 33-1 
engine is mounted backwards with a v drive so the stuffing box is under the 
engine so limited access. Hope this helps John of the 34 aforementioned. 

  

On Thu, Apr 4, 2024, 7:00 PM John McCrea via CnC-List  
wrote:


36-1 Owners,

 

Hello. I am looking for any insight into how any 36 owners have managed the 
lack of access to the stuffing box. Each time I want to get it, we have to pull 
the muffler, and then the access is still very limited. On the other 3 boats I 
have owned, it was a piece of cake. I'm not sure what they were thinking.

 

I looked into the PYI system, but my yard wanted to cut the shaft and put in a 
new one. It is less than 10 years old, so that is a no-go. We are going to pack 
with Teflon instead of the old-style flax that was in there and hope for better 
results. But having to adjust it once it is in the water is a real challenge. I 
have seen the access on the later model 34, and I am very jealous. Thanks.

 

John McCrea

Talisman

1979 36-1 

Mystic, 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 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: C

[Glenn Henderson via CnC-List]

I have a C 41 for sale, 6'06" draft

On Thu, Apr 4, 2024 at 5:47 PM david coleman via CnC-List <
cnc-list@cnc-list.com> wrote:

> Let me know if you would be interested in c 43 landfallsw florida.draft
> 5.5.
> David
>
> On Thu, Apr 4, 2024, 4:51 PM sail51--- via CnC-List 
> wrote:
>
>> Hi
>>
>> I am in SW Florida and interested in possibly purchasing a shoal draft
>> version of a C 4. If you know of anyone with one for sale on the east
>> coast please feel free to have them contact me. Thanks
>> 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
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: C

[sail51--- via CnC-List]

David Thanks for the note ..  Made me realize my note was missing the second digit of the number,  C 41,   … which is the model I’m interested in, but appreciate your offer Thanks Bud  From: david coleman via CnC-List Date: Thursday, April 4, 2024 at 5:46 PMTo: Stus-List Cc: david coleman Subject: Stus-List Re: CLet me know if you would be interested in c 43 landfallsw florida.draft 5.5.David On Thu, Apr 4, 2024, 4:51 PM sail51--- via CnC-List  wrote:HiI am in SW Florida and interested in possibly purchasing a shoal draft version of a C 4. If you know of anyone with one for sale on the east coast please feel free to have them contact me. ThanksPlease 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/stumurrayThanks for your help.StuPlease 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