Understanding the Polar Diagram - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > Skills and Seamanship > Learning to Sail
 Not a Member? 


Like Tree1Likes
Reply
 
LinkBack Thread Tools
  #1  
Old 10-10-2013
Senior Member
 
Join Date: Mar 2013
Location: NC
Posts: 356
Thanks: 30
Thanked 18 Times in 18 Posts
Rep Power: 2
FirstCandC is on a distinguished road
Understanding the Polar Diagram

http://www.cc27association.com/pdf/iii_polar.pdf

Per the above link, if the wind is at 20 knots on a beam reach, my boat should theoretically be traveling at a speed of 7.25 knots? Is this diagram based on a 100 jib and main?

Thanks.
__________________
1977 C&C 27 MKIII
Sea Mist
Reply With Quote Share with Facebook
  #2  
Old 10-10-2013
Zanshin's Avatar
Senior Member
 
Join Date: Aug 2006
Location: Germany
Posts: 2,165
Thanks: 0
Thanked 14 Times in 14 Posts
Rep Power: 8
Zanshin is on a distinguished road
Re: Understanding the Polar Diagram

Yes to the first part of your question. Since the configuration isn't specified in the diagram, I would assume what other manufacturers call "race conditions" which means that the polars are generated in the best possible configuration - often with the lightest fixed boat weight, lots of crew on the rails, and as much sail as the boat can carry. If the C&C can carry a 125% or more then that is what I would assume.

More important than the actual (and only hypothetically reachable speeds) are the curves themselves. So in this example, if you were to change your course by 30 degrees more off the wind you would speed up to almost 8 knots. With a bit of trigonemetry (or a race computer) you could figure out which wind angle will get you the fastest speed over ground- which is not necessarily going to approach that shown in the polars.

I've got official polars for my boat that I find useful despite not even coming close to their posted speeds on any point of sail (except for when heading closer to the wind than the angle in my polor, when my actual speed of 0 matches the theoretical speed of 0 )
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by Zanshin; 10-10-2013 at 09:35 AM.
Reply With Quote Share with Facebook
The Following User Says Thank You to Zanshin For This Useful Post:
FirstCandC (10-10-2013)
  #3  
Old 10-10-2013
jzk's Avatar
jzk jzk is offline
Senior Member
 
Join Date: Feb 2008
Location: Chicago, IL
Posts: 1,640
Thanks: 1
Thanked 8 Times in 8 Posts
Rep Power: 7
jzk is on a distinguished road
Re: Understanding the Polar Diagram

There are two plots for each speed. One is downwind with a spinnaker, the other is upwind with the jib. You can see where they cross.
Reply With Quote Share with Facebook
  #4  
Old 10-10-2013
grumpy old man
 
Join Date: Apr 2011
Posts: 3,565
Thanks: 1
Thanked 72 Times in 68 Posts
Rep Power: 4
bobperry will become famous soon enough
Re: Understanding the Polar Diagram

Probably safe to assume the plot includes a genoa. This is something you enter into the data before you plot.

I really don't use polar plots. I use the tabular form where there is far more data presented including VMG's upwind and down, heel angle and an indication of when to reef. You don't get any of this on the polar plot. It is very helpful to be able to see the difference in boat speed to VMG.

I tried to upload on of the tabular VPP's here but it doesn't want to take it.
I'll see what I can do.

OK, let's ee if you can read this sample from one of my boats.
It works! It's a bit small to read but I think you get the idea.
Attached Thumbnails
Understanding the Polar Diagram-plot-data.jpg  
__________________
Please visit my blog. It's fun to read.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Bob's Blog ....


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by bobperry; 10-10-2013 at 01:08 PM.
Reply With Quote Share with Facebook
  #5  
Old 10-10-2013
jzk's Avatar
jzk jzk is offline
Senior Member
 
Join Date: Feb 2008
Location: Chicago, IL
Posts: 1,640
Thanks: 1
Thanked 8 Times in 8 Posts
Rep Power: 7
jzk is on a distinguished road
Re: Understanding the Polar Diagram

Quote:
Originally Posted by bobperry View Post
Probably safe to assume the plot includes a genoa. This is something you enter into the data before you plot.
You can see there are two plots. One is for a head sail, and the other a spinnaker.
Reply With Quote Share with Facebook
  #6  
Old 11-10-2013
Junior Member
 
Join Date: Feb 2013
Posts: 14
Thanks: 5
Thanked 0 Times in 0 Posts
Rep Power: 0
aaronsailor is on a distinguished road
Re: Understanding the Polar Diagram

Is there a place I can obtain a polar diagram for several different boats? Or am I going to have to search for every boat specifically?
Reply With Quote Share with Facebook
  #7  
Old 11-10-2013
grumpy old man
 
Join Date: Apr 2011
Posts: 3,565
Thanks: 1
Thanked 72 Times in 68 Posts
Rep Power: 4
bobperry will become famous soon enough
Re: Understanding the Polar Diagram

Aaron:
You can go to U.S.Sailing and purchase polars for a wide variety of boats. Maybe you can find some nice yacht designer willing to spend some time digging through his files and providing you with some examples. I don't know any nice yacht designers, try Bruce Farr, so I'd go to U.S. Sailing.
aaronsailor likes this.
__________________
Please visit my blog. It's fun to read.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Bob's Blog ....


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #8  
Old 11-10-2013
Faster's Avatar
Just another Moderator
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 14,604
Thanks: 67
Thanked 179 Times in 175 Posts
Rep Power: 10
Faster has a spectacular aura about Faster has a spectacular aura about Faster has a spectacular aura about
Re: Understanding the Polar Diagram

Trying to post that plot of Bob's a bit larger...

__________________
Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Reply With Quote Share with Facebook
  #9  
Old 11-10-2013
grumpy old man
 
Join Date: Apr 2011
Posts: 3,565
Thanks: 1
Thanked 72 Times in 68 Posts
Rep Power: 4
bobperry will become famous soon enough
Re: Understanding the Polar Diagram

Thanks Faster.

I think Aaron will need much more info on each boat than just a polar. It would be helpful for him to have an overview of the entire design. Try an assemble a complete picture is what I have in mind.

Here is a sail plan for the polar you posted of my boat. This rig design is now obsolete but I think it was the one used for that polar. Maybe you can fix the sail plan so it's bigger please. Thanks.

Attached Thumbnails
Understanding the Polar Diagram-kims-sail-plan.jpg  
__________________
Please visit my blog. It's fun to read.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Bob's Blog ....


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by Faster; 11-10-2013 at 11:24 AM.
Reply With Quote Share with Facebook
  #10  
Old 11-10-2013
Faster's Avatar
Just another Moderator
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 14,604
Thanks: 67
Thanked 179 Times in 175 Posts
Rep Power: 10
Faster has a spectacular aura about Faster has a spectacular aura about Faster has a spectacular aura about
Re: Understanding the Polar Diagram

Quote:
Originally Posted by bobperry View Post
.... Maybe you can fix the sail plan so it's bigger please. Thanks.
Done
__________________
Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
C 27 TR Polar Chart Mark1948 Catalina 2 08-08-2012 10:17 PM
Velocity Predictions Polar Diagram CowbaySailor Seamanship & Navigation 11 07-17-2011 12:26 PM
Polar plots chucklesR General Discussion (sailing related) 7 02-01-2008 04:18 PM
How To Find Polar Diagram fo C&C 34? IrishMistRacing Racing 2 06-13-2007 12:02 AM
Polar datas for X 412 ArcaneX Racing 1 09-25-2005 04:40 PM


All times are GMT -4. The time now is 07:20 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.