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post #11 of 22 Old 11-10-2013
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Re: Understanding the Polar Diagram

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Originally Posted by jzk View Post
You can see there are two plots. One is for a head sail, and the other a spinnaker.
You are right. That is how usually it is done. Normally it is specified what is the front sail upwind, being the more normal a jib or a small genoa.

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post #12 of 22 Old 11-10-2013
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Re: Understanding the Polar Diagram

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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?
I don't know of what boat you are talking about. If it is a relative modern one there is a lot of information on the web. If the boat races search ORC international certificates, google for image while searching Polar speeds, look at manufacturers boat catalogs, on site like this one>

Boats & Polars | BLUR

On a ORC certificate you will not get a polar but something similar to what Bob Perry posted about Silver>

http://www.ssf.se/tk/PDF/6193.pdf

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post #13 of 22 Old 11-10-2013
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Re: Understanding the Polar Diagram

Paulo is right. My tabular form contains a lot more data than a simiple polar. I pretty much only use the tabular form, of the VPP. I need all that extra data.

Please visit my blog. It's fun to read.


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Bob's Blog ....

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Please also visit my new web site
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post #14 of 22 Old 11-18-2018
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Re: Understanding the Polar Diagram

Great thread guys.... I'm hoping someone out there maybe able to help me with Polars for a Catalina 25

Regards

Tim
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post #15 of 22 Old 11-18-2018
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Re: Understanding the Polar Diagram

I can't post links yet with my small post count but one cool site for getting polar data is:

jieter github io/orc-data/site

(fill in the dots)

They visualize data downloaded from the ORC site.
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post #16 of 22 Old 11-18-2018
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Re: Understanding the Polar Diagram

In the original post, when do you use the vertical or horizontal axis for reading the theoretical speed? I see the two curves for head sail or kite, but I dont understand the two speed axis'
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post #17 of 22 Old 11-18-2018
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Re: Understanding the Polar Diagram

If I understand your question, the axis are just the direction your heading relative to the wind. To the right on the x-axis at 90 degrees you are on a beam reach. Up on the Y-axis, you are heading directly into the wind. That is why the curves die off before you get to zero degrees. Sorry if that wasn't what you were asking.

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post #18 of 22 Old 11-18-2018
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Re: Understanding the Polar Diagram

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If I understand your question, the axis are just the direction your heading relative to the wind. To the right on the x-axis at 90 degrees you are on a beam reach. Up on the Y-axis, you are heading directly into the wind. That is why the curves die off before you get to zero degrees. Sorry if that wasn't what you were asking.
No, I understand the wind direction. But I see what appears to be predicted speed readings on the vertical AND the horizontal. I dont understand how you decide which to use to predict speed.
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post #19 of 22 Old 11-18-2018
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Re: Understanding the Polar Diagram

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Originally Posted by CrispyCringle View Post
No, I understand the wind direction. But I see what appears to be predicted speed readings on the vertical AND the horizontal. I don't understand how you decide which to use to predict speed.
Think polar or circular coordinates, NOT cartesian or rectangular coordinates. The speed is the radius, not X or Y. Everything is angle and radius. Also remember that these are generally plotted in TRUE wind direction and speed, though I've seen apparent wind plots.

The advantages of a polar plot vs. tabulation are:
* It describes the performance of the boat at a glance. Things like the onset of planing are obvious. When to switch from working sails to kite are obvious.
* They facilitate certain graphic approximations, like fast and slow targets (Google it) and the best down wind course in fluctuating wind speeds.

Tabulations can contain a lot more data, but they can also be overwhelming. A polar plot is visual.

It's not just racer stuff, it gets cruisers where they are going faster and more safely.
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Last edited by pdqaltair; 11-18-2018 at 11:27 AM.
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post #20 of 22 Old 11-18-2018
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Re: Understanding the Polar Diagram

I have a polar for my boat that can with its documents. Itís posted in the front of the log book so crew will look at it and feel bad every 3 to 4 hours.😊
What I find more useful is to just learn your boat. Then you know what she should do when the sails are trimmed correctly, stores are loaded correctly and the bottom is sufficiently clean.
Itís deviation from that which should catch your attention and have you puzzling out whatís going on to slow you down.
Computor generated polars are fine when considering which boat to buy, handicapping race boats and the like but once you own the boat I think their main function is to allow you to see how much slower you are when actually sailing the boat. I use that as a cue something is off and I need to investigate. But in the day to day the ďpolarĒ youíve developed on your own boat is more useful to figuring out sheís giving her best.

s/v Hippocampus
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