# Polar Diagram Cal 40

Discussion in 'Sailboats' started by ath, Jun 22, 2008.

1. Joined: May 2005
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Location: Marina Del Rey, CA

### athJunior Member

Anyone know where I can find a VPR for a Cal 40? I found this but alas I am a novice and can't make sense of it.

2. Joined: Feb 2002
Posts: 2,283
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Location: Port Gamble, Washington, USA

### tspeerSenior Member

Here are the same data from the site, just formatted to make it easier to understand. Save this as a .csv file, and you can read it directly into a spreadsheet to plot the polars. The first column is the true wind speed in knots, the second is the true wind angle in degrees, and the third column is the boat speed in kt.

Since many spreadsheets, like Excel, don't have a true polar plotting capability, you'll have to multiply the true wind speed by the cosine and sine of the true wind angle (converted to radians) to get the upwind and crosswind velocities that you can plot using a scatter plot format.

TWS, TWA, V
6,,
,30.0, 2.50
,49.0, 4.40
,60.0, 5.10
,75.0, 5.60
,90.0, 5.80
,105.0, 5.83
,120.0, 5.40
,135.0, 4.70
,142.0, 4.30
,180.0, 3.10
8,,
,30.0, 3.20
,49.0, 5.30
,60.0, 6.15
,75.0, 6.57
,90.0, 6.75
,105.0, 6.78
,120.0, 6.50
,135.0, 5.89
,145.0, 5.25
,180.0, 4.04
10,,
,30.0, 3.50
,47.0, 5.85
,60.0, 6.65
,75.0, 7.00
,90.0, 7.15
,105.0, 7.25
,120.0, 7.10
,135.0, 6.70
,151.0, 5.90
,180.0, 4.95
12,,
,30.0, 3.80
,46.0, 6.00
,60.0, 6.90
,75.0, 7.30
,90.0, 7.40
,105.0, 7.60
,120.0, 7.52
,135.0, 7.20
,164.0, 6.15
,180.0, 5.80
16,,
,30.0, 4.10
,45.0, 6.25
,60.0, 7.10
,75.0, 7.55
,90.0, 7.87
,105.0, 7.90
,120.0, 8.20
,135.0, 8.00
,173.0, 7.05
,180.0, 6.95
20,,
,30.0, 4.00
,45.0, 6.30
,60.0, 7.20
,75.0, 7.70
,90.0, 8.10
,105.0, 8.20
,120.0, 8.60
,135.0, 8.70
,174.0, 7.60
,180.0, 7.50

3. Joined: May 2005
Posts: 51
Likes: 0, Points: 0, Legacy Rep: 10
Location: Marina Del Rey, CA

### athJunior Member

4. Joined: Feb 2002
Posts: 2,283
Likes: 251, Points: 83, Legacy Rep: 1673
Location: Port Gamble, Washington, USA

### tspeerSenior Member

A polar is just a graphical way of saying, "This boat will go this fast on this point of sail in this wind." Nothing more or less. If the boat will plane, then it goes faster than a displacement boat and the polar will have a different shape.

What you're really asking about is the velocity prediction program that produced the numbers in the polar. The VPP that's in the IMS rating system won't account for planing. VPPs based on the Delft University series of tow tank tests won't account for planing. But other VPP's may. If you did tow tank tests with appropriate hull forms at planing speeds, then you'd be able to use those data in the VPP to predict the performance when planing.

You don't actually need a VPP to produce polars - you can go sailing and record how fast you're going and in what direction. However, getting good data without a lot of scatter is exceedingly difficult.

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