Bahia 46: Polar Diagram for a Bahia 46

[barrymac]

Found another one while shopping!

Sent from my SM-N9005 using Cruisers Sailing Forum mobile app

[barrymac]

In case anyone is looking I have manually created csv files, that can be used by qtVlm, by eye from the two polar diagrams posted here.

The slightly more detailed second one was included by the manufacturer in a boat I viewed.

I would use these files as a starting point but of course one would need to record their own polar performance with their own loading, sails and capabilities. ;-)

You will need to rename the files by changing the extension from .txt to .csv because the forum here does not allow csv file uploads

[Suijin]

There are two kinds of polars...those calculated by the naval architect as target boat speeds, and those developed off of real-world data. For the most part, the delta between the two is a function of lading, sail condition, sea state blah blah blah.

One line is for one set of sails. Polars usually have a different set of data points and line for the kite.

And yeah, that bump at 100 degrees is weird. All I can think is that it's where enough of a hull came up that there was a jump up in speed.

If you want to create polars for your existing boat, there is an app for that You input TWS and course off the wind and app logs the data through GPS and creates the diagram.

Honestly, most polars for a given type of boat look pretty much the same, and unless you're racing are kinda more trouble than they are worth other than eyeballing them and going "yep, it's as I suspected."

It's worth pointing out that the greatest value in them is in determining your best point of sail for VMG beating to windward. It's the highest point of arc of plot line, so in the case of the FP 46, it's 50 degrees.

[barrymac]

Well Suijin I can only imagine what ideal world the architect lives in but that is exactly why I would like to create my own. I have acquired a vessel and I'm already thinking about what possible sails to add. The spinnaker seems tiny.

The only PC software I have found for generating Polars so far is Adrena Optima which costs a few hundred euro.

I have seen NavGauge which sort of does it in a browser, but really I'd love to find something that would output an averaged CSV file.

The android app Sail Tracker Pro apparently has the option to share an image file of a generated polar but I haven't had the chance to test it yet.

You know of anything free and or open source that would do the trick by any chance?

[Suijin]

Barry, the one I was thinking of is iPolar. I have it on my iPhone but have never used it...was for a boat I race on but we ultimately found a few other polars that we could use.

i-Marine Apps: iPolar

Downside is that it does not look like there is anyway of exporting the data so that you can get it off your phone. Not sure how that works.

I believe that there are some open source race routing programs that will aid in developing polars for your boat, but I'm not entirely sure. I researched Bluewater Racing at one point and got that impression, but I can't confirm it. You'd need to have GPS input to your PC, like through a USB puck, if you don't have it networked on your boat.

Or, you could just do it by hand, collecting the data and dumping it into Excel. I don't think you need a ton of points...you can pretty easily extrapolate along apparent curves.

[colemj]

Originally Posted by Suijin

And yeah, that bump at 100 degrees is weird. All I can think is that it's where enough of a hull came up that there was a jump up in speed.

I suspect that bump is the spinnaker.

Mark

[Suijin]

Originally Posted by colemj

I suspect that bump is the spinnaker.

Mark

In a correctly drawn polar diagram, there is a separate "with kite" graph line. An example:



But yeah, I think you're right as far as that diagram goes, now that I think of it. However, since it's only one line for 20 knots or whatever it is, hard to tell. If there were data points for 5, 10, and 15 knots it would be clearer exactly what was going on.

[bobmcd625]

Ralph (or anyone else)
Did you ever find a polar diagram for a Westsail 32? I am looking at one to buy for the SF Bay and would like to see one.
Bob