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Polar Charts for Twister
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Scott Bishop
14 Posts
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23rd January 2018 - 8:27 am
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Hi All, I'm running some software iRegatta that requires Polar charts to be input. If you need them then I have posted the .csv for main/spinaker, main/jib and main/code-zero at blog site here: http://vintageracingyachts.com.....-iregatta/ . Hope that helps cheers Scott. 

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John MacMullen and Ann Musgrave
191 Posts
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10th February 2018 - 7:02 pm
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That's really interesting Scott. I assume that the Polars that you've generated are 'theoretical'. How have they equated to the real thing when you are out there? Have you recorded the 'actuals' to produce an 'achieved' diagram?

On a more general note what sort of boats are you racing against and how are you doing? What sort of handicap/time correction factor do you have?

Polars have always interested me in the sense of knowing if the increase in speed for sailing an off rhumb line course will make up for the increased distance. But I've never got around to doing it and, so often, there are other tactical considerations that intrude.

Nowadays if you pay the money you can buy the kit which will give all the optimums but I'm still not sure. Years ago we did a series on a near 50 footer where the owner had all the toys plus some. Trouble was with eyes firmly fixed on all the dials and white knuckles on the wheel he had no 'feel' and sailed it like a brick ...... so embarrassing to be aboard at times!

Good luck and I look forward to hearing your progress.

John

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Martin Pascoe
9 Posts
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19th February 2018 - 7:56 am
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Scott, certainly interesting. I’m happy with the maths that if you can get a greater than 10 % increase in speed then it’s worth heading 10 degrees off course, but telling the helming part of my brain that is much more difficult. I’m also interested in how different your sail plan is from mine on Cabrach. She has main 18.5 sq m, jib 21.5 sq m and symmetrical spin 50sq m ( which will only set about 20 degrees either side of downwind) all measurements approximate. Do you really have a code zero or is it just theoretical? I’ve often wondered if we could have a 105% non overlapping jib for upwind in a breeze and a code zero to compensate for the loss of area in the light stuff. I’m never sure if the big overlap is doing any good,it might be just a leftover from the old rules of the sixties. The experiment would be a bit expensive for a boat that joins in a race once or twice a year. Twisters may have similar hulls, but the rigs are remarkably different. Martin

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