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Old 29-11-2020, 03:47   #46
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Re: Creating polars for an older cruising boat

It's funny, everybody uses them, they just don't always have a spread sheet or a graph or software running calculations. It might be in your head but you are using the same information and modifying it to the conditions.

Same = same.
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Old 29-11-2020, 04:45   #47
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Re: Creating polars for an older cruising boat

All this discussion of polars, what caught my eye was the comment that Open CPN can create them. Anybody care to elaborate?

Secondly, it would be very interesting to back check routing using polars and weather prediction data after a passage. It would be fun to see how close the predictions came to reality as determined by a back check. Anybody ever try this?

jon
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Old 29-11-2020, 07:42   #48
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Re: Creating polars for an older cruising boat

On smartphones/tablets, the SailTimer app (www.SailTimerApp.com) and the iRegatta app (https://www.zifigo.com/node/644#weathermap) can both record boat speed, wind speed and wind angle to learn your boat’s custom polars. Not sure about iRegatta, but SailTimer can save multiple polars for different sail combinations. This gives more accurate navigation than downloading a one-size-fits-all polar for one model of boat. Both apps also let you edit or smooth the polar.
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Old 02-12-2020, 17:56   #49
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Talking Re: Creating polars for an older cruising boat

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Originally Posted by GILow View Post
So, I am getting serious about weather routing at last, and starting to develop my own polars before I head out cruising.

After owning this boat for 8 years I have a general sense of how she sails in various winds, but I am hampered by the fact that most of my sailing has been done on a bit of water that is shallow with really bad chop and a freakishly sharp wave action.

I am always amazed when I look at photos from when I bought the boat home. The speeds shown on the instruments in the background of the photos are so much higher than I get sailing around my local waters. But those photos were taken in Bass Strait with at least 30 meters under the keel.


I wondered if anyone had created their own polars for a heavy old cruising boat like mine. She's a Swanson 42. She has a LOT of beam, canoe stern and a cutaway forefoot keel. I've got her down to about 15 tons now, plus she has a feathering prop, so I am thinking something like a Tayana 42 or some of the Pacific Seacraft variants might have similar sailing performance. Perhaps even a HC 38?

If I could look at some polars created for similar boats I think I could extrapolate them to fill in the gaps that have been created by the fact that any time the wind gets over 15 knots here, the sea state turns to crap and my boat stops dead in the water. Most of the time I can go faster in 12 knots of wind than 17.

Can anyone point me to some suitable data?

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Old 02-12-2020, 18:58   #50
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Re: Creating polars for an older cruising boat

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Just learn to get the best out from your vessel
Gee, do you think so?
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