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Teamstone 04-01-2019 05:12 PM

Generic Polars
 
I have an Allmand 35 and it appears Polars were never published. Is there such a thing as a generic polar to at least use as a guideline?

Thanks
Tom

capta 04-01-2019 07:15 PM

Re: Generic Polars
 
OK, I'll bite; what the heck is a Polars, generic or otherwise?

colemj 04-01-2019 08:40 PM

Re: Generic Polars
 
Not really. Actually, published polars for most boats will never be reached because they are calculated using very optimistic data.

However, it is easy to make your own polars if you can get boat data into a computer. OpenCPN has a polar plugin where you simply sail the boat and it collects polar data and makes it into a plot. There are phone/tablet apps that do the same.

Or just go sailing and take some general notes about wind, speed, angle, etc - then make some tuning/rigging/trim changes and see how that effects things in general.

One usually only is interested in polars for upwind work to determine optimum VMG, and most people find they understand this intuitively after sailing their boat for a while.

Mark

colemj 04-01-2019 08:42 PM

Re: Generic Polars
 
Polars are a set of plots or tables of boat speed vs. wind angle for specific wind speeds.

Mark

SanderO 04-01-2019 08:57 PM

Re: Generic Polars
 
Quote:

Originally Posted by colemj (Post 2051593258)
Polars are a set of plots or tables of boat speed vs. wind angle for specific wind speeds.

Mark

target optimal boat speeds for each wind angle drawn on a polar plot... bow being 0, beam being 90 stern being 180 drawn for a range of wind speeds.

Geoff54 04-02-2019 01:21 AM

Re: Generic Polars
 
There are Velocity Prediction Programs which will create polars - No idea how accurate they are.
I saved these links some time ago intending to play with VPPs to help decide on replacement sails but never got around to it.
You can download a trial VPP from Techsail ? Sailing Yacht Performance Analysis
I found this thread interesting at the time - old, so the links may not work
PCSail - Excel sheet to make VPP for Sailing yachts - Cruisers & Sailing Forums
As I said, I was looking at this some time ago, so you might Google, " Velocity Prediction Program" and see what you can discover.

Minnewaska 04-02-2019 08:18 AM

Re: Generic Polars
 
Unless you sail in flat water, with a perfectly clean bottom, brand new sails and have perfect trim, they are totally useless. If you have all these things, they are modestly useless. Besides, getting to know how a new boat sails in various conditions is part of the mating process. Embrace it, don't overthink it.

cb32863 04-02-2019 10:13 AM

Re: Generic Polars
 
Quote:

Originally Posted by Minnewaska (Post 2051593310)
Unless you sail in flat water, with a perfectly clean bottom, brand new sails and have perfect trim, they are totally useless. If you have all these things, they are modestly useless. Besides, getting to know how a new boat sails in various conditions is part of the mating process. Embrace it, don't overthink it.

They are not "totally useless", seriously. You can use them as a guide when you are sailing if you see fit to do so. We use them in racing all the time. Just because you have no use for them, doesn't mean others do not.

dadio917 04-02-2019 02:11 PM

Re: Generic Polars
 
interesting thread for me at the moment. My wife and I are getting ready for a couple 2000+ mile passages and have been updating com gear over our old SSB/pactor and intreach. Have added an iridium Go and a subscription to predictweather.com. Besides weather forecasts they run weather routes which will help us a) stay in wind and b) maybe avoid too much wind and swell, and c) avoid something worse. The idea is to run the route each day. The routing runs on their servers so the data required to transmit is small.

The routing SW uses boat polars to figure how best to point and how far the boat can get in a given time and condition. Hard to say given all the inaccuracies of weather forecasting how much decent polars add. OR how polars determined for one boat would map to another of the same make but probably set up differently. but still I've been wondering.

Predictweather lets you choose from their data base of polars, a detailed set of data one could measure, or just put in a few rough guesses at how the boat will do at a few angels to the wind in 15knts. They don't have polars for a Valiant 39 but do for a 40. What I've been playing with is derating the V40 by 10% to make up for the hull size. Their SW allows for that. I guess after a week or so at sea we'll get calibrated.


Anyways...that's why I've just discovered a use for boat polars and would love to find some data base that has a Valiant 39.

Teamstone 04-02-2019 02:17 PM

Re: Generic Polars
 
Quote:

Originally Posted by colemj (Post 2051593256)
Not really. Actually, published polars for most boats will never be reached because they are calculated using very optimistic data.

However, it is easy to make your own polars if you can get boat data into a computer. OpenCPN has a polar plugin where you simply sail the boat and it collects polar data and makes it into a plot. There are phone/tablet apps that do the same.

Or just go sailing and take some general notes about wind, speed, angle, etc - then make some tuning/rigging/trim changes and see how that effects things in general.

One usually only is interested in polars for upwind work to determine optimum VMG, and most people find they understand this intuitively after sailing their boat for a while.

Mark

Thought of that but the one thing I don't have is wind instrumentation.


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