Magnum
RIP
Does anyone use this data in their day to day sailing? If so how?
Polar Curves
- Thread starter Magnum
- Start date
jimi
Well-Known Member
to avoid lond distance swimming bears
Angele
Well-Known Member
The racing community does. It shows the theoretical maximum speed of their boat at a particular wind angle and speed. I think they constantly tweak things until they are within a whisker of what the boat is capable of achieving.
The rest of us just open another beer.
The rest of us just open another beer.
sarabande
Well-Known Member
sail selection for speed and angle of wind; optimising vmg, weather routing (very important if out for more than 24 hours), passage planning.
You should be getting a full polar with the boat from the designer's velocity prediction program; if you don't, it's relatively easy to make up the data table from real life into a spreadsheet, and then convert it to a graphic. Perhaps your wind/speed electronics incorporates a data logging system which will make that much easier.
EDIT
Maxsea is a nav software package which does clever things with wind / boatspeed data.
http://www.maxsea.fr/timezero/Produ.../tabid/149/id/932/language/en-US/Default.aspx. There are other apps around, too.
You should be getting a full polar with the boat from the designer's velocity prediction program; if you don't, it's relatively easy to make up the data table from real life into a spreadsheet, and then convert it to a graphic. Perhaps your wind/speed electronics incorporates a data logging system which will make that much easier.
EDIT
Maxsea is a nav software package which does clever things with wind / boatspeed data.
http://www.maxsea.fr/timezero/Produ.../tabid/149/id/932/language/en-US/Default.aspx. There are other apps around, too.
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tcm
...
yeah, the polar curves are specially designed to pi$$ you off, describing how fast your boat would go if you had no fuel or water or gear or antifoul PLUS you were sh!t hot at sailing and didn't have to pay if the boat breaks. But anyway, no, to answer the question, i have never looked at the polar curves during the sailinfg eg "quick, go get the polar curves willyer?"
sarabande
Well-Known Member
I am convinced that boats go faster if you use the polar curve sheet as a fan....
sarabande
Well-Known Member
just discovered that B&G produce the Deckman program which just about covers most decent tech tools for sailing more efficiently. It includes a polar generator.
http://www.bandg.com/Products/Deckman-Tactical-Software/More-about-Deckman/
http://www.bandg.com/Products/Deckman-Tactical-Software/More-about-Deckman/
Magnum
RIP
We have that on our new boat. Not used it yet though!
sarabande
Well-Known Member
Ah, should have thought you would be ahead of the game !
Polars are useful , as well as fun, and extend your 'feel' for selecting the right sail combinations, and for how the boat is moving.
Polars are useful , as well as fun, and extend your 'feel' for selecting the right sail combinations, and for how the boat is moving.
snowleopard
Well-Known Member
One particular area where polars can be very useful is when running in multis and lightweight flyers, especially with asymmetrics. If the polar shows a 'dent' at the 180° position, it is more efficient to tack downwind as the extra speed obtained from going onto a broad reach is more than the loss from covering extra distance.
As polars are almost always theoretical and my efforts to produce one experimentally failed because of wind fluctuations, I couldn't deduce the optimum angle from the plot. When I tried it out there was a marked increase in speed by heading off the direct downwind line but the VMG dropped. I can now head straight for my destination in a leisurely fashion with no feelings of guilt!
This boat goes faster tacking downwind at 30° off the direct line:
This boat is best sailed direct downwind:
Also you can see that in the first polar, though the boat will make progress at 20°-30°, the best upwind VMG will be obtained at 40°
As polars are almost always theoretical and my efforts to produce one experimentally failed because of wind fluctuations, I couldn't deduce the optimum angle from the plot. When I tried it out there was a marked increase in speed by heading off the direct downwind line but the VMG dropped. I can now head straight for my destination in a leisurely fashion with no feelings of guilt!
This boat goes faster tacking downwind at 30° off the direct line:
This boat is best sailed direct downwind:
Also you can see that in the first polar, though the boat will make progress at 20°-30°, the best upwind VMG will be obtained at 40°
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Bilgediver
Well-Known Member
I think this was one of the least used features of the Phillips AP8 GPS. it would take the NMEA inputs from the instruments and produce a diagram.
One mate with a Westerly Storm used this to perfect his tweeking...Must have worked as he won races but the Saturday tweeking could be hard work and often gave me Tiller Elbow. I am a wheel man : The Dolphins thought it was fun and often chased us.
davidej
Well-Known Member
I have googled unsucessfully to get a polar for my boat -probably more for acedemic interest than as a true sailing tool.
It is a bene 361 any suggestions?
It is a bene 361 any suggestions?
snowleopard
Well-Known Member
For most modern boats you should be able to get polars, stability curves etc from the manufacturers.
Juniperskip
Well-Known Member
For racing or tweaking fun you need to translate your polars into a chart of target speeds for true wind direction/speed.
The Navman software will help with this but a simple chart with numbers(digital!!) is the usual way. For racing I have a separate one for sail selection ie foresail or A-sail choice either pre-start or at a mark rounding....
The Navman software will help with this but a simple chart with numbers(digital!!) is the usual way. For racing I have a separate one for sail selection ie foresail or A-sail choice either pre-start or at a mark rounding....
sarabande
Well-Known Member
Juniper - can you clarify that with regard to VMC and VMG pls ?
)Not being whingy; want to learn)
)Not being whingy; want to learn)
PembrokeshirePromise
Well-Known Member
<<i have never looked at the polar curves during the sailinfg eg "quick, go get the polar curves willyer?">>
That cos they don't do them for cling film round the guard rails ... ;-)
That cos they don't do them for cling film round the guard rails ... ;-)
dt4134
Well-Known Member
For racing you have a target boat speed against which you compare your actual boatspeed. It is one bit of information that helps you decide whether you're sailing well enough.
For example, close-hauled you should know what boat speed and what angle you should be getting to the wind at various windspeeds.
Similarly downwind the polars will guide you on the correct 'tacking' angles and expected boatspeed.
They'll also give you information on sail changes. For example you might be on a leg that gives you a course where the apparent wind angle lies in the cusp between the spinnaker and No.1. The polars will help you decide how to deal with that.
Also some trimming steps are guided by the relationship between the boatspeed and the target speed. For example, after a tack, you would typically go to full trim at about 1 knot below target speed. Below that you're trimming to accelerate out of the tack rather than for maximum speed (analogous to changing gears in a car).
Juniperskip
Well-Known Member
Didn't mention VMC or VMG on my offering??
Did you mean Visual Meteorological Conditions (VMC) or Velocity Minimum Critical (Vmc) ????
For VMG, your polars will give you your theoretical Upwind & downwind VMG targets for a given sail config/true windspd/angle. I also use VMG to waypoint a lot for racing and cruising to sail optimal angles but this is not polar related per se.
Sorry can't be more helpful......
sarabande
Well-Known Member
VMC = best speed for the required (arbitrary) course.
I know quite a bit about the use of polar diagrams for racing, but I was wondering if you had a wrinkle about using separate polars for each sail to optimise VMG and VMC.
It sounds as if you are using the procedure in a different way from me, and I was looking for enlightenment.
thanks anyway.
I know quite a bit about the use of polar diagrams for racing, but I was wondering if you had a wrinkle about using separate polars for each sail to optimise VMG and VMC.
It sounds as if you are using the procedure in a different way from me, and I was looking for enlightenment.
thanks anyway.
Keen_Ed
Well-Known Member
Might want to rethink that one. Deckman is know to be extremely powerful, with many functions for racing, but less (a lot, lot less) easy to use than other programs.
Take a look at Expedition - AIUI, a lot more user friendly with all the functionality. Or maybe even something like Seatrack.
Again, AIUI, the only people who need Deckman's fuctionality are Americas's cup/Volvo ocean race navigators. Unless you've basically got one guy spending all day navigating (and calibrating the instruments - a non trivial task), it's a sledghammer/nut situation.
