Wind speed v temperature

Discussion in 'Laser Talk' started by Timb, Nov 25, 2007.

  1. Timb

    Timb New Member

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    Hi Guys,
    How much effect does air temperature have on the boat performance? I find warm wind is less powerful for a given wind speed but I wonder how much of that is because I am warmer and in a better or more positive state of mind.
    Thanks Timb
     
  2. Merrily

    Merrily Administrator Staff Member

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    Colder air is denser and has more force, so it's not all in your head. This time of the year in Ohio, even if you can barely see the wind on the water, you can still count on surprisingly good sailing.
     
  3. GeoffS

    GeoffS Member

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    Probably the best term for it is from aviation: Density Altitude

    http://en.wikipedia.org/wiki/Density_altitude

    Cold and dry is denser than hot and humid.
    I don't know if it's just the windchill, but 20 kn at 20F feels much stronger than 20kn at 80F.

    Cheers,

    Geoff S.
     
  4. OliLaser

    OliLaser Guest

    not so much to do with air tempurature, as it is air tempurature compared to water temp.
     
  5. Timb

    Timb New Member

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    I Can see the air temp argument and wonder if anyone has any thoughts on how big the differance is like would 15 knots in cold air equal 20 knots in warm air.
    Where does the water temp come into it?
    Timb
     
  6. Merrily

    Merrily Administrator Staff Member

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    I don't understand. I know that the air can be more or less stable depending on water temperature, but what do you mean?
     
  7. schloe

    schloe New Member

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    water temp has nothing to do with it.

    You can use the formulas here to do a calculation (and use F = M x V)

    http://en.wikipedia.org/wiki/Density_of_air

    Somebody answer this, I don't have time:

    20 knots in 20 degrees is equivalent to X knots in 80 degrees?????
     
  8. glasky

    glasky Member

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    Warmer air is more turbulent
     
  9. noc

    noc New Member

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    Assuming constant conditions (barometric pressure, relative humidity, turbulence, wind speed), and just varying air temperature the effect should follow the ideal gas law. This states that the number of air molecules hitting the sail per time varies as Temp2/Temp1, where Temp[1,2] are in degrees Kelvin. For example, if Temp1 = 20 degrees F = 273+ (20-32)*5/9 = 266.3 degrees K, and Temp2 = 80 degrees F = 273+ (80-32)*5/9 = 299.7 degrees K, then Temp2/Temp1 = 1.125. So, a 15 Kt breeze at 20 degrees F feels like a 16.9 Kt at 80 degrees F.

    Of course, from personal experience, sailing in 20F isn't anything at all like sailing in 80F.
    Discuss.
     
  10. mental floss

    mental floss Member

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    Well done Noc. But isn't that intuitively obvious to the most casual observer?
     

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