Simplified calculation example of a sail of Sailboat:

Whether it is an airplane wing or sail of a sailboat calculating the lift can be done in the same way (is neglected in this first approach, the aspect ratio and twist, For more advanced calculation, with twisted shapes and distributions of elliptical chords we use Heliciel)

We assume in this example that:

  • the lift of the wing is in the axis of the vessel (for other angles, lift and drag vectors must beings projected on the axis of the boat)

  • twisted shapes and distributions of chords.

  • speed is the apparent wind speed

  • The strength of resistance to forward is 2100 N.

we seek:

  • -The Lift of the sails wch balances the ship resitance: 2100 N=Lift=ship resitance

To realize this goal, we can play on:

with Mecaflux

  1. - select a profile with drag and lift ,we use for our sail the profile Be50 (polar profiles are already set in mecaflux but you can change the Cd and Cl)

  2. - Enter the parameters of the fluid:

    -speed :10 knots FORCE3 small breeze , temperature:20°C, density:air (1.225 Kg/m3)

  3. - Enter the profile chord (the width of the sail, take 4 meter)

  4. - Enter the height of the sail (say 10 meters)

  5. - the angle of incidence of the Sail (try 10.5°)

  6. - Click to calculate

calcul voile

The diagram shows the profile BE50 after calculating the value of the lift 782 Newtons with 10 knots of wind

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we seek to balance resistance to the advancement of 2100 N, the wind and the sails are therefore too low

  1. - Change the profile chord (the width of the sail, take 6 meter)

  2. - Change the height of the sail (say 18 meters)

  3. - Click to calculate

the lift force for b50 is 2112 Newtons (215 kg.f) with 10 knots of wind

so we will have almost two times higher than the ship sail for the advance to 10 knots by Force 3

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see by force 7 or 30 knots:

  1. - Change the parameters of the fluid-velocity: 30 knots (force7), temperature: 20 ° C, density air (1.225 kg/m3)

  2. - we keep 18 m high

  3. - the profile chord (the width of the sail,we keep 6 meter)

  4. - Click to calculate

The lift force for b50 is 19,013 Newtons (1939 kg.f) with 30 knots of wind:: 19013/2112= 9 times more lift with three times more wind. It's time to reduce sail area.

In fact we see, by changing the height and width of the profile, that with a sail 6 meters high and 2 meters wide by force 7 we have enough lift to propel our boat at 10 knots...