simplified calculation of sailing boat sail

 

 

Example a simplified calculation of sailing boat sail :

The sail calculation is like the wing calculation, whether an aircraft wing or sail a boat load of the lift can be done in the same way

(if we neglect to first approach the elongation and spin)

 sailing boat sail

We assume in this simplified example that :

  • The lift force of the sail is paralell to the axis of the vessel (for other cases the drag and lift force vectors will be projected on the axis of the vessel)

  • the spin and length of the sail are neglected.

  • Velocity is the apparent wind speed

  • The displacement resistance or drag force is 2100 N.

Wanted:

To do this we must adjust those parametres :

 

With Mecaflux

  1. - Select a profile with drag and lift for our sail we use the Profile BE50 (as it is with Archer A very close) (the Polar profiles are already in MECAFLUX parameterized but you can change the Cx and Cz .

  2. - Enter parameters of the fluid speed: 10 knots breeze force3, temperature: 20 ° C, density: Air (1225 Kg/m3)

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

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

  5. - L ' angle incidence of the sail (try 10.5 °. The pattern proposed are those studied in wind tunnels are confined to the angles of interest, beyond the patterns left behind and are practically healthy)

  6. -Click on calculate

 

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

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we seek to balance a diplacement resistance of 2100 N, wind speed or sail surface is thus too low

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

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

  3. -Click on calculate

the lift force for b50 is 2112.604 Newtons (215.485633 Kg.f) with 10 knots of wind

*****************

With 30 knots of wind:

  1. - Change the parameters of the fluid speed: 30 knots , Temperature: 20 ° C, density: Air (1225 Kg/m3)

  2. - We keep 18 m height

  3. - We keep 6 m wide Profile (rope)

  4. -Click on calculate

The lift force for b50 is 19013 Newtons (1939. Kg.f) with 30 knots of wind is: 19013/2112 = 9 times more lift force with 3 times more wind . It is time to reducing the sail area.

In fact we see, by changing the height and width of the profile, that a sail of 6 meters high and 2 meters wide by 30 knots of wind we have adequate lift to propel our boat to 10 knots.

 

Exemple External flow drag and lift

( MECAFLUX gives the results of a fineness sufficient to consider but for the realization of aircraft other than the model you need to invest in software modeling aerodynamic much more expensive setup time and money and testing prior to endanger the lives of people ...)

mecaflux is a calculation software simplified . HELICIEL is software for calculating propeller wing sail fuller .

 

 

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 mis à jour le 10 /2009

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