Spinnakers aerodynamic coefficients (calculation)

Calculation template

How does it work?

Spinnakers are sails set forward of the mast, or of the foremast mast if there is more than one mast, where the measurement between the half luff point and the half leech point (SHW) is equal or greater than 75% of the foot length (SFL).

ThrustDriving Force Coefficients.
SideHeeling Force Coefficients.
LiftLift Coefficients.
Drag TotalDrag Total = Zero-lift Parasite Drag + Induced Drag.
The Induced Drag component also includes the effect of the variation of Parasite Drag with lift (Quadratic Parasite Drag).
DragDrag = Zero-lift Parasite Drag = Friction Drag + Pressure Drag.
Parasite Drag is also known as Viscous Drag. Pressure Drag is also known as Form Drag.
Eff. spanEffective Height / Reference Height.
CEHeight of the Aerodynamic Center of Effort / Reference Height.

There are two types of spinnakers:

  • Symmetric: it is symmetric in shape, material, and cut, about a line joining the head to the center of the foot. It shall not have adjustable leech lines.
  • Asymmetric: any spinnaker not qualifying as symmetric.
Symmetric spinnaker
Asymmetric spinnaker

Symmetric spinnakers are considered tacked on a pole, while asymmetric ones can be tacked either on a pole or on the boat’s centerline. The term spinnaker also applies to “gennaker“ which can be considered as an asymmetric spinnaker tacked on the boat’s centerline.

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