Leeway

The leeway is calculated after the Apparent Wind Angle. It could be appropriate to define a coefficient associated with the calculated value of the leeway, depending of the state of the sea.
On a boat like the J/105, the spinnaker is very important in the leeway. We will consider a formula that will involve actually two segments in the curve, one from head-to-wind to the spinnaker hoist, and another one from the spinnaker hoist to dead-downwind.

Leeway

This formula will be based on two user-entered parameters and one calculated one.

Calculated parameter:
- The angle at which the spinnaker can be carried. This value is given by the polars.
User parameters:
- Leeway upwind, close-hauled (AWA = 25°)
- Leeway with the spinnaker, close-hauled

In the formula - as seen on the graphic - we consider that the first section is a parabollic curve expressed as y = x², having as its unit the difference between the value given for the leeway at AWA=25° and the split; the second section is considered as the quarter of an ellipse, having as value the difference between the split and AWA=180° as an axis, and the value given by the user for the leeway with the spinnaker close-hauled as the other axis.
This formula seems to work...

The result of such a formula has to be tuned with the coefficient we talked about above, applied to the result with regard to the state of the sea.

Any comment ?