Headsails “Set Flying” aerodynamic coefficients (calculation)

Headsail calculation

Calculation template

How does it work

A headsail is a sail 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, known as mid width, is less than 75% of the foot length (if mid width length ≥ 75% of the foot length, the sail is considered a spinnaker).

Headsails may be set on the forestay or set flying. The IMS defines a sail Set Flying as a sail set with no sail edge attached to the forestay.

With this template, you can calculate the aerodynamic coefficients of flying headsails as determined by the Offshore Racing Congress (ORC).

There is a wide variety of flying headsails: they can be conceived for close reaching and upwind sailing, or they can be designed to give their maximum performance at wider angles. The driver of the flying headsails performances with wind angle has been identified in the ratio HHW/HLP, ranging from 50% (jib-like performance) to 85% (spinnaker-like performance), where:

HHWHeadsail Half WidthThe shortest distance between the half leech
point and the luff.
HLPHeadsail Luff PerpendicularThe shortest distance between the clew
and the luff.
Do you want to read more articles like this?


Send us a Message

    Related Articles

    International Measurement System: Sails

    The International Measurement System (IMS) is a set of rules that defines what and how is measured on a boat. It is used by the Offshore Racing Congress (ORC) as a measurement platform on its ORC Rating Systems (ORC International and ORC Club). In this article, we deep dive into sails from the IMS perspective.

    Points of sail

    The points of sail refer to the course a boat is sailing in relation to the wind. They are defined in reference to the wind angle, which is the angle between the course sailed and the direction of the wind. The following terms are used: close-hauled, close reach, beam reach, broad reach, run, dead-run.

    Wind triangle

    The wind experienced by a fixed observer (true wind) is not the same wind an observer on a moving yacht will feel (apparent wind). The wind triangle helps us understand what the true and apparent winds are and how they are related.