If no specifications are provided by the manufacturer or the calss rule, calculating the sail area for the main sail requires know-how and experience. There are fundamentally two methods for calculating the area. The simplest formula:
(P x E) / 2 = area in m²
Example calculation without roach: P = 13m x E = 4,20m = 54,6 / 2 = 27,3m²
This formula doesn’t include the extra area at the leech (black area), called roach. However, almost every main sail has a raoch. To calculate this extra area, an empirical formula is used. The sail area of a main sail including the roach is calculated:
P x E x 0,585 = sail area in m²
Example calculation including raoch: P = 13m x E = 4,20m x 0,585 = 31,94m²
For the calculation of the head sail area you can use two methods.
Either, the calculation of the dimensions I and J as a basis for a 100% head sail:
(I x J) / 2 x X% = sail area in m2 and you set the percentage of your genoa for X.
Genoa 1 = 150 - 155%
Genoa 2 = 130 - 135%
Genoa 3 = 105 - 110%
Working jib = 85 - 95%
Or, if the length of the luff (L) as well as the LP is given:
(L x LP) / 2 = sail area in m2
Symmetric spinnaker measurements include: leech length (SL), half width (SMG) as the distance between midpoints on the luff and leech and the foot length (SF).
The formula for computing the sail area is :
(SL x (SMG + SF) / 2) x 0,95 = sail area in m2
The formula for computing the sail area is:
SL x SF x 0,8 = sail area in m2