# MAIN SAIL 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

# HEAD SAIL / GENOA / JIB 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

# SPINNAKER (SYMMETRICAL) 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

# GENNAKER The formula for computing the sail area is:

SL x SF x 0,8 = sail area in m2