Spinnaker/Gennaker

Definition

ERS Section G:

“SPINNAKER” applies to symmetric and asymmetric (“gennaker”) sails .

G.1.3 Sail Types

(f) SPINNAKER
A sail set forward of the mast spar or of the foremost mast spar if more than one mast, where the measurement between the half luff point and the half leech point is equal or greater than 75% of the
foot length.

Sail Area Measurement Instructions

Reference text

IYRU Measurement and Calculation of Sail Area Instruction – issue April 1985

Instruction

6 SPINNAKER

6.2 The area of the spinnaker shall be taken as: SF x SL/ 2 + 2 x (SMG – SF/ 2) x SL/ 3 where:

  • SF = Width of foot; measured round the edge of the sail between the lowest point on the leeches.
  • SL = Leech length, measured round the edge of the sail from the highest point on the sail at the head to the lowest point of the sail on the leech. If the two are not equal, SL shall be the mean of the two leech lengths.
  • SMG = Width at half height; shall be taken as twice the distance between the mid-point of the leech shall be determined by measuring round the edge of the sail half the length of the leech from the head.

For guidance, you may refer to International Measurement Manual 2017 article K.4.2.6 Spinnakers

Sail corners

Compasses are very usefull to determine spinnaker corners

SMG

Measuring Spinnaker Mid Girth

All pictures by Armelle Molard

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