Section 7 ; article 23

7.23 Gennaker girth

The distance at mid-height, between the mid point of the gennaker luff and the mid point of the gennaker leech.

Also know as mid-girth rule after "MID height - GIRTH" rule


This measurement is then used in :

Section 1 ; paragraph 14 - article 3 (SMG - Mid hight Girth measurement)


1.14.3 The gennaker must satisfy the following two shape and size conditions :


SMG > 75% * SF

Gennaker sail area = SF * (SL1+SL2) / 4 + (SMG-SF/2) * (SL1+SL2) / 3 =< 17,50 sq. mtr.

Where :

* SMG is the width at mid-height, which shall be taken between the mid
point of the luff and the mid point of the leech.

* SF is the length of the foot of the sail measured around the edge of
the sail, between the lowest points of the luff and the leech ;

* SL1 is the length of the luff of the sail measured along the edge of
the sail, from the highest point of the sail, to the lowest point of the sail
on the luff ;

* SL2 is the length of the leech of the sail measured along the edge of
the sail, from the highest point of the sail, to the lowest point of the sail
on the leech.



It is not intended by any party to be a limit on the aspect ratio of the spi although it does limit it some as a side effect. The only intention of the mid-girth rule is to make a distinction between jibs (and addition headsail like boom jibs) and spinnakers. They are both triangular sails and are both ahead of the mast. However one can only be set on courses below a reach while the other can be set on all course. Somebody in the past decided that a mid height width measurement would be a good disciminator between the two types of headsails and used that to make up the definition of a spinnaker (gennaker)

We are still stuck with that definition.

By the way ; there is not a single beach catamaran class that allows anything else than 75 % mid girth spinnakers. Not the F18's, Not the F20, not the Tornado's, not the M20's, not the I-17's, not the FX-one's, not even the US nacra 6.0NE class that has no following outside of the US. The F16 class is not unique with regard to this mid girth rule.


Wouter