The rule

 The Mini-Transat Rule

The rule is very simple:

Max Lenght overall (LOA) 6.5 m (21.3 ft)
 Max width 3.0 m (9.8 ft)
 Max depth 2.0 m (6.6 ft)
 Max height  14.0 m from keel bottom to mast top
 Freeboard (average)  0.75 m minimum
 Min. cabin volume m3  1/6 of max width

In addition, there are two rules for stability: the boat may not heel more than 10 degrees with full ballast tanks/canting keel fully rotated, and also it will have to be able to right itself with a weight of 45 kilos attached to the mast top, heeled over to 100 degrees.

Sunday night was "petole" - mirror seas. Everyone becalmed for most of the night. Some of the hardest conditions. With no talk, no sounds, the flap flap flap of the sails certainly can send you a bit nuts.