World Sailing declares Thilo Keller/AST design does not comply with 'A' Class Rules

World Sailing rule interpretation - Thilo Keller/AST AC Nano design.

The foil system presented in the facebook video ( at foiling week by Thilo Keller/AST has caused many questions about legality. The Technical Committee was asked to look into it, and by a unanimous Technical Committee decision, found that the foil concept of Thilo Keller's "AC nano" didn't comply with the A-Cat Class rules.

The case was appealed by Thilo Keller/AST and taken to the highest authority, World Sailing, for a rule interpretation under World Sailing regulation 10.12.


According to Regulation 10.12.1 (f), 

rule interpretations shall have the status of a class rule and, unless otherwise sanctioned in the Agreement, shall remain valid for a maximum period of 2 years or until superseded by a Class Rule change or modification carried out following the procedures of this Regulation.


The following interpretation was published by World Sailing today (10th of August 2017):

The following interpretation to the A-Class Catamaran Class Rules has been made to be effective 10th August 2017:


8.1 No part of each hull or hull appendages below the waterline shall be less than 0.75 meters from the centerline.


The distance between any point of the daggerboard to its closest point on the centreplane of the boat shall be measured through the full range of motion (i.e. extension/retraction, cant and rake) permitted by the daggerboard case configuration and without taking into account the daggerboard deformation produced by forces expected during its normal use while racing. 

(Can also be found here: