Dear Members,

In the past months there have been several questions from members about the correct interpretation of Rule 3. With the introduction of winglets on rudders and the development of curved foils many questions opened up about how boats could be constructed within the rules. While the intention of the Rule 3 was always clear to most of us it was also clear that if this rule was challenged, there were many possibilities to achieve exactly what it was meant to prevent.

In short the rule without further clarification was quite insufficient and would possibly become a source for arguments over it's correct interpretation.

As a result the technical committee went to work to find a suitable solution to the problem. Many possibilities were discussed , including the possible removal of the rule or a complete re-write. After a long debate the Technical Committee decided to make some clear definitions which now makes rule 3 more meaningful.

While this is not technically a rule change it does bring new meaning to rule 3, so it is possible that some boats which have been built within the rule may now be compromised. If anyone believes their boat is affected by the changes they should contact IACA. It is not our intention to outlaw any current boats but we do need to enforce these point on any new constructions.

It is not the intention of IACA to make new rules limiting development of the class, but we have taken the stand point that it is our role to ensure that the "intention" of our existing rules are adhered to. It is important that our class rules are not manipulated by clever designers to create something which is clearly against the original intention.

As a development class there will always be those who wish to push the boundaries and those who would like to limit development. It is a fine line between creating the perfect class and setting a path of self destruction. Nothing we have done is irreversible but it does buy us time. If members feel that we have acted against the best interests of the class they should submit an official submission to IACA.

Rule 3.
The over all length of the catamaran shall not be more than 5.49 meters (18 feet).
The length shall be measured between perpendiculars to the extremities of the hulls with the catamaran in her normal trim.

The measurement shall be taken parallel to the centre line of the craft and shall exclude rudder hangings, but if the athwart ships width of a rudder within 153mm (6 inches) of the bottom of the hull is more than 76mm (3 inches), the length shall be taken to the aftermost point of the rudder

New interpretations 6 and 7.
6. Bottom of the hull measurement points are the lowest points on the hull at all transverse sections.

7. Rudder hangings means fittings that support the rudder appendage such as rudderstock, case, cheeks & tiller. They are solely to support the rudder appendage and be no further aft than required to provide steerage and no larger than required to support the rudder.

They are not to artificially extend the length of the boat by either fairing into the hull at the keel line or extending the overall length of the rudder assembly. As a guide the Technical Committee defines that the rudder appendage and rudder in a fully down position shall fit within 5.79m
from the forward perpendicular extremity of the hull.

Best regards,
Andrew Landenberger
IACA President

Further guideline drawings will follow.
Check full IACA Rules at

Updated Measurers Guideline