Interpretation and Diagrams on 'Canting Keel'

by America's Cup Measurement Committee on 17 May 2007
In the first week of May the America's Cup Measurement Committee released their latest decision relating to the use of a canting keel in the 2007 America's Cup.

For the first time drawings were released which show what was intended by the canting keel.

The concept is that the keel strut is retained inside a keel box and is allowed to cant to leeward just prior to tacking. When the boat is tacked the keel is initially offset and provides original righting moment before returning to the centre position.

the advantage of such a mechanism would be that it would provide additional righting moment just after the boat tacked, giving more power and acceleration, but increasing leeway slightly.

The Interpretation and four diagrams that form part of the Interpretation follow:

 ACC Version 5.0 Public Interpretation No 38    

May 8, 2007                                                                             

In response to the following:

Please issue a Public Interpretation in response to the following questions to clarify the restrictions under ACC Rule (Version 5.0) on altering the support of a fixed appendage to vary the heeled righting moment while racing:

                        1.         With reference to the answer in the second paragraph of PI 32, does the term

                        ‘components’ include reference t
a) hydraulic cylinders,
b) locking systems, or
c) structural response damping systems
any of them, with moving parts or variable geometries?

2.                   2.         With reference to answer 4 of PI 22, would a fixed appendage supporting structure that deforms gradually over time, either due t a) creep, b) passive locking system, or c) the presence of a damping system, contravene the requirements for a fixed appendage within Rule 17 or any other Rule?

3.                   3.         With reference to answer 9 of PI 22, would the requirements for a fixed appendage of Rule 17 also be contravened by the constraint of a fixed appendage in a deflected position arising from the hydrodynamic and gravitational forces as described in answer 4 of the same PI 22? (i.e., Is it permissible to constrain a fixed appendage, by a mechanism which would maintain the deflection either to one side or the other, while deflected to leeward before tacking resulting in some deflection to windward, or less deflection to leeward, on the new tack?) (See as examples Figures 1 & 2).

4.                   4.         Would the answer to the previous questions be similar if the fixed appendage, or its supporting structure, was not fully constrained but instead restrained thus producing a similar but time dependent behavior when changing tacks (ie, the fixed appendage would gradually return to have similar deflection to leeward on both tacks over some finite period of time)? (See as an example Figure 3).

5.                   5.         Would the control or adjustment of the constraint or restraint of a fixed appendage while racing contravene rule 17? (See as an example Figure 4).

INTERPRETATION:

1.         Yes. However, any component as described with moving parts or variable geometry shall be fixed, and if deemed necessary by the Measurement Committee, disabled to prevent movement, alteration or adjustment whilst racing.

1.                   2.         Yes, an appendage that is supported by structure that alters the deflection of the appendage due to gradual deformation either due to creep, a passive locking system or a damping system would be considered to be a moveable appendage. If the axis of rotation of the appendage is not at an angle to the MWL plane exceeding 45 degrees then it will not comply with Rule 17.10 (b).

2.                   3.         Possibly. The definition of “fixed” as used in Rule 17 would be contravened if a fixed appendage was constrained by a mechanism which would maintain the deflection to leeward before tacking resulting in some deflection to windward, or less deflection to leeward, on the new tack.

3.                   4.         Yes. See answer 3 above.

4.                   5.         Yes. See answer 3 above.

The supplied attached sketches form part of this interpretation

END

This interpretation is made by the Measurement Committee in accordance with Rule 3.3 of Version 5.0 of the America’s Cup Class Rule.

Ken McAlpine ACC Technical Director