Does it cant? Interpretation 22 and the Keel Rule

by Sail-World on 17 Apr 2007
Over the past couple of days rumour control in Valencia has it that one of the competitors in the 2007 America's Cup has developed a so-called canting keel.

Further investigation has revealed that the keel does not cant, but rather a way may have been found to reduce the amount of keel strut deflection as a 20 tonne bulb is suspended away from the hull of a heeling America's Cup yacht.

We present the relevant section of the ACC Rule and the Interpretation 22 which has given rise to the speculation.

Extract from America's Cup Class rule Version 5 (governing measurement rule for the 32nd America's Cup)

17.10 The maximum number of movable appendages shall be two, and:
(a) movement is limited to rotation only;
(b) the axis of rotation of each movable surface shall be in the vertical fore and aft
centreline plane of the hull and at an angle to the MWL plane exceeding 45 degrees;
(c) appendage rotation shall not increase the righting moment nor change the fore and aft
trim. A moveable appendage whose nett density is less than 5000kg/cubm does does
not infringe this rule;
(d) any part of a moveable appendage that extends aft of the after end of the MWL, shall
not exceed a transverse width of 250 mm above a point 200 mm below the MWL plane;
(e) a movable device whose sole purpose is the removal of weed or debris from the hull or
appendages, and which in no other way enhances the performance of the yacht, shall
not constitute a movable appendage. Such a device may be retracted;
(f) appendages which contain ballast shall not rotate.

17.11 Fixed appendages shall not deform more than 5% of their span, measured from the fair body
attachment of the appendage, when subjected to a pressure of 6.4 kPa applied normal to a
plane defined by the chordwise and spanwise axes of the appendage.

Interpretation 22

June 15, 2006


Please issue a Public Interpretation in relation to the following questions:

1. Further to Rule 17.11, is lateral deflection of a fixed appendage limited or restricted by the ACC Rule whilst racing?

2. In the context of Rule 17.10, is a deflecting appendage a 'movable appendage'?

3. Is lateral deflection of an appendage considered to be a rotation movement in the context of Rule 17.10?

4. Would any Rule be breached, should lateral deflection of a fixed appendage be passively controlled by a low pressure hydraulic system?

5. Would any Rule be breached, should lateral deflection of a fixed appendage be actively controlled by:

a) Lateral traction/compression by a hydraulic/mechanical system applied to the head of the keel from the inside of the boat; or
b) Vertical traction/compression by a hydraulic/mechanical system applied to the inside lateral(s) of the keel fin; or
c) Vertical traction/compression by a hydraulic/mechanical system applied to the side(s) of the keel bulb?

6. Would any Rule be breached, should lateral deflection of a fixed appendage be locked by:
a) Lateral constraint by a hydraulic/mechanical system applied inside the head of the keel from the inside of the boat?; or
b) Vertical constraint by a hydraulic/mechanical system applied to the inside lateral(s) of the keel fin?; or
c) Vertical constraint by a hydraulic/mechanical system applied to the side(s) of the keel bulb?

7. Is it permitted by the Rule to rotate an appendage about a horizontal longitudinal axis if that rotation compensates the lateral deflection of the said appendage thus bringing it back to the centre line plane?

8. If the answer to the previous question is yes, could the rotation then be locked?

9. Is it permitted by the Rule to deflect the internal structure of the yacht if it compensates the deflection of a fixed appendage thus bringing it back to the centre line plane?

10. If the answer to the previous question is yes, could the deflection then be locked?

INTERPRETATION:

1. Beyond the restrictions imposed by rule 17.11 the lateral deflection of fixed appendages is not limited or restricted by the ACC Rule whilst racing.

2. In the context of Rule 17.10 a deflecting appendage which has no means of inducing or altering deflection other than by; lift or drag generated by the motion of the appendage through the water, or loads due to self weight or other attached appendage(s), is not a movable appendage. Attention is also drawn to rule 17.11

3. No.

4. The Oxford Dictionary defines 'Fixed' as:

Placed or attached firmly; fastened securely; made firm or stable in position, definitely and permanently placed; stationary or unchanging in relative position.
Any means of inducing or altering deflection of a fixed appendage other than by; lift or drag generated by the motion of the appendage through the water, or loads due to self weight or other attached appendage(s), would contravene the definition of 'fixed' as used in rule 17.

5. (a) Yes, see answer 4 above.
(b) Yes, see answer 4 above.
(c) Yes, see answer 4 above.

6. (a) No. However any adjustment of the locking mechanism after measurement that results in an alteration to the location or deflection of a fixed appendage may constitute a change to that appendage for the purposes of Rule 45.2 (a).
(b) No, see answer 6(a) above.
(c) No, see answer 6(a) above.

7. No, any movement of an appendage other than that permitted by Rule 17.10 is not permitted. Attention is drawn to Rule 17.10(b)

8. The answer to question 7 is 'No'.

9. No, any induced deflection or alteration of the position of a fixed appendage would contravene the definition of 'fixed' as used in rule 17. Also see answer number 4 above.

10. The answer to question 9 is 'No' END

This interpretation is made by the CORD Measurement Committee in accordance with Rule 3.3 of Version 5.0 of the America’s Cup Class Rule.
Ken McAlpine ACC Technical Director