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APPENDIX C
Justification for use of new kar
A new formula based on the ABS Offshore Racing Yacht (1994) 'F' factor has been devised.
Kar=1,14-0,0019(b/L0,4)
Since the factor is no longer a function of area, It should be renamed.
kpr is suggested.
ABS F factor (ABS value v Approx)
The formula works for both panels and stiffeners. A fit is also possible to kar, but requires at least two equations, since the basis of kar is on structural component AREA rather than span.
Kar=8,2L0,36/b0,6
THIS IS THE EQUATION FOR THE PLATING ONLY (and is based on AD = 2,5b2)
Kar (ISO v Approx)
F is typically 25% - 50% larger than kar (Panels) and 30% lower than kar (stiffeners). The large difference between F (ABS) and kar (ISO) makes it necessary to have two equations for kpr (see blue text above). In order to avoid more than two equations, internals are treated using the LR SSC approach - This is an interim suggestion for the present.
IT MAY BE NECESSARY TO MAKE FURTHER ADJUSTMENTS AS PART OF THE VERIFICATION PROCESS.
APPENDIX D
Comparison with existing equations
While, it will not be possible for the simplified method to EXACTLY replicate the pressure values from the ISO draft (pre-Baltimore), it is essential that the values under the new scheme should be similar. OTHERWISE WE ARE BACK TO SQUARE ONE WITH OUR VALIDATIONS.
FIRST SERIES: V/√L < 3,0 (Essentially sail boats)
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SECOND SERIES: V/√L = 10 (Motor)
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THIRD SERIES: V/√L = 12 (MOTOR)
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Note:
1. Agreement is good for the basic pressure (i.e. uncorrected for reduction factors) for all boats, all speeds
2. The agreement for design pressures for power boats is good for all cases
3. Differences for sail are solely due to use of a different reduction factor
4. Poor agreement with ISO and new acceleration is irrelevant for sail boats as Pb2 governs scantlings. (With the new scheme, Pb2 won't be needed of course).
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