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Proposed National Keelboat Rating System – In Action !! (part 4)

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Proposed National Keelboat Rating System – In Action !! (part 4)

Part | 1 | 2 | 3 | 4 | 5 |

We
will now compare two production yachts with similar IRC ratings and
show how the above system looks for the sweet spot: The two yachts selected are the
Archambault A-35 (ORC measures) and Beneteau First 36.7 (ORC
measures)
.

Basic dimensions are: Archambault A35 First 36.7
Mainsail *** 37.26 39.11
Jib *** 30.67 42.49
Spinnaker (0.83) *** 81.84 81.90
Displacement
mass
****
4905 5677
LOA ** 10.59 10.64
BO ** .101 0.367
SWL ** 10.144 9.795
SO ** 0.345 0.478
Immersed
waterline
– upwind **
10.504 10.276
downwind ** 10.489 10.273
Dynamic hull speed – upwind * 7.065 6.988
– downwind * 7.060 6.987
Downwind
Power Factor
#
1.184 1.122
Downwind:Sq.root(SA/D)
#
.0154 0.144
Basic VMG downwind[wind averaged] hull speed * 8.35 7.84
Circular
random factor (BASE) #
1.079 1.040
Fine
Tuning Factors %:
   
Stern
Profile/Beam
aspect
1.00 0.20
Main/Jib Bias -0.55 0.64
Accelerative 0.12 0.09
Form Stability -0.10 -0.10
Hull Mass & Crew stability 0.04 0.16
Wave-making HF 0.23 -0.11
Rig factor (spreaders / stays) 1.25 1.00
Aluminium spars (std mass)   -0.50
Carbon Spars 1.25  
Spinnaker bias 0.14 0.08
Code Zero 0.39  
Sail
fabric
– aramid
1.00 1.00
Jib battens 0.25  
Penalty pole 0.06  
Generation Factor – age
allowance
0.20 0.14
Fine
tune overall factor
1.0504% 1.0260%
Final
factor
# (base x
fine tune %)
1.133 1.067
IRC
#
(averages)
1.030 1.035
IRC “mark-up” 10.0% 3.1%
Comparative
performance advantage
6.9% 0.0%
DLR 131 168