Page 5 - WestlawnMasthead17_Mar.11.pub

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(The 5.144 converts knots to meters per second and keeps
all the units consistent.)
or in English units:
(The units here aren’t internally consistent but, inst
are set up to give the same result as the standard
ric E
T
.)
Where:
E
T
= Transport efficiency
Kts = Boat speed, in knots
Tonnes = Metric tons
Tons = Long tons of 2,240 lb.
kW = Total installed propulsion power, kW
BHP = Total installed engine power, brake horsepo
Propulsion Efficiency
Almost all ordinary boats are driven by propellers. (J
are the other alternative, see part 2.) Except for hig
speed boats, the larger the propeller diameter and t
slower the shaft RPM, the more efficient the propul-
sion. Remember, for large diameter you need low
shaft RPMs. Indeed, one of the most frustrating things I r
up against as a designer is finding deep reduction gears t
mate with smaller engines—engines under 300 or 400 H
It’s like looking for a unicorn. No one seems to make the
Comparing Boats
In order to clearly see the effects of our three basic effi-
ciency criteria: going slower, slender hulls, and efficient p
T
5.144 x Kts x Tonnes
E =
kW
T
7 x Kts x Tons
E =
BHP
Iron Kyle
—45-ft. Tug Yacht
Continued next p
Table 1 - Normalized Boat Characteristics
Original (Not Normalized) Boat Characteristic Table
BOAT NAME
LOA DWL BEAM
BEAM
WL DISP lb.
DISP
tons DL Ratio
DWL/
BWL
Iron Kyle (n)
43.42 39.17 13.00 12.25 45,000 20.1 334.4 3.2
Imagine (n)
51.17 45.67 13.17 12.00 45,000 20.1 210.9 3.8
Peregrine (n)
51.72 50.67 14.88 13.13 45,000 20.1 154.4 3.9
Ironheart
67.00 63.25 11.00 10.25 45,000 20.1 79.4 6.2
BOAT NAME
LOA DWL BEAM
BEAM
WL DISP lb.
DISP
tons
DL Ra-
tio
DWL/
BWL
Iron Kyle
45.17 40.67 13.50 12.670 50,400 22.5 334.5 3.2
Imagine
56.50 50.52 14.50 13.340 60,900 27.2 210.9 3.8
Peregrine
45.17 44.25 13.00 11.476 29,975 13.4 154.4 3.9
Ironheart
67.00 63.25 11.00 10.250 45,000 20.1 79.4 6.2
Summer Moon 2* 82.25 72.92 17.00 16.260 137,400 61.3 158.2 4.5
*Summer Moon 2 will be discussed in part 2.