Iveco Marine Diesel Engines, Installation Handbook

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MARCH 2004 INTRODUCTION
1.21
MARINE ENGINES INSTALLATION
For example, if the above mentioned calculation is applied to a hull having floating length L = 25 feet,
it results in:
■
Displacing hull, limit value knots
■
Semi-gliding hull, limit speed knots
Values above 3 are for gliding hulls.
Practically, this type of hull, according to the bottom shape, starts to glide at a relative
speed .
It means that a hull with length L=10m (32.8 ft) should have a speed above knots
to be able to glide.
Power definitions for boat propulsion
In the powered boat propulsion system there are different power levels, from the engine up to pro-
peller. We think it is advisable to identify them from a qualitative point of view, as follows:
■
BHP (Brake horse power): it is the power available to the engine flywheel as defined by the inter-
national regulations.
■
SHP (shaft horse power): it is the power available to the output shaft of the reducer-inverter; there-
fore after the mechanical losses due to the shaft efficiency.
■
DHP (delivered horse power): it is the power which can be actually used by the propeller, there-
fore after the mechanical losses of the axis line (bearings, stuffing box) and of the reducer-inverter,
the power absorption by additional accessories which take power from the engine (not included in
the BHP) and the deductions due to the environmental conditions.
■
EHP (effective horse power): it is the propeller net efficiency power which is actually translated into
thrust for the boat motion.
1. EHP - 2. Reducer - 3. Engine - 4. DHP - 5. SHP - 6. BHP.
Figure 12
1
3
2
4 5 6