Engine Layout And Load Diagrams Introduction; Propulsion And Engine Running Points; Propeller Curve; Propeller Design Point - Man B&W S80ME-C7 Project Manual

MAN B&W
Engine Layout and Load Diagrams
Introduction
The effective power 'P' of a diesel engine is pro-
portional to the mean effective pressure p
engine speed 'n', i.e. when using 'c' as a constant:
P = c x p x n
e
so, for constant mep, the power is proportional to
the speed:
P = c x n (for constant mep)

When running with a Fixed Pitch Propeller (FPP),
the power may be expressed according to the
propeller law as:
P = c x n (propeller law)
3
Thus, for the above examples, the power P may
be expressed as a power function of the speed 'n'
to the power of 'i', i.e.:
P = c x n
i
Fig. 2.0.0 shows the relationship for the linear
functions, y = ax + b, using linear scales.
The power functions P = c x n
tions when using logarithmic scales:
log (P) = i x log (n) + log (c)
y
2

0
0 
Fig. 2.01.01: Straight lines in linear scales
MAN B&W MC/MCC, ME-B, ME/MEGI engines
e
will be linear func-
i
y=ax+b
a
b
2
y=log(P)
i = 0
and
i = 
i = 2
i = 3
Fig. 2.01.02: Power function curves in logarithmic scales
Thus, propeller curves will be parallel to lines hav-
ing the inclination i = 3, and lines with constant
mep will be parallel to lines with the inclination i = .
Therefore, in the Layout Diagrams and Load Dia-
grams for diesel engines, logarithmic scales are
used, giving simple diagrams with straight lines.

Propulsion and Engine Running Points

Propeller curve

The relation between power and propeller speed
for a fixed pitch propeller is as mentioned above
described by means of the propeller law, i.e. the
third power curve:
P = engine power for propulsion
n = propeller speed
c = constant

Propeller design point

Normally, estimates of the necessary propeller
power and speed are based on theoretical cal-
culations for loaded ship, and often experimental
tank tests, both assuming optimum operating
x
conditions, i.e. a clean hull and good weather. The
combination of speed and power obtained may
178 05 403.0
be called the ship's propeller design point (PD),
MAN Diesel
P = c x n , in which:
3
2.01
Page  of 2
i
P = n x c
log (P) = i x log (n) + log (c)
x = log (n)
178 05 403.1
198 38 338.4