International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 6
Number 2
June 2012
235
1 SYMBOLS
B –fuel consumption [kg/h];
b
e
– unit fuel consumption [kg/kWh];
G
K
–air consumption [kg/s];
D – propeller dimension [m];
J advance of propeller;
K
Q
torque coefficient;
K
T
thrust coefficient;
L – work [kJ];
M mass [kg];
N – power [kW];
n – rotational speed of a propeller [1/s];
p – pressure [Pa];
Q – torque [Nm];
R- Vessel resistance [N];
T – propeller thrust [N];
T temperature [K];
t temperaturę [
o
C];
t suction coefficient ;
w wake fraction;
x content relative to dry air mass;
v
p
propeller advance speed [m/s];
ρwater density [kg/m
3
];
η
p
freewheeling propeller efficiency;
Index’s:
h – per hour;
m concern measured parameters;
o – ambient parameters;
r concern reduced parameters.
2 INTRODUCTION
Measurements performed on vessels are aimed at de-
termining the up-to-date technical condition of the
elements of the main propulsion or the evaluation of
the operating elements of a vessel. The diagnostic
measurements should be performed in a continuous
manner, and the measurements to determine propul-
sion characteristics should be performed at specified
time points, e.g. after completing the construction
works on the vessel, after repairing elements of the
propulsion system, etc. The measurements are per-
formed on a vessel to develop propulsion forecast
for a new built ship, or to evaluate current operating
parameters of an exploited vessel. Irrespective of the
aim of the measurements, it should be noted that a
vessel always works in different conditions and the
conditions may affect the quality and reliability of
measurements. The change of the conditions for ves-
sel movement is induced by parameters linked with:
the vessel, i.e. vessel loading, use of reserves
(change in displacement), change in the condition
of hull, propellers, engines, etc.
hydrometeorological conditions
vessel operation region.
The evaluation of factual propulsive characteris-
tics in exploitation is performed during vessel sea
trials [2].
In order to fully evaluate the propulsive charac-
teristics, the following should be measured: torque
Conditions of Carrying Out and Verification of
Diagnostic Evaluation in a Vessel
A. Charchalis
Gdynia Maritime University, Gdynia, Poland
ABSTRACT: The paper presents some problems of carrying out measurements of energetic characteristics
and vessel’s performance in the conditions of sea examinations. We present the influence of external condi-
tions in the change of vessel’s hull resistance and propeller characteristics as well as the influence of weather
conditions in the results of examinations and characteristics of gas turbine engine. We also discuss the manner
of reducing the results of measurements to the standard conditions. We present the way of preparing propul-
sion characteristics and the analysis of examination uncertainty for the measurement of torque.
236
on propulsion shafts; propeller thrust; rotational
speed of shafts, vessel speed and the use of fuel by
particular engines. Fig. 1 presents a block diagram
of a vessel as the object of sea propulsion trials.
Figure 1. Block diagram of a vessel.
Figure 2. Resistance characteristics of a hull: 1. nominal ambi-
ent conditions (design); 2. degraded ambient conditions: 3. im-
proved ambient conditions.
3 CHANGE IN VESSEL FLOATATIONAL
RESISTANCE
Vessel resistance is determined at the design stage
swith the use of computing methods and experimen-
tally with the use of model trials. They are the ba-
sis for selecting the propulsive system. At the design
stage the resistance of a vessel is determined for
standard navigational conditions. During exploita-
tion, displacement, and consequently draught, hull
state, external conditions, etc. change continuously.
This leads to a change (deterioration) in resistance
characteristics and a change in the type of main en-
gine load when the same vessel speed is developed.
Thus, the information on resistance characteristics
and the evaluation of the influence of particular con-
ditions which, in turn, affect their values is signifi-
cant in the diagnostic assessment of the state of pro-
pulsion system elements and of propulsive charac-
teristics [3]. Fig. 2 illustrates exemplary resistance
characteristics for a vessel operating in improved or
worsened operating conditions.
4 CHANGE IN PROPELLER
CHARACTERISTICS
Just like a hull, vessel propellers work in vastly var-
ying conditions. It is especially applicable to chang-
es in propeller draught resulting from displacement,
permanent draught change and the angle of the in-
coming water during wave navigation, as well as de-
terioration in the condition of propeller blade surface
(increased roughness). In order to evaluate the con-
ditions in which a propeller operates at the rear of a
vessel hull, it is important to know the cooperation
relationship between the hull and propeller. Fig. 3 il-
lustrates exemplary hydrodynamic characteristics of
a propeller operating at the rear of a vessel hull.
Figure 3. Hydrodynamic characteristics of a propeller: -------
free propeller characteristics in undisturbed water velocity
field; - - - - characteristics of the working propeller after the
ship's hull.
5 THE INFLUENCE OF EXTERNAL
CONDITIONS ON ENGINE
CHARACTERISTICS
The propulsive system of a vessel operates in vastly
varying conditions. The change of conditions is
caused by continuous change in displacement, and
also draught, change of region where a vessel oper-
ates, change of hydrometeorological conditions, and
changes in the condition of the hull, propeller and
engines. In order to diagnose the propulsive system
of a vessel in time, it is necessary to take changes in
operating conditions into consideration.