Propulsion Systems - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 125

Wageningen Kaplan Meyne

Fig. 8.3 Several forms of propellers

8.4 Propulsion of Ships

The propulsion in a ship includes all of the elements from the engine to the
propeller. The technology has been continuously and intensively changing over the
last decades. Steam engines and their connected propulsion elements have been
replaced by diesel engines or gas turbines. Highly developed technology is what
determines the current propulsion systems. They have been improved for eco-
nomic reasons and for environmental protection in the course of fulfilling the
increasing level of requirements [ 21 ].
The most complex transmission systems are used in military technology in
which the highest technology for fuel consumption, maintenance, redundancy,
efficiency and availability is required.

8.4.1 Propeller Systems

Propellers are ceaseless flow machines which take mechanical work and pass it to
the surrounding water in form of flow energy. As the trend moves toward larger
ships and higher velocities, the propeller's efficiency must also be increased [ 22 ].
This requirement has led to the broad ranged application of nozzle propellers
with an inflow ring. They consist of a steel ring attached in front of the propeller,
which bundles the inflow of the water to the propeller and changes the flow
direction [ 23 ].
Inflow rings (Mewis Duct) and higher skew increase the degree of effectiveness
of the propeller and the drive performance of ships by up to 10%, primarily for
large ships (see Fig. 8.3 )[ 24 ].
Besides the engine, the propeller is one of the main sources of vibrations on a
ship. In a lot of cases, it is necessary to change the geometry of the propeller to
keep the vibrations at an endurable level for the crew and for the ship construction
[ 25 ].
The number of blades in the propeller is variable. The pressure difference of the
water stream in front of and behind the propeller determines the number of blades.
Propellers can theoretically consist of one blade or of an unlimited number of