ISSN 1068-798X, Russian Engineering Research, 2018, Vol. 38, No. 2, pp. 77–79. © Allerton Press, Inc., 2018.
Original Russian Text © A.P. Kushnir, E.V. Kurnasov, 2017, published in Vestnik Mashinostroeniya, 2017, No. 11, pp. 14–16.
Optimization of Marine Thrusters
A. P. Kushnir* and E. V. Kurnasov
Moscow State Institute of Radioengineering, Electronics, and Automation, Moscow, Russia
Abstract—Improving the maneuverability of ships by increasing the tractional force of the thrusters is consid-
ered. To minimize the losses associated with swirling liquid flow and the variable attack angles in reversing,
the traditional configuration must be modified, and the inclination of the thruster blades must be optimized.
To increase the efficiency, the rotors should have different speeds and blade inclinations.
Keywords: thruster, maneuverability, ship, screws, pressure head, velocity triangle, controllability, blades
Thrusters are intended to improve the maneuver-
ability of ships. They are needed because, in motion of
the ship over short distances, the water pressure on the
rudder is sharply reduced, and the vessel is no longer
controllable. Using thrusters, the ship may be moved
broadside and even perform a complete rotation in
place. Accordingly, thrusters are essential for seagoing
and coastal vessels and also for ferries, in crossing
small inlets, in canals, and also in docking or setting
sail [1, 2].
According to the rules formulated by the Russian
River Register, thrusters are recommended for ships
whose lateral projection area exceeds 800 m
Thrusters differ in design, but the most common
practice is to use stationary thrusters mounted trans-
verse to the ship in the water channel (at the bow or the
stern). The thruster may take the form of single or dou-
ble screws. The transverse force in the thruster is created
by propellers as a result of the pumping of water through
a water channel that runs across the ship. The propeller
rotors take the form of screws of fixed or variable pitch,
acting as reversible axial pumps .
The thruster (Fig. 1) consists of a water channel 3
(a cylindrical pipe) within the ship, containing a pro-
peller in the form of double rotors 1, which is capable
of forward or reverse traction . Protective gratings 2
are mounted at the input of pipe 3. The torque is trans-
mitted from motor 4 to rotors 1 through vertical shaft
5, conical gear 6, and horizontal shafts 7. As a rule, the
liquid flow is reversed by changing the direction of
The function of the thruster is to provide the max-
imum tractional force. That is very difficult, for the
following reasons. First, the power of the thruster
motors is much less than the power of the primary
marine drives. Second, the flow through the water
channel must be reversible. That limits the geometry
of the propeller blades and hence limits the thruster
efficiency, even when using screws of variable pitch.
The efficiency of single-screw thrusters is especially
low . Since the drive power may be hundreds of kW,
it is very important to increase thruster efficiency.
The tractional force of the thruster is directly pro-
portional to the pressure difference in the waveguide
and hence to the pressure head created by the propel-
ler. Theoretically, the pressure head Н corresponding
to a single screw (rotor) is determined by the Euler
are the output and input azimuthal
velocities of the rotors, respectively; V
the azimuthal projections of the absolute output and
input flow velocities of the liquid, respectively; g is the
acceleration due to gravity.
We now consider the input and output liquid flow
at the first (Fig. 2a) and second (Fig. 2b) rotors.
For the sake of convenience, we write the absolute
flow velocity V as the vector sum of the relative veloc-
out out in in
Fig. 1. Thruster system.