Introduction
We have already studied propellers used for ship propulsion.
The conventional propeller used is the fixed pitch propeller. But now
the modern developments had led to some other types of propulsors. In
this article we will discuss about these various types of propulsors and
their definitions. Some of these propulsors include:
- Controllable pitch propellers,
- Azimuth propellers,
- Vertical axis propellers,
- Paddle wheels,
- Shrouded propellers.
Controllable Pitch Propellers
Shrouded Propellers
The propeller is
sheltered in a duct or shroud. The propeller does not create any
divergence of wake, ie the wake can be controlled to a certain extent.
By this there is a maximum utilization of thrust.
Azimuth Propellers
The propellers are
placed in a housing or pod. It can create thrust in any direction
(ahead, astern). Usually there will be two propellers. One forward of
the duct and one aft of the duct. From the figure shown it may be clear
that there is no need for a rudder. These finds application in cruise
ships, ro-ro ferries, and large container ships.
Vertical Axis Propellers
In
this type of propulsion, a horizontal disc carrying a number of blades
are fitted. The blades themselves can rotate about their own vertical
axes. The same amount of lift forces can be produced in comparison with
the fixed pitch propellers. For variation of thrust the blade angles are
varied. This finds application in tugs, ferries, and the drive is
provided with the help of bevel gears.
Paddle Wheels
In this method a number of paddles are mounted and they are rotated about an horizontal transverse axis. These can be fitted even on either sides of the ship and exerts a good turning moment. This is a very old method that had been used widely in those days.Conclusion
Though
there are different types of propulsors, the most popular being the
fixed propeller due to its cost and reputation. The above mentioned
propulsors have been used on modern and special kind of ships.
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