There are several different kind of propulsion systems as much
as applications, a lot of research has been made to try to get the most
efficient system in order to lower operation costs (fuel consumption) without
sacrificing performance and life of the vessel. Attempts of radical
designs have been made without results, but others have succeeded and are becoming
popular as the marine field takes the chance to test one of them, anyway,
some of the classical designs have slightly changed too and here are a
few of the most common:
|
From the desktop of
Leonardo Montoya |
These
are just some examples of them for the reader to know the advantages
of each equipment
All of
them have some common applications, these are some of their
characteristics
-
The
most common due to its relatively low cost is the fixed
pitch propeller, these wheels are also known as “constant
face pitch”, this means that the pitch on all the surface of the
blade (unlike the
blade angles) does not change, they are used in most commercial
vessels such as tugs, draggers, fishing vessels, trawlers.
-
Variable
pitch propellers.-
As mentioned, most of
the wheels have a constant pitch, but there are some special
applications (large vessels or high speed boats) where the
necessity of taking out the highest efficiency is a must. On these
wheels, pitch may vary on each radius (depending on design), but
it is most common to find the ones where pitch is
usually reduced near the tip in order to reduce the blade pressure
and the possibility of cavitation.
-
Controllable
pitch propellers.-
These propellers allow the operator to adjust the pitch at will,
depending on the operation, this is due to an hydraulic mechanism
or a mechanical link that allows the blades to turn on their own
axis. They offer a big advantage in operation cost, but they are
considerably more expensive than the solid ones.
-
Ducted
propellers.-
They are surrounded by a hydrodynamic profile shaped shroud, the
advantages on these are the increase of thrust (around 40%). There
are many profiles that reduce the speed, but there are new
improved designs that actually increase it when compared to
standard open wheels, there are nozzles designed to operate for
maximum performance on the ahead condition and some for both
(ahead and astern thrust). The application for these is limited
for low-speed boats (operation below 14 knots) such as trawlers,
tugs, draggers.
If you
have any questions or any suggestions to any subject in these
technical issues or If you want to be removed from this mailing list,
please send an e-mail with your comments to technicalletter@ricepropulsion.com
www.ricepropulsion.com
|
Open wheel (skewed design)
Variable pitch propeller
Controllable pitch propeller inside a
nozzle
Z-drive unit
Water jet unit
|