Propulsion And Manoeuvring Systems
Summary
TLDRThis script offers an in-depth look at various ship propulsion and maneuvering systems, emphasizing the importance of hull form and engine power for optimal performance. It discusses traditional single propeller setups, controllable pitch propellers for thrust optimization, and advanced rudder systems like flap, rotor, and Schilling rudders that enhance maneuverability. The script also touches on diesel and steam turbine engines, the impact of rudder design on steering, and the use of autopilots for precise navigation.
Takeaways
- 🚢 The chapter provides an overview of common propulsion and maneuvering systems in ships, emphasizing the importance of hull form, engine power, and propeller and rudder systems for optimal performance.
- 🔄 Most ships use a traditional single fixed propeller and rudder, which can be challenging for maneuvering in confined waters.
- 🛠 Some vessels are equipped with alternative propeller and rudder systems to balance maneuverability and economy more effectively.
- 💡 Diesel engines are widely used due to their cost-effectiveness, with low-speed engines operating directly onto the shaft and medium to high-speed engines often used in smaller vessels.
- ⚙️ The response time of steam turbines to control orders is slow, which requires careful planning when maneuvering.
- ⚓ Controllable pitch propellers (CPP) allow for thrust optimization under different load conditions and can be adjusted using a hydraulic mechanism.
- 🔄 The direction of a ship's turn can be influenced by the rotation direction of the propeller, with most sea propellers being left-handed, moving anti-clockwise.
- 🌀 Ducted propellers provide increased power output and better steering, especially at low speeds, by utilizing a shroud that forces water through a smaller aperture.
- 🛳 Conventional rudders are a compromise between economy and necessity, with different designs like spade, balanced, and semi-balanced rudders serving different types of vessels.
- 🛑 Advanced rudder systems like flap, rotor, and T rudders offer improved maneuverability and turning performance, though they come at a higher cost.
- 🕹 The Schilling rudder system uses a fixed-pitch propeller with two synchronized rudders controlled by a joystick, providing unique maneuvering capabilities.
- 🔄 The direction of a ship's turn can be influenced by the design of the propellers, with twin-screw ships often having right-hand turning starboard propellers and left-hand turning port propellers to reduce cavitation and enhance transverse thrust.
Q & A
What is the main focus of the chapter discussed in the transcript?
-The chapter focuses on an overview of the most common propulsion and maneuvering systems used in ships, including the relationship between hull form, engine power, and propeller and rudder systems.
Why do traditional single fixed propellers pose a challenge for ship handlers?
-Traditional single fixed propellers are designed primarily for economical travel from point A to B, which can be challenging for ship handlers when maneuvering in confined waters due to limited maneuverability.
What are controllable pitch propellers and how do they optimize thrust?
-Controllable pitch propellers are a type of propulsion system that allows for the modification of the pitch to optimize thrust under different load conditions, improving maneuverability and fuel efficiency.
How do diesel engines operate in ships, and what are some considerations for ship handlers?
-Diesel engines, especially low-speed ones, operate directly onto the shaft. Ship handlers must consider the difficulty of starting the engine when making headway and the potential limitations of starter availability.
What is the main drawback of steam turbines from a ship handler's perspective?
-Steam turbines have a slow response to control orders for changing the direction of shaft rotation, which requires careful planning of each movement when maneuvering the ship.
What are ducted propellers and what advantages do they offer?
-Ducted propellers are enclosed in a tube or tunnel with the propeller inside. They offer more output power, reduced propeller wash, better steering at low speeds, and improved turning characteristics.
What is the difference between a conventional rudder and a flap rudder?
-A flap rudder has an additional flap on the trailing edge for steering, allowing up to twice the steering power compared to a traditional rudder, making the ship more maneuverable.
What is the purpose of the rotor rudder, and how does it improve ship turning performance?
-The rotor rudder is a conventional rudder with a rotating cylinder mounted vertically on the edge. It smooths the water flow at high rudder angles, improving the ship's turning performance.
What is the Schilling rudder system, and how does it differ from other rudder systems?
-The Schilling rudder system features a fixed-pitch propeller that is constantly running, with two rudders that can rotate through a total arc of 145 degrees. It is controlled by a single joystick, offering a unique and efficient maneuvering capability.
How do twin-screw ships achieve better maneuverability, and what factors contribute to this?
-Twin-screw ships achieve better maneuverability through a combination of factors including propeller configuration, the effect of talk, transverse thrust, the pivot point, and the skill of the ship handler.
What is the importance of planning turns in confined waters, and how can autopilots assist with this?
-Planning turns in confined waters is crucial for navigational safety and precision. Modern autopilots with preset turning radius or fixed rate of turn modes can assist in executing and controlling turns accurately.
Outlines
🚢 Ship Propulsion and Maneuvering Systems Overview
This paragraph introduces the common propulsion and maneuvering systems found on modern ships, emphasizing the relationship between hull form, engine power, and rudder systems. Traditional setups often consist of a single fixed propeller and rudder, designed for economical travel. Challenges arise when maneuvering in tight spaces. Some vessels have advanced systems for improved maneuverability and economy. Diesel engines are prevalent due to their cost-effective operation, with low-speed engines running at 85-130 RPM, and medium to high-speed engines offering better responsiveness and power efficiency. Steam turbines are used in larger, high-speed ships but have slow response times. Controllable pitch propellers offer thrust optimization and are controlled by a Combinator for balanced performance and fuel savings.
🌀 Advanced Propeller and Rudder Technologies
The second paragraph delves into advanced propeller and rudder technologies, such as controllable pitch propellers that allow for speed adjustments and low-speed maneuvering. Ducted propellers provide increased power and better steering characteristics. Conventional rudders are discussed, highlighting their limitations and the benefits of semi-balanced designs. The paragraph also explores various rudder types, including spade, full, and heel rudders, each with specific applications and advantages. Modern autopilots with preset steering modes for turns are mentioned, emphasizing the importance of planning and precision in maneuvering.
🛳️ Enhanced Rudder Systems for Improved Maneuverability
This section discusses the development of more efficient and advanced rudder systems over the past few decades. Flap rudders, rotor rudders, and T rudders are introduced, each offering increased steering power and improved turning performance. The flap rudder uses an additional flap for enhanced maneuverability, while the rotor rudder smooths water flow for better performance at high angles. The T rudder combines features of flap and rotor designs for optimal performance, albeit at a higher cost. Special rudders capable of deploying up to 70 degrees are also mentioned, providing outstanding lateral motion when used with bow thrusters. The paragraph concludes with a unique rudder system featuring a fixed-pitch propeller with twin Schilling rudders controlled by a joystick, offering a different approach to maneuvering.
⭕️ Twin-Screw Ships and Autopilot Maneuvering Strategies
The final paragraph examines twin-screw ships, which are designed with right-hand and left-hand turning propellers to reduce cavitation and maximize transverse thrust. The importance of the rudder's position in the propeller slipstream is highlighted, along with the factors contributing to a ship's maneuverability. Autopilots with preset turning radius and rate of turn modes are discussed, emphasizing the benefits of planning turns for precision and predictability. The paragraph provides a mathematical formula for calculating the rate of turn and suggests using the largest possible radius and accounting for external factors like wind and current. The importance of adjusting heading manually when necessary is also noted, along with the advantages of using a low rate of turn for safety, economy, and comfort.
Mindmap
Keywords
💡Propulsion Systems
💡Maneuvering Characteristics
💡Diesel Engine
💡Steam Turbine
💡Controllable Pitch Propellers
💡Ducted Propellers
💡Conventional Rudders
💡Advanced Rudder Systems
💡Twin-Screw Ships
💡Autopilot Systems
💡Rate of Turn
Highlights
Overview of common propulsion and maneuvering systems in ships
Maneuvering characteristics are related to hull form and engine power
Traditional ships use single fixed propeller and rudder systems
Challenges in maneuvering in confined waters with traditional systems
Some vessels equipped with advanced propeller and rudder systems for better balance
Diesel engines are widely used for their cost-effective operation
Low speed diesel engines operate directly onto the shaft with specific RPM ranges
Difficulties in starting diesel engines while making headway due to propeller resistance
Medium and high speed diesels are popular in smaller vessels for their responsiveness
Steam turbines are found in large ships requiring high speed but have slow response
Controllable pitch propellers optimize thrust under different load conditions
Combinator balances engine revolutions against propeller pitch for fuel savings
Ducted propellers offer more output power and better steering characteristics
Conventional rudders are a compromise between economy and necessity
Advanced rudder designs like flap, rotor, and T rudders improve maneuverability
Twin Schilling rudder system with a constantly running propeller offers unique maneuvering
Twin-screw ships have specific propeller and rudder configurations for better maneuverability
Autopilots with steering modes for preset turning radius or fixed rate of turn
Importance of planning turns with the largest possible radius and adjusting for conditions
Mathematical formulas for calculating rate of turn and turn radius
Autopilots capable of following a preset curve for precision track keeping
Transcripts
This chapter will give you a general
overview of the most common propulsion
and maneuvering systems used today ships
maneuvering characteristics are directly
related to her hull form optimal
performance depends upon the whole shape
in conjunction with engine power and the
propeller and rudder systems most ships
are still equipped with traditional
single fixed propeller and single rather
designed for getting the ship from A to
B as economically as possible
this often represents a challenge to the
ship handler with reference to
maneuvering in confined waters in order
to achieve a better balance between
maneuverability and economy some vessels
are equipped with propeller and rudder
systems that differ considerably from
the traditional systems general
information about some of these new
systems will be given later in this
chapter the diesel engine is very widely
used as it tends to be the least
expensive to run low speed diesel
engines operate directly onto the shaft
maximum speed RPM is in the range 85 to
130 RPM the ship handler must remember
the difficulties can be experienced in
starting the engine when still making a
lot of headway
this is because the propeller will be
trying to turn in the water stream and
because of the direct drive the engine
tends to turn in the forward direction
another important thing to remember is
that sometimes there might be a limited
amount of starter available IE too many
starting orders during a short time
interval may empty the start air
reservoir making engine starts
impossible for some time
medium and high speed diesels are
popular arrangements in smaller vessels
fairies car carriers and other special
ships one or several engines drive shaft
through a gearbox
since clutch the engines are normally
operated from the bridge and are very
responsive and like their low speed
relatives can develop almost as much
power astern as ahead but of course the
application of this astern power is less
efficient as ships hulls propellers and
rudders are usually designed to work in
the head direction the steam turbine is
often found in large ships and on ships
where high speed is required a turbine
ship while being smooth running and more
reliable in the mechanical sense has one
major drawback from the ship handlers
point of view its response to control
orders for change of direction of shaft
rotation are slow
thus when maneuvering a turbine driven
ship each movement must be carefully
planned controllable pitch propellers
are very practical because by modifying
the pitch they allow for thrust
optimization under different load
conditions with the controllable pitch
propellers the user can modify the pitch
normally by means of a hydraulic
mechanism click on each hotspot to learn
more about CP pitch is the distance of
propeller drives forward for each
complete revolution assuming it is
moving through a solid element just like
a wood screw does when using a CP
propeller the main engine has to be
clutched in so the propeller is
continuously turning usually at quite
high revolutions as it is neither
practicable more economical to run an
engine continuously at excessive
high-rpm it is important to have some
kind of combined control over both RPM
and pitch so that the pitch for slow
speeds is balanced by a reduction in
revolutions on most ships this is
achieved by installing a Combinator
which automatically balances engine
revolutions
against propeller pitch that's producing
a savings in fuel and better propeller
performance to use ahead power a ship
with CP propeller is not restricted to
the old step progression that has been
associated with fixed pitch propellers
any speed can be selected by adjusting
the Combinator control to the required
setting it is also possible to set the
propeller pitch for extremely low speeds
so when it is essential to proceed at
very slow speeds the propeller and
rudder are still active and steerage way
can be maintained for a lot longer than
usual when low speed or stop are
demanded the blades of the CP propeller
are set with a very fine angle and pitch
if the ship's speed is too high and does
not already matched the propeller speed
the flow of water through it will be
restricted and turbulence will develop
behind the propeller which will also
have an adverse effect upon the rudder
if the ship's speed is not reduced
slowly and progressively in much the
same way as a large directional unstable
ship the rudder will be shielded and the
steering may become erratic or poor one
of the most common concerns mentioned by
many navigators and pilots is the
uncertainty as to which way the bear
will count if at all when a CP
propellers put a stern to answer this
question it is necessary first to know
which way the propeller is turning when
it is viewed from astern the majority of
the sea propeller is left-handed ie they
move in an anti-clockwise direction the
effect however is similar to a fixed
pitch right-handed propeller working
astern IE the bow make aunt to starboard
it is important to note that the
transverse thrust on some ships with CP
propellers maybe weekend unreliable user
vortices or turbulence around the
propeller blades it
therefore advisable to exercise some
caution when anticipating the effects of
stern power on some CP ships many
vessels ranging from tugs to large
ocean-going ships are equipped with
ducted propellers a shroud or duct is a
tube or tunnel light construction with
the propeller inside the forward end of
the duct has a larger diameter than the
aft end the increased power comes from
the propeller constantly drawing a
massive water into the duct which then
has to be forced out through a smaller
aperture the main advantages which can
be expected of the ducted propeller are
more output power from the propeller
reduced propeller wash to a smaller arc
thereby reducing erosion of canal and
river banks better steering especially
at low speed better turning
characteristics conventional rudders
found on thousands of ships worldwide
represent a compromise between economy
and necessity conventional rudders
normally function satisfactorily for
normal steering and cause change
requirements in open waters the basic
conventional rudder is efficient up to
maximum 45 degrees at high angles the
rudder is not capable of maintaining a
smooth water flow across both sides of
the rudder and the rudder stalls IE
loses its effect if the runner has its
entire area after the rudder stock then
it is unbalanced a rather with between
twenty and forty percent of its area
forward of the stock is balanced most
modern brothers are of the semi balanced
design this means that a certain
proportion of the water force acting on
the after part of the rudder is
counteracted by the force acting on the
forward part of the rudder hence the
steering gear can be lighter and smaller
there are several types of rudder
designs pick the hot spots to see the
three most common types
this is the most used rather type on
ferries and smaller ships the Spade
rather provides good maneuverability
this type of brother is most commonly
used on bigger ships it is not as
effective a speedrunner of the same size
the heel rather is supported with
bearings on the top and bottom providing
an enjoyable rudder construction
conventional riders are somewhat
restricted when it comes to
maneuverability at slow speed in
confined waters several manufacturers
have developed more efficient and
advanced radar systems the last two or
three decades and quite a few ships are
now fitted with modern and more
efficient rudders click the rudders to
see some examples the flap rudder is
different from a conventional rather in
that it utilizes an additional flap on
the trailing edge for steering this
allows up to twice the steering power
compared to a traditional rudder
translating into a much more
maneuverable ship the rotor is
essentially a conventional rudder but
with the addition of a rotating cylinder
mounted vertically on the edge of the
rudder
the purpose is to smooth the water flow
at high rudder angles and thereby
improve ship turning performance the
purpose of the tea rather is to combine
the advantages of the flap and rotor
rather in order to get the best possible
rather performance the performance is
indeed excellent but unfortunately the
price is high
not many ships invest in this excellent
rudder system this is an alternative
design to the flap rudder the shape of
the rudder is such that it can be turned
up to 70 degrees
and still retain excellent performance
the four body of the rudder is
elliptical in shape but runs into a rear
body section which is concave expected
turning performance with flap rotor and
T rudder systems this diagram shows the
expected increase internal performance
for a ship equipped with a modern flap
or rotor rotor system as can be seen
from the diagram considerable turning
improvements are obtained special
rudders deploying up to 70 degrees are
used in much the same way as
conventional rudders when used in
combination with a good bow thruster it
is possible to develop outstanding
lateral motion care should be taken not
to move with two high-speed as this may
damage the road system or result in
unnecessary wear and tear some systems
don't allow a rudder angle of more than
35 degrees when the speed is more than 5
knots
this system is totally different from
all other rudder systems both in design
and operation the most unusual but
essential feature of this system is the
propeller which even though it is fixed
pitch is constantly running with the
engine permanently on ahead revolutions
normally in maneuvering speed full ahead
immediately astern of the propeller in
place of the conventional rudder are two
shilling rudders each of which can
rotate through a total arc of 145
degrees the rudders do not act
independently of each other but are
instead synchronized to work in harmony
with each other in response to a single
joystick control on the bridge between
shielding rudder system with its
constantly running propeller seems a
little strange at first however most
officers after a short period of
instruction appear to get the feel for
it relatively quickly in this diagram
you can see different joystick
missions and corresponding rather
positions if the joy-stickies back from
normal full ahead with the joystick in
full forward the rudders progressively
open outwards deflecting the propellers
wash or drive and thus reducing the
ship's speed to obtain stern power up to
the equivalent of full astern the
joystick is pulled right back until each
runner has rotated right around to 105
degrees
thus closing the gap between them the
propeller wash is then deflected
forwards and works in much the same way
as the reverse thrust of an aircraft's
jet engines when it is deployed to stop
the aircraft after landing study the
diagram carefully to understand how the
twins Schilling rather system works
the conventional propeller and rudder
arrangement has been around for a long
time the propeller can be designed to
turn clockwise or anti-clockwise the
position of the rudder which normally
lies in the propeller slipstream is
critical
with regard to cavitations as well as
efficiency conventional rudders normally
have a maximum rather angle of about 35
degrees
generally speaking a ship with a right
hand turning propeller can be expected
to have slightly smaller turning radius
to Port to starboard and vice versa for
a ship with left-hand turning propeller
conventional design twin-screw ships are
normally designed with the right hand
turning starboard propeller and a
left-hand turning port propeller and
equipped with two rudders one behind
each propeller the reason for making the
outward turning propellers is twofold
reducing cavitations and taking greatest
benefit from the transverse thrust the
essence of good maneuverability of
twin-screw ships is not the result of
one factor alone but rather several
factors combined these factors are the
router configuration the effect of talk
the effect of transverse thrust the
pivot point the turning ability a
competence ship handler in order to make
the turning maneuvers accurate and
predictable several modern autopilot
have steering modes for executing and
control of turns with preset turning
radius or fixed rate of turn in confined
waters the simplicity of the geometrical
shape of the circle will ease the
navigation and the control of the actual
track today when documentation of proper
route planning is an IMO requirement and
more and more ships are equipped with
Exodus and advanced auto pilots even
turns in open waters should be planned
and executed in an optimal way pick the
Waypoint
course and track mode buttons on the
autopilot to see the difference between
them
when turning with constant rate of turn
the radius may not remain constant do to
speed reduction during the term however
if the turn is made with very low rate
of turn for example 6 degrees per minute
the speed loss is next to nothing
no constant rate of turn setting on the
autopilot is most useful on passenger
ships fairies and other ships operating
in good weather with stabilizes inactive
in order to avoid rack and save fuel a
low rate of turn setting during a course
change avoids banking the ship even with
stabilizes inactive in general a low
rate of turn should be used whenever
possible as this has many advantages
seen from a safety economic and comfort
point of view the mathematical formula
for calculation of rate of turn is as
follows
for practical use the formula can be
simplified as follows if we know the
rate of turn
we can rearrange the formula and get the
turn radius exercise calculate the rate
of turn for a ship with speed 20 knots
and the turn radius of 0.5 nautical
miles you can use this calculator by
filling in the numbers in the gray areas
many ships are equipped with auto pilots
capable of following a preset curve
based on turn radius input turning with
a pre-planned fixed radius is
recommended
whenever precision track keeping is
required during a turn the following
points should be taken into account when
planning a turn using a fixed turning
radius use largest possible radius
established the wheel / point as
accurately as possible 121.5 ships
lengths from the start point of the
turning radius is a normal value for
most ships estimate wind current shallow
water if
ex cetera and be prepared to adjust
heading manually whenever necessary
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