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This chapter will give you a general
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overview of the most common propulsion
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and maneuvering systems used today ships
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maneuvering characteristics are directly
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related to her hull form optimal
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performance depends upon the whole shape
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in conjunction with engine power and the
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propeller and rudder systems most ships
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are still equipped with traditional
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single fixed propeller and single rather
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designed for getting the ship from A to
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B as economically as possible
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this often represents a challenge to the
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ship handler with reference to
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maneuvering in confined waters in order
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to achieve a better balance between
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maneuverability and economy some vessels
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are equipped with propeller and rudder
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systems that differ considerably from
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the traditional systems general
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information about some of these new
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systems will be given later in this
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chapter the diesel engine is very widely
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used as it tends to be the least
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expensive to run low speed diesel
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engines operate directly onto the shaft
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maximum speed RPM is in the range 85 to
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130 RPM the ship handler must remember
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the difficulties can be experienced in
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starting the engine when still making a
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lot of headway
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this is because the propeller will be
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trying to turn in the water stream and
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because of the direct drive the engine
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tends to turn in the forward direction
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another important thing to remember is
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that sometimes there might be a limited
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amount of starter available IE too many
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starting orders during a short time
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interval may empty the start air
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reservoir making engine starts
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impossible for some time
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medium and high speed diesels are
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popular arrangements in smaller vessels
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fairies car carriers and other special
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ships one or several engines drive shaft
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through a gearbox
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since clutch the engines are normally
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operated from the bridge and are very
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responsive and like their low speed
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relatives can develop almost as much
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power astern as ahead but of course the
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application of this astern power is less
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efficient as ships hulls propellers and
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rudders are usually designed to work in
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the head direction the steam turbine is
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often found in large ships and on ships
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where high speed is required a turbine
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ship while being smooth running and more
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reliable in the mechanical sense has one
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major drawback from the ship handlers
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point of view its response to control
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orders for change of direction of shaft
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rotation are slow
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thus when maneuvering a turbine driven
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ship each movement must be carefully
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planned controllable pitch propellers
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are very practical because by modifying
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the pitch they allow for thrust
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optimization under different load
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conditions with the controllable pitch
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propellers the user can modify the pitch
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normally by means of a hydraulic
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mechanism click on each hotspot to learn
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more about CP pitch is the distance of
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propeller drives forward for each
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complete revolution assuming it is
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moving through a solid element just like
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a wood screw does when using a CP
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propeller the main engine has to be
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clutched in so the propeller is
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continuously turning usually at quite
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high revolutions as it is neither
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practicable more economical to run an
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engine continuously at excessive
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high-rpm it is important to have some
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kind of combined control over both RPM
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and pitch so that the pitch for slow
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speeds is balanced by a reduction in
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revolutions on most ships this is
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achieved by installing a Combinator
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which automatically balances engine
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revolutions
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against propeller pitch that's producing
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a savings in fuel and better propeller
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performance to use ahead power a ship
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with CP propeller is not restricted to
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the old step progression that has been
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associated with fixed pitch propellers
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any speed can be selected by adjusting
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the Combinator control to the required
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setting it is also possible to set the
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propeller pitch for extremely low speeds
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so when it is essential to proceed at
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very slow speeds the propeller and
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rudder are still active and steerage way
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can be maintained for a lot longer than
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usual when low speed or stop are
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demanded the blades of the CP propeller
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are set with a very fine angle and pitch
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if the ship's speed is too high and does
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not already matched the propeller speed
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the flow of water through it will be
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restricted and turbulence will develop
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behind the propeller which will also
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have an adverse effect upon the rudder
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if the ship's speed is not reduced
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slowly and progressively in much the
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same way as a large directional unstable
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ship the rudder will be shielded and the
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steering may become erratic or poor one
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of the most common concerns mentioned by
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many navigators and pilots is the
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uncertainty as to which way the bear
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will count if at all when a CP
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propellers put a stern to answer this
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question it is necessary first to know
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which way the propeller is turning when
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it is viewed from astern the majority of
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the sea propeller is left-handed ie they
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move in an anti-clockwise direction the
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effect however is similar to a fixed
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pitch right-handed propeller working
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astern IE the bow make aunt to starboard
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it is important to note that the
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transverse thrust on some ships with CP
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propellers maybe weekend unreliable user
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vortices or turbulence around the
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propeller blades it
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therefore advisable to exercise some
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caution when anticipating the effects of
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stern power on some CP ships many
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vessels ranging from tugs to large
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ocean-going ships are equipped with
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ducted propellers a shroud or duct is a
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tube or tunnel light construction with
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the propeller inside the forward end of
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the duct has a larger diameter than the
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aft end the increased power comes from
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the propeller constantly drawing a
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massive water into the duct which then
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has to be forced out through a smaller
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aperture the main advantages which can
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be expected of the ducted propeller are
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more output power from the propeller
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reduced propeller wash to a smaller arc
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thereby reducing erosion of canal and
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river banks better steering especially
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at low speed better turning
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characteristics conventional rudders
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found on thousands of ships worldwide
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represent a compromise between economy
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and necessity conventional rudders
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normally function satisfactorily for
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normal steering and cause change
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requirements in open waters the basic
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conventional rudder is efficient up to
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maximum 45 degrees at high angles the
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rudder is not capable of maintaining a
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smooth water flow across both sides of
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the rudder and the rudder stalls IE
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loses its effect if the runner has its
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entire area after the rudder stock then
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it is unbalanced a rather with between
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twenty and forty percent of its area
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forward of the stock is balanced most
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modern brothers are of the semi balanced
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design this means that a certain
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proportion of the water force acting on
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the after part of the rudder is
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counteracted by the force acting on the
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forward part of the rudder hence the
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steering gear can be lighter and smaller
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there are several types of rudder
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designs pick the hot spots to see the
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three most common types
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this is the most used rather type on
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ferries and smaller ships the Spade
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rather provides good maneuverability
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this type of brother is most commonly
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used on bigger ships it is not as
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effective a speedrunner of the same size
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the heel rather is supported with
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bearings on the top and bottom providing
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an enjoyable rudder construction
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conventional riders are somewhat
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restricted when it comes to
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maneuverability at slow speed in
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confined waters several manufacturers
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have developed more efficient and
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advanced radar systems the last two or
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three decades and quite a few ships are
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now fitted with modern and more
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efficient rudders click the rudders to
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see some examples the flap rudder is
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different from a conventional rather in
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that it utilizes an additional flap on
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the trailing edge for steering this
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allows up to twice the steering power
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compared to a traditional rudder
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translating into a much more
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maneuverable ship the rotor is
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essentially a conventional rudder but
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with the addition of a rotating cylinder
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mounted vertically on the edge of the
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rudder
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the purpose is to smooth the water flow
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at high rudder angles and thereby
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improve ship turning performance the
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purpose of the tea rather is to combine
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the advantages of the flap and rotor
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rather in order to get the best possible
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rather performance the performance is
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indeed excellent but unfortunately the
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price is high
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not many ships invest in this excellent
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rudder system this is an alternative
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design to the flap rudder the shape of
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the rudder is such that it can be turned
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up to 70 degrees
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and still retain excellent performance
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the four body of the rudder is
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elliptical in shape but runs into a rear
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body section which is concave expected
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turning performance with flap rotor and
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T rudder systems this diagram shows the
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expected increase internal performance
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for a ship equipped with a modern flap
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or rotor rotor system as can be seen
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from the diagram considerable turning
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improvements are obtained special
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rudders deploying up to 70 degrees are
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used in much the same way as
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conventional rudders when used in
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combination with a good bow thruster it
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is possible to develop outstanding
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lateral motion care should be taken not
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to move with two high-speed as this may
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damage the road system or result in
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unnecessary wear and tear some systems
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don't allow a rudder angle of more than
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35 degrees when the speed is more than 5
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knots
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this system is totally different from
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all other rudder systems both in design
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and operation the most unusual but
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essential feature of this system is the
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propeller which even though it is fixed
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pitch is constantly running with the
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engine permanently on ahead revolutions
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normally in maneuvering speed full ahead
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immediately astern of the propeller in
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place of the conventional rudder are two
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shilling rudders each of which can
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rotate through a total arc of 145
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degrees the rudders do not act
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independently of each other but are
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instead synchronized to work in harmony
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with each other in response to a single
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joystick control on the bridge between
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shielding rudder system with its
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constantly running propeller seems a
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little strange at first however most
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officers after a short period of
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instruction appear to get the feel for
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it relatively quickly in this diagram
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you can see different joystick
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missions and corresponding rather
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positions if the joy-stickies back from
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normal full ahead with the joystick in
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full forward the rudders progressively
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open outwards deflecting the propellers
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wash or drive and thus reducing the
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ship's speed to obtain stern power up to
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the equivalent of full astern the
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joystick is pulled right back until each
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runner has rotated right around to 105
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degrees
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thus closing the gap between them the
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propeller wash is then deflected
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forwards and works in much the same way
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as the reverse thrust of an aircraft's
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jet engines when it is deployed to stop
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the aircraft after landing study the
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diagram carefully to understand how the
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twins Schilling rather system works
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the conventional propeller and rudder
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arrangement has been around for a long
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time the propeller can be designed to
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turn clockwise or anti-clockwise the
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position of the rudder which normally
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lies in the propeller slipstream is
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critical
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with regard to cavitations as well as
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efficiency conventional rudders normally
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have a maximum rather angle of about 35
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degrees
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generally speaking a ship with a right
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hand turning propeller can be expected
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to have slightly smaller turning radius
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to Port to starboard and vice versa for
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a ship with left-hand turning propeller
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conventional design twin-screw ships are
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normally designed with the right hand
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turning starboard propeller and a
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left-hand turning port propeller and
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equipped with two rudders one behind
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each propeller the reason for making the
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outward turning propellers is twofold
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reducing cavitations and taking greatest
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benefit from the transverse thrust the
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essence of good maneuverability of
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twin-screw ships is not the result of
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one factor alone but rather several
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factors combined these factors are the
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router configuration the effect of talk
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the effect of transverse thrust the
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pivot point the turning ability a
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competence ship handler in order to make
00:16:08
the turning maneuvers accurate and
00:16:10
predictable several modern autopilot
00:16:12
have steering modes for executing and
00:16:14
control of turns with preset turning
00:16:17
radius or fixed rate of turn in confined
00:16:20
waters the simplicity of the geometrical
00:16:23
shape of the circle will ease the
00:16:25
navigation and the control of the actual
00:16:27
track today when documentation of proper
00:16:32
route planning is an IMO requirement and
00:16:35
more and more ships are equipped with
00:16:37
Exodus and advanced auto pilots even
00:16:40
turns in open waters should be planned
00:16:42
and executed in an optimal way pick the
00:16:46
Waypoint
00:16:47
course and track mode buttons on the
00:16:49
autopilot to see the difference between
00:16:51
them
00:17:33
when turning with constant rate of turn
00:17:35
the radius may not remain constant do to
00:17:38
speed reduction during the term however
00:17:41
if the turn is made with very low rate
00:17:44
of turn for example 6 degrees per minute
00:17:46
the speed loss is next to nothing
00:17:49
no constant rate of turn setting on the
00:17:51
autopilot is most useful on passenger
00:17:54
ships fairies and other ships operating
00:17:57
in good weather with stabilizes inactive
00:18:00
in order to avoid rack and save fuel a
00:18:03
low rate of turn setting during a course
00:18:05
change avoids banking the ship even with
00:18:08
stabilizes inactive in general a low
00:18:12
rate of turn should be used whenever
00:18:13
possible as this has many advantages
00:18:16
seen from a safety economic and comfort
00:18:20
point of view the mathematical formula
00:18:29
for calculation of rate of turn is as
00:18:31
follows
00:18:32
for practical use the formula can be
00:18:37
simplified as follows if we know the
00:18:41
rate of turn
00:18:42
we can rearrange the formula and get the
00:18:44
turn radius exercise calculate the rate
00:18:50
of turn for a ship with speed 20 knots
00:18:52
and the turn radius of 0.5 nautical
00:18:56
miles you can use this calculator by
00:19:00
filling in the numbers in the gray areas
00:19:02
many ships are equipped with auto pilots
00:19:07
capable of following a preset curve
00:19:10
based on turn radius input turning with
00:19:13
a pre-planned fixed radius is
00:19:15
recommended
00:19:16
whenever precision track keeping is
00:19:18
required during a turn the following
00:19:21
points should be taken into account when
00:19:23
planning a turn using a fixed turning
00:19:25
radius use largest possible radius
00:19:30
established the wheel / point as
00:19:33
accurately as possible 121.5 ships
00:19:37
lengths from the start point of the
00:19:39
turning radius is a normal value for
00:19:41
most ships estimate wind current shallow
00:19:46
water if
00:19:47
ex cetera and be prepared to adjust
00:19:49
heading manually whenever necessary
