Technical Field
[0001] The present invention relates to a propeller ship with front positioned twin rudders,
having one propeller shaft and two rudders in a bow direction with respect to a propeller.
Background Art
[0002] A ship is utilized as a means which can transport materials and person in large quantities
and efficiently.
[0003] For that purpose, it is important for the ship to safely sail along a desired course
and call at a port. As a result, a propulsion mechanism and a steering mechanism of
the ship have been developed while being changed.
[0004] Basic factors required for the rudder are a turning performance (a performance which
indicates how quick a direction can be changed when keeping steering) and a course
keeping performance (a course stability: a performance how straight the ship can travel),
and these factors are frequently conflicting functions, however, there has been designed
variously to make them compatible.
[0005] On the basis of a turning performance of the ship, in relation to a ship main body,
and a water flow effect to the rudder, the rudder has been generally attached in tandem
at a backward position with respect to the propeller, in a stern.
[0006] The same airfoil theory as that of an airfoil of an airplane is applied to an effect
of the rudder, and the rudder is well installed within a limited space in the stern.
[0007] The turning performance of the rudder depends on thrust in lateral direction acting
on a surface of the rudder. This is lift acting on the rudder surface. The lift is
theoretically expressed as open water rudder performance in a uniform laminar flow
by the following expression.
where, V: Inflow speed of water to rudder
α: Inflow angle of inflow water to rudder
A: Effective rudder area for the rudder lift
Fp: Gradient of rudder open water normal force coefficient
p: Density of seawater
[0008] Meanwhile, in order to make the lift of the rudder larger, it has been known in Patent
Document 1 that two rudders are provided in parallel at backward positions of a propeller
for the single propeller, in a stern of a specifically designed ship.
Citation List
Patent Literature
Summary of Invention
Technical Problem
[0010] The structure of the Patent Document 1 has an advantage that the lift can be enlarged,
however, has no objects to achieve improvement of fuel consumption, reduce a ship
construction cost, or enlarge an amount of cargo per ship total length.
[0011] A main object of the present invention is to provide a structure of a propeller ship
which can achieve improvement of fuel consumption, enlarge an amount of cargo per
ship total length, and reduce a ship construction cost.
Solution to Problem
[0012] The present invention achieving the object mentioned above is as follows.
<Invention described in claim 1>
[0013] A propeller ship with front positioned twin rudders wherein rudders are provided
at laterally symmetrical positions of a ship center line in a front side of a propeller
and in a rear side of a buttock line.
(Operation and effect)
[0014] The rudders are provided at the laterally symmetrical positions of the ship center
line. In a rudder area which is necessary for securing a turning performance and a
course keeping performance (a course stability) which are necessary in a ship having
a certain size, an area of each of the rudders in the case where two rudders are provided
can be made about 25 % to 50 % smaller per one rudder area than that in the case where
one rudder is provided. A total area of two rudders is the same as or somewhat larger
than that of a conventional case with one rudder. The rudder is desirably provided
so as to make a clearance as small as possible with a ship bottom line.
[0015] Generally, the rudder necessarily goes under the seawater surface at the sailing
time. Making it possible to reduce the rudder height according to the present invention
means making it possible to reduce a draft depth at the sailing time. As a result,
it is possible to reduce an output of a main engine on the same ship speed, and the
fuel consumption is improved.
[0016] Meanwhile, an effect achieved by a stern thruster can be expected by provision of
a stern thruster in the front side of the propeller.
[0017] The "buttock line" means a shape line of the stern obtained by cutting the stern
by a vertical surface which is parallel to a central vertical cross sectional surface
of a hull. It particularly refers to a line formed by a cross line to a parallel portion
of the hull.
<Invention described in claim 2>
[0018] The propeller ship with front positioned twin rudders described in claim 1, wherein
a stern thruster is provided in the front side of the propeller and in the rear side
of the buttock line, and a propeller axis of the stern thruster has a relationship
that the center line of the propeller axis passes through a plate surface of each
of the rudders.
(Operation and effect)
[0019] It is possible to enhance maneuverability in correction of course in a narrow port
or getting to or leaving the shore, by the provision of the stern thruster in the
stern side.
[0020] Meanwhile, in the case where the ship sails at a low speed in the port, the rudder
cannot work effectively at all. To cope with this, the maneuverability can be enhanced
by starting the stern thruster and bringing the water flow thereof into the rudder
plate surface.
<Invention described in claim 3>
[0021] The propeller ship with front positioned twin rudders described in claim 2, wherein
the stern thruster is positioned 3 to 25 m ahead of the propeller.
(Operation and effect)
[0022] The stern thruster is preferably positioned 3 to 25 m ahead of the propeller. It
has been known that the maneuverability by the stern thruster becomes appropriate
in correction of course in the narrow port or in getting to and leaving the shore,
in the case where the stern thruster is positioned 3 to 25 m ahead of the propeller.
<Invention described in claim 4>
[0023] The propeller ship with front positioned twin rudders described in claim 1, wherein
the rudder has laterally symmetrical rudder surfaces.
(Operation and effect)
[0024] The present invention is not characterized by the surface shape of the rudder, but
takes into consideration use of the general rudder. In the case where the rudder has
the laterally symmetrical rudder surfaces, it is possible to enhance the maneuverability
by synchronously using two rudders, using only one rudder, or using in combination.
<Invention described in claim 5>
[0025] The propeller ship with front positioned twin rudders described in claim 1, wherein
a steering machine is provided within a hull in the front side of the propeller and
the rear side of the buttock line.
(Operation and effect)
[0026] In the case where the rudder and the steering machine are provided in the front side
of the propeller, it is not necessary to arrange an after-peak tank, steering room
and the like backward in the ship and it is possible to shorten the ship, for example,
about 5 m to 20 m in comparison with a propeller ship having one rudder in the rear
side of one propeller according to a conventional example.
[0027] As a result, since a volumetric capacity of a cargo tank can be increased about 5
% to 15 % per the same total length in the case of a cargo ship, a utility value of
the ship is enhanced. Further, it is possible to shorten the total length of the ship
and the ship constructing cost is reduced.
<Invention described in claim 6>
[0028] The propeller ship with front positioned twin rudders described in claim 1, wherein
an additional propeller and a driving unit for the additional propeller are provided
in addition to said propeller, one or a plurality of the additional propellers is
disposed at a ship bottom or at a boot top of the ship bottom, in a position different
from where said propeller is disposed, and operating condition is selectable between
regular operating condition in which propelling force is obtained by driving said
propeller and the other operating condition in which propelling force is obtained
by driving the additional propeller.
(Operation and effect)
[0029] A compact additional propeller and a driving unit therefor are provided in addition
to said propeller, that is, the regularly used propeller. The output of the driving
unit for the additional propeller can be 35% or less, more preferably, 25% or less
than the output of a driving unit of the main engine.
[0030] When cargo (freight) is loaded, the ship is operated by driving the regularly used
propeller, having a state of draft close to designed load draft. If necessary, the
ship is operated also with the additional propeller in a combined manner.
[0031] When the ship navigates back to a port after unloading the cargo, the ship is mainly
operated by the compact additional propeller. Especially in days of calm and steady
sea condition, there is little necessity to secure stability of the ship too severely
during navigation. Accordingly, the ship is made to travel by means of the compact
additional propeller, keeping a draft line further lower.
[0032] As a result, apparent displacement is decreased and contact area with water of a
shell is reduced because the draft line is lowered. Furthermore, a waterplane area
coefficient can be improved, and significant reducing effects of fuel consumption
can be obtained.
[0033] Further, since the compact additional propeller is driven, small output of the driving
unit is enough (35% or less, more preferably, 25% or less of the output of the driving
unit of the main engine). From this viewpoint, the significant reducing effects of
fuel consumption can be obtained.
[0034] In the case where the ship leaves a port after fully loaded with the cargo and then
shifts to regular navigation, the ship navigates with the deep draft, driving the
regularly used propeller. Further, in the case where the ship navigates using ballast
after unloading the cargo, the ship is operated with the additional propeller after
shifting to normal navigation. However, in the case of bad weather, ballast water
is filled even in an unload condition. This enables the ship to travel in a stabilized
state by means of the compact additional propeller or the regularly used propeller.
Further, the additional propeller and the regularly used propeller can be used in
a combined manner, if necessary.
[0035] Since the additional compact propeller is mainly used at the time of ballast navigation,
a propeller immersion ratio for the regularly used propeller is not so largely limited
so that a propeller diameter of a designed propeller can be made larger than the propeller
diameter according to the relation between ship and propeller design in the related
arts. This enables propeller efficiency to be upgraded, increasing the efficiency
of about 5% to 7%. Thus, by adopting the designed propeller having the larger diameter,
the propeller efficiency is increased, and the output required for the main engine
is reduced at the same speed of the ship, thereby significantly improving fuel efficiency.
<Invention described in claim 7>
[0036] The propeller ship with front positioned twin rudders described in claim 6, wherein
a position of the additional propeller is selectable between a state of being assembled
at the outside of the ship and the other state of being retracted to the inside of
the ship.
(Operation and effect)
[0037] In the case where the additional propeller is assembled at the outside of the ship
and kept with unused condition under sailing, the propeller acts as resistance in
the deep draft. Therefore, preferably the additional propeller is retracted to the
inside of the ship.
Advantageous Effects of Invention
[0038] As described above, according to the present invention, it is possible to achieve
the improvement of the fuel consumption and it is possible to enlarge the cargo amount
per total length of the ship. Brief Description of Drawings
[0039]
Fig. 1 is a side elevational view showing a stern portion in a front face of a propeller
ship with front positioned twin rudders;
Fig. 2 is a plan view of the propeller ship with front positioned twin rudders;
Fig. 3 is a cross sectional view of the propeller ship with front positioned twin
rudders as seen from a rear side;
Fig. 4 is a schematic side elevational view of a propeller ship in a load condition
in the case where an additional propeller is provided;
Fig. 5 is a schematic side elevational view of the propeller ship while operating
in an unload condition in the case where the additional propeller is provided;
Fig. 6 is an assembling drawing of an example of the additional propeller (a duct
propeller);
Fig. 7 is a side elevational view showing a stern portion in a front face of a ship
with single propeller and single rudder according to a conventional example; and
Fig. 8 is a plan view showing the stern portion in the front face of the ship with
single propeller and single rudder according to the conventional example.
Description of Embodiments
[0040] First of all, a description will be given of the conventional example. A ship with
single propeller and single rudder is provided as shown in Figs. 7 and 8 as an example
of a tanker or a large cargo ship, an engine room 50 is arranged within a hull of
a stern portion, and the ship is propelled by rotationally driving a propeller 51.
[0041] A rudder 52 is provided in a rear side of the propeller 51, a steering room 53 is
arranged above the propeller 51, a steering machine 54 is provided in the steering
room 53, a rudder stock 55 is integrated with the rudder (a rudder plate) 52, and
the ship can be turned by the steering machine 54. Reference numeral 56 denotes an
after-peak tank. A cargo space 57 is arranged in a front side of the engine room 50
so as to be connected to a bow side.
[0042] Next, a description will be given of an embodiment according to the present invention
with reference to the accompanying drawings.
[0043] Figs. 1 to 6 show an example of a propeller ship with front positioned twin rudders
according to the present invention.
[0044] The present invention is characterized in that rudders 12 and 12 are respectively
provided at laterally symmetrical positions of a ship center line in a front side
of a propeller 11 and in a rear side of a buttock line.
[0045] The rudder 12 can employ both of a balance type and an unbalance type according to
a relationship to a rudder stock 12a. Further, it is desirable to have laterally symmetrical
rudder surfaces as shown in Fig. 2. Two rudders 12 and 12 can appropriately select
synchronous use, single use, and combined use.
[0046] By arranging the rudders 12 and 12 in the front side of the propeller 11, the steering
room 53 is also arranged in the front side of the propeller 11 and the steering machine
54 is provided in the steering room.
[0047] A stern thruster 40 can be provided in the front side of the propeller 11 and in
the rear side of the buttock line. Further, a propeller axis 40a of the stern thruster
40 is arranged so as to have a relationship that the propeller axis 40a passes through
a rudder plate surface of each of the rudders 12 and 12.
[0048] It is possible to enhance maneuverability in course correction in a narrow port or
getting to or leaving the shore by the provision of the stern thruster 40 in the stern
side.
[0049] On the other hand, in the case where the ship sails at a low speed in the port or
the like, the rudder cannot work effectively at all. Accordingly, by starting the
stern thruster 40 and bringing the water flow thereof into the rudder plate surfaces,
the rudder can work effectively and the maneuverability is enhanced.
[0050] The stern thruster 40 is desirably positioned 3 to 25 m ahead of the propeller.
[0051] According to the present invention, since the rudder and the steering machine are
provided in the front side of the propeller, it is not necessary in the ship to arrange
backward the after-peak tank 56, steering room 53 (see Fig. 7) and the like, as is
different from the example shown in Figs. 7 and 8, and it is possible to shorten the
ship, for example, about 5 m to 20 m in comparison with the propeller ship having
one rudder in the rear side of one propeller according to the conventional example.
[0052] As a result, in the case of the cargo ship, since the volumetric capacity of the
cargo tank can be about 5 % to 15 % increased per the same total length, a utility
value of the ship is enhanced. Further, it is possible to reduce a ship construction
cost.
[0053] Said propeller 11 is the regularly used propeller. As shown in Figs. 4 to 6, a propeller
ship with front positioned twin rudders can be provided, wherein an additional propeller
and a driving unit for the additional propeller are provided in addition to the regularly
used propeller 11, one or a plurality of the additional propellers is disposed at
a ship bottom or at a boot top of the ship bottom, in a position different from where
said propeller is disposed, and operating condition is selectable between regularly
used operating condition in which propelling force is obtained by driving the regularly
used propeller and the other operating condition in which propelling force is obtained
by driving the additional propeller.
[0054] FIG. 4 is a schematic side elevational view of a propeller ship, for example, a commercial
ship 10 loaded with cargo, such as a cargo ship. The commercial ship 10 obtains propelling
force by driving a regularly used propeller (main propeller) 11 by a main engine (propulsion
engine) 50 such as a diesel engine. The reference sign 14A represents a water line
in an unload condition, indicating a state of trim by head in which the water line
gradually becomes higher in a bow direction and intersects with a ship bottom line
in a stern direction. In FIG. 5, the reference sign 14B represents a water line, indicating
a state of trim by stern which is a reverse state of the state of trim by head.
[0055] As is referenced in FIG. 6, the propeller ship is provided with an additional propeller
20 and a duct propeller 21, including a driving unit 22 for the additional propeller.
[0056] This additional propeller 20 is disposed at a position different from the regularly
used propeller 11, more specifically, in a bow area, a stern area, or an intermediate
position at a ship bottom or a boot top of the ship bottom. The case of disposing
the additional propeller at the stern position is indicated by the reference sign
20A, and the case of disposing the same at the intermediate position is indicated
by the reference sign 20B.
[0057] The output of the driving unit 22 of the additional propeller 20 is small, which
is 25% or less than the output of a driving unit of the main engine 50.
[0058] Further, operating condition is selectable between regular operating condition in
which propelling force is obtained by driving the regularly used propeller 11 and
the other operating condition in which propelling force is obtained by driving the
additional propeller 20.
[0059] Explaining an example of the additional propeller 20, an electric motor or a hydraulic
motor may be used as the driving unit 22, and further, if necessary, may be connected
with the main engine (propulsion engine) 50 so as to obtain drive power.
[0060] The duct propeller 21 that includes a duct 21A around thereof is configured to be
rotated when rotational drive force of an output shaft 23 by the driving unit 22 is
transmitted to a vertical shaft 25 through a pair of bevel gears 24 and then transmitted,
as rotational force of a propeller drive shaft 27, through a pair of bevel gears 26
provided at the vertical shaft 25.
[0061] On the other hand, the duct propeller 21 is configured to be rotatable around the
vertical shaft 25 when rotational drive force of a transmission shaft 28 by the driving
unit 22 is transmitted to a driving small gear 29 and a large gear 30 engaged therewith.
[0062] Further, a device including the duct propeller 21 disposed below a ship bottom 10A
is assembled at the outside of the ship bottom 10A as illustrated in FIG. 6, but preferably,
the device is configured to be retractable to the inside of the ship because such
assembly of the duct propeller at the outside is to be an obstacle during normal navigation.
The reference sign 10B indicates a shielding member that shuts after the device is
retracted to the inside of the ship.
[0063] With this configuration, when cargo R is loaded, the propeller ship is operated by
driving the regularly used propeller 11 with the main engine 50 in a state of draft
close to designed load draft.
[0064] After the cargo is unloaded, especially in a day of calm weather or in a quiet sea,
the propeller ship is operated with the compact additional propeller 20, keeping the
draft line low as illustrated in FIG. 5 because there is little necessity to secure
stability of the ship too severely at the time of navigating the ship as shown in
FIG. 5. In this case, as indicated by an outlined arrow in FIG. 5, a moving direction
of the ship can be suitably selected, and the bow and the stern are monitored from
the bridge 13 depending on the moving direction of the ship.
[0065] As a result, by lowering the draft line, apparent displacement is decreased and the
contact area with the water of the shell is reduced. Further, a waterplane area coefficient
can be improved and significant reducing effects of fuel consumption can be obtained.
[0066] Moreover, since the compact additional propeller 20 is driven, small output from
the driving unit 22 is enough, and the ship can be operated with the output of 35%
or less, especially 25% or less, and best of all, about 10% to 5% of the output of
the driving unit in the main engine 50. From this viewpoint, significant reducing
effects of fuel consumption can be obtained. In a day of calm weather (when Beaufort
scale is 0 to 3), travel speed of approximately 5 to 10 knots is enough.
[0067] In the case where the propeller ship leaves a port after fully loaded with the cargo
R and then shifts to regular navigation, the ship navigates with the deep draft, driving
the regularly used propeller 11 mainly or in a combined manner with the additional
propeller.
[0068] Further, in the case of bad weather, ballast water BW (reserve space for the ballast
water is not illustrated) is filled even in an unload condition. This enables the
propeller ship to travel in a stabilized state by means of the compact additional
propeller 20 or the regularly used propeller 11.
[0069] On the assumption that the duct propeller 21 can rotate around a vertical axis, the
propeller ship can propel in the stern direction by driving the duct propeller 21
as shown in Fig. 6 in a necessary driving state.
[0070] If the duct propeller 21 is rotatable around a vertical shaft line 25 (the vertical
axis), by appropriately rotating the additional propeller around the vertical axis
in the combined driving state of the additional propeller and the regularly used propeller,
a steering function can be added and maneuverability (directional property) can be
improved. Further, when the ship is docked at a port, the duct propeller is oriented
sideways so as to be utilized as a slide thruster.
[0071] Further, a propeller idling prevention device for preventing the regularly used propeller
11 from rotating may be provided.
[0072] If necessary, the duct propeller 21 may be provided on the right and left sides with
respect to a center line of the ship. The duct propellers 21, 21 on the right and
left sides rotate around the vertical shaft line, thereby improving the maneuverability.
Further, when the propeller is utilized as the slide thruster, the propeller ship
can be more easily get to the shore.
Industrial Applicability
[0073] The present invention is applicable to a standard cargo ship, a container ship, a
tanker, an LNG carrier, a car carrier, a bulk carrier, a cargo-passenger ship, and
so on.
Reference Signs List
[0074]
- 10
- Propeller ship
- 11
- Regularly used propeller (main propeller)
- 12
- Rudder
- 12a
- Rudder stock
- 20
- Additional propeller
- 21
- Duct propeller
- 22
- Driving unit
- 40
- Stern thruster
- 50
- Main engine (propulsion engine: driving unit)
- 54
- Steering machine