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Download PDF Chapter 011, Propeller, Ship and Rudder Interaction

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The present invention of a twin-rudder system for very large vessels in a fourth embodiment is constituted so that fins are appended on a propeller boss cap, so that the propeller boss caps generate a stream in the same direction as a propeller slip stream generated by propeller blades. Thanks to the aforementioned constitution in accordance with the present invention, it is possible to reduce generation of hub vortex at the central part of a flux of the propeller slip stream, and accordingly propulsive efficiency is improved.

In the case that a rudder exits behind a propeller just in the center of the propeller axis, the rudder has the effect of restraining generation of the hub vortex to some extent. In the present invention, however, there is no rudder in the center of the propeller axis; therefore, a degree of effectiveness to restrain generation of hub vortex by appending the fins on the propeller boss cap is extremely great. The present invention of a twin-rudder system for very large vessels in a fifth embodiment is constituted so that an auto-pilot is provided for controlling rudder angles of the respective rudders by operating steering gears provided for the respective rudders, and has such control function that the respective rudders are operated so that the maximum outboard operable angle is larger than the maximum inboard operable angle.

Thanks to the aforementioned constitution in accordance with the present invention, it is possible to make two rudders effectively generate rudder force because, when two rudders are turned to the maximum operable angle in the same direction on the occasion of ship's turning or changing head maneuver, namely, in case of hard port, for instance, when the port rudder is turned to the maximum outboard operable angle in the port direction, and the starboard rudder is turned to the maximum inboard operable angle, that is smaller than the angle of the port rudder, in the port direction, less influence is exerted upon the port and starboard rudders by mutual interfering action of a deflected propeller slip stream, and in addition, it is possible to make a required working angle range of steering gears small.

The present invention of a twin-rudder system for very large vessels in a sixth embodiment is constituted so that an auto-pilot is provided with a functional circuit for crash stopping maneuver that controls the respective rudders at crash stopping, and a crash stopping push button to start the functional circuit for crash stopping maneuver, the functional circuit for crash stopping maneuver having control function to make the respective rudders turn to the maximum outboard operable angle, respectively.

Thanks to the aforementioned constitution in accordance with the present invention, it is possible to make two rudders generate brake force against onward movement of a ship at crash astern maneuver or crash stopping maneuver of the ship, when crash stopping is required, by pushing the crash stopping push button of the auto-pilot for starting the functional circuit for crash stopping maneuver, which makes the port and starboard rudders turn up to the maximum outboard operable angle, respectively. Furthermore, taking advantage of such function as making the respective rudders turn toward outboard, respectively, it is possible for a ship having a main prime mover of diesel engine and a fixed pitch propeller to reduce ship speed as desired to a level below the speed corresponding to the allowable lowest revolution dead slow of the main diesel engine, and that in the meantime, ship's heading angle can be controlled during navigation with such reduced ship speed, with the respective rudder being operated toward outboard and their angles being controlled, though the reducible minimum speed depends on what the possible maximum angle of the rudders toward outboard is.

The present invention of a twin-rudder system for very large vessels in a seventh embodiment is constituted so that an auto-pilot is provided with a functional circuit for crash stopping maneuver that controls the respective rudders at crash stopping, the functional circuit for crash stopping maneuver having control function to make the respective rudders turn to the maximum outboard operable angle, respectively, in response to a fuel shut-off signal issued by a main engine control system at crash astern maneuver. Thanks to the aforementioned constitution in accordance with the present invention, it is possible to make two rudders generate brake force against onward movement of a ship at crash astern maneuver of the ship by making the port and starboard rudders automatically turn up to the maximum outboard operable angle, respectively, in response to a signal issued by the main engine control system, that starts the functional circuit for crash stopping maneuver, having no need of doing such special operation as pushing a crash stopping push button of an auto-pilot.

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The mode for carrying out the present invention is described and illustrated below with reference to the accompanying drawings. In FIG. The respective rudder blades 4 , 5 have horizontal sectional profile consisting of; semicircular leading edge portions 16 , 17 protruded forward; mid body portions 18 , 19 that are continuative with the leading edge portions 16 , 17 , increase their width up to the maximum width portions 18 b , 19 b in streamline shape, and then gradually decrease their width toward the minimum width portions 18 a , 19 a ; and fish tail trailing edge portions 20 , 21 that are continuative with the mid body portions 18 , 19 , and gradually increase their width toward rear end faces 20 a , 21 a having a fixed width.

The port reaction fin 10 of the port rudder blade 4 , that faces on the board-side where the blades of the propeller 3 rotate in the ascending direction, has a blade section having a fixed chord length originated from the leading edge portion 16 of the rudder blade 4 toward the rear, and assumes a posture that makes such attack angle a that the ratio of a forward vectored thrust to a drag, both produced by a propeller slip stream of the propeller 3 having a stream component in the ascending direction, becomes maximum.

The end plate 12 provided on the end face 10 a of the port reaction fin 10 is arranged in parallel with the axis of the propeller 3 , or along streamline vector of a propeller slip stream of the propeller 3. The starboard reaction fin 11 of the starboard rudder blade 5 , that faces on the board-side where the blades of the propeller 3 rotate in the descending direction, has a blade section having a fixed chord length originated from the leading edge portion 17 of the rudder blade 5 toward the rear, and assumes a posture that makes such attack angle a that the ratio of a forward vectored thrust to a drag, both produced by a propeller slip stream of the propeller 3 having a stream component in the descending direction, becomes maximum.

Hydrodynamic Performance of Ichthyoid Rudder at Different Rudder Angle Settings

The end plate 13 provided on the end face 11 a of the starboard reaction fin 11 is arranged in parallel with the axis of the propeller 3 , or along streamline vector of a propeller slip stream of the propeller 3. Accordingly, lift is largely produced by blade function or by hydraulic pressure of the stream, and that lift becomes further large as reactive force caused by the deflected stream at the fish tail trailing edge portion 20 or 21 is added as lift.

Furthermore, by virtue of two sheets of the rudders 1 , 2 , total vertical length of the portions near the leading edge portions 16 , 17 of the rudder blades where lift is most intensively generated comes to about twice as long as that in case of a single rudder, and that total vertical length of the fish tail trailing edge portions 20 , 21 that are another source of lift generation also comes to about twice as long, and thus as a whole, great lift can be generated. Furthermore, by virtue of co-work of rudder angles of two rudders 1 , 2 , the lift becomes larger as a whole by effect of mutual interaction.

In the single rudder system with the conventional rudder 51 of Mariner type as shown in FIG. As the range where generation of rudder force depends on velocity of a water current, not a propeller slip stream, becomes large, it is unable to generate enough force due to a reduced stream velocity when navigating with low speed in narrow waters or ports.


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In the mode for carrying out the present invention, larger rudder force can be generated as a propeller slip stream of the propeller 3 acts on the almost whole surface of the rudder blades 4 , 5 , and because it acts on the rudder blades 4 , 5 , with its energy being confined inside the top end plates 6 , 7 and the bottom end plates 8 , 9 , and high maneuverability can be exhibited even when navigating with a low speed in narrow waters and ports.

Furthermore, in the neutral position of the rudders when a ship goes straight ahead, the reaction fins 10 , 11 of the respective rudder blades 4 , 5 convert rotating energy of a propeller slip stream of the propeller 3 , which rotatively streams rearward between both rudder blades 4 , 5 , into lift having a forward vectored component. Accordingly, an increase in viscous pressure resistance at the fish tail trailing edge portion 20 , 21 in the neutral position of the rudders when a ship goes straight ahead, and deteriorative tendency of a thrust deduction coefficient in a self-propulsion factor caused by two sheets of the rudders 4 , 5 are compensated with the forward vectored thrust generated by the reaction fins 10 , 11 , and in addition, decrease in resistance by reduced rudder area, and thus propulsive efficiency comes to be equal with or higher than that of a conventional single rudder system.

Furthermore, as construction and weight per a rudder are remarkably lightened, compared with those in a conventional system, rudder manufacturing becomes easy, and it becomes possible to change a conventional way of rudder supporting system of Mariner type into a hanging rudder system of simple construction. Furthermore, even if a rudder of one side or its steering gear got out of order, ship maneuvering capability can be maintained by remaining rudder, and thus safety is remarkably improved, compared with a case of a conventional single rudder system.

Furthermore, when the respective rudder blades 4 , 5 are turned toward outboard, the respective rudder blades 4 , 5 generate lift and drag by a propeller slip stream of the propeller 3 , and the lift is offset each other and the remaining drag decreases advance thrust by the propeller 3. Accordingly, it is possible to give a ship brake force and reduce ship speed without controlling revolution of the propeller 3.

In addition, as the gap m between the tips of the leading edge portions 16 , 17 of the respective rudder blades 4 , 5 is quite small, and a runaway stream of a propeller slip stream of the propeller 3 passing through the gap rearward is small in quantity, advance thrust by the propeller 3 decreases and drag generated on the rudder blades 4 , 5 becomes maximum, and thus it is possible to stop a ship quickly, and safety is remarkably improved. Furthermore, as it is not necessary for steering gears to turn the rudders in both directions, port and starboard, with the same large angles, though the rudders 1 , 2 are subject to large operable angle as aforementioned, it is advantageous that a required working angle range for the steering gears can be narrowed.

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Conversely speaking, if the maximum operable angle of the respective rudders 1 , 2 toward outboard is increased more, using the maximum available working angle range of steering gears as far as possible, it is possible to further improve the aforementioned turning ability, changing head ability and stopping ability. Furthermore, as shown in FIG.

Furthermore, by virtue of co-workability of two rudders 1 , 2 , a degree of freedom for controlling direction of a propeller slip stream of the propeller 3 becomes high, and thus it becomes possible to further improve maneuverability. The following maneuver, for instance, becomes possible, though it depends on an attribute of ship, with the propeller 3 being kept running ahead in either case. Regarding the members that basically act similar to the arts explained in FIG.

As shown in FIG. Thanks to this constitution in accordance with the present invention, it is possible, in the neutral position of the rudders when a ship goes straight ahead, to reduce viscous pressure resistance caused by a stream at the fish tail trailing edge portions 22 , 23 by half, and improve propulsive efficiency.

On the other hand, decrease of lift generation at the fish tail trailing edge portions 22 , 23 can be restrained to the minimum as a whole by virtue of the matter that stream deflecting action by the fish tail trailing edge portions 22 , 23 is performed on the outboard side with emphasis where such action is more effectively performed, in view of such structure that operable rudder angles of the respective rudders 1 , 2 toward outboard are made larger than those toward inboard, and thus it is possible to still exhibit excellent maneuverability; namely, superior course keeping quality, turning ability, changing head ability and stopping ability, than a case of a conventional single rudder system.

A propeller slip stream, which the propeller blades 3 b produce, generate hub vortex at the central part of a flux of the propeller slip stream, and it acts as force that lowers advance force of the propeller 3 , and hence propulsive efficiency becomes low to that extent. However, the fins 3 c provided on the boss cap 3 a of the propeller 3 create a stream even at the central part of a flux of the propeller slip stream made by the propeller blades 3 b , and thus generation of hub vortex is restrained.

Accordingly, a lowering of propulsive efficiency can be restrained. In the conventional art, in which a rudder 51 exists behind a propeller 3 just at its center, the rudder 51 has an effect to restrain generation of hub vortex to some extent. On the other hand, in the mode for carrying out the present invention, in which there exists no rudder behind the propeller 3 just at its center, there is a condition susceptible to generation of hub vortex, and accordingly, effectiveness of restraining generation of hub vortex by providing the fins 3 c on the boss cap 3 a becomes significantly larger than that in case of the conventional art of a single rudder.

In order to prove the aforementioned respective effects in a twin-rudder system for very large vessels in accordance with the present invention, tank tests by model ships have been carried out, and in addition, computer simulation on motion of a typical very large crude oil carrier has been carried out based on tank test data. Furthermore, a fine tank test for propulsive performance has also been carried out using a large model ship that has ship form close to actual standard ship form of very large crude oil carriers.

Results of these are explained in the following. Using a model ship with a length of 4 m, a tank test has been carried out. The test has been based on specifications shown in FIG.


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Indexes of various maneuvering ability of a ship are indicated by magnitude of lateral force acting on a rudder and advance force acting on a ship when the rudder s is are given angle s under a condition that a propeller is running, and that propulsive performance of a ship when she goes straight ahead is indicated by magnitude of advance force acting on her in the neutral position of the rudder s , and hence these values have been measured in the tank test.

Results of the test are shown in FIG. Further added is that magnitude of respective force is expressed with non-dimensional figures, that is, with the ratio to 1. As is seen from FIG.

Propulsion And Manoeuvring Systems

In the light of these results, it has been proved that the twin-rudder system in accordance with the present invention is superior to the conventional single rudder of Mariner type in ship's maneuverability. In addition, as for advance force in the neutral position of the rudder s , meaningful difference between both is not recognized, and thus it can be said that the twin-rudder system in accordance with the present invention has equal propulsive performance with the conventional single rudder of Mariner type.

Results are shown in FIG. Furthermore, as is seen from FIG. In order to more finely examine propulsive performance in case of applying the mode for carrying out the present invention to very large crude oil carriers, a tank test has been carried out, using a model ship with a length of 7 m that had been already prepared as having a single rudder, and having ship form close to actual standard ship form of very large crude oil carriers of , DWT class.


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Specifications of the very large crude oil carrier and her rudder subject to the test are as shown in FIG. Propulsive performance tests have been carried out, using the same model ship, for two cases, respectively; namely, a case where a conventional single rudder of Mariner type is equipped, and a case where a twin-rudder system in accordance with the mode for carrying out the present invention is equipped, and both have been compared.

It is necessary, however, to make modifications against the matter that the test has been carried out in such a manner that the twin-rudder system was fitted on the model ship, with the ship stem form, which was for a single rudder, being left as it was, and modifications of rudder design so as to be in conformity with behavior of a stream around the ship stem and the propeller that has become clear as a result of the test; for instance, modifications on rudders' sectional profile, modifications on the top and bottom end plates in terms of rake angle and area, modifications on the interval of the axes of two rudders, etc.

Among other things, it is definite that reducing size of the skegs that is compelled to have been extremely large, as is understood from FIG. Furthermore, in an actual ship, it is common practice that fins are attached to a propeller boss cap to improve propulsive efficiency, dissolving loss caused by hub vortex of a propeller, though such fins have not been attached in this model ship test. In addition, taking into consideration the reduction in resistance by skeg size reductions and optimization of the aforementioned items, it is anticipated that this difference becomes larger.

As mentioned above and understood from FIG. In the next place, thanks to the actual proofs of effect of the present invention by the tank tests and the computer simulation, trial design has been carried out in the case of applying the present invention to a very large crude oil carrier of , DWT class that is to satisfy the IMO International Maritime Organization requirements for maneuvering performance, in the form of comparing it with a case of a conventional rudder system. The results are shown in FIG. The auto-pilot 31 that makes a rudder angle control system is composed of an automatic steering apparatus 31 a , a steering wheel 31 b , a rudder angle control operation for crash astern 31 c , a port rudder angle control operation 32 p and a port control amplifier 35 p that control operation of the port steering gear 34 p , and a starboard rudder angle control operation 32 s and a starboard control amplifier 35 s that control operation of the starboard steering gear 34 s , and that the port rudder angle control operation 32 p and the starboard rudder angle control operation 32 s make a rudder angle control operation A port rudder angle feedback controller 37 p detects an actual turning amount of the port rudder 33 p , and feeds it back to the port control amplifier 35 p , and a starboard rudder angle feedback controller 37 s detects an actual turning amount of the starboard rudder 33 s , and feeds it back to the starboard control amplifier 35 s.

This relation is shown in a graph in FIG. Furthermore, a crash stopping push button P B of the rudder angle control operation for crash astern 31 c has a function circuit that, when the push button P B is on, automatically shuts off, by a relay R Y , input signals to the port control amplifier 35 p and the starboard control amplifier 35 s issued by the automatic steering apparatus 31 a or the steering wheel 31 b of the auto-pilot In the following, action of the aforementioned constitution is explained.

First, turning or changing head maneuver of a ship is explained.

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The port control amplifier 35 p operates the port rudder 33 p in the port direction by controlling the port hydraulic pump unit 36 p so as to operate the port steering gear 34 p. An actual moving amount of the port rudder 33 p is detected by the port rudder angle feedback controller 37 p and fed back to the port control amplifier 35 p. Accordingly, explanation is omitted. In case of making a ship crash stop, the crash astern maneuvering mode is activated. In the crash astern maneuver, the crash stopping push button P B of the rudder angle control operation for crash astern 31 c of the auto-pilot 31 is pushed at the time when fuel supply to a main engine running ahead has been shut down, and hereby input signals to the port control amplifier 35 p and the starboard control amplifier 35 s issued from the automatic steering apparatus 31 a or the steering wheel 31 b are automatically shut off, and the port and starboard control amplifiers 35 p , 35 s are placed under control of the rudder angle control operation for crash astern 31 c by action of the relay R Y.

The rudder angle control operation for crash astern 31 c issues a control signal to the port control amplifier 35 p so as to make the port rudder 33 p turn hard port, and issues a control signal to the starboard control amplifier 35 s so as to make the starboard rudder 33 s turn hard starboard. When actual rudder angles of the port and starboard rudders 33 p , 33 s have reached the positions hard port and hard starboard, respectively, the port and starboard control amplifiers 35 p , 35 s receive the respective rudder angle feedback signals, and make the operation of the port and starboard hydraulic pump units 36 p , 36 s stop, and thus the port and starboard rudders 33 p , 33 s are kept at the rudder angles hard port and hard starboard, respectively.

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