Fish Tail Rudder For Ship

Single Fish Tail Rudder provide crabbing ability when used with a bow-thruster
Single Fish Tail Rudder provide crabbing ability when used with a bow-thruster


Fish Tail Rudder is a rudder designed under such conception as to effectively utilize the propellers slip stream for rudder action, and featured by having a fish-shaped horizontal cross section, top and bottom end plates, and optimized rudder height and chord length, and being so arranged that the rudder can be turned as much as 70 degrees rudder angle port and starboard respectively, which is double that of the conventional rudders.


Fish Tail Rudders are of one piece construction, and there is no moving part in the water.
So no special maintenance work is required.
It is easy for the rudders to be of sturdy construction to meet the ice navigation.


1 Lift Coefficient of the rudder is high. (Please refer to Fig.A) It is about 1.3 times higher than that of the conventional rudder. A) Tactical diameter is small.
B) Advance is small.
2 Ship’s ahead thrust becomes null at 70 degrees rudder angle, with only side thrust being produced. A) The ship turns on the spot.
B) Better sideways berthing.
C) By jointly using a bow thruster, the ship can be sideways moved or diagonally moved, keeping the ship’s heading.
D) No stern thruster is required.
3 Lift Coefficient when going astern is also high. (Please refer to Fig.A) Even when the ship goes astern, steering of the ship is effective.
4 Ship’s course-keeping ability is excellent. A) Course maintained by minimum helm correction.
B) Decreased ship’s flapping contributes to the fuel oil saving.
5 The top and the bottom end plates bring a secondary effect. Ship’s pitching is decreased.
6 There are no moving parts in the water. Maintenance free.
Fish Tail Rudders provide the economical effect and the safety of the ship at sea and contribute to the reduction of working down, physical fatigue and mental stress of the crew and accordingly, the reduction of the marine accident and the high reliability.
Comparison of Lift Coefficient between Fish Tail Rudder and Conventional Rudder (Result of Tank Test)
Comparison of Lift Coefficient between Fish Tail Rudder and Conventional Rudder (Result of Tank Test)


There are the following 6 kinds of Fish Tail Rudders, and they can be installed on any kind of vessels :

1. Single Fish Tail Rudders (Monovec Fish Tail Rudders).

This is a single rudder for a vessel provided with a single screw propeller.There are two kinds of rudder supporting; lower pintle and hanging types.

2. Twin Fish Tail Rudders.

This system is for a vessel provided with twin screw propellers, and rudders for each propeller.

3. Ocean Fish Tail Rudders.

This is a Fish Tail Rudder developed for ocean-going vessels.
This is an epoch-making rudder of less drag and higher lift coefficient than the conventional rudder.

4. Mariner Type Fish Tail Rudders.

This is a Fish Tail Rudder of Mariner type for large vessels developed with the subsidy of the Ship and Ocean Foundation.
This Mariner type rudder is featured to give high lift coefficient and good course keeping and large rudder angle.

5. Mariner Type Ocean Fish Tail Rudders.

This rudder is Mariner type Fish Tail Rudder having Ocean Fish Tail Rudders features.

6. VecTwin Rudders

This system consists of two special aerofoil rudders equipped after a single fixed-pitch screw propeller of a uni-directional.
This rudder system produces thrust which can be directed to any angle of 360 degrees ell around, including “hovering” condition (zero resultant thrust), and that magnitude of the thrust can be changed freely, With the screw propeller rotation being kept in the ahead direction. This control is done by a single lever of Joystick.
The stopping distance with the rudders in the clam-shell position of reflectance is halved compared with a conventional ship and heeding is controlled.
(please refer to the separate pamphlet.)


The following 3 kinds of the rudder supporting type are prepared for Fish Tail Rudders :

Rudder Types
Rudder Types


Fish Tail Rudder provides the ship quick response to steering orders, and also provide a larger ratio of angular velocity of shipis turn to the rudder angle high manoeuvrability.Accordingly, Fish Tail Rudder is very much advantageous, compared with the conventional rudder; an smaller advance and less oveershoot angle.


The typical vessels equipped with Fish Tail Rudders are shown in the following table. The largest vessel is the 145,000m³ LNG, and the smallest one is the 19GT pusher boat. Thus, Fish Tail Rudders have been adopted in every kind of vessels over wide range of the size, and are satisfactory in service.
From the viewpoint of safe operation of vessels and capability of easy berthing/unberthing, increasing demands for Fish Tail Rudder are expected.

Ship’s Kind Lpp (m) GT Speed (kn)
Mine-sweeper 57.7 490
Large Patrol Boat 87 1,000
Fishery Controll Boat 57 490
Fishery Survey Ship 76 2,000 17
Geological Survey Ship 80.5 2,126 17.3
Training Boat 46 230 14.5
Shuttle Tanker 231.5 78,000 15.5
Chemical Tanker 102 6,000 13.5
Tanker 117 5,944 16.3
Bulk Carrier 175 44,398 17.3
Special Container 95 4,053 14.2
PCTC 6,500 Cars 190 52,479 21.3
RO/RO Ship 150 8,280 23
Cement Carrier 152 13,787 15.7
Refuse Carrier 112 6,526 15.2
Ferry 105 2,200 22.5
Salvage Boat 77 2,300 18
Pusher Boat 11.95 19 10
Tuna Long Liner 56 499 14
Ore Carrier 28000 175,000 16
145,000m³ LNG 27300 121,597 21

Read more : Ocean Fish Tail Rudder; Thordon SXL Rudder Carrier BearingsThordon Thorseal Rudder Seals


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