Special Rudder
Fish Tail Rudder
Outline
The Fish Tail Rudder:proven at sea to outperform all other high performance rudders.
Fish Tail Rudders have been installed on board more than about 3,000 various vessels in last 30 years in Japan.
The number of vessels equipped with Fish Tail Rudders has become increasingly more and more, and this means that performance of the rudder has been well evaluated by customers.
Conception
Fish Tail Rudder is a rudder designed under such conception as to effectively utilize the propeller's 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.
Construction
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.
Performance & Effect
| Performance | Effects |
|---|---|
| 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. |
|
| Ship’s ahead thrust becomes null at 70 degrees rudder angle, with only side thrust being produced. |
|
| 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. |
| Ship’s course-keeping ability is excellent. |
|
| The top and the bottom end plates bring a secondary effect. | Ship’s pitching is decreased. |
| 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. | |
Fig.A:Comparison of Lift Coefficient between Fish Tail Rudder and Conventional Rudder (Results of Tank Test）.
| Fish Tail Rudders | Conventional Rudder（NACA0025） | |
|---|---|---|
| Velocity | 2.0m/s | 2.0m/s |
| Area | 0.103m2 | 0.125m2 |
| Taper | 1.0 | 1.25 |
| Aspect Ratio | 0.853 | 0.98 |
| Reynolds No. | 0.604×106 | 0.619×106 |
| Test Results by HSVA Hamburg | ||
Kinds
There are the following 6 kinds of Fish Tail Rudders, and they can be installed on any kind of vessels:
-
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.
-
Twin Fish Tail Rudders
This system is for a vessel provided with twin screw propellers, and rudders for each propeller.
-
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.
-
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.
-
Mariner Type Ocean Fish Tail Rudders
This rudder is Mariner type Fish Tail Rudder having Ocean Fish Tail Rudders features.
-
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.
Types
The following 3 kinds of the rudder supporting type are prepared for Fish Tail Rudders:
Lower Pintle Rudder
Hanging Rudder
Mariner Rudder
68,000DWT Shuttle Tanker [M.V. Hal Dean] Equipped with Fish Tail Rudder with Lower Pintle Type.
Correspondence to IMO.Recommendation
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.
Comparison of Turning test Results at Sea. Trial.
Vessels Equipped with Fish Tail Rudders
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(kt) |
|---|---|---|---|
| Mine-sweeper | 57.70 | 490 | – |
| Large Patrol Boat | 87.00 | 1,000 | – |
| Fishery Controll Boat | 57.00 | 490 | – |
| Fishery Survey Ship | 76.00 | 2,000 | 17.0 |
| Geological Survey Ship | 80.50 | 2,126 | 17.3 |
| Training Boat | 46.00 | 230 | 14.5 |
| Shuttle Tanker | 231.50 | 78,000 | 15.5 |
| Chemical Tanker | 102.00 | 6,000 | 13.5 |
| Tanker | 117.00 | 5,944 | 16.3 |
| Bulk Carrier | 175.00 | 44,398 | 17.3 |
| Special Container | 95.00 | 4,053 | 14.2 |
| PCTC 6,500 Cars | 190.00 | 52,479 | 21.3 |
| RO/RO Ship | 150.00 | 8,280 | 23.0 |
| Cement Carrier | 152.00 | 13,787 | 15.7 |
| Refuse Carrier | 112.00 | 6,526 | 15.2 |
| Ferry | 105.00 | 2,200 | 22.5 |
| Salvage Boat | 77.00 | 2,300 | 18.0 |
| Pusher Boat | 11.95 | 19 | 10.0 |
| Tuna Long Liner | 56.00 | 499 | 14.0 |
| Ore Carrier | 280.00 | 175,000 | 16.0 |
| 145,000m3 LNG | 273.00 | 121,597 | 21.0 |
Single Fish Tail Rudder provide crabbing ability when used with a bow-thruster.