Propulsion and steering arrangement for a ship
The invention relates to a steering and propulsion arrangement for a ship. The inventive steering and propulsion arrangement comprises a screw propeller 3 and a rudder 6 . A streamlined propulsion bulb 10 is made integral with or fixedly connected to the rudder. The invention also relates to a ship 2 provided with the inventive arrangement.
1. A propulsion and steering arrangement for a ship ( 2 ), the arrangement comprising:
a) a rotary propeller ( 3 ) having a hub ( 5 ) and at least two propeller blades,
b) a turnable rudder ( 6 ) arranged downstream of a propeller ( 3 ),
c) on the rudder ( 6 ), a streamlined bulb ( 10 ) integral with the rudder ( 6 ), the bulb being separated from a propeller ( 3 ) by a gap (e) and
d) a cap ( 13 ) on a propeller hub ( 5 ), the hub cap ( 13 ) bridging a gap (e) between the propeller ( 3 ) and the bulb ( 10 )
characterised in that the rudder is twisted, in that a twist of the rudder is greatest in an area of the bulb ( 10 ) and decreases with a distance from the bulb ( 10 ) and in that a twist angle (β) at a certain distance from the bulb is smaller below the bulb than above the bulb.
2. An arrangement according to claim 1 , wherein a maximum diameter of the bulb ( 10 ) is 1% -40% greater than a diameter of a propeller hub ( 5 ).
3. An arrangement according to claim 1 , wherein the bulb ( 10 ) extends along an axis ( 15 ) parallel with or coaxial with an axis of rotation of a propeller ( 3 ).
4. An arrangement according to claim 1 , wherein the bulb ( 10 ) extends along an axis ( 15 ) that defines an acute angle with an axis of rotation of a propeller ( 3 ).
5. An arrangement according to claim 4 , wherein a rear end ( 16 ) of the bulb ( 10 ) is at a level above a front end of the bulb ( 10 ) and an angle between the bulb ( 10 ) and a propeller axis is 1°-14°.
6. An arrangement according to claim 1 , wherein the hub cap ( 13 ) meets the bulb ( 10 ) at a location between a propeller ( 3 ) and a part of the bulb ( 10 ) where the bulb ( 10 ) reaches its maximum diameter.
7. An arrangement according to claim 1 , wherein a twist of the rudder ( 6 ) decreases from a front end ( 8 ) adjacent a propeller ( 3 ) to a rear end ( 9 ) which is a distal end in relation to a propeller ( 3 ) such that a rear end ( 9 ) of the rudder ( 6 ) extends along a straight line.
8. An arrangement according to claim 1 , wherein at least a part of the rudder ( 6 ) is continuously twisted from a front end ( 8 ) of the rudder ( 6 ) to a rear end ( 9 ) of the rudder.
9. An arrangement according to claim 1 , wherein a twist of the rudder ( 6 ) decreases linearly with a distance from the bulb ( 10 ).
10. An arrangement according to claim 1 , wherein the hub cap ( 13 ) and a front end of the bulb ( 10 ) are designed keep a distance between the bulb ( 10 ) and the cap ( 13 ) constant when the rudder ( 6 ) is turned.
11. An arrangement according to claim 1 , wherein a maximum twist of the rudder ( 6 ) is 15°.
12. An arrangement according to claim 1 , wherein the rudder ( 6 ) is twisted in different directions above and below the bulb ( 10 ).
13. An arrangement according to claim 1 , wherein a part of the rudder ( 6 ) and the bulb ( 10 ) that is located upstream of a rudder stock ( 7 ) has a projected side area that is less than 30% of a total projected side area of the rudder ( 6 ) and the bulb ( 10 ).
14. An arrangement according to claim 10 , wherein a forward end ( 11 ) of the bulb ( 10 ) has a central surface ( 20 ) with a radius of curvature (R 1 ) and the central surface ( 20 ) is surrounded by an annular surface ( 21 ) that has a radius of curvature (R 3 ) that is smaller than the radius of curvature (R 1 ) of the central surface ( 20 ) and is from 4% to 25% of a maximum bulb diameter (D B ).
15. A ship provided with an arrangement according to claim 1 .