Rudders for high-speed ships

A high-speed water vessel including a steering arrangement for reducing cavitation and its effects. The arrangement includes a twisted rudder pair located downstream of a high-speed propulsor. The rudder pair may also be contoured at a bottom portion thereof. The propulsor has at least one propeller having a propeller diameter. In operation, the propulsor produces a slipstream that contracts with distance from the propeller. To avoid the effects of cavitation, the twisted rudder pair is positioned outside and adjacent to the slipstream diameter, with the rudders of the rudder pair separated by a distance that is less than the diameter of the propellers. The rudders of the rudder pair may be in a substantially parallel orientation with respect to each other. In gas turbine applications, the rudder pairs may be rotated towards each other to produce a rudder bucket for producing a negative thrust for stopping the high-speed water vessel.

FIELD OF THE INVENTION

The present invention relates generally to a high-speed water vessel, more particularly, a steering arrangement in a high-speed water vessel for reducing or eliminating cavitation and its effects.

STATEMENT OF GOVERNMENT INTEREST

BACKGROUND OF THE INVENTION

Currently, ships or sea vessels that are commercially utilized in the marine industry and U.S. Navy are propelled by waterjets discharged into the air above the water surface, and by propulsors that provide thrusting forces based on the rotation of propellers. The Navy is constantly searching for advanced technology to build high-speed ships. With the recent advance in hydrodynamic theories of ship resistance, hull form design methods and advanced propulsion technology, the Navy is developing high-speed ships with sprint/transient speeds of 38 to 45 knots. In the first phase of development, waterjet propulsion systems have been selected for high-speed ships.

Propeller drive systems are also being developed for high-speed ships. Typical surface ship propellers are limited to a maximum speed of 35 knots due to propeller cavitation and thrust breakdown. At full power, the ship speeds of most naval surface water vessels are in the order of 30 knots. However, propellers with advaced blade sections have been developed recently to achieve efficient operations at higher speeds. Twisted rudders have been successfully designed to avoid cavitation on the existing surface water vessels up to ship speeds of about 35 knots. At speeds above 35 knots, even twisted rudders may experience cavitation and erosion problems. The design technology of twisted rudders so successfully developed for existing surface water vessels that travel at speeds up to 35 knots, may not be adequate for speeds that exceed 35 knots. A rudder design for high-speed ships that avoids or reduces the effects of caviation and erosion is required.

Additionally, as opposed to waterjet propulsion system slipstreams, slipstreams produced by rotating propellers include rotational and tangential vectors. These vectors can be attributed to the rotational movement of the propellers. Consequently the rudders must also be designed to compensate for these variations in slipstream flow, particularly in high-speed environments.

SUMMARY OF THE INVENTION

The present invention addresses aspects of problems outlined above. Preferred embodiments of the present invention provide an apparatus for guiding a high-speed water vessel, whilst reducing the cavitation effects.

In one aspect, the invention is a high-speed water vessel having a hull with an underside. The apparatus includes at least one high-speed propulsor attached to the underside of the hull, with the at least one high-speed propulsor having one or more propellers. In this high-speed water vessel, the one or more propellers have a propeller diameter, and the one or more propellers generate a propeller slipstream downstream of the at least one high-speed propulsor. In this aspect, the slipstream has a slipstream diameter. In the high-speed water vessel, at least one twisted rudder pair is located downstream of the at least one high-speed propulsor, with the rudder pair rotatably mounted within a zone of effectiveness. According to the invention, the zone of effectiveness is the region within the downstream projection of the propeller diameter that lies outside the slipstream diameter profile. The invention further includes a controller for controlling the rotation of the at least one twisted rudder pair. The controller rotates the at least one twisted rudder pair so that portions of the rudder pair rotate from a position outside the slipstream diameter to a position within the slipstream diameter.

In another aspect, the invention is a steering arrangement mounted to a high-speed ship with a hull. The steering arrangement includes a propulsion system attached to the hull, the propulsion system having at least one high-speed propulsor having at least one propeller. In this aspect the at least one propeller has a propeller diameter, and the propeller generates a slipstream downstream of the propulsion system. Additionally, the slipstream has a slipstream diameter. The steering arrangement has at least one pair of twisted rudders that are rotatably attached to the hull. In this aspect the at least one pair of twisted rudders are positioned downstream of the at least one high-speed propulsor of the propulsion system. The rudders are positioned in a substantially parallel spaced relationship so that the pair of rudders are positioned adjacent to and outside the slipstream diameter but separated by a distance that is less than the propeller diameter.

DETAILED DESCRIPTION

FIGS. 1A,1B, and1C illustrate one embodiment of a high-speed water vessel steering arrangement.FIG. 1Ashows a surface water vessel100having a hull110immersed in water120and extending vertically above the water surface during normal forward travel. A propulsor130is positioned underwater on a bottom portion of the hull110closely spaced from its stem end140. Rudders150of a pair of twisted rudders are mounted, via a seat160, to the bottom of the hull110between the stem end140and the propulsor130.FIG. 1Aalso shows an adjustment member165mounted inside the ship for turning the rudders150.

FIGS. 1A-1Cshow the rudders150of the pair of twisted rudders downstream of the propulsor130. The propulsor130may be an electrical propeller engine, a gas turbine engine, combinations thereof, or any other known propeller engine. The propulsor130is designed to propel the water vessel100at a sprint/transient speed of about 40 knots to about 55 knots.FIG. 1Ashows a maneuvering control170connected to propulsor130and the adjustment member165for automatically controlling the steering of the water vessel. The maneuvering control170is part of a ship controller that controls the overall operations of the high-speed ship. The adjustment member165may include turning bars and may be mechanically attached to the rudders150to enable concurrent turning or adjustment of the rudders. Alternatively, the adjustment member165may use separate mechanisms to enable both rudders150of the pair of twisted rudders to turn independent of each other.

FIG. 1Dshows an embodiment of a high-speed water vessel steering arrangement, similar to that ofFIGS. 1A-1C. However, the rudders150of the rudder pair each include a contoured bottom portion155. As would be explained below, the contoured rudder design is used in gas turbine engines to help create a braking force on the high-speed ship. For the sake of simplicity,FIGS. 1A-1Deach show only one propulsor and only one pair of twisted rudders, however a surface water vessel100may include two or more propulsors and accompanying rudder pairs.

FIGS. 2A and 2Bare perspective views of a rudder200in accordance with an embodiment of the present invention. The rudders ofFIGS. 2A and 2Bmay be used in the arrangement shown inFIGS. 1A-1Cto produce benefits as outlined below.FIGS. 2A and 2Bshow the rudder having a leading edge210and a trailing edge220, with the rudder having a streamlined formation from the leading edge to the trailing edge along the body of the rudder.FIG. 2Ashows a longitudinal portion230of the leading edge. The longitudinal portion230is twisted at a substantially central location235along the longitudinal portion. InFIG. 2B, the dotted line shows the change in shape of the rudder along the leading edge. This change in shape is a result of the twisted design, which is implemented at a substantially central location along the longitudinal portion230. The twisted leading edge design accommodates for the rotational and tangential vectors associated with the slipstream generated by the propulsor130.

FIGS. 2C and 2Dshow another embodiment of a rudder250that may be used in a rudder pair for steering the vessel100. The rudder ofFIGS. 2C and 2Dmay be used in the arrangement shown inFIG. 1Dto produce benefits as outlined below. The rudder250has a leading edge210and a trailing edge240, with the rudder having a streamlined formation from the leading edge to the trailing edge along the body of the rudder. However, the trailing edge240of the rudder250is blunted as opposed to a sharp edge. Similar to the embodiments ofFIGS. 2A and 2B, theFIG. 2Crudder has a longitudinal portion230that is twisted at a substantially central location235along the longitudinal portion.FIG. 2Dshows the rudder250having a contoured bottom portion255. In operation, rudders250of a rudder pair are arranged so that the contoured bottom portions face each other, similar to the illustration ofFIG. 1D. As would be outlined below, the contoured bottom portions255are essential to the production of a negative thrust to slow down and stop the high-speed ship.

The rudders ofFIGS. 2A-2Dmay comprise of steel, composite materials, and combinations thereof. The rudders may be sized according to considerations such as, vessel size, speed of the vessel, rudder drag, turning capability, and directional stability. Depending on the size, the rudders may also comprise a steel skeleton frame with core material forms made of polyurethane for filling the general structure around the steel frame.

FIG. 3Ais a perspective view of a slipstream velocity profile310of a high-speed propulsor in accordance with an embodiment of the present invention.FIG. 3Bis a perspective view of a slipstream diameter profile of a high-speed propulsor in accordance with an embodiment of the present invention. A determination of the slipstream profile is essential to the determination of positioning of the rudders.FIGS. 1A-1Dshow rudders150of a rudder pair located downstream of the propulsor130, however the exact positioning of the rudder is determined by the velocity, size, and location of the slipstream generated by the propulsor130.

The slipstream velocity profile for the high-speed propulsor130is determined using a momentum theory, and is represented by the equation (1):
VA(1+s)=VA√(1+CT)  (1)
According to the formula, VAdenotes the ship speed and CTdenotes the propeller thrust coefficient. The s denotes the slip ratio downstream of the propeller. At a ship speed of 45 knots for example, with a typical thrust coefficient of 0.5, the slip stream velocity is obtained by: VA(1+s)=45√(1+0.5)=55 knots
A sketch of the velocity distribution in an axial direction behind a propeller propulsor is shown inFIG. 3A, with the ship speed denoted by VAand slip stream velocity by VA(1+s).

The slipstream diameter profile downstream the high-speed propulsor130is determined using the following continuity equation (2):
Dr=Dp√[1+√(1+CT)]/[2√(1+CT)]  (2)
According to the equation, Dpdenotes the propeller diameter, Drdenotes the slipstream diameter, and CTdenotes the propeller thrust coefficient. From this equation it can be seen that the propeller slipstream experiences contraction downstream of the propulsor.FIG. 3Billustrates, in an exaggerated manner, the slipstream diameter profile320, showing the variation of the diameter Drwith distance from the propeller. As illustrated, the diameter profile320is within the downstream projection330of the propeller diameter.

FIGS. 4A and 4Bare illustrative views of a steering arrangement400for the high-speed water vessel in accordance with an embodiment of the present invention. Steering arrangement400includes a propeller410of a propulsor, the propeller having a propeller diameter Dp. The arrangement also includes rudders420of a rudder pair, the rudders located downstream of the propeller.FIGS. 4A and 4Billustrate Drthe slipstream diameter. A zone of effectiveness430is illustrated as the region that extends from the outside of the slipstream diameter Drto the inner edge of the propeller diameter Dp. In other words, the zone of effectiveness is the region within a downstream projection of the propeller diameter, but outside the slipstream diameter profile.FIGS. 4A and 4Bshow the rudders420in an orientation for guiding the water vessel in a forward/non-turning direction. In this orientation, the rudders420are located in the zone of effectiveness430. The rudders420are positioned within the zone of effectiveness430in order to reduce the effects of cavitation in high-speed applications.FIG. 4Bshows the rudders being substantially parallel to each other.

According to wing theories and existing rudder design practice, a rudder can be designed to operate cavitation-free if the incoming flow velocity entering the rudder is less than 45 knots. However, in high-speed applications as detailed in equation (1), the incoming flow velocity in the slipstream exceeds 45 knots. In these applications, rudder cavitation effects can be reduced or alleviated by placing the rudder outside the slipstream. Although outside the slipstream diameter Dr, the rudders420are placed within the propeller diameter Dpand adjacent to the slipstream diameter Dr. In the arrangement400, the rudders420may be of configuration200or configuration250as illustrated inFIGS. 2A-2D.

In addition to the accelerated flow in axial direction, as stated above, the slipstream also contains large rotational and tangential velocity vectors produced by the rotating propeller. Consequently, the velocity distributions on the rudder surface facing and adjacent to the slipstream will be different from the velocity distribution on the rudder surface facing away from the slipstream. A small side force will be produced. The non-symmetrical flows on both sides of rudder surfaces, which produce greater accelerated flow on one side of rudder surface can trigger cavitation. However, the rudder configurations ofFIGS. 2A-2Dcompensate for non-symmetrical flow by including the leading edge twist along portions of the leading edge that encounter the slipstream. The leading edge twist aligns the rudder with the flow that it encounters in arrangement400.

FIG. 4Cis an illustrative view of the steering arrangement400for the high-speed water vessel in accordance with an embodiment of the present invention. Similar to the illustrations inFIGS. 4A and 4B,FIG. 4Cshows a propeller410having a propeller diameter Dp. The arrangement also includes rudders420of a rudder pair, the slipstream diameter Dr, and zone of effectiveness430.FIG. 4Cshows the rudders420in a turning configuration where portions of the rudders420cross the slipstream diameter boundary, and enter into the slipstream. InFIG. 4C, the dotted-line illustration of the rudder420depicts the rudder in the original orientation ofFIGS. 4A and 4B.

When the ship executes a high-speed turning maneuver, the maneuvering control170sends a signal to the adjustment member165to rotate the rudders into the slipstream as shown inFIG. 4C. The rudders now encounter accelerated flows from the slipstream. Rudder effectiveness is proportionate to velocity squared. When the rudders encounter the high velocity slipstream, significant side forces can be produced to turn the ship effectively at all speeds. When turning is required at zero ship speed, in addition to rotating the rudders, the maneuvering control170initiates enough rotation of the propellers of the propulsor130to produce the requisite accelerated flow to execute the turning maneuver. With respect to the mechanics of turning, the rotation of the twin rudders can be linked together via a turning bar arrangement so that only the turning bar arrangement is needed to turn both rudders for steering. Alternatively, each rudder may be rotated by separate mechanisms associated with adjustment member165to enable independent movement between the rudders.

As stated above, the rudders discussed herein may be of configuration200or configuration250as illustrated inFIGS. 2A-2D. Additionally, the propulsor130may be an electrical drive system, a gas turbine engine, combinations thereof, or any other known propeller engine. When an electrical drive system is used, when backing or emergency stopping is needed, the polarity of the electric drive can be reversed to change the direction of shaft rotation and negative propeller thrust is produced to stop the water vessel. The rudder effectiveness for an electric drive propulsion system can be addressed by: (a) ability to provide directional stability of the ship in straight cruise without experiencing rudder cavitation; and (b) ability to generate adequate side force and turning moment to steer and control the craft. The rudders200ofFIGS. 2A and 2Bmeet these requirements.

Gas turbine engines, unlike electrical engines, are not reversible, and therefore the propeller is typically equipped with a controllable pitch device to generate the negative thrust forces to effect stopping. An advantage of one embodiment of the present invention is that the rudders can be used to produce large negative thrust for stopping and backing without a controllable pitch device.FIG. 4Dshows the rudders420turned in stopping or braking orientation. When braking is required, the maneuvering control170may shut off the engine and/or send a signal to the adjustment member165to turn the rudders towards each other forming a rudder bucket450, as shown inFIG. 4D. To increase the efficiency of this braking action, it is best to use twisted contoured rudders with blunt trailing edges, i.e., rudders of configuration250, as illustrated inFIG. 2D. The rudders250ofFIG. 2Dprovide the most effective rudder bucket. The contoured bottom255prevents the slipstream flow from escaping in a downward direction, the ship hull prevents slipstream flow from escaping in an upward direction, and the blunt trailing edges prevent the slipstream flow from escaping downstream of the rudder. Consequently, after contacting the rudder, the only possible outlet for the slipstream flow is the direction of entry. Therefore, all of the slipstream flow is redirected in an opposite direction, producing a negative thrust. This negative thrust can be used to stop or backup the vessel. The rotation of the each rudder of the twin rudders shown inFIG. 4D, is preferably performed by separate mechanisms associated with adjustment member165to enable independent movement between the rudders. Alternatively, only one turning mechanism may be associated with adjustment member to turn both rudders. It should be noted that although the braking orientation illustrated inFIG. 4Dis directed to a gas turbine engine, the braking orientation may also be used with an electrical or hybrid drive system.

The rudder effectiveness for a gas turbine propulsion system can be addressed by: (a) ability to provide directional stability of the ship in straight cruise without experiencing rudder cavitation; (b) ability to generate adequate side force and turning moment to steer and control the craft; and (c) ability to produce negative thrust for stopping and backing maneuvers. The rudders250ofFIGS. 2C and 2Dmeet these requirements.