Abstract:
A method for maintaining the heading of a ship during movements caused by waves approaching the ship from a stern direction by activating a control surface in a bow of the ship such that the control surface converts a water flow along the bow into a lateral force that opposes roll, yaw, or heeling movements and course changes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of pending U.S. patent application Ser. No. 12/346,463 filed on Dec. 30, 2008, which is a continuation of International patent application PCT/EP2007/056613 filed on Jun. 30, 2007, which designates the United States and claims priority from European patent application 06116486.9 filed on Jun. 30, 2006. The contents of all prior applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention concerns a ship for use at high speed and/or heavy seas having a single long and slender hull, a bow and the aft end of the hull having a flat or slightly V-shaped bottom with at least one aft rudder, one or more propellers and/or water jets as propulsions means whereby the foreship has a draught that is equal or more than the draught of the aft end characterized in that the bow has a control surface that converts the water flow along the forward moving ship into an adjustable lateral force. 
     BACKGROUND OF THE INVENTION 
     For most ships of such design the condition of sailing in relative large stern quartering or following waves can become dangerous due to the occurrence of “broaching”. Broaching is the peculiar ship behavior, which consists of a coupled yaw-, sway- and roll motion. Ships may experience this broach motion in the described wave condition and once it occurs it can lead to seriously large roll angles and eventually end in a “capsize”. 
     The broaching phenomenon may be roughly explained as follows: In stern quartering and following waves the ship stern is lifted asymmetrically by the incoming wave and it starts the ship to heel (and also pitch). Broaching is particularly prone in waves with a wave length close to the ship length. So simultaneously the ship puts its bow in the face of the (next) wave. Caused by the asymmetry of the hull due to the introduced heeling angle and the directionally destabilizing effect of the now deeply immersed bow sections the ship starts to yaw. Combined with the forward speed this may lead to an increase in the heeling angle which on its turn worsens the hull asymmetry and therewith to further course instability. This may lead to the ship coming beam side to the waves in principal a potentially dangerous situation as it may lead to an even further increase in heel. 
     With fast ships this broaching phenomenon may be encountered more frequently than with regular ships and may have more serious effects because fast ships are generally smaller and sail therefore in relatively larger waves. Also the high forward speed worsens the heeling influence induced by the centrifugal forces once the ship is in a turn and the encounter frequency between the ship and the following waves. In particular the longer and higher waves may have a lower frequency making their impact bigger. 
     Ships are normally directionally controlled by either a helmsman or an autopilot. In general the applied control is aimed at keeping the ship on a preset course. From experience, full scale and model scale measurements it is known that this directional control applied in following waves worsens the broaching behavior of the ship, due to the unfavorable phase between the steering force applied and the herewith induced heeling moment. 
     SUMMARY OF THE INVENTION 
     In order to overcome these disadvantages, according to the invention is a ship in accordance with the claims hereof. In this way the resistance against broaching is increased by using the additional control surface for directional control and to make beneficial use of the forces generated by this surface for controlling the roll and sway motion. By applying a control surface in the most forward position as feasible, this control surface may be regarded as an additional control surface for controlling both yaw and heel simultaneously. Then the following improvement occurs: In the situation that the ship sails in stern quartering waves from starboard the stern can be lifted by a wave where after the ship starts to heel to port. The asymmetry of the hull underwater shape induces a yawing moment trying to turn the ship to starboard. Corrective action is applied on the control surface near the bow to correct this course change and the force asked for is a lateral force directed to port. This force implies a rolling motion to starboard and so de-creasing the heeling angle. 
     In accordance with another embodiment of a invention the ship of this design is especially favorably for the application of this invention. Such a ship is known from the publication Keuning, J. A.; Toxopeus, S.; Pinkster, J.; The effect of bow-shape on the sea keeping performance of a fast monohull; Proceedings of FAST 2001 conference, September 2001; page 197-206; ISBN 0 903055 70 8, publisher The Royal Institute of Naval Architects. In this publication the ship is described as the AXE BOW design. The increased draught and increased freeboard makes the ship suitable for sailing through heavy seas while ensuring that the control surface remains in heavy seas sufficiently submerged. 
     In accordance with another embodiment of the invention the more or less vertical bow is particularly suitably for incorporating a control surface according to the invention. 
     In accordance with another embodiment of the invention this fillet radius makes it possible to reduce the length of the ship and so reducing the wet surface and the flow resistance without disadvantageously influencing the ships behavior in waves. 
     In accordance with another embodiment of the invention this improves the ships behavior in heavy seas as the added resistance in waves is reduced. 
     In accordance with another embodiment of the invention this makes for a simple construction with effective steering and control capabilities. 
     In accordance with another embodiment of the invention this makes for an easy construction with good water flow along the hull, thereby minimizing additional drag when not activated. 
     In accordance with another embodiment of the invention this embodiment combines at high speeds good control capabilities with high efficiency. 
     In accordance with another embodiment of the invention the reducing of the heeling and broaching can be combined in an easy way. 
     In accordance with another embodiment of the invention the use of the control surface can be manually adapted to the changing circumstances and wave conditions. 
     In accordance with another embodiment of the invention the use of the control surface is adapted automatically to the changing circumstances and wave conditions. 
     In accordance with another embodiment of the invention the control surface is only activated when its use improves the ships behavior. 
     These and other objects of the present invention are achieved by provision of a method for maintaining a forward moving ship with a foreship having a bow and an aft ship having a stern and an aft rudder on a preset course, wherein a helmsman or an automatic steering system activate lateral forces on the forward moving ship for maintaining the ship on the preset course using the aft rudder, characterized in that with incoming waves from stern quarters, the helmsman or the automatic steering system switch to steering with a control surface in the foreship such that the control surface converts a water flow along the bow into an adjustable lateral force on the bow to correct course alteration that is occurring and to counteract roll movement. 
     In some embodiments, the control surface comprises a bow rudder. In some embodiments, the control surface comprises an adjustable flap on each side of the bow. In some embodiments, the control surface comprises a vertical mounted rotor. In some embodiments, the helmsman can switch from steering with the aft rudder to steering with the control surface. In some embodiments, the helmsman can switch from steering with the aft rudder to steering with the aft rudder and the control surface. 
     Further objects of the present invention are achieved by provision of a method for maintaining the heading of a ship during movements caused by waves approaching the ship from a stern direction by activating a control surface in a bow of the ship such that the control surface converts a water flow along the bow into a lateral force. 
     In some embodiments, the lateral force counteracts a course alteration and/or roll movement of the ship. 
     In some embodiments, the control surface is activated by a control system, and includes a bow rudder, at least one flap on the side of the bow, and/or a vertically mounted rotor. 
     In some embodiments, the control surface is only activated when waves approach the ship from a stern direction. 
     Other objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below with reference to several exemplary embodiments by means of a drawing, in which: 
         FIG. 1  shows a perspective view of a ship according a first embodiment of the invention. 
         FIG. 2  shows a body plan of the design of the ship according to the invention, whereby  FIG. 2   a  shows the various cross sections,  FIG. 2   b  shows the side view and  FIG. 2   c  shows the bottom view. 
       FIGS.  3  and  4 show the ship of  FIG. 1  respectively from behind and from the top with schematically an indication of the forces in waves. 
         FIG. 5   a  shows the bow of the ship of  FIG. 1  with the first embodiment of the control surface in perspective view,  FIG. 5   b  show the same embodiment in front view and  FIG. 5   c  shows a section Vc-Vc of  FIG. 5   a.    
         FIG. 6   a  shows a second embodiment of the control surface in a perspective view and  FIG. 6   b  shows section VIb-VIb of  FIG. 6   a , and 
         FIG. 7   a  shows a third embodiment of the control surface in a perspective view and  FIG. 7   b  shows section VIIb-VIIb of  FIG. 7   a.    
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a ship  1  which is designed in accordance with the body plan according to  FIG. 2 . The ship  1  is designed for high speeds and has a single long and slender hull, whereby the length of the hull is at least five times the beam and for longer ships as much as seven to eight times the beam. In shorter ships the beam is relatively larger as the hull must include the propulsion means and a wider beam ensures that there remains sufficient stability. The ship  1  in an aft ship  11  has one or more propellers  9  and one or more aft rudders  10 . For maneuvering at low speed there is a bow thruster  6  in a foreship  3  near a bow  4 . The lay out on deck is as usual for instance with a wheel house  2 . In the bow  4  there is a bow rudder  5  of which the function will be explained later. 
     As can be seen in  FIG. 2  the hull of the ship  1  has a special design, in more detail the design is such that a reduction of the Froude Kriloff forces in particular in the foreship  3  is achieved by minimizing the change in momentaneous submerged volume of the hull with sides  8  whilst it makes larger relative motions relative to the water level due to waves or the ships motions. 
     This results in a design applying sides  8  as much as feasible. A further measure in the design is to reduce the change in waterline beam of the sections in particular in the foreship whilst it makes the foresaid larger relative motions. This implies there is a minimal flare in the bow sections and a bow  4  has a more or less vertical line or the bow  4  extends less than 5 degrees forward and backward. By doing so the change of the added mass of the sections is minimized and with that also the changes in the hydrodynamic lift in the foreship  3  are minimized. By increasing the free board and bringing the deck line higher towards the bow  4  in the foreship  3  sufficient reserve buoyancy is guaranteed. 
     The amount of increased shear in the foreship  3  is dependent on ship size, speed and wave climate involved. A downwards sloping centre line towards the foreship  3  prevents the sections there to leave and re-enter the water whilst the ship  1  is performing larger relative motions. The amount of negative slope in the bottom  7  is dependent on ship size, speed and wave climate involved. The dead rise angle of the sections from bow to stern is carefully determined in order to minimize exciting forces and yet maintain sufficient hydrodynamic lift with minimal resistance. 
     Summarized the shape of the hull is such that the hull is long and slender, there is no flare in the bow sections and the sides  8  at the bow sections are almost vertical. Near the bow  4  the sides  8  make an angle α seen in a horizontal plane which is smaller than 40 degrees. There is an increased sheer forward and down sloping centre line forward and the entry of the waterlines are rounded. In order to reduce the wet surface the bow  4  is rounded with a radius R of at least 0.1 m. Depending on the beam of the ship the radius can be at least 1% of the beam. A further advantage of this radius R is that vortex shedding along the sides  19  of the ship is avoided in this way. This vortex shedding might occur in this design at small yaw angles when the bow is too sharp as is usual with fast ships. The vortex shedding must be avoided as it might lead to course instability. In order to prevent that the rounded bow  3  generates too much stagnation point resistance and/or generates too much spray the radius R is less than 4% of the beam. 
       FIGS. 3 and 4  show the behavior of ship  1  in waves W that approach the aft ship  11  from the stern quarter. A water level s is the normal situation when the ship  1  is level. When waves W approach the aft ship  11  from the port stern quarter the waves create a water levels&#39;. The waves W push against the port side  8  of the aft ship  11  and change the direction of the ships axis  1  from the on course situation indicated with  12  to the off course direction whereby the ships axis is indicated with  1 ′ and the ship is indicated with  13 . 
     When the ship  1  is off course the ship  1  can be brought on course using aft rudders  10 . These rudders  10  are then brought in a position as shown in  FIGS. 3 and 4  and a force A is generated on the aft rudders  10 . This force creates with the force of the waves W a tilting torque. Summarized the forces A on the aft rudders  10  reinforce the forces of the waves W on the side  8 . If the ship  1  is brought on course using a bow rudder  5  a force B is generated on the bow rudder  5 . This force B has the same direction as the force generated by the waves W and so counteracts the tilting torque of the waves W. Summarized the force B on the bow rudder  5  used for bringing the ship  1  on course reduces the tilting due to the waves W. This advantageous result is only for waves W that are incoming from the stern quarter as for waves W coming in from the front (not shown) using the bow rudder  5  would result in increased tilting. 
     The bow rudder  5  is only used when the waves W coming in sideways result in the course change as indicated before when waves are coming in from the stern quarter of the ship  1 . In the situation whereby the ship  1  is designed with its maximum draught in the foreship  3 , as described before, waves W coming in sideways or a few compass points forward will result in the same behavior and the use of the bow rudder  5  is then also an advantage. 
     The ship  1  is provided with an automatic steering system  25  that can switch over from steering with the aft rudder  10  to steering with the bow rudder  5  or with both rudders. When steering using the automatic steering system  25  the switching over can be effected by manually indicating with a wave direction indicator  26  to the automatic steering system  25  from which direction waves W are coming in, which automatic steering system  25  will then take this information into account. The automatic steering system  25  can also include an algorithm  27  for calculating the direction from which the waves W are coming in. The automatic steering system  25  is then provided with sensors  28  for determining the movements of the ship  1 , for instance using gyroscopes. 
       FIGS. 5   a ,  5   b  and  5   c  show the bow rudder  5  mounted in the foreship  3  in more detail. The bow rudder  5  is the lowest part of the bow  4  and has a rotation axis  14  which is more or less vertical. The bow rudder  5  is shaped such that when it is in its middle position the contour of the rudder  5  follows the shape of the hull as indicated in  FIG. 2  and the water flow F is not influenced by the bow rudder  5 . Part of the bow rudder  5  is in front of the rotation axis  14  so that the torque for rotating the bow rudder  5  is partly balanced, similar as can be used in known rudders. The rotation of the bow rudder  5  is effected in the same manner as usual with known rudders. 
       FIGS. 6   a  and  6   b  show a second embodiment of the bow  4  of the ship  1 . Instead of a conventional rudder located in the bow  4  the lateral forces B for steering the ship  1  are now generated by the flow F along a side flap  16 . On each side of the bow  4  there is a side flap  16 , these side flaps  16  rotate around a more or less vertical axis  17 , which axis  17  is supported at the lowest part of the bow  4  by a support  15 . When not activated the side flaps  16  follow the contour of the foreship  3  and are positioned against a brace  18 . For moving the side flaps  16  so that they can generate an adjustable lateral force B there is a mechanism  19 . This mechanism  19  can be formed by two hinged levers connected to each other and respectively the foreship  3  and the side flap  16 . The hinge connecting these levers can be moved in vertical direction by a hydraulic cylinder (not shown). This hydraulic cylinder can be located above the water level and is con-trolled such that either the one or the other side flap  16  is moved outside the contour of the foreship  3  in order to generate the lateral force B. 
       FIGS. 7   a  and  7   b  show a third embodiment of the bow  4  of ship  1 . A submerged part of the bow  4  now consists of a rotor  20  that can rotate around a more or less vertical rotation axis  21 . For driving the rotor  20  there is a drive  23  that drives the rotor  20  via a transmission  22 . The drive  23  can be electric or hydraulic and can be located above the water level. During rotation the rotor  20  acts as a so called Magnus rotor and generates asymmetric pressure fields at the different sides of the bow  4  so that a lateral force B is the result. By changing the speed of rotation of the rotor  20  the magnitude of the lateral force B can be adjusted.