NO20171607A1

NO20171607A1 - Side pulling maneuverable tug

Info

Publication number: NO20171607A1
Application number: NO20171607A
Authority: NO
Inventors: Mark Callaway
Original assignee: Kongsberg Maritime CM AS
Priority date: 2017-10-09
Filing date: 2017-10-09
Publication date: 2019-04-10
Also published as: NO345097B1

Description

INTRODUCTION

The present invention relates to a tug design with the capability of a transit direction of travel perpendicular to a pulling/towing direction of travel.

BACKGROUND

A tug, or tugboat, is a powerful boat or ship that is used for towing and pushing marine vessels. By towing and pushing the vessel, one or more tugs may maneuver the vessel during difficult maneuvering operations, such as in a harbor, in a narrow canal or during rescue operations of vessels in distress. During towing operations the tug maneuvers the vessel by pulling a towline connected between a winch on the tug and the vessel. Tugs are manually captained and the winch is manually controlled by either the captain or one of the crew. The captain receives, via radio communication, order from the towed vessel to provide thrust at a certain angle relative to the towed vessel. The captain will maneuver the tug to that location and then lock the winch and apply thrust. The winch is manually controlled so that the towline is not let in the water or tension is not applied when it is not supposed to.

A problem with traditional tugs is that they cannot pull in the direction transversal to the direction of travel as they risk capsizing. However, the capability of pulling in the transversal direction could be a big advantage in towing operations as the tug can quickly change direction of the force applied on the tow.

SUMMARY OF THE INVENTION

The present invention relates to a tug where what is considered a bow or a stern depends on the mode of operation. The first and the second distinct mode of operation includes a transit mode and a pushing/pulling mode. The shape and layout of the tug makes the tug extremely maneuverable and a direction of pull and an amount of thrust, which is provided to the assisted vessel, is easy to adjust. The tug design provides a tug where a moment arm between tug line and thrusters is as low as possible to improve stability. The maneuverability is achieved by locating the thrusters at both ends of the vessel. In transit mode the thrusters are inline.

The tug pulls in the transverse direction relative to the transit direction. The location of thrusters far from the center of pull and the large moment arm enable quick and smooth adjustment of the direction of pull. The thruster location in relation to the hull allows the water in/out of the propellers to be unaffected and allows for higher thrust. The tug can be asymmetric around a center line or plane of symmetry and have additional buoyancy to counteract the moment arising from the tow point and thrusters around the vessel center of gravity. The tug winch fairlead can be located at the lowest and most outboard location possible to minimize the moment arm. The tug may have a tunnel thruster at the center of the vessel to provide additional thrust if required. The towing wire and the fairlead could be above or below the waterline of the vessel, and the towline could extend from a well below sea level at the side of the tug to reduce or eliminate torque on the tug. The fairlead can also be movable in a vertical direction along the centre plane of the vessel to move the fairlead above or below the waterline and to adjust the moment imposed on the tug by the towline and the thrusters.

The present invention concerns a tug with a hull and at least one first azimuth thruster at a first azimuth thruster end of the hull and at least one second azimuth thruster at a second azimuth thruster end of the hull, and cable attachment means. The hull includes a wide side with a wide hull portion and a narrow side with a narrow hull portion extending between the first azimuth thruster end and the second azimuth thruster end, whereby the hull is asymmetric about a line extending between the first azimuth thruster end and the second azimuth thruster end, and whereby the tug is adapted to travel in a transit direction along the line extending between the first azimuth thruster end and the second azimuth thruster end in a first mode of operation and to travel in a pushing or pulling direction along a line perpendicular to the line extending between the first azimuth thruster end and the second azimuth thruster end in a second mode of operation.

The tug further includes pulling cable attachment means such as a winch or a bollard. The tug may include at least one tunnel thruster providing a force along a plane of symmetry of the hull equidistant from each azimuth thruster. A keel may extend with a longitudinal axis along a line extending between the first azimuth thruster end and the second azimuth thruster end. The at least one tunnel thruster includes a tunnel thruster longitudinal axis parallel to or coinciding with the plane of symmetry.

The tug may further including a wide side with a wide hull portion and a narrow side with a narrow hull portion extending between the first azimuth thruster end and the second azimuth thruster end, whereby the hull is asymmetric about a line extending between the first azimuth thruster end and the second azimuth thruster end.

The tunnel of the tunnel thruster may extend through the keel.

Two neighbouring tunnel thrusters may be symmetrically located in relation to the plane of symmetry.

The tug may further include a dynamic positioning system and an automated control system.

The tug may further include proximity sensors providing input to the automated control system.

The tug may further include load cells along the gunwale providing input to the automated control system.

The tug may further include hull pitch sensors providing input to the automated control system.

The tug may further include cable tension sensing means providing input to the automated control system, and the automated control system may control a winch.

The cable attachment means may include a winch and a fairlead.

The fairlead may be movable.

The fairlead is be located in the plane of symmetry.

The tug may, further including a winch and a fairlead, wherein the fairlead is located in the plane of symmetry Ps adjacent a gunwale on the wide hull portion.

The winch may be a drum winch with a horizontal drum.

The winch may be a drum winch with a vertical drum.

The cable attachment means may be a bollard.

Furthermore, the present invention relates to a method of operating a tug with a hull and at least one first azimuth thruster and at least one second azimuth thruster at a first azimuth thruster end of the hull, a second azimuth thruster end of the hull and a fairlead. The method comprises the steps of: positioning the at least one first azimuth thruster and the at least one second azimuth thruster in a transit position to provide a thrust substantially in a direction along the longitudinal axis of the keel while the at least one tunnel thruster not is operating, sailing the tug to a vessel requiring a tug service, connecting the tug and the vessel requiring a tug service with a towing cable, positioning the at least one first azimuth thruster and the at least one second azimuth thruster in a pulling position to provide a thrust in a direction substantially perpendicular to the longitudinal axis of the keel while the at least one tunnel thruster is operating.

The tug may further comprise at least one tunnel thruster providing a force along a plane of symmetry in the hull equidistant from each azimuth thruster.

A keel may be provided along a longitudinal axis along a line extending between the first azimuth thruster end and the second azimuth thruster end. The at least one tunnel thruster may include a tunnel thruster opening extending through the keel. Provided the tug has such a tunnel thruster, will the method also include operating the tunnel thruster when tug is moving in the pushing or pulling direction along the line perpendicular to the line extending between the first azimuth thruster end and the second azimuth thruster end in the second mode of operation

The solution of the invention is suited for autonomous tugs, and the tug is highly stable due to the asymmetric hull form. The tug can quickly and safely change direction of the pull and the tug provides increased maneuverability due to additional transverse thruster or thrusters which provide an extra thrust point.

The solution is particularly suited as an autonomous vessel as there are no requirements for any room for a crew or a particular direction of operation. With the shown design, stability is maintained while mass, buoyancy, drag, moment of inertia is reduced and efficiency and manoeuvrability is increased.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a side elevation of a tug of the invention;

Fig. 2 is a front / rear view of the tug of fig.1;

Fig. 3 it a top view of the tug of figs.1 and 2;

Fig. 4 corresponds to fig.1, apart from showing an embodiment without a centrally located tunnel thruster; and

Fig. 5 is a schematic representation of the force vectors acting on the tug.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Figs. 1, 2 and 3 show a towing vessel or tug 1 of the invention from a long side, a short side and a top side respectively.

Fig. 1 shows a preferred embodiment of a tug 1 from the long side. The tug 1 is symmetrical about a centreline in a direction transversal of an ordinary direction of travel when the tug 1 is in transit and not towing or pushing. A tunnel thruster 9 is located in a centrally located tunnel thruster opening 10 in a keel 6 in the centreline. A winch 12 is also centrally located, but the location of the winch 12 is less critical. A first azimuth thruster 7 at a first end of the tug is located at the same distance from the centreline as a second azimuth thruster 8 at a second end of the tug at the opposite side of the centreline. The two azimuth thrusters 7, 8 are in line with or aligned with the keel 6 and thus the tunnel thruster 9.

Fig. 1 shows the azimuth thrusters 7, 8 in a position that typically is used when the tug 1 is in transit (first mode of operation) and moving in a direction along the direction of the keel 6. Alternatively, one of the azimuth thrusters 7, 8 is turned 180° such that both the azimuth thrusters face more or less the same direction. Clearly the azimuth thrusters are used for controlling the direction of travel of the tug and are turned accordingly. Locating the azimuth thrusters 7,8 as far from each other as practical on the hull provides good control authority. The centrally located tunnel thruster 9 will not reduce the control authority. Several smaller tunnel thrusters may also be used and such tunnel thrusters should then be located close together and symmetrically about the plane of symmetry Ps to maintain control authority and to provide a thrust at the centre of the tug without affecting the directional control. Fig.1 also include schematic representations of a dynamic positioning system DPS 23, an automated control system 24, hull pitch sensors 25, a cable tension sensor 26, load cells 27 for controlling a pushing force between the tug 1 and a vessel and proximity sensors 28 measuring the distance between the tug 1 and other objects.

Fig. 2 shows the tug 1 from the short side. The view on fig.1 is perpendicular to the view on fig.1. The winch 12 is located on the deck and a winch rope or cable exits through a centrally located fairlead 13. The fairlead 13 is aligned with the centreline and the tunnel thruster to ensure that torque on the tug imposed by the pull in the winch wire and the thrust from the tunnel thruster is kept to a minimum. A horizontal distance Dh between the tunnel thruster in the keel 6 and the fairlead 13 also contributes to stability during pulling operations.

The centreline of the tunnel thruster 7 is aligned with the keel 6. The hull of the tug 1 includes a wide hull portion 14 and a narrow hull portion 15. The fairlead 13 is located close to the gunwale above the wide hull portion 14. The narrow hull portion 15 includes a steep side portion and the wide hull portion 14 includes a more inclined side portion.

Fig. 3 shows the tug 1 from above. The tug 1 includes a wide side 2 and a narrow side 3. The first azimuth thruster 7 is located close to a first azimuth thruster end 4 and the second azimuth thruster 8 is located close to a second azimuth thruster end 5. A first horizontal distance Df from the centre of the first azimuth thruster 7 to the centreline or the plane of symmetry Ps through the centre of the fairlead 13 equals a second horizontal distance Ds from the centre of the second azimuth thruster 8 to the centreline through the centre of the fairlead 13. The distances Df and Ds are greater than the distance Dh. The interrelation between these distances provides control authority while maintaining a certain inherent stability when the tug is pulling sideways. The tug is not adapted for lengthwise pulling. The winch 12 and the fairlead 13 are located on the deck 11.

Fig 4. Corresponds to fig 1, apart from showing an embodiment without a centrally located tunnel thruster. Furthermore, fig.4 also shows a vertically adjustable fairlead 13 that may move along fairlead tracks 17 at each side of a towline well 18. The fairlead may be adjusted up or town to increase or decrease the moment imposed on the tug by the thrusters and the towline. The invention is intended to encompass embodiments with or without a movable fairlead and centrally located tunnel thruster.

Fig. 5 is a schematic representation of the force vectors acting on the tug and shows how an arm I between the fairlead 13 and an axis between the thrusters 7, 8 is short compared to arm II and arm III between a centre of the tug CL, thruster 7 and thruster 8. The arm II and arm III form long moment arms about the winch and fairlead 13 located at the centre of the tug, thus providing good control authority of the tug when towing. The short length of arm I provides a reduced “flipping/capsizing torque” about the axis between the thrusters and increases the stability of the tug about the axis between the thrusters.

The asymmetric design provides stability while towing and low drag and speed while in transit. Furthermore, the design allows the distance Dh to be smaller than for common tugs, and the design and the lack of crew allows the tug to be completely enclosed. The enclosed hull allows the freeboard and thus the height of the vessel and moment arm between the fairlead and the thrusters to be kept to a minimum. Furthermore, the lack of hull in front of the thrusters when the tug is pulling or pushing sideways provides completely undisturbed flow of water into the thrusters.

The asymmetric design also provides increased buoyancy on the wide side 2 of the hull to counteract pitching (in the clockwise direction on fig.2) resulting from the torque imposed by the forces from the thrusters 7, 8, 9 and the winch cable running through fairlead 13.

The tug is adapted to be autonomous and is accordingly designed without a wheelhouse or other accommodation facilities for a crew. The tug may however include controls for on-board manual override.

The tug can be fully electric, can include hybrid propulsion with a combustion engine driving a generator for providing power to electric motors or can be driven directly or hydraulically by one or several combustion engines. The tug can be adapted to be charged from a suitable charging facility and may include proximity sensors and other sensors for automatic docking and connection at a charging facility. Electric motors are advantageous as they have high efficiency, are easily controllable, provide high torque already from a low speed, are quiet and without local emissions, are cost effective to run and have a wide speed range. Electric motors are thus suitable for both high thrust and high transit speed operations.

The propellers in the thrusters will typically be fixed pitch propellers, but variable pitch propellers may also be used. The pitch of the propeller in the centrally located tunnel thruster can be smaller than the pitch of the propellers in the azimuth thrusters as the tunnel thruster only is used for low speed and high force operation.

The tug is typically controlled by a dynamic positioning system (DPS) and includes a GPS and other typical systems for control. The tug will include communication systems to communicate with a control base, with the vessel to be maneuvered and with other systems. The tug will typically also include proximity sensors and on-board cameras. The tug will typically be operated completely autonomous without input from a control room. Although a tug is capable of operating individually, the tug typically forms a single unit in a fleet of similar tugs that operate in cooperation to fulfil the task of manoeuvring a vessel.

The winch is typically an electric or hydraulic winch and includes a winch motor and a transmission. The transmission may be of a self-locking worm gear type, but the winch will typically include a winch brake to lock the winch drum and thus the wire in position. The winch may include means for indicating the amount of pull in the winch cable. The means may include means for indicating current or pressure in an electric or hydraulic motor respectively, winch mount load cells, drum brake load cells, hydraulic braking circuit pressure sensors, wire mounted load cells etc. The signal indicating cable pull can be fed to the control systems and can be monitored for control and to ensure operation within design conditions. The fairlead may also include load sensors to indicate the direction of the cable.

Alternatively may other systems be used to indicate the winch cable angle. Such systems may include cameras and a vision system or a system for mechanically reading the winch angle.

Vertical and horizontal is in the context of this disclosure intended to indicate directions in relation to the hull of the tug when the tug is at rest at sea and is intended to indicate directions in relation to the tug.

1 Vessel

2 Wide side

3 Narrow side

4 First azimuth thruster end

5 Second azimuth thruster end

6 Keel

7 First azimuth thruster

8 Second azimuth thruster

9 Tunnel thruster

10 Tunnel thruster opening

11 Deck

12 Winch

13 Fairlead

14 Wide hull portion

15 Narrow hull portion

17 Fairlead tracks

18 Towline well

23 Dynamic positioning system DPS 24 Automated control system

25 Hull pitch sensors

26 Cable tension sensor

27 Load cells

28 Proximity sensors

Claims

1. A tug with a hull and at least one first azimuth thruster (7) at a first azimuth thruster end (4) of the hull and at least one second azimuth thruster (8) at a second azimuth thruster end (5) of the hull, and cable attachment means, further including a wide side (2) with a wide hull portion (14) and a narrow side (3) with a narrow hull portion (15) extending between the first azimuth thruster end (4) and the second azimuth thruster end (5), whereby the hull is asymmetric about a line extending between the first azimuth thruster end (4) and the second azimuth thruster end (5), and whereby the tug is adapted to travel in a transit direction along the line extending between the first azimuth thruster end (4) and the second azimuth thruster end (5) in a first mode of operation and to travel in a pushing or pulling direction along a line perpendicular to the line extending between the first azimuth thruster end (4) and the second azimuth thruster end (5) in a second mode of operation.

2. The tug of claim 1 further comprising at least one tunnel thruster (9) providing a force along a plane of symmetry Ps in the hull equidistant from each azimuth thruster (7, 8); and

a keel (6) with a longitudinal axis along a vertical plane extending between the first azimuth thruster end (4) and the second azimuth thruster end (5) and wherein the at least one tunnel thruster (9) includes a tunnel thruster longitudinal axis parallel to or coinciding with the plane of symmetry Ps.

3. The tug of claim 1 or 2, wherein the opening (10) of the tunnel thruster (9) extends through the keel (6).

4. The tug of claim 1, 2 or 3 wherein the at least one tunnel thruster (9) is one tunnel thruster located in the plane of symmetry Ps.

5. The tug of any of the proceeding claims further including a dynamic positioning system (23) and an automated control system (24).

6. The tug of any of the proceeding claims further including proximity sensors (28) providing input to the automated control system.

7. The tug of any of the proceeding claims further including load cells (27) along the gunwale providing input to the automated control system (24).

8. The tug (1) of any of the proceeding claims, further including hull pitch sensors (25) providing input to the automated control system (24).

9. The tug of any of the proceeding claims, further including cable tension sensing means (26) providing input to the automated control system (24), and wherein the automated control system (24) controls a winch (12).

10. The tug of any of the proceeding claims, wherein cable attachment means include a winch (12) and a fairlead (13).

11. The tug of claim 10, wherein the fairlead (13) is movable.

12. The tug of claim 10, wherein the fairlead (13) is located in the plane of symmetry.

13. The tug of claim 2, further including a winch and a fairlead (13), wherein the fairlead (13) is located in the plane of symmetry Ps adjacent a gunwale on the wide hull portion (2).

14. A method of operating a tug (1) with a hull and at least one first azimuth thruster (7) at a first azimuth thruster end (4) of the hull and at least one second azimuth thruster (8) at a second azimuth thruster end (5) of the hull and a fairlead (13), , comprising the steps of:

positioning the at least one first azimuth thruster (7) and the at least one second azimuth thruster (8) in a transit position to provide a thrust substantially in a direction along the longitudinal axis of the keel;

sailing the tug (1) to a vessel requiring a tug service;

connecting the tug (1) and the vessel requiring a tug service with a towing cable; positioning the at least one first azimuth thruster (7) and the at least one second azimuth thruster (8) in a pulling position to provide a thrust in a direction substantially perpendicular to the longitudinal axis ofthe tug in a pushing or pulling mode of operation..

15. The method of claim 14, wherein the tug further comprises at least one tunnel thruster (9) providing a force along a plane of symmetry of the hull equidistant from each azimuth thruster (7, 8) and a keel (6) with a longitudinal axis along a vertical plane extending between the first azimuth thruster end (4) and the second azimuth thruster end (5) and wherein the at least one tunnel thruster (9) includes a tunnel thruster longitudinal axis parallel to or coinciding with the plane of symmetry Ps, the method further comprising operating the at least one tunnel thruster (9) in the the keel (6) while the tug is in a pushing or pulling mode of operation.