NL2017577B1 - Tugboat having azimuthal propelling units - Google Patents

Abstract

A tugboat (1) having azimuthal propelling units, comprising two juxtaposed azimuthal propelling units (10, 20), characterized in that each of the juxtaposed propelling units (10, 20) has a main shaft (14) with a main axis (11, 21) extending at an angle (α and/or β) relative to a main plane of symmetry (2) and/or to a transverse center plane (5) of the tug boat.

Description

Patent center

The Netherlands

Θ 2017577

BI PATENT (51) Int. CL:

B63H 5/125 (2017.01) B63H 25/42 (2017.01) B63B 35/66 (2017.01) B63H 5/15 (2017.01) (21) Application number: 2017577 © Application submitted: 05/10/2016

(Ti) Application registered: (73) Patent holder (s): 13/04/2018 Rotortug Holding B.V. in Rotterdam. (43) Application published: - (72) Inventor (s): Antonie Marius Kooren in Rotterdam. (w) Patent granted: 13/04/2018 (74) Agent: (45) Patent issued: ir. C.M. Jansen et al. In The Hague. 13/04/2018

Tugboat having azimuthal propelling units (57) A tugboat (1) having azimuthal propelling units, including two juxtaposed azimuthal propelling units (10, 20), characterized in that each of the juxtaposed propelling units (10, 20) has a main shaft (14) ) with a main axis (11, 21) extending at an angle (a and / or β) relative to a main plane of symmetry (2) and / or a transverse center plane (5) or the tug boat.

NL BI 2017577

This patent has been granted regardless of the attached result of the research into the state of the art and written opinion. The patent corresponds to the documents originally submitted.

P112884NL00

Title: Tugboat having azimuthal propelling units

The invention relates to a tugboat with azimuthal propelling units.

Within the framework of the present invention, by the expression azimuthal propelling unit is meant as a propelling unit whose propelling direction in horizontal direction can be varied through 360 °. Such azimuth propelling units are already known per se, for instance in the form of a nozzle having a propeller arranged therein.

Specific requirements are imposed on a tugboat with regard to thrust and maneuverability. For instance, it is desired that a tugboat cannot only produce hauling power in forward direction, but also in rearward direction, and even in lateral direction, although the hauling power producible in lateral direction will be less than the hauling power producible in longitudinal direction.

For instance from the article Schottel tugs in Small Ships, Vol.99, No.1204, December 1976, page 95, it is already known to fit a tugboat with azimuth propelling units because of the maneuverability provided. Such tugboats, also known by the name of tractor tug, have two azimuth propelling units which are juxtaposed in transverse direction and viewed in the longitudinal direction of the tugboat, in a central position. However, some drawbacks are attached to this. For instance, it is not properly possible to continue using the tugboat if one of the propelling units has been damaged.

From W01997020730 a tug boat is known to have three azimuth hal propelling units. Two azimuthhal propelling units are provided on a first longitudinal position, on the opposite side or a mid-sectional plane of the tugboat. A third azimuthhal propelling unit is positioned at a longitudinal position different from the longitudinal positions of said two azimuthhal propelling units. In this known tugboat, which is known in the field as Rotor tug®, each propelling unit has a propeller shaft and a main shaft. The propeller can be rotated around the main shaft at least 360 degrees and the main shafts extend parallel to each other, in a vertical direction when the tug boat is level.

For tug boats, especially for use in harbors and waterways with draft restrictions and / or harbors and waterways featuring tug pens with draft restrictions, it is important to provide sufficient towing force, for pulling and / or pushing assisted vessels. There is therefore a desire for alternative tug boats that have optimum power and draft, while remaining agile and reliable.

Generally, the object of the invention is to provide a tugboat which, in respect of the above-mentioned aspects, performs better than the tugs known thus far.

An object of the invention is to provide a tugboat which can 15 produce more power than the rotor tug type tugs known thus far, without the draft being increased. An object of the invention is to provide a tugboat which can produce similar power as the rotor tug type tugs known thus far, with the draft being decreased. In known tugs, an increase in power can be realized by using two stronger propelling units, but a consequence is that the dimensions of the propelling units are increased as well, which has an adverse effect on the draft of the ship.

In order to realize the above objectives, a tugboat according to the present invention may have three azimuthal propelling units viewed from the top, lie in a triangular pattern, or at least the main axis or two such propelling units on opposite sides of a mid sectional plane of the tug boat extend at an angle relative to a vertical line when the tug boat is in a level position. Such angle preferably is formed by or includes an angle with the mid sectional plane or the tug boat. Such angle may be formed by or include an angle in a plane parallel to said mid sectional plane.

Thus, it is possible to produce a greater thrust which is distributed on the tugboat in a better manner and / or a similar thrust with a reduced draft. In comparison with the known rotor tugs for example the same thrust can be obtained with similar propelling units, but with a narrower draft, or an increased thrust can be obtained with the same draft using larger propelling units. Moreover in improved an improved towing behavior can be obtained through the improved arrangement or the thrusters in relation to the towing points.

These and other aspects, characteristics and advantages of the present invention will be specified by the following description of a preferred embodiment of a tugboat according to the invention, with reference to the accompanying drawings,

FIG. 1 schematically shows a side view of a tug boat according to the prior art;

FIG. 2 schematically shows an azimuthal propelling unit;

Fig 3 shows schematically in top plan view a tugboat according to the present invention, to illustrate the positions of the three propelling units;

FIG. 4 is a schematic longitudinal section on the line II-II in

FIG. 3;

FIG. 5 is a schematic cross-sectional task on the line V-V in FIG. 3

FIG. 5A shows in a view according to fig. 5 part of a tug boat with two juxtaposed propelling units with sideways thrust, showing their main direction of thrust and general wake;

FIG. 6 shows in front view of a tugboat according to the prior art;

FIG. 7 shows in front view of a tugboat according to the present invention;

FIG. 8 shows in a side view of a tugboat according to fig.

FIG. 9 shows in side view a tug boat according to fig. 7 in a second embodiment;

FIG. 10 shows in side view a tug boat according to fig. 7 in a third embodiment; and

FIG. 11 shows in side view a tug boat according to fig. 7 in a fourth embodiment.

FIG. 1 schematically shows in side view a tugboat 1. Hereherr, it is assumed that the tugboat 1 is afloat in approximately even throat, or - zero trim condition, and the expression 'horizontal' and 'vertical' are meant relative to the water surface. Fig 3 schematically shows the contour of a tug boat 1 seen from above, showing the position of propelling units 10, 20, 30. They are shown as positioned at the corners of a triangle, by way of example. A tug boat according to the disclosure can for example be but is not limited to a tug boat designed for harbor assistance to vessels, for near shore assistance to vessels and / or for open water assistance to vessels.

Additional or alternatively a tug boat according to the present disclosure can be a boat for assistance in fire fighting, such as a fire boat, or for other assistance in harbors, near shore, or off-shore such as ice-breaking, anchor handling, hose handling, supply, in-field support, dive support, ROV support and / or other offshore support. In this description juxtaposed should, in relation to propelling units as will be described, understood as meaning at least that at least two units are positioned on opposite sides of an intermediate plane, especially an intermediate vertical plane, extending in a longitudinal direction of the tug boat. Such units can be referred to as juxtaposed propelling units.

Viewed in the transverse direction, the tugboat 1 is substantially symmetric relative to a vertical main plane of symmetry 2 (II - II in Fig. 3), extending in the longitudinal direction of the tugboat 1. The tugboat 1 has a front extreme point 3 located in the main plane of symmetry 2, and a rear extreme point 4 also located in the main plane of symmetry 2. The horizontal distance between the front and rear extreme points 3 and 4 is indicated as the length L of the tugboat 1. Herein below, horizontal length positions will be indicated as measured relative to the rear extreme point 4.

By reference numeral 5, a vertical plane is indicated in the figures 5 which is perpendicular to the main plane of symmetry 2, and which intersects that main plane of symmetry 2 according to a vertical line precisely halfway the front and rear extreme points 3 and 4 That vertical line M will be referred to as the center of the tugboat 1, and the vertical plane 5 will be referred to as the transverse center plane of the tugboat 1.

Herein below, horizontal width positions will be indicated as measured relative to the main plane of symmetry 2.

The body portion of the tugboat 1 located behind the transverse center plane 5 will be referred to as the stern 6 or star side, and the body portion of the tugboat 1 located before the transverse center plane 5 will be referred to as the bow 7 or bow side.

By a reference sign Ls, the horizontal position is indicated of a towing point 8 provided on the star 6, ie a point intended for securing a towing cable or the like thereto, or for guiding, via that point, a towing cable or the like to a towing winch, or towing hook. The tugboat 1 can have several towing points; for instance, a towing point 8A can be provided on the bow 7 and a towing point 8B can be provided on the stern 6. If the tugboat has several towing points on the bow 7 and / or stern 6, the towing point 8 is meant to be the last point of physical contact between towing line 100 and tugboat 1. Herein a contact point is understood as also including a line contact or relatively small area of contact. Similarly the length position of any towing point 8, 8A can be indicated by reference sign L with an indicator, such as 8 or 8A. Towing points 8, 8A can for example include a winch 101, such as but not limited to a render recovery winch, for winching a towing line 100. The tug boat can be further provided with a fencing system, for allowing pushing as well as pulling or a vessel to be assisted, or for operating in close proximity to other vessels and / or structures.

The tugboat 1 comprises three azimuthal propelling units 10, 20 and 30, whose propelling direction in horizontal direction can be varied through 360 ° relative to the respective main axis 11, 21, 31 associated with the propelling units 10, 20 and 30. Each propelling unit may be driven by a separate driving engine or different propelling units can be driven by the same engine, for example through appropriate gear boxes, or engine-driven generators in combination with electric-driven propelling units, not shown for simplicity's sake. Such azimuthal propelling units are known per se, for instance in the form of a screw, a nozzle having a propeller arranged therein, or a so-called Voith Schneider unit. An example of such propelling unit is shown in Fig. 2, by way of example only, not limiting the scope of this disclosure in any way. As the nature and construction of such azimuthal propelling units do not represent a subject of the present invention, and a skilled person need not have specific knowledge for a proper understanding of the present invention, they will not be further described further than necessary for the disclosure.

As a for example seen in Fig. 2 a propelling unit has a propeller 12 mounted on a propeller shaft 13. The propeller shaft 13 extends at an astute, for example substantially right angle (90 degrees) to a main axis or main shaft 14 , traditionally referred to as a vertical axis 11, 21, 31, though in the present invention for at least one of the propelling units 10, 20, 30 the main shaft 14 may extend non-vertical and may enclose an angle relative to the planes 2 and / or 5. The propeller 12 will normally be enclosed by a nozzle 15 extending around it. The propeller shaft 13 is driven by the main shaft 14, and can rotate around the main axis 11, 21, 31 over an angle of 360 degrees or more in order to directly the thrust of the propelling unit 10, 20, 30 in any desired direction. As can be seen in fig. 2 the main shaft 14 extends through a thruster well 17, which can also be referred to as well 17, which will be fixed in and / or formed by the hull of the tug boat 1, such that connections to the propelling unit 10, 20.30, such as to a motor or electrics, controls and the like can be achieved inside said hull 18 .. Furthermore it will be clear that the forces acting on the propelling unit 10, 20, 30, for example by the thrust generated by the propeller 12, or forces between the hull 18 and the propelling unit 10, 20, 30 will have been transferred to the hull 18 and vice versa through the thruster well 17. This means that the thruster well 17 will have to be sufficiently strong, for example reinforced by ribs, beams, brackets or the like, again requiring space. Thus building the propelling units 10, 20, 30 into a tug boat hull 18 requires space inside the hull 18, limiting the possible arrangements for positioning the propelling units 10, 20, 30 in a tug boat 1 according to the prior art.

Viewed in horizontal direction, the three azimuthhal propelling units 10, 20 and 30 can be arranged according to an isosceles triangle, the triangle being placed symmetrically relative to the main plane of symmetry

2. It is preferred that two azimuthhal propelling units 10 and 20 are located on one side of the transverse center plane 5, and that the third azimuthhal propelling unit 30 is located on the other side of the transverse center plane 5, seen in said longitudinal direction L of the boat 1.

Preferred illustrated, a first azimuth propelling unit 10 and a second azimuth propelling unit 20 may be located below the bow 7, symmetrically on both sides of the transverse center plane 5. By this it is meant that the length position Lio of the main shaft 14 or the first azimuthhal propelling unit 10 is equal to the length position L20 or the main shaft 14 or the second azimuthhal propelling unit 20. These positions are greater than 0.5 L, while the width position is B10 or the main axis 14 or the first azimuthal propelling unit 10 is equal (but opposite) to the width position B20 or the main axis 14 of the second azimuthal propelling unit 20. As regards the length positions Lio and L20, they may be greater than 0.65L and preferably greater than 0.7 L In combination with geometry or hull 18 this further restricts available space, further limiting possible arrangements. If a towing point is provided on the bow 7, the length position is preferably greater than or equal to Lio and L20. If a towing point is provided on the star 6, the length position is preferably greater than or equal to L30.

The main axis 14 of the third azimuth propelling unit 30 preferably lies in the main plane of symmetry 2, and has a length position L30 narrower than 0.5, and may be greater than or equal to 0.15 L or less.Leo may be narrower than or equal to 0.4 L, for example narrower than or equal to 0.25. L30 may be greater than or equal to Ls or narrower than Ls for the towing point 8 at the stern.

The position and especially the length position L or B is defined by the position P in which the main shaft 14 of a propelling unit crosses the hull 18 or an imaginary plane of the hull 18 as a continuation of the hull 18 about the relevant thruster well 17 or opening in which the thruster well 17 is mounted in the hull 18. As will be discussed for at least one of the propelling units 10, 20, 30 in the present invention the main shaft 14 extends non-vertical, such that the lower end 14A or the main shaft is not directly below the said position P, contrary to the tug boat according to the prior art, in which the said lower end 14A or each of the main shafts 14 is indeed directly below said position P since the main shaft 14 or each propelling unit 10, 20, 30 extends vertically, said shafts 14 in the prior art hence extending parallel to each other and parallel to the main planes 2 and

5.

In the present invention for at least one and preferably at least two of the propeller units 10, 20, 30, the main shaft 14 or at least the axis 11, 21 and / or extends non-vertical, such that it encloses an angle with a vertical line through the relevant point P. Fig. 5 schematically shows a vertical cross sectional view through the axis 11, 21 of the main shafts 14 of the first and second propeller units 10, 20. These axis 11, 21 in this embodiment lie in a plane V- V parallel to the plane 5, as indicated in fig. 3. As can be seen in this view each of the axis 11, 21 includes an angle with the mid-sectional plane 2, in fig. 5 represented by the vertical line between the two units 10, 20. The angle a can for example be between 1 and 15 degrees, such as for example between 1 and 10 degrees, for example between 2 and 10 degrees, such as but not limited to between 2 and 8 degrees.

FIG. 6 shows in front view the position of especially the first and second propelling units 10, 20 or a tug boat of the prior art, having the main axis 11, 21 extending vertically, parallel to each other. In contract fig. 7 shows a tug boat according to the invention, which is shown as substantially identical to that or fig. 6 but having the main axis 11, 21 of the first and second propeller units 10, 20 angled relative to each other and to the plane 2, as shown in fig. 5. As can be seen the horizontal distance D _prop between the centers of the propellers 12 when the propeller shafts 12 extend parallel to each other, perpendicular to the plane V - V, in the prior art tug boat can be narrower than said distance D _prop in a tug boat according to the invention when the distance D _p between the points P where said axis 11 and 21 cross the actual or imaginary surface of the hull 18 is the same. This can have the advantage that the moment that each of the propellers can be exert by thrust relative to the center M of the tug boat 1 can be exert can be larger, with the same propeller 12 or could be the same with a smaller propeller 12.

In each of the propelling units 10, 20, 30 has a main direction of thrust, preferably directed perpendicular to the main axis 11, 21, 31. The main direction of thrust should be understood as meaning a center line extending from the center of the propeller 12 in a direction parallel to and preferably coinciding with an axis 12A or the propeller shaft

12. This line or main direction of thrust Extends as a center line of the substantially cone shaped wake W or water displaced by the relevant propeller. As can be seen in fig. 5A the juxtaposed propelling units 10, 20 can be mounted such that when their main directions of thrust are seen in top view are directed in the same direction and in said top view parallel to each other or even coinciding, the main direction of thrust Dt of a first 10 of the two juxtaposed propelling units is directed below the main direction of thrust Dt of the second 20 of the two juxtaposed propelling units 10, 20 or vice versa, depending on the said direction of thrust. Thus they do not interfere or at least extend a lesser than in the prior art tug boat. Moreover, as can be seen in the hull 18 interferes less or not with the wake W of the propellers 12 than in the tug boat according to the prior art.

As can be seen in a comparing or fig. 6 and fig. 7, when using the same size propeller 12 the distance T between the lowest points of the nozzles and the water line WL of the tug boat 1 can be reduced by inclining the axis 11, 21. This can reduce the draft. Or the same distance T can be maintained while a larger propeller 12 can be used, increasing propeller efficiency and power.

As can be seen in fig. 7 the hull 18 can have an inclined surface area 18A at and near the respective points P as discussed. By inclination of the axis 11, 21 or the respective propelling units 10, 20 the nozzle 15 can be brought closer to the said surface, i.e. the distance c between the said area

18A and the nozzle 15 measured at the axis 11, 21 can be shorter than in the prior art, again resulting in a narrower distance T when using the same size propeller 12 or with the same distance T a larger propeller can be used. The nozzle 15 can be brought closer to the hull 18 at least since by inclination of the axis 11, 21 said axis 11, 21 will be closer to or form a normal to said inclined surface area 18A, meaning that during rotation of the propeller 12 with the nozzle 15 around the main shaft 14 or axis 11, 21 the nozzle will stay substantially at the same distance from the hull surface 18A, whereas in the prior art when rotating the propeller and nozzle around said vertical axis, it would run into the hull when rotated towards the center plane 2 if the same limited distance C were chosen when the propeller is facing the bow or stern.

By inclination of the axis 11, 21 or the respective propelling units 10, 20 the position of the thruster well 17 or each of the propelling units 10, 20 will be tilted too, allowing a repositioning with slightly outward along the surface 18A of the hull 18 when compared to the same hull of the prior art, bringing the propellers 12 even further outward, increasing the distance Dprop even further. Moreover, design and construction of the thruster well 17 can be easier and more effective since the angle between the said surface area 18A and the relevant bottom side of the thruster well 17 is reduced.

In the alternative of the axis 11, 21 or the respective propelling units 10, 20 can have the advantage that they can be placed further from the plane 5 in the tug boat 1, for example closer to the voice or bow 7, at a length position L10 +, L20 +, increasing the distance between the center C or the boat and the respective propellers 12 compared to the prior art tug boat, as seen in a comparison between figs. 8 and 9, in Fig. 8 a side view is shown with the units 10, 20 in a conventional length position Lio, L20, which may or may not be according to the invention, and in Fig. 9 a side view is given in an embodiment of the invention having the units 10, 20 further forward, at length position L10 +, L20 +. Thus the moment that can be exerted through the thrust of each propeller 12 relative to said center C can be increased, when using the same propeller or the same moment when using a narrower propeller. Smaller can be understood in this respect as smaller in size and / or in thrust.

As can be seen in the front views or fig. 6 and 7, by bringing the propellers 12 or the first and second units 10, 20 further apart, their wake will interfere less with the propeller 12 or the third unit 30 when they have a thrust straight backward and vice versa. Moreover the wake of the propellers 12 and thus their thrust will be less obstructed by or interfere with the hull 18 of the tug boat 1 due to the inclination of the axis 11, 21.

FIG. 10 shows an alternative embodiment of the present invention, in which the main shafts 14, or at least the main axis 11, 21 or the first and second propeller units 10, 20 are inclined, that is include an angle 6 with a vertical plane V - V parallel to the plane 5. In this embodiment the axis 11, 21 are inclined such that the lower ends 14A of the shafts 14 are brought forward relative to the points P. This can be combined with the angular position as disclosed here before in relation to ia fig. 5 and 7, seen in front view the axis 11, 21 can be parallel to each other and extend vertical. As can be seen in fig. 10 this can bring the propellers 12 of the units 10, 21 further forward, increasing the moment that can be relative relative to the center C. Moreover, the distance T can be reduced when using the same size propeller or the same distance T can be maintained as in the prior art tug boat when using a larger propeller 12. Furthermore the nozzle and thus the propeller can be positioned closed to the hull 18. In execution the wake of the propellers 12 and thus the thrust may interfere less with the hull 18, increasing efficiency.

FIG. 11 shows a further alternative model, in which the third propelling unit 30 has a main shaft 14 with a main axis 11 extending at an angle γ in the mid sectional plane 2 or a plane parallel to that plane 2, which angle γ can for example be such that the lower end 14A is located behind the relevant point Pe behind the upper end 14B of said shaft 14. The angle γ can for example be between 1 and 15 degrees, such as for example between 1 and 10 degrees, for example between 2 and 10 degrees, such as but not limited to between 2 and 8 degrees. In the drawings the angles α, β and γ may not be scale and can be represented larger for clarity.

In FIG. 11 both the first and second propelling units 10, 20 and the third propelling unit 30 have main axis 11, 21, 31 which are included relative to a vertical plane, seen in side view. It will be clear that also only the third propelling unit 30 can have such inclination. The inclinations of the axis 11 and 21 may differ from that of the third axis 31. In different the axis 11, 21 may be inclined in two directions, ie angles α, β may both differ from 0 or 180 degrees and may both for example be between 1 and 15 degrees, such as for example between 1 and 10 degrees, for example between 2 and 10 degrees, such as but not limited to between 2 and 8 degrees, bearing the angles α, β may be the same or different for the respective axis 11, 21.

The three azimuthal propelling units 10, 20 and 30 can be mounted entirely below the bottom 9 of the tugboat 1. However, it is also possible that the azimuthal propelling units 10, 20 and 30 are partly recessed in the bottom 9 of the tugboat 1 , so that the tugboat 1 will have a less great draft. This applies in particular to the third azimuth propelling unit 30, located at the center of the tugboat 1, because, viewed in the cross section, the bottom 9 of the tugboat 1 is generally more or less V-shaped, so that in fact, the lowermost point of the third azimuth propelling unit 30 may determine the draft of the tugboat 1 if propellers of the same size are used. When such recesses 9A are used the inclination of the axis 11, 21, 31 may be further beneficial since the thrust of the propellers will be less influenced by the sides and edges of such recess, increasing the effective thrust that can be achieved for these units 10, 20, 30.

In conventional tractor tugboats, the propelling units are disposed at equal length positions. A consequence is that when the boat is moved truly transversely to the longitudinal direction, and, moreover, a pulling or pushing force is exerted in that direction, a fairly large part of the installed power is lost: this loss can be about 50%, or higher depending on the arrangement and type of the propelling units installed. In conventional tugboats with the screws mounted at the rear of the boat, that loss may be just 70%. Owing to the presence of a third propelling unit 30 at a length position different from that of the other two propelling units, as known in the prior art, the maneuverability in lateral direction is improved, and the maximally producible pulling or pushing force transverse to the longitudinal direction is increased considerably. By repositioning of the main axis 11, 21 of the two propelling units which are side by side at a same side of the transverse plane 5, the thrust side ways can be further further increased since part of the thrust or a first of the two propelling units 10, 20 which seen in direction of thrust is in front of the second of the two propelling units 20, 10 will pass below said second propelling unit. Considering that thrust, i.e. the water displaced by the propeller 12 or said second propelling unit will pass below the hull 18 to a greater extend than when the axis 11, 21 would be vertical, further increasing efficiency.

Since the third azimuthhal propelling unit 30 is located in the main plane of symmetry 2, it is possible in an easy way to travel straight on utilizing only one or two propelling units, viz. the third propelling unit 30 or propelling units 10 and 20. This possibility, which can be used for instance when the tugboat 1 travels in even throat or zero trim condition, provides a saving of fuel and reduced wear.

The three propelling units can jointly develop a thrust greater than the thrust that can be produced by two propelling units at an equal draft. It is equally possible to realize a greater total thrust while the three propelling units are individually chosen to be narrower than the individual propelling units of the conventional tugboat, the draft of the tugboat can be reduced as well.

It will be understood by anyone skilled in the art that changes and modifications of the embodiment described are possible, which fall within the framework of the present invention and within the protective scope of the claims. For instance, incorporation tug boat according to the present invention can be provided with another number of propelling units, for example two or four. It is also possible that one or several, for instance the third one, or the propelling units are retractably mounted, enabling a propelling unit that is not being used to be retracted to a position within the profile of the bottom of the boat. As a result, the resistance during traveling will be reduced, which means a saving of fuel.

The position of the propelling units can be reversed, i.e. one unit 5 at the front and two units at the rear irrespective of the towing points 8 on bow 7 and star 6.

Claims (15)

Conclusions A tugboat (1) comprising at least three azimutal propulsion units of which there are at least two juxtaposed propulsion units (10, 20), characterized in that each of the juxtaposed propulsion units (10, 20) has a main shaft (14) has with a major axis (11, 21) 5 which extends at an angle (a and / or 6) with respect to a main plane of symmetry (2) and / or with respect to a transverse center plane (5) of the tugboat. A tugboat according to claim 1, wherein the main shafts (14) of the two adjacent propulsion units (10, 20) are main shafts (11, 21) 10 with an inclination defined by said angle or angles (a and / or 6) mirrored with respect to the main symmetry plane (2) of the tugboat (1). A tugboat according to claim 1 or 2, wherein the main shafts (14) of the two adjacent propulsion units (10, 20) are main axes (11, 21) which are inclined and lie essentially in a plane (V - V) parallel to the transverse center plane (5). A tugboat according to any one of claims 1 or 2, wherein the main shafts (14) of the two adjacent propulsion units (10, 20) have main axes (11, 21) that are angled with respect to 20 of the transverse center plane (5) and with respect to the main plane of symmetry (2). A tugboat according to any one of the preceding claims, wherein the tugboat (1) has a third azimutal propulsion unit (30) at a length position (L ^ SO) different from the length positions (L10, L20) of 25 said two adjacent azimutal propulsion units (10, 20). A tugboat according to claim 5, wherein the third azimutal propulsion unit (30) is arranged at a longitudinal position (L30) which is positioned before or equal to the longitudinal position (L8) of the towing point or the rear towing point (8), respectively the tugboat (1). 5 A tugboat according to any one of claims 5 or 6, wherein the third azimuthal propulsion unit (30) has a main shaft (14) with a main shaft (31) that is angled (γ) with respect to the main symmetry plane ( 2), wherein the angle (γ) is between 1 and 15 degrees, such as for example between 1 and 10 degrees, for example between 2 and 10 degrees, 10 such as but not limited to between 2 and 8 degrees. A tugboat according to any one of the preceding claims, wherein the propulsion units (10, 20) placed next to each other each have a main shaft (14) with a main shaft (11, 21) extending under: an angle (a) with respect to the main plane of symmetry (2) of the tugboat (1), wherein the angle (a) is between 1 and 15 degrees, such as for example between 1 and 10 degrees, for example between 2 and 10 degrees, such as but not limited to between 2 and 8 degrees; and / or an angle (6) with respect to the transverse center plane (5) of the tugboat (1), the angle (6) being between 1 and 15 degrees, such as For example between 1 and 10 degrees, for example between 2 and 10 degrees, such as but not limited to between 2 and 8 degrees. A tugboat according to any one of the preceding claims, wherein at least one and preferably each propulsion unit (10, 20, 30) is mounted on a hull (18) of the tugboat (1) via a bowl or tube (17) in 25 extends the hull (18). A tugboat according to claim 9, wherein said bowl or tube comprises a circumferential wall which extends around a part of the main shaft (14) and / or main shaft (11, 21, 31) of a propulsion unit (10, 20, 30), the underside of the circumferential wall being mounted on or on an inclined surface portion (18A) of the hull (18), preferably such that said circumferential wall is substantially cylindrical or truncated cone-shaped and has a center axis that is substantially parallel to and preferably 5 coincides with the major axis (11, 21, 31) of the relevant propulsion unit (10, 20, 30). A tugboat according to any one of the preceding claims, wherein the hull (18) of the boat is provided with a recess or recess (9A) such that a propeller (12) or propeller nozzle is in the immediate vicinity of or 10 partially extends into said recess or recess (9A). A tugboat according to any one of the preceding claims, wherein each propulsion unit (10, 20, 30) has a main thrust direction, which is preferably directed parallel to the direction of the main shaft (11, 21, 31), the adjacent propulsion units (10, 20, 30) placed together such that 15 are mounted that when their main thrust directions are directed in the same direction in plan view and substantially intersect, the main thrust direction of a first of the two adjacent propulsion units is directed under the main thrust direction of the second of the two adjacent propulsion 20 units (10, 20). A tugboat according to any one of the preceding claims, wherein at least for the propulsion units (10, 20) placed next to each other the main axis (11, 21) crosses the hull, viewed in front or rear view, at substantially right angle. 25 A tugboat according to any one of the preceding claims, wherein a separate drive motor is associated with each propulsion unit (10, 20, 30), the tugboat further comprising a fire extinguishing installation with one extinguishing pump that can be connected to one of the three drive motors mentioned, preferably the drive motor associated with the third propulsion unit (30). A tugboat according to any one of the preceding claims 1-14, wherein with each propulsion unit (10, 20, 30) a separate drive motor 5 is associated, wherein the tugboat further comprises a fire extinguishing installation with two fire pumps that can be connected to two of said three drive motors, preferably the drive motors associated with said two juxtaposed propulsion units (10, 20), and wherein a maximum of one drive motor is provided with a 10 slip coupling between said drive motor and the associated propulsion unit. 1/6 101