Note: Descriptions are shown in the official language in which they were submitted.
WO 2021/170493
PCT/EP2021/054099
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A vessel
The present invention relates to a vessel comprising
a hull including a bow and a stern and having a length-to-beam
ratio which is smaller than 10:1, preferably smaller than 5:1,
wherein the hull has a vertical centre plane extending in a
direction from the bow to the stern.
Such a vessel is known, for example in the form of a
tug boat of which the length-to-beam ratio is about 3:1. A
typical known tug boat has two azimuth thrusters for
propelling and manoeuvring the tug boat, which azimuth
thrusters are located at either side of the centre plane. The
azimuth thrusters are drivably coupled to respective diesel
engines and can be operated by a helmsman, for example by
means of respective joysticks.
An object of the invention is to provide a highly
manoeuvrable vessel.
This object is achieved with the vessel according to
the invention, wherein at each side of the centre plane the
vessel has at least two azimuth thrusters including respective
propellers, which azimuth thrusters are located next to each
other in transverse direction of the centre plane and wherein
each azimuth thruster is drivably coupled to its own prime
mover. Hence, a row of at least four azimuth thrusters extends
in transverse direction of the hull. In practice, the same
number of azimuth thrusters will be located at both sides of
the centre plane.
Due to the relatively small length-to-beam ratio the
relatively wide beam provides the possibility to apply a
plurality of azimuth thrusters at each side of the centre
plane. For achieving a similar power level, an increasing
number of azimuth thrusters may have decreasing propeller
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diameters of the individual azimuth thrusters. Consequently,
the total height of the series of azimuth thrusters can be
kept relatively small.
The application of relatively small azimuth thrusters
also provides the opportunity to apply relatively small
cooperating prime movers. An advantage of relatively small
azimuth thrusters and prime movers is that their response time
is relatively short, which leads to improved manoeuvrability
of the vessel.
In a practical embodiment the azimuth thrusters are
aligned in transverse direction of the centre plane.
Distances between centrelines of the propellers of
each two neighbouring azimuth thrusters may be the same in
order to achieve a symmetric arrangement. The distance between
centrelines of the propellers of the neighbouring azimuth
thrusters which are located at either side of the central
plane, i.e. the two azimuth thrusters which are located
closest to the central plane, may be different from the
distance between the centrelines of the propellers of each two
neighbouring azimuth thrusters at each side of the centre
plane.
In a particular embodiment the propellers of the at
least two azimuth thrusters have different diameters. The
propeller of one of the at least two azimuth thrusters which
is located at a larger distance from the centre plane than the
other one of the at least two azimuth thrusters may have a
larger diameter than the propeller of the other one of the at
least two azimuth thrusters.
The azimuth thrusters may be located at the bow or at
the stern.
At least one of the prime movers may be an internal
combustion engine. The internal combustion engine may be a
diesel engine having a maximum speed above 1000 rpm. Such a
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diesel engines may be known as a high-speed diesel engine. If
the desired power per individual azimuth thruster is
relatively large such that a low-speed diesel engine must be
applied, it is in the spirit of the present invention
preferred to apply a higher number of relatively small azimuth
thrusters including high-speed diesel engines instead of
applying a smaller number of relatively large azimuth
thrusters including low-speed diesel engines.
The at least two azimuth thrusters and their prime
movers may be functionally coupled to a common controller for
operating the at least two azimuth thrusters simultaneously.
The common controller may be a joystick such that an operator
can operate two joysticks, one for simultaneously controlling
the at least two azimuth thrusters including their prime
movers at one side of the centre plane and one for
simultaneously controlling the at least two azimuth thrusters
including their prime movers at the other side of the centre
plane.
In a particular embodiment at each side of the centre
plane a skeg is mounted to a lower side of the hull, which
skeg extends in longitudinal direction of the hull, for
example from the bow to about halfway the hull. In this
embodiment the vessel has at least two skegs which may have a
relatively small height, which reduces draught of the vessel,
improves seakeeping behaviour and facilitates easy docking.
Furthermore, at least two skegs improve course stability and
manoeuvrability and allows relatively large steering forces
during escorting a large vessel.
The skeg may be located at a horizontal position
between axes of rotation of the respective propellers of the
at least two azimuth thrusters as seen in a direction from the
stern to the bow.
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Furthermore, the maximum height of the skeg may be
smaller than the diameter or 1.5 times the diameter of each of
the propellers of the respective azimuth thrusters, or even
smaller than 80% thereof.
The vessel may be a tug boat.
The invention will hereafter be elucidated with
reference to very schematic drawings showing embodiments of
the invention by way of example.
Fig. 1 is a side view of an embodiment of a vessel
according to the invention.
Fig. 2 is a plan view of a part of the vessel as
shown in Fig. 1 on a larger scale.
Fig. 3 is a rear view of the vessel as shown in Fig.
1 on a larger scale.
Fig. 4 is a similar view as Fig. 3, but showing an
alternative embodiment.
Figs. 1-3 show an embodiment of a vessel according to
the invention. The vessel is a tug boat 1, which has a hull 2
including a bow 3 and a stern 4. Such a tug boat 1 is
typically used as an escort tug, anchor handling tug, salvage
tug, oil recovery vessel, safety stand-by vessel or as ship
handling tug near offshore terminals and FPSOs (Floating
Production Storage and Offloading vessels). The tug boat 1 may
be used for assisting large ships which are much larger than
the tug boat 1. The tug boat 1 may be connected to the large
ship by a towing cable for towing the large ship in a specific
direction or the tug boat 1 is manoeuvred against the large
ship in order to be able to push it in a certain direction.
The hull 2 of the tug boat 1 as shown in Figs. 1-3
has a length of about 50 m and a beam of about 16 in, hence a
length-to-beam ratio of about 3. The hull 2 has a vertical
centre plane CP which extends in a direction from the bow 3 to
the stern 4, see Figs. 2 and 3. A central skeg 5 is mounted to
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a lower side of the hull 2. The central skeg 5 extends in
longitudinal direction of the hull 2 from the bow 3 to about
halfway the hull 2 at the centre plane CP.
The tug boat 1 is provided with a series of four
azimuth thrusters 6, which are arranged in an aligned row that
extends in transverse direction of the centre plane CP. The
azimuth thrusters 6 have respective propellers 6a which are
located below the hull 2, in this case at the stern 4. In an
alternative embodiment the azimuth thrusters 6 may be located
at the bow 3 or elsewhere in between.
The application of an azimuth thruster for propelling
a vessel is well-known, for example in ASD (azimuth-stern-
drive) tug boats. The entire propulsion unit can turn in the
horizontal plane and thrust can be produced in any desired
direction.
In the embodiment as shown in Figs. 1-3 at each side
of the centre plane two azimuth thrusters 6 are located next
to each other in transverse direction of the centre plane CP
and the azimuth thrusters 6 are drivably coupled to respective
prime movers in the form of high-speed diesel engines 7 via
respective propeller shafts 8. The high-speed diesel engines 7
are located within the hull 2 below a deck 9. The high-speed
diesel engines 7 provide a fast response when increased thrust
is desired.
Fig. 3 shows that the propellers 6a of the outer two
azimuth thrusters 6 have larger diameters than the propellers
6a of the inner two azimuth thrusters 6.
The pair of azimuth thrusters 6 and their prime
movers 7 at one side of the centre plane CP can be operated
simultaneously by a first joystick and the pair of azimuth
thrusters 6 and their prime movers 7 at the other side of the
centre plane CP can be operated simultaneously by a second
joystick.
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Fig. 4 shows an alternative embodiment, which
distinguishes from the embodiment as shown in Fig. 3 in that
two skegs 5a, 5b are mounted to a lower side of the hull 2.
The skegs 5 extend in longitudinal direction of the hull 2
from the bow 3 to about halfway the hull 2 at a distance from
the centre plane CP. As seen from behind of the hull 2, each
of the skegs 5a, 5b is located at a horizontal position
between axes of rotation of the propellers 6a of the
neighbouring azimuth thrusters 6. Due to the application of
two skegs 5a, 5b their dimensions in vertical direction are
relatively small, which creates a relatively small draught.
Hence, the combination of at least two relatively small
azimuth thrusters 6 and at least one skeg 5a, 5b at each side
of the centre plane CP allows a small draught and facilitates
docking, for example. The height of each of the skegs 5a, 5b
may vary along its longitudinal direction. The maximum height
may be smaller than the diameter or 1.5 times the diameter of
each of the propellers 6a.
The invention is not limited to the embodiments shown
in the drawings and described hereinbefore, which may be
varied in different manners within the scope of the claims and
their technical equivalents.
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