Note: Descriptions are shown in the official language in which they were submitted.
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Vessel
The present invention relates to a vessel, especially a tug vessel, comprising
a towing device
and a hull, wherein the towing device comprises: a towline; a tow point where
the vessel
exerts a force, especially a horizontal force, onto the towline when applying
a tensile force to
an object by means of the towline, the tow point being provided on the vessel;
and a first
propulsion system and a second propulsion system.
Such a vessel is known from NL-1,023,447. Figure 2 of NL-1,023,447 shows a tug
vessel with a towing device. The towing device (30) is arranged in the mid
section of the
vessel and consists of a circular guiding ring (31, 32), a towline (22) and a
towing hook (33)
where the towline applies force onto the vessel when applying a tensile force
to a towed
object by means of the towline. The towing hook (33) is mounted on the guiding
ring (31, 32)
and moveable along the guiding ring. As can be seen in figure 2d, the vessel
has two
propulsions systems in the form of conventional fixed screws. Both propulsion
systems are
arranged at the stern part of the vessel. According to NL-1,023,447 it is
anticipated ¨ see
page 4 lines 31-34 - that these screw propulsions can be of the type having
screw blades
adjustable with respect to the fixed screw shaft so that they are continuously
adjustable from
forward to backward propulsion. Further NL-1,023,447 mentions ¨ see page 8
line 10-11 ¨
that also other propulsion systems like Voith Schneider propulsions can be
used.
When it is required to exert maximum force on a towed object both propulsions
of the
vessel of NL-1,023,447 are required and are ¨ both - directed in a direction
essentially
parallel to the length direction of the vessel so that the vessel has maximum
stability against
capsizing. In case both propulsions would be directed in a same direction
essentially
transverse to the vessel of NL-1,023,447, this automatically results in
turning of the vessel
around the towing point or centre of mass of the vessel so that this situation
can not be
maintained. When towing in transverse direction of the vessel, the propulsions
of NL-
1,023,447 will be directed in different directions so that one on the
propulsions is actually
pulling and the other is directed in opposite direction to prevent rotation of
the vessel around
the towing point/centre of mass of the vessel.
The present invention has as its object to improve the vessel according to the
preamble of claim 1.
This object is according to the invention achieved by providing a vessel
comprising a
towing device and a hull, wherein the towing device comprises:
= a towline;
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= a tow point ¨ such as a fairlead, a bitt, or a tow hook ¨ where the
vessel exerts a force,
especially a horizontal force, onto the towline when applying a tensile force
to an object
by means of the towline, the tow point being provided on the vessel;
= a first propulsion system and a second propulsion system;
characterized, in that the first propulsion system and second propulsion
system each
comprise an omni-directional propulsion device; and in that, viewed in
longitudinal direction
of the vessel, the tow point is arranged in between the first omni-
directional propulsion
device and the second omni-directional propulsion device.
It is to be noted, that the vessel according to the invention can be used for
tugging ¨
in which case the vessel is, viewed in transport direction of the towed
object, ahead of the
object ¨ as well as for assisting in manoeuvring an object ¨ in which case the
vessel might,
viewed in transport direction of the towed object, behind the towed object.
Further, the term
'omni-directional propulsion device' is in the field of vessel propulsion a
well defined term.
This term stands for a propulsion device which can be adjusted for providing
thrust in any
desired direction within a range of 360 around a central axis. Well known
examples of such
'omni-directional propulsion device' are so called "Voith-Schneider"
propulsion devices and
so called "azimuthal" propulsion devices. The term tow point is well known
from tug vessels.
It is the point where the vessel, when attached to a towed object and during
towing, exerts
onto the towline effectively the horizontal force which is about equal to the
horizontal
component of the tensile force of the towline. It is noted that this does not
mean that the
towline (also called towing cable) extends horizontally. Although the
towed/assisted object,
which is in general a vessel (but in this application called an object), as
well as the tug (in this
application called a vessel) will obviously move in a horizontal plane, the
towline is hardly
ever horizontal, in particular when assisting vessels in port. Towline angles
are then typically
20-45 degrees.
The configuration according to the invention has two omni-directional
propulsion
devices with in between the towing point and/or the centre of buoyancy of the
vessel. This
allows both omni-directional propulsion devices being used simultaneously for
propulsion in
the same direction irrespective of the position of the vessel with respect to
the extension
direction of the towline. Consequently the maximum available propulsion power
can also be
used when the towline extends transverse to the length direction of the
vessel. The two
omni-directional propulsion devices being provided at opposed sides of the
towing point
and/or centre of buoyancy of the vessel, prevents the length axis of the
vessel from rotating
with respect to the towline. This improves the manoeuvrability of the vessel
and improves the
ability of the vessel in assisting in manoeuvring an object as especially in
this case the
transverse orientation of the vessel with respect to the towline is
advantageous. When the
vessel is transverse to the towline and the object pulls the vessel as the
vessel is, viewed in
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transport direction of the towed object, behind the towed object, a
transversely oriented
vessel will experience a much larger resistance from the water than a vessel
having its
length direction in the same direction as the direction of extension of the
towline.
According to a further embodiment of the invention, the first and second omni-
directional propulsion device are provided in the vertical longitudinal
sectional plane of the
vessel. This means that the first and second omni-directional propulsion
devices are each
provided in or close to (which means within 10% of the width of the vessel)
the vertical
longitudinal sectional plane of the vessel. This arrangement allows for a
slender hull with
fine entrances at bow and stern. The slender hull will be more energy
efficient, have better
seakeeping characteristics and can reach higher speeds than a wider hull.
According to a further embodiment of the invention, the tow point is provided
in the
vertical longitudinal sectional plane of the vessel. This means that the tow
point is provided in
or close to (which means within 20% of the width of the vessel) the vertical
longitudinal
sectional plane of the vessel. This arrangement allows the towline and towing
winch being
stored in the centre of the vessel, which is advantageous with respect to the
weight
distribution of the vessel.
In order to improve the stability of the vessel and, as a result, to improve
towage
performance, the hull comprises, according to a further embodiment: a main
hull; and a left
and right side hull provided at the left respectively right longitudinal side
of the main hull;
wherein the side hulls are arranged for providing additional buoyancy
counteracting
capsizing and/or wherein the side hulls are arranged to increase stability,
and as a result also
maximum towing forces, without requiring (substantial) increase of water
displacement. Such
side hulls can be of basically two types. The first type of side hull is the
so called sponson
type. A sponson is a bulge formed onto the main hull. With the sponson type,
there is no gap
between the main hull and side hull through which water could flow. In case
the side hulls are
of the sponson type, the main hull and side hulls form so to say one integral
hull. The second
type of side hull is the so called outrigger type. An outrigger is sometimes
also called an
`arna' (plural `amas'). In case of two side hulls of the outrigger type, this
results in a kind of
trimaran. An outrigger is a floating body carried by one or more carriers,
like beams or other
structures, at a distance from the main hull so that, between the main hull
and side hull a gap
results through which water can flow. The advantage of applying a side hull of
the outrigger
type is that a high degree of stability can be obtained with a narrow main
hull of low
displacement (when compared with typical mono-hull type tugs of similar
stability and towage
performance). Furthermore, propulsion efficiency, indirect towage performance
and course
stability are increased. The advantages of a side hull of the sponson type
(when compared
woth normal `monohull' tugs) are essentially the same as those of the
outrigger type,
although their effectiveness is less pronounced.
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For improved stability against capsizing, the draught of the main hull is,
according to a
further embodiment of the invention, larger than the draught of the side
hulls. According to a
further elaboration of this embodiment, the draught of the side hulls is
larger than zero, such
as 5 to 10 % of the draught if the main hull.
In order to ensure that the side hulls become effective at relative small
heeling of the
vessel, the draught of the main hull is, according to a further embodiment of
the invention, at
least 25%, especially at least 50%, larger than the draught of the side hulls.
In order to provide, on the one hand, low water resistance when the vessel
runs at
cruising speed without towing an object and to provide, on the other hand,
good stability
against capsizing when towing an object with a towline extending transversely
to the vessel,
the water displacement of the side hulls is according to a further embodiment,
when the
vessel is in horizontal condition, at most 20% of the total water displacement
of the vessel,
especially at most 15% of the total water displacement of the vessel, such as
at most 12% or
at most 10% of the total water displacement of the vessel. The term
'horizontal condition of
the vessel' means the condition in which the heeling is zero degrees.
In order to increase lateral resistance and towline forces of the vessel in
transverse
direction under influence of a towing load and to improve course stability of
the vessel, the
hull, especially the main hull, is according to a further embodiment of the
invention, provided
with at least one keel. According to a further elaboration of this embodiment
of the invention,
the hull, especially the main hull, is provided with two keels which are
mutually parallel. In
order to avoid dry dock structures when the vessel is on shore, the two keels
have, according
to a further embodiment of the invention, a draught larger than or equal to
the draught of the
first and second omni-directional propulsion device and are arranged to
support the vessel
onto the keels when on shore. This arrangement allows placing the vessel
directly on shore
without damaging the omni-directional propulsion devices.
According to a further embodiment of the invention, the first and second
propulsion
system are arranged to provide the vessel a continuous bollard pull of at
least 300 kN (7--. 30 t
BP), preferably at least 450 kN (7--. 45 t BP), such as at least 650 kN (7--.
65 t BP).
According to a further embodiment of the invention, said continuous bollard
pull is at
most 1500 kN (-=-: 150 t BP).
Unlike in ground vehicles, the statement of installed horsepower is not
sufficient to
understand how strong a tug vessel is. This because other factors, like
transmission losses,
propulsion type, efficiency of the propulsion system, have an influence as
well. Therefore, in
the field of tug vessels bollard pull values (BP) are used. In general these
values are stated
in tons. The bollard pull value represents the maximum pulling force that a
vessel can exert
on another vessel or object. The bollard pull values as used in this
application are so called
continuous bollard pull values (sometimes also called steady or sustained
bollard pull
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values). These are determined by practical trial in still water having a depth
of at least 20 m.
The vessel is connected by a cable to the fixed world, for example a bollard,
and a load cell
(dynamometer) provided in or on the cable measures the tensile force in the
cable at
maximum thrust of the vessel. The (continuous) bollard pull value is the
tensile force which
can be measured during a period of 5 to 10 minutes after the initial peak
value has
disappeared. Various test procedures to determine bollard pull are in
existence. For
reference, the procedures as described by the major Classification Societies
can be utilized (
Rules for Building and Classing Steel Vessels under 90 meters, American Bureau
of
Shipping, Part 5, Chapter 8, Appendix 2, Guidelines for Bollard Pull tests;
or, Rules for Ships,
Det Norske Veritas, Part 5, Chapter 7, Section 2, Appendix A, Bollard Pull
testing Procedure
or Bollard Pull Certification Procedures, Lloyd's Register of Shipping,
Guidance Information).
According to a further embodiment of the invention, the first and second
propulsion
system are arranged for providing equal propulsion forces when operated at
maximum
power. Taking into account that according to the invention the first and
second propulsion
system can, under all towing conditions, be operated to provide propulsion in
the same
direction, this means that the towing vessel can exert maximum pushing and
pulling forces in
all directions (i.e. 360 degrees in horizontal plane). For example, when
pushing sideways
against an object, full bollard pull force is available. While the fender
contact area sideways
is large, the chances of damage to the object are reduced when pushing
sideways. Also,
when assisting objects 'under way' the propulsion forces can at all times be
directed in the
ideal direction, thereby maximizing towline forces and/or increasing fuel
economy.
According to a further embodiment of the invention, the vessel comprises a
further
propulsion, which further propulsion has a maximum power of at most 30%, such
as at most
20%, of the sum of the maximum power of the first propulsion system and second
propulsion
system. In mathematical form this means:
"Maximum power of further propulsion 0.3 x (maximum power of first propulsion
system +
maximum power of second propulsion system)".
For example, as envisaged by the inventor, the further propulsion can consist
of a left and
right propulsion unit, each having a maximum power of 170 kW, i.e. the further
propulsion
has a maximum power of 2x170 kW. The first and second propulsion system can
each have
a power of 2000 kW, i.e. the sum of their maximum powers is 4000 kW. In this
example the
maximum power of the further propulsion thus is 8,5% of the sum of the maximum
power of
the first and second propulsion system.
This further propulsion is primarily intended for cruising operation (such as
transits,
mobilizations) and standby without towing any object. This configuration
allows the further
propulsion being used during cruising whilst the first and second propulsion
system, which
are primarily intended for towing operation of the vessel, can be turned off.
Realizing that the
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first and second propulsion system are primarily designed for towing operation
and that their
propulsion power is for cruising operation far oversized, it will be clear
that the energy
efficiency of the first and second propulsion system will be very low
(inefficient) with respect
to a further propulsion which is primarily designed for cruising operation.
This configuration
thus allows very efficient usage of fuels. According to a further elaboration
of this
embodiment, the further propulsion is arranged for driving a generator and/or
for driving one
or more towing winches directly or indirectly via for example a generator
generating electric
power for operating said winch and optionally providing electric power for
other systems as
well.
According to a further embodiment of the invention, the further propulsion
comprises
2 propulsion elements, which are both provided at the same distance from the
stern of the
vessel and at opposing sides of the vertical longitudinal sectional plane of
the vessel. This
allows arrangement of the further propulsion system without hindering the
first and second
propulsion systems in their operation, allows for easy manoeuvring of the
vessel and ensures
good water flow to the propulsion elements.
Vessel according to one of the preceding clauses, wherein the vessel is
provided with
a so called articulated barge coupling system. So called articulated barge
couplings are
known from the prior art, also in relation to vessels. Such couplings are
intended for coupling
a vessel to a barge which is to be manipulated by the vessel.
According to a further embodiment of the invention, the towline extends from
the tow
point to the object to which the towline is attached. According to a further
aspect of the
invention, the invention also relates to an assembly of a vessel according to
the invention
and an object, the towline extends from the tow point to the object to which
the towline is
attached.
According to a further embodiment of the invention, the tow point is, measured
from
the stern of the vessel, provided at a distance of 20% to 50 % of the length
of the vessel,
preferably at a distance of 30% to 50% of the length of the vessel, more
preferably at a
distance of about 40% to 45% of the length of the vessel. This means that the
tow point is
arranged close to the rotating point of the under water body of the vessel.
This allows easy
positioning of the vessel with respect to the towline.
According to the invention, the tow point can be formed by a bitt or a tow
hook, which
both actually attach the towline to the vessel at the location of the tow
point.
According to a further embodiment of the invention, the towing device further
comprises a fairlead for guiding the towline, wherein the fairlead forms the
tow point. This
allows the towline to be attached to the vessel in another more practical
location.
According to another further embodiment of the invention, the towing device
further
comprises: a towing winch mounted on the vessel for winding and unwinding the
towline; and
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a fairlead for guiding the towline towards the towing winch. Here the fairlead
provides
guidance for the towline in order to ensure it is properly received on the
winch. The winch
allows the length of the tow part of the towline to be adjusted depending from
circumstances.
According to a further embodiment of the invention, the towing winch is
provided at
the vertical longitudinal sectional plane of the vessel. This provides a
symmetric weight
distribution over the vessel.
According to a further embodiment of the invention, the towing winch is,
measured
from the stern of the vessel, provided at a distance of 20% to 60 % of the
length of the
vessel, preferably provided at a distance of 30% to 60 % of the length of the
vessel, more
preferably at a distance of about 40% to 50% of the length of the vessel. This
provides a
symmetric weight distribution over the vessel.
According to a further embodiment of the invention, the vessel is a tug
vessel.
According to a further embodiment of the invention, the towing device further
comprises a, guiding arc mounted on the vessel, wherein, viewed in vertical
direction, the
guiding arc is provided above the deck and wherein the guiding arc extends
along the deck,
which guiding arc is arranged for guiding the towline along the deck while
swinging the
vessel with respect to the towline while applying a tensile force to an
object. This guiding arc
allows the towline to swivel with respect to the vessel. Although this guiding
arc can be in
accordance with known prior art like disclosed in NL-1,023,447, it is
according to this
invention preferred to arrange this guiding arc in accordance with the non-
published earlier
NL-application NL-2003746, titled 'vessel' and filed on November 3, 2009 in
the name of
'Bald Dielen Assessoria LTDA', Brasil. All teaching of the guiding arc in NL-
2003746 is
hereby incorporated by reference.
Below, the invention will be further explained with reference to the drawings.
These
drawings are all of schematic nature. In these drawings:
Figure 1 shows a first embodiment of the invention in a perspective view;
Figure 2 shows a second embodiment of the invention in a perspective view from
above;
Figure 3 shows the second embodiment of figure 2 in a perspective view from
below;
Figure 4 shows the second embodiment of figures 2 and 3 in a bottom view;
Figure 5 shows a third embodiment of the invention in a bottom view;
Figure 6 shows a fourth embodiment of the invention in a bottom view;
Figure 7 shows a fifth embodiment of the invention in a perspective view from
below;
Figure 8 shows the fifth embodiment of figure 7 in a perspective view from
above,
when used for pushing or pulling a barge;
Figure 9 shows a side view of figure 8;
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Figure 10 shows a schematic diagram of the effective pulling force of various
types of
vessels;
Figure 11 shows schematically the forces during indirect towing of a prior art
vessel
(Fig. 11A) and of a vessel according to the invention (Fig. 11 B); and
Figure 12 shows schematically a prior art vessel (Fig. 12A) and a vessel
according to
the invention (Fig. 12B) during assisting a vessel object in a channel.
In the description below, different embodiments of the vessel are indicated by
different reference numbers, but same or similar parts of these embodiments
are indicated
with the same reference number or sign.
Figure 1 shows a first embodiment 10 of the vessel according to the invention.
The
vessel 10 comprises a main hull 61 (without side hulls as are present in the
other
embodiments). The main hull 61 has a length direction L and a transverse
direction T (see
figure 2) extending horizontally, transverse to the longitudinal direction. On
the deck 84 there
is indicated an imaginary longitudinally deck centre line 81 extending in
longitudinal direction
and defining the longitudinally centre of the deck. The so called 'vertical
longitudinal sectional
plane' of the vessel is defined by the longitudinally deck centre line 81 and
a vertical through
the longitudinally deck centre line 81.
The vessel 10 further comprises two omni-directional propulsion devices 71 and
72,
which in all shown embodiments 10, 20, 30, 40, 50 are a so called azimuthal
propulsion
device. It is however noted that in all embodiments of the invention, the omni-
directional
propulsion device can also be of a different type, like a Voith-Schneider
propulsion device. A
characteristic of a omni-directional propulsion device is that the direction
of the thrusting
force generated by the omni-directional propulsion device can be adjusted to
be directed in
any desired direction essentially perpendicular to the vertical axis 85 as
indicated in figure 1,
i.e. the propulsion direction can be rotated (as indicated with arrow R in
figure 4) around a
vertical axis 85. In case of a azimuthal propulsion device, the thrusting
propeller (which
rotates around a horizontal axis for thrusting action) is actually rotated
around the vertical
axis 85. As will be realized, it is for the invention not required that the
vertical axis 85 extends
exactly vertical.
The vessel according to the invention further has a so called towing point 65
defining
the position where the towline 64 acts in horizontal direction on the vessel.
According to the
invention, this towing point 65 is positioned, viewed in longitudinal
direction of the vessel 10,
in between the first omni-directional propulsion device 71 (further called
ODPD) and the
second ODPD 72. As follows from figure 1, it is not required that the towing
point 65 is
arranged at the same vertical height as the ODPDs 71 and 72. In general the
towing point 65
will, viewed in vertical direction, be arranged higher than the ODPDs 71, 72.
Although it is
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preferred that both the ODPDs 71, 72 as well as the towing point are arranged
in the vertical
longitudinal sectional plane (as shown in all figures), it is not required
that these are all
arranged in the vertical longitudinal sectional plane, neither is it required
that these are
arranged in one plane parallel to the vertical longitudinal sectional plane.
It is for example
very well conceivable that the towing point as arranged at a side of the main
hull, whilst the
ODPDs 71 and 72 are arranged in or around the vertical longitudinal sectional
plane.
Figures 2-4 show a second embodiment 20 of the vessel according to the
invention.
The main differences between the vessel 20 and 10 are the following:
= on deck 84 of the main hull 61 there is provided a guiding arc 69 for
guiding the towline
64 so that it can rotate around the tow point 65. For details and advantages
of this
guiding arc 69, reference is made to the earlier mentioned NL-2003746 of
applicant,
which is fully incorporated into this application by reference. As will be
understood, this
guiding arc 69 can also be applied with the embodiment 10 of figure 1.
Further, it is to be
noted that it is also conceivable to leave this guiding arc away from the
embodiment 20
as well as from the embodiments 30, 40, 50 (to be discussed below);
= The vessel 20 provided with two side hulls 62 in the form of so called
outriggers 62.
These outriggers 62 are carried by transverse carriers 75 (see figure 4) so
that there is a
gap 86 between the main hull 61 and side hulls 62. When in water, water can
pass
through this gap 86. Above water level, the gap might be closed, for example
by the
carrier.
= The vessel 20 is provided with two keels 66 on the main hull 61. As will
be clear also
embodiment 10 could be provided with two keel (or one keel arranged centrally,
like in
embodiment 30 and 40, to e discussed below). Further it will be clear that
also more
keels as well as one keel or no keel are conceivable with the embodiment 20
(as well as
with the other embodiments 30, 40, 50 to be discussed below).
= The vessel 20 is provided with a further propulsion 73 consisting of two
propulsion
elements 74, each provided on one side of the vessel. These serve for
thrusting the
vessel during transit (i.e. when no load is towed). As will e clear also
embodiment 10 can
e provided with such an additional propulsion. Further it will be clear that
the additional
propulsion 73, 74 can also be left away from the embodiment 20 as well as the
other
embodiments 30, 40 and 50 (discussed below).
In figure 2, reference number 82 indicates the water line of the main hull 61
and
reference number 83 indicates the water line of the side hull 62. It can be
seen that the
draught D1 of the main hull is larger than the draught D2 of the side hull 62.
In this
embodiment the draught D1 is about 150% of the draught D2, i.e. 1.5 times
larger. Further it
can be seen that the draught D4 of the keels 66 is larger than the draught D3
of the ODPDs
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71, 72, so that when on shore the vessel 20 can stand on the keels 66 without
damaging the
ODPDs 71, 72.
Figure 5 shows a third embodiment 30 of the vessel according to the invention.
The
main differences between the vessel 30 and vessel 20 is that vessel 30 has
only one central
keel 66 whilst vessel 20 has two keels 66 spaced apart. As will e clear, the
vessel 30 can in
addition be provided with two keels 66 spaced apart, like shown in figures 2-
4. Further all
remarks made in relation to vessel 10 concerning leaving away parts of the
vessel, apply to
the third embodiment 30 as well.
Figure 6 shows a fourth embodiment 40 of the vessel according to the
invention. The
main differences between the vessel 40 and vessel 30 is that vessel 40 has
side hulls in the
form of so called sponsons 63, whilst vessel 30 has side hulls in the form of
so called
outriggers 62. Each sponson 63 is formed onto and against a side of main hull
61 so that
there no gap between the sponson 63 and main hull 61. As will be clear, the
remarks
concerning leaving away of the vessel 20 or vessel 30 (as well as concerning
adding parts to
said vessels 20, 30) apply to vessel 40 as well.
Figure 7 shows a fifth embodiment 50 of the vessel according to the invention.
The
main differences between the vessel 50 and vessel 40 is that vessel 50 has two
keels whilst
vessel 40 has one keel. As will be clear, the remarks concerning leaving away
parts of the
vessel 20 or vessel 30 or vessel 40 (as well as concerning adding parts to
said vessels 20,
30, 49) apply to vessel 50 as well.
Figures 8 and 9 show an assembly of, one the one hand, a vessel 50 provided
with a
so called articulated barge coupling system and, on the other hand, a barge
70. As will be
clear the vessel 50 can be replaced by any other vessel 10, 20, 30 or 40.
Figures 10-12 give an impression of the advantages of the vessel according to
the
invention over prior art tug vessels.
Figure 10 shows a schematic diagram of the effective pulling force of various
types of
vessels. Reference number 90 indicates schematically the positioning of the
vessel; graph
91a indicates the effective pulling force of a Voith-Schneider tug having two
Voith-Schneider
devices arranged in the stern part of the vessel (like the configuration of
the vessel 100
shown in figures 11A and 12A); graph 91b indicates the effective pulling force
of an ASD tug
(ASD=Azimuthal Stern Drive) as indicated with 100 in figures 11A and 12A;
graph 91c
indicates the effective pulling force of a so called tractor tug; and graph 92
indicates the
effective pulling force of a vessel according to the invention.
In the diagram of figure 10, it is assumed that all vessels have the same
installed
power of 100 ppu (=propulsion power unit). Taking into account Voith-Schneider
devices
have a lower efficiency, the graph 91a for a Voith-Schneider tug shows
considerable lower
values (a maximum of 75 ppu against a maximum of about 100 ppu for the
others).
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Assuming the vessel is, in figure 10, oriented with its back (stern) facing to
the left, its front
facing to the right, its left side (port side) facing upwards and its right
side (starboard side)
facing downwards, the towline is rotated over 360 around the vertical through
the tow point
and the bollard pull force is determined for each rotation angle. As one can
see from graph
92, the bollard pull force of a vessel according to the invention is about 100
in all directions
(circular graph 92). However, the bollard pull force for the prior art vessels
decreases very
considerable when the towline is rotated from a direction parallel to the
length direction of the
vessel towards a direction perpendicular to the length direction of the
vessel, see the about
perpendicular/oval graphs 91a, 91b and 91c. The advantages of the vessel
according to the
invention over the prior art vessels, are evident and speak for them selves.
Figure 11 shows schematically the forces during indirect towing of a prior art
vessel
(Fig. 11A) and of a vessel according to the invention (Fig. 11B). Indirect
towing means that,
viewed in the direction X in which the towed vessel object 60 moves, the
towing vessel 100
(an ASD tug according to the prior art) or 50 (according to the invention) is
behind the towed
vessel object 60 in order to keep the towed vessel object 60 in its course by
exerting pulling
forces on the stern of the towed vessel object 60. The prior art towing vessel
100 and
invented towing vessel 50 are compared under similar circumstances. The angle
13 between
the length direction of the towing vessel 50, 100 and the direction of
movement X of the
towed vessel object 60 is in both cases the same. Further the angle y between
the towline
and the line perpendicular to the length direction of the towed vessel object
60 is in both
cases the same. Also the maximum bollard pull force of the towing vessels 50,
100 is the
same (for the ASD tug 100 this maximum bollard pull force is in the length
direction of the
ASD tug 100), i.e. both towing vessels 50, 100 have comparable power. As
follows clearly
from comparison of figures 11A and 11B, the invented towing vessel can exert a
considerable larger towing force FT on the towline than the prior art ASD tug.
This appears to
be due to the fact that the thrusting forces P1 and P2 of the MDPDs 71 and 72
of the
invented towing vessel are directed essentially transverse to the direction X
of movement of
the towed vessel object 60, whilst the thrusting forces P1 and P2 of the MDPDs
171 and 172
of the ASD tug 100 are directed essentially in the direction X of movement of
the towed
vessel object 60. The advantages of the vessel according to the invention over
the prior art
vessels, are evident and speak for them selves.
Figure 12 shows schematically a prior art vessel (Fig. 12A) and a vessel
according to
the invention (Fig. 12B) during assisting a vessel object in a channel. As
follows clearly from
comparison of figures 12A and 12B, the invented towing vessel 50 requires in
case of towing
action in transverse directions much less space than a prior art ASD tug 100.
This means
that the invented towing vessel 50 can assist a towed vessel object through
much smaller
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channels (the bank of which is indicated with 101) than a prior art ASD tug
vessel 100.
Evidently this is also advantageous in crowded waters.
Although a vessel 50 is shown in figures 11B and 12B, it will be clear that
this vessel
50 can be replaced by any other embodiment of a vessel according to the
invention, like a
vessel 10, 20, 30 or 40.
The invention can be further described by the next following clauses:
1] Vessel (10, 20, 30, 40, 50) comprising a towing device and a hull
(61, 62, 63) ,
wherein the towing device comprises:
= a towline (64);
= a tow point (65)- such as a fairlead, a bitt, or a tow hook - where the
vessel (10, 20, 30,
40, 50) exerts a force, especially a horizontal force, onto the towline (64)
when applying a
tensile force to an object (60) by means of the towline (64), the tow point
(65) being
provided on the vessel;
= a first propulsion system (71) and a second propulsion system (72);
characterized, in that the first propulsion system and second propulsion
system each
comprise an omni-directional propulsion device (71, 72); and in that, viewed
in longitudinal
direction of the vessel, the tow point (65) is arranged between the first omni-
directional
propulsion device (71) and the second omni-directional propulsion device (72).
2] Vessel (10, 20, 30, 40, 50) according to clause 1, wherein the first and
second omni-
directional propulsion device (71, 72) are provided in the vertical
longitudinal sectional plane
of the vessel.
3] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
tow point (65) is provided in the vertical longitudinal sectional plane of the
vessel.
4] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein each
omni-directional propulsion device (71, 72) comprises one chosen from the
group: a Voith-
Schneider propulsion device or an azimuthal propulsion device.
5] Vessel (20, 30, 40, 50) according to one of the preceding clauses,
wherein the hull
comprises:
= a main hull (61); and
= a left and right side hull (62, 63) provided at the left respectively right
longitudinal side of
the main hull (61).
6] Vessel (20, 30, 40, 50) according to clause 5, wherein the draught (D1)
of the main
hull (61) is larger than the draught (D2) of the side hulls (62, 63).
7] Vessel (20, 30, 40, 50) according to clause 6, wherein the draught (D1)
of the main
hull (61) is at least 25%, especially at least 50%, larger than the draught
(D2) of the side
hulls (62, 63).
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8] Vessel (20, 30, 40, 50) according to one of clauses 5-7, wherein, in
horizontal
condition of the vessel, the water displacement of the side hulls (62, 63) is
at most 20% of
the total water displacement of the vessel (20, 30, 40, 50), especially at
most 15% of the total
water displacement of the vessel, such as at most 12% or at most 10% of the
total water
displacement of the vessel.
9] Vessel (40, 50) according to one of clauses 5-8, wherein each side hull
comprises a
sponson (63) formed onto the main hull (61).
10] Vessel (20, 30) according to one of clauses 5-8, wherein each side hull
comprises an
outrigger (62) attached to the main hull (61) by one or more transverse
carriers (75).
11] Vessel (20, 30, 40, 50) according to one of the preceding clauses,
wherein the hull,
especially the main hull (61), is provided with at least one keel (66).
12] Vessel (20, 50) according to clause 11, wherein the hull, especially
the main hull (61),
is provided with two keels (66) which are mutually parallel.
13] Vessel (20, 50) according to clause 12, wherein the keels (66) have a
draught (D4)
larger than or equal to the draught (D3) of the first and second omni-
directional propulsion
device (71, 72) and are arranged to support the vessel (20, 50) onto the keels
(66) when on
shore.
14] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
first and second propulsion system (71, 72) are arranged to provide the vessel
a continuous
bollard pull of at least 300 kN (= 30 t BP), preferably at least 450 kN (= 45
t BP), such as at
least 650 kN (= 65 t BP).
15] Vessel (10, 20, 30, 40, 50) according to clause 14, wherein said
continuous bollard
pull is at most 1500 kN (= 150 t BP).
16] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
first and second propulsion system are arranged for providing essentially
equal propulsion
forces when operated at maximum power.
17] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
vessel comprises a further propulsion (73), which further propulsion (73) has
a maximum
power of at most 30%, such as at most 20%, of the sum of the maximum power of
the first
propulsion system (71) and second propulsion system (72).
18] Vessel (10, 20, 30, 40, 50) according to clause 17, wherein the further
propulsion (73)
is arranged for driving one or more towing winches and/or a generator
generating electric
power.
19] Vessel (10, 20, 30, 40, 50) according to clause 17 or 18, wherein the
further
propulsion (73) comprises 2 propulsion elements (74), which are both provided
at the same
distance from the stern (67) of the vessel and at opposing sides of the
vertical longitudinal
sectional plane of the vessel.
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20] Vessel (50) according to one of the preceding clauses, wherein the
vessel is provided
with an articulated barge coupling system (68).
21] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
towline (64) extends from the tow point (65) to the object (60) to which the
towline (64) is
attached.
22] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein,
measured from the stern of the vessel, the tow point (65) is provided at a
distance of 20% to
50 % of the length of the vessel, preferably at a distance of 30% to 50 % of
the length of the
vessel, more preferably at a distance of about 40% to 45% of the length of the
vessel.
23] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
towing device further comprises a fairlead for guiding the towline, and
wherein the fairlead
forms the tow point (65).
24] Vessel (10, 20, 30, 40, 50) according to one of the preceding
clauses, wherein the
towing device further comprises:
= a towing winch mounted on the vessel for winding and unwinding the towline;
and
= a fairlead for guiding the towline towards the towing winch.
25] Vessel (10, 20, 30, 40, 50) according to clause 24, wherein the towing
winch is
provided at the vertical longitudinal sectional plane of the vessel.
26] Vessel (10, 20, 30, 40, 50) according to one of clauses 24 - 25,
wherein, measured
from the stern (67) of the vessel, the towing winch is provided at a distance
of 20% to 60 %
of the length of the vessel, preferably provided at a distance of 30% to 60 %
of the length of
the vessel, more preferably at a distance of about 40% to 50% of the length of
the vessel.
27] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
vessel is a tug vessel.
28] Vessel (10, 20, 30, 40, 50) according to one of the preceding clauses,
wherein the
towing device further comprises a, guiding arc (69) mounted on the vessel,
wherein, viewed
in vertical direction, the guiding arc (69) is provided above the deck (84)
and wherein the
guiding arc (69) extends along the deck (84), which guiding arc (69) is
arranged for guiding
the towline (64) along the deck (84) when swinging the vessel with respect to
the towline
while applying a tensile force to an object.
It is to be noted that within the scope of the claims, many variants of the
invention are
conceivable. For example: the first propulsion system can according to the
invention also
comprise two (or more) of said first omni-directional propulsion devices,
which in case of two
of said first omni-directional propulsion devices could according to the
invention be arranged
symmetrically with respect to the vertical longitudinal sectional plane of the
vessel; and/or
the second propulsion system can according to the invention also comprise two
(or more) of
said second omni-directional propulsion devices, which in case of two of said
second omni-
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directional propulsion devices could according to the invention be arranged
symmetrically
with respect to the vertical longitudinal sectional plane of the vessel.
List of used reference numbers/signs
10 vessel
20 vessel
30 vessel
40 vessel
50 vessel
60 object
61 main hull
62 side hull of outrigger type/outrigger
63 side hull of sponson type/sponson
64 towline
65 tow point
66 keel
67 stern
68 articulated barge coupling system
69 guiding arc
70 barge
71 first propulsion system/first omni-directional
propulsion device (the aft
unit)
72 second propulsion system/ second omni-directional
propulsion device
(the forward unit)
73 further propulsion
74 propulsion element
75 transverse carrier
81 longitudinal deck centre line
82 water line of main hull
83 water line of side hull
84 deck
85 vertical rotation axis of omni-directional propulsion
device
86 gap
90 schematic representation of a tug vessel
91a-c effective pulling force of prior art vessels
92 effective pulling force of vessel according to the
invention
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100 prior art vessel
171 (first) propulsion system of prior art vessel
172 (second) propulsion system of prior art vessel
D1 draught of main hull
D2 draught of side hull
D3 draught of first/second propulsion device
D4 draught of keel
L longitudinal direction of vessel
P1 thrust direction of first propulsion device
P2 thrust direction of second propulsion device
R rotation of omni-directional propulsion device
T transverse direction of vessel
X direction of movement of towed object
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