Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DIRECTIONAL BOW THRUSTER SYSTEM FOR SHIPS IN ICE LADEN WATERS
FIELD OF THE INVENTION
This invention relates to a directional bow thruster sys-
tem for ships in ice laden waters, said ships being equipped
with means for water lubrication of ice present in front of the
bow skin.
BACKGROUND OF THE INVENTION
Ships sailing in arctic waters, e.g. ice-breakers often
have a long stem sloping at an acute angle towards and past the
water line. This stem forms a proportionately flat surface
which may slide up on the ice edge in front of the ship, where-
in the ice will break at the edges of the channel by the aid of
the ships weight.
It is unfavorable to provide such a ship with normal bow
thrusters, on one hand because broken ice may harm the thruster
propellers, and on the other hand since the propeller instal-
lation, because of the long sloping stem, will be placed com-
paratively adjacent to the motion centre of the ship, and
therefore will have a proportionally small lever ratio.
Other known devices for improving maneuverability for
ships comprise directional thruster systems with water jets.
Those systems seldom risk to be harmed by occurring broken ice
in the water. However, also a conventional water jet system
will have to be placed comparatively close to the motion centre
of the ship (preferably at the ships side), resulting in an
unfavorable lever ratio. A further disadvantage with water jet
systems is that they may be the cause of ice covering when
parts of the jet stream blows back onto the ship. Such jet
streams emitted from side mounted thruster systems may cause
irritation when maneuverinq at a quay.
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One object of the invention is to provides an efficient and
reliable bow thruster system for ships in ice laden waters,
which system does not have the above mentioned disadvantages.
According to one aspect of this invention there is provided a
directional bow thruster apparatus for ships in ice-laden
waters, comprising first and second nozzles arranged in the
stem of the ship such that the nozzles being arranged to
expel fluid in directions substantially opposite to each
other and transverse to the centre line of the ship, supply
means for supplying to the nozzles either high pressure
fluid, in a first mode of operation, to manoeuvre the ship or
low pressure fluid, in a second mode of operation, to
lubricate the ice in front of the ship, and control means to
direct the high pressure fluid to one or both of the nozzles
during the first mode of operation of the supply means,
wherein the nozzles are mounted in a blunt, essentially flat
sloping part of the stem, are close to the water line and are
each comprising double conduits, connecting a common outlet
opening from opposite sides at an angle of about 3.
The preferred embodiment of the present invention therefore a
directional bow thruster system for ships in ice laden
waters, said ships being equipped with means for water
lubrication of ice present in front of the bow skin,
comprising a number of water lubrication nozzles which are
mounted in reinforced apertures in the stem of the ship above
the water line, and conduit means connecting said nozzles to
a system for supply of a high pressure fluid via control
means, so that the nozzles are able to deliver high pressure
jet streams in directions substantially transverse the
centerline of the ship.
Half the number of apertures may be arranged to act towards
one side of the centerline of the ship, while the other half
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is arranged to act towards the other side. Each of these
nozzles may for a slight downward-outward protrusion of the
bow skin, said protrusion comprising two outlet openings,
mounted side by side in the longitudinal direction of the
ship and directed to each side of the centerline.
Alternatively, the nozzles may be mounted in a blunt,
essentially flat sloping part of the stem and are each
comprising double conduits, connecting a common outlet
opening from opposite sides at an angle of about 30.
Reference to the accompanying drawings, in which:
Fig. 1 is a side view of a ship, which is suitable for
application of the invention,
Fig. 2 is a diagrammatical section through the stem of the
ship, showing a nozzle according to a first embodiment of the
invention,
Fig. 3 shows the nozzle in Fig. 1 in a larger scale,
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Fig. 4 is a section along line IV-IV in Fig. 3.
Fig. 5 is a vertical transversal section through another
embodiment of the nozzle,
Fig. 6 is a diagrammatical plane view of the forward port
side of the ship showing the system for delivery of
high pressure fluid to the nozzles, and
Fig. 7a-d shows four different regulating states, during use
of the device according to the invention.
The ship shown in Fig. 1 is of a modern ice breaker
construction having a comparatively short midships section
and flat bottom, which rises up above the water-line at the
stem and after body. The bottom skin 10 of the stem is blunt
and spoon shaped, without a marked bow line, in order to
press the ice downward. The flat bottom of the ship is
provided with a plow. The sharp front edge of the plow cuts
the ice and presses the broken ice aside, under the edges of
the broken channel.
At ships of this kind, a conventional bow thruster
propeller would be placed directly within the stream of
broken ice, if it was placed inside the plow 11. However, if
it was placed in a more protected position further aft, the
thruster would have a very short lever ratio, because of the
short distance from the motion centre 12 of the ship. The
reference number 13 marks the approximate position of a
conventional directional jet thruster system. The reference
number 14 designates the position of the directional bow
thruster system according to the invention, wherein it is
evident that the lever ratio is about 40% better in the
latter case.
Fig. 2 shows in a larger scale how the directional bow
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thruster system is mounted within the stem, near above the
water line 15 of the ship. It is known to provide ice
breaking ships with nozzles for watering the ice immediately
in front of the stem. Since a water film is maintained
between the ice and the ship, wear and propulsion energy is
reduced considerably. During normal ice breaking, these
nozzles 16 are supplied with
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low pressure water via a conduit 17, which is connected to a
pump 18 and a sea water inlet 19 (see Fig.6).
Fig. 3 and 4 show the nozzle 16 in larger scale in the
longitudinal and transverse direction. This nozzle forms a
slight downward-outward protrusion of the stem skin 10. The
protrusion comprises two outlet openings 16a, 16b mounted side
by side in the longitudinal direction of the ship and directed
to each side of the ship. The conduit 17 is divided into two
branch conduits 17a, 17b leading into their respective outlet
opening. Each of the branch conduits 17a, 17b comprise a valve
20a and 20b respectively, which enables individual regulation
and closing of the fluid flow through the respective outlet
opening. Since the outlet openings mainly protrude outside the
skin 10, the jets may be almost horizontally directed towards
each side of the centerline of the ship.
In the embodiment shown in Fig. 5, two branch conduits
17a, 17b connect to a common outlet opening 16, at an angle of
about 30 to the plane of the opening. Guide rails 21 have been
cast in the parts of the conduits which are adjacent the nozzle
openings, in order to prevent the forming of swirls in the
water stream. The skin plating 10 is strengthened with ribs 22
in the area of these outlet openings 16, which preferably are
circular, wherein a section through the conduit has such an
elliptical shape, that they when cut at a 30 angle form essen-
tially circular openings.
Fig. 6 show the left front part of the ship. This half is
provided with three nozzles 16 of the kind shown in Fig. 3.
Besides, a number of common outlet openings 23 for watering are
connected to the conduit 17, via a cut-off coc~, and are arran-
ged for watering of the ice in the area of the ships flanks,
where the ice will be sheared. The pump 18 may, e.g. be provi-
ded with a two-speed regulation, for delivery of, on one hand a
small fluid flow at a low pressure, and on the other hand, a
larger flow at a high pressure. In Fig. 7a the said first state
of control is shown, which is used for watering of the ice 25
in front of the stem. Herewith, all valves 20a, 20b and 24 are
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open. Fig. 7b-d illustrates the second state of control, in
whic~ the pump deliver its large pressure at high pressure,
~hich is used for maneuvering of the ship, e.g. in beside or
out from a quay. In this condition, the valve 24 is closed.
Fig. 7c shows a neutral position, which is an alert state,
ready for maneuvering of the ship, wherein the both valves 20a,
20b are completely open, so that the resulting high pressure
streams 26 neutralize each other. via control means at the
bridge, for regulating the valves 20a, 20b, it is possible to
choke any of the streams while maintaining a constant pressure
and flow from the pump 18, either to starboard or port as is
shown in Fig. 7b and 7d, so that a reaction force will be pro-
duced which can be utiliz~d for the maneuvering of the ship.
Since the nozzles 16 are placed well below ~he stem, there is
no risk for the water jet streams to cause ice covering or
irritation, when maneuvering at a quay.
Independently of which kind of nozzle is used, the direc-
tional bow thruster system according to the invention will
improve maneuverability considerably, since it is situated well
forward, in front of the water line. Besides, the bow thruster
system is cost effective, since already present systems for
watering of the ice may be upgraded to form part of the inven-
tion.
The invention i5 not limited to the above described em-
bodiment, but several modifications are possible within the
scope of the accompanying claims. For example, the nozzles 16
may be designed differently. The system for supply of high
pressure water may also be designed differently. The system
shown in Fig. 6 may be doubled for the starboard side of the
ship, but may also be a single system serving both sides. The
directional bow thruster system according to the invention may
be adapted for sharper stems.
