Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 0220893~ 1997-06-26
Propulsion device for an ice-going vessel
The invention relates to a propulsion device according to
the preamble of claim l for use in an ice-going vessel.
Already for a number of years, propeller nozzles have
been used in ice-breaking vessels. They offer the advan-
tage of a significant increase (25 - 40 ~) in bollard
pull as compared to open propellers. Improvements in ice-
0 breaking capacity have been based on high bollard pull in
both breaking very thick ice and cutting loose a ship
stuck in unpenetratable ice.
According to practical experiences, a problem of nozzles
has been their tendency to plug during breaking ice, par-
ticularly thick ice. This has caused a clear discrepancy
situation as the benefits and disadvantages of the pro-
peller nozzle occur broadly under the same conditions.
Resultingly, the technology of using nozzle propellers in
ice-breaking vessels has progressed slowly. In forward
ice-breaking, astern-mounted nozzle propellers has in
many cases proven a successful arrangement free from
significant ice-plugging problems. However, ice-breaking
vessels equipped with nozzle propellers have invariably
had problems in running the vessel astern, whereby the
nozzles have readily become plugged.
In the art is further known an icebreaker construction in
which azimuth-type propulsion is implemented by mounting
CA 0220893~ 1997-06-26
the nozzle of the propulsion device immediately close to
the underside of the hull. However, this arrangement has
been found to cause the following additional problems
associated with the use of a propeller nozzle in ice.
Namely, the broken ice which glides along the hull drifts
against the nozzle, where it will become stuck in front
of the nozzle, against the vertical stem of the
propulsion device, and quite often, against the hull.
Already when propulsion is used for forward drive, the
tendency of nozzle plugging appears already when running
at partial power. When an icebreaker is run in thick,
homogeneous ice or in an old channel made in thick ice,
nozzle plugging may occur when running at partial power
and intermittently even at full power. When the vessel is
run astern, nozzle plugging occurs more frequently.
It is an object of the present invention to overcome the
disadvantages of the above-described technology and
provide an entirely novel type of propulsion device for
an ice-going vessel.
The goal of the invention is achieved by arranging the
flow through the propulsion device so as to keep the
passage of the inlet flow essentially free from any plug-
ging obstacles. In a preferred embodiment o~ the inven-
tion, the hull clearance of the propulsion device is made
essentially larger than the thickness of unbroken ice in
the operating conditions of the vessel.
CA 0220893~ 1997-06-26
More specifically, the propulsion device according to the
invention for an ice-going vessel is characterized by
what is stated in the characterizing part of claim 1.
The invention offers significant benefits.
The inlet side of the propeller nozzle is kept fully free
from obstacles that could hinder the passage of ice into
the nozzle and therethrough.
Hydrodynamically, the suction side of the nozzle is
designed to have no flow-disturbing parts.
The nozzle propeller according to the invention can pass
practically all ice clumps with dimensions smaller than
the length of the propeller blade. These ice clumps are
approximately at least 50 ~ thicker than the ice clumps
that conventional nozzle propulsion devices can pass
without becoming plugged.
Owing to the use of the suction-type nozzle propeller
propulsion device, the sensitivity of the nozzle to
plugging at partial-power propulsion is reduced essen-
tially. Resultingly, the operator of the ice-breaking
vessel can be assumed to be able to use the suction-type
nozzle propulsion practically without any problem of
nozzle plugging even when running at partial power.
The hydrodynamic propulsion is estimated to increase as a
result of the unobstructed suction-side flow pattern of
CA 0220893~ 1997-06-26
the nozzle. According to practical experience, the addi-
tional flow resistance, which is caused by the support
structures arranged to the outlet side of the nozzle, is
smaller than the gain obtained by the unobstructed inlet-
side suction flow.
In the following, the invention will be examined ingreater detail with the help of the exemplifying embodi-
ments illustrated in the appended drawings in which
o
Figure l is a side view of a conventional propulsion
device; and
Figure 2 is a side view of a propulsion device according
to the invention;
By virtue of adapting the novel suction-type azimuth
propulsion in an ice-breaking vessel, the propulsion
device may now be steered in any possible direction.
The invention concerns the conversion of a propeller
nozzle of the type shown in Fig. l into a suction-type
nozzle propeller used in an azimuth propulsion device.
According to the invention, the propeller and the nozzle
are mounted for azimuth propulsion in front of the
vertical shaft of the traction-force exerting propulsion
device.
CA 0220893~ 1997-06-26
Referring to Fig. l, therein is shown a conventional
prior-art propelling-force exerting azimuth propulsion
device for use on an ice-breaking vessel. The basic
components of the device are:
la vessel hull
2a vertical shaft of azimuth propulsion device
3a propeller
4a propeller hub
0 5a propeller blade
6a nozzle
7a nozzle support strut
8a collar between vessel hull and nozzle
9a clearance between vessel hull and nozzle
lOa vessel hull rear fin
In conventional structures, the vessel hull la is made
flat over the entire attachment area of the azimuth
propulsion device. The nozzle 6a is adapted immediately
close to the hull la, thus permitting free azimuth
steering of the propulsion device while keeping the hull
clearance 9a to a minimum.
The vertical shaft 2a of the azimuth propulsion device is
adapted to the front side of the nozzle 6a, and the
nozzle is connected to the shaft by nozzle support struts
7a. The vertical shaft 2a blinds a relatively large
portion of the nozzle suction area. Thereby the passage
of ice through the nozzle is restricted as the shaft
offers a backing surface to the approaching ice chunks.
CA 0220893~ 1997-06-26
The propeller 3a is located in the interior of the nozzle
and throat clearance of the nozzle is slightly smaller
than the length of the propeller blade 5a.
The support struts 7a of the nozzle 6a form in front of
the nozzle such a structural restriction that by itself
limits the maximum size of ice chunks passing through the
nozzle.
In constructions of conventional technology, the diameter
of the propeller hub 4a is relatively large thus also
restricting the passage of ice chunks through the nozzle.
Shown in Fig. 2 is a pull-exerting azimuth propulsion
device according to the invention.
The differences between conventional technology and the
present invention are as follows:
In prior-art constructions, the vertical shaft 2a of the
azimuth propulsion device is located in front of the
nozzle. According to the invention, the vertical shaft 2b
of the azimuth propulsion device is at the rear of the
nozzle with respect to the flow.
In conventional technology, the nozzle support struts 7a
are placed in front of the nozzle. According to the
invention, the nozzle support struts 7b are at the rear
of the nozzle, in the exit flow of the propeller,
displaced from the inlet flow area.
CA 0220893~ 1997-06-26
According to prior-art techniques, the nozzle of the
azimuth propulsion device is adapted immediately under
the hull with the nozzle-to-hull clearance 9a reduced to
the minimum value permitted by the construction.
According to the invention, the nozzle-to-hull clearance
9b of the nozzle is most advantageously slightly larger
than the thickness of unbroken ice under the operating
conditions of the vessel.
o
According to the invention, a slight extra benefit can be
attained by adapting a collar 8b onto the vertical shaft
of the azimuth propulsion device, between the hull and
the nozzle. An advantageous shape of the nozzle can be,
e.g., cylindrical, or alternatively, narrow-pointed in
the direction of traction. The collar 8b may be provided
with a hydrodynamically advantageous, smoothed envelope
so shaped as to optimally guide the water flow into the
propeller.
According to the invention, in conjunction with the use
of a pulling or pushing propulsion device, the rear fin
lOb of the vessel may be removed, with proper regard to
the structural strength constraints of the propulsion
device, from the hull, particularly when operating in
multiyear ice.
The invention can be used with different types of nozzle
profiles. According to the invention, most advantageously
a nozzle is used which is optimized with respect to the
CA 0220893~ 1997-06-26
traction force exerted by the nozzle in the traction
direction.
According to the invention, the propeller hub 4b is most
advantageously shaped on the suction side of the nozzle
so as to permit easy passage of ice chunks through the
nozzle. This means that the diameter of the hub 4b should
be as small as possible on the front side of the
propeller. Additionally, the hub design may be
0 complemented with ice guides constructed on the hub that
aid the passage of the ice chunks via the nozzle. Such
guides act optimally by minimizing the power consumed in
breaking the ice chunks and maximizing the increase of
the longitudinal momentum component of the ice chunks as
they pass through the nozzle.
The power transmission chain from the power source of the
vessel to the propulsion device may be implemented in any
suitable manner using either an electric, hydraulic or
mechanical system.
