Note: Descriptions are shown in the official language in which they were submitted.
CA 02949013 2016-11-18
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A RETRACTABLE THRUSTER, A SWIMMING VESSEL AND A METHOD
FOR RETRACTING AND EJECTING A PROPELLER OF THE RE-
TRACTABLE THRUSTER
FIELD
A retractable thruster is provided that may be used in
swimming vessels, for example in a ship, an offshore
vessel, a fishing vessel, a naval vessel, a luxury lin-
er, an oil tanker, a tug, a ferry or similar applica-
tions.
BACKGROUND
Retractable thrusters are usually used as auxiliary
propulsion for swimming vessels. For example, in naval
vessels retractable thrusters may be used to provide
additional thrust or a so called take-home feature.
A retractable thruster enables a propeller to retract
into a bottom well of a hull of the swimming vessel.
When the propeller is not in use and is retracted, the
drag of the swimming vessel is reduced. Further, the
retractable thruster may be retracted when the swimming
vessel enters shallow waters.
In ice conditions, when the propeller of the retracta-
ble thruster is in its lowest position, there is a risk
that loose ice fills the bottom well in such a way that
the retracting of the propeller is not possible because
the ice jams the lifting operation.
SUMMARY
According to a first aspect, there is provided a re-
tractable thruster for a swimming vessel. The retracta-
ble thruster comprises a propeller and a lifting and
lowering arrangement. The lifting and lowering arrange-
ment is configured to move the propeller in the verti-
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cal direction between a retracted position and an
ejected position. In the retracted position the propel-
ler is substantially inside a bottom well of the swim-
ming vessel and in the ejected position the propeller
is substantially outside the bottom well. Further, the
retractable thruster comprises a water-permeable pro-
tective element configured to be located inside the
bottom well above the propeller and configured to ver-
tically move with the propeller. In the ejected posi-
tion the water-permeable protective element is config-
ured to substantially prevent loose ice passing through
the water-permeable protective element to the inside of
the bottom well and when the propeller is moved from
the retracted position to the ejected position, the wa-
ter-permeable protective element is configured to push
ice out of the bottom well. Thus, the water-permeable
protective element prevents jamming of the lifting and
lowering arrangement caused by loose ice and possibly
freezing of the ice inside the bottom well. "Substan-
tially inside a bottom well" means that a larger por-
tion of the propeller is inside the bottom well than
outside the bottom well when the propeller is in its
retracted position. "Substantially outside the bottom
well" means that a larger portion of the propeller is
outside the bottom well or the propeller is fully out-
side when the propeller is in its ejected position.
"Substantially prevent loose ice from drifting inside
the bottom well" means that only a minor portion of ice
or substantially small ice blocks are permitted to go
into the bottom well past or through the water-
permeable protective element.
According to a second aspect, there is provided a re-
tractable thruster for a swimming vessel. The retracta-
ble thruster comprises a propeller and a lifting and
lowering arrangement. The lifting and lowering arrange-
ment is configured to move the propeller in the verti-
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cal direction between a retracted position and an
ejected position. In the retracted position the propel-
ler is substantially inside a bottom well of the swim-
ming vessel and in the ejected position the propeller
is substantially outside the bottom well. Further, the
retractable thruster comprises a water-permeable pro-
tective element configured to be located inside the
bottom well above the propeller and configured to ver-
tically move with the propeller. In the ejected posi-
tion the water-permeable protective element is config-
ured to substantially cover a waterside opening of the
bottom well and when the propeller is moved from the
retracted position to the ejected position, the water-
permeable protective element is configured to push ice
out of the bottom well. Thus, the water-permeable pro-
tective element prevents loose ice from drifting inside
the bottom well through the water-permeable protective
element and prevents jamming of the lifting and lower-
ing arrangement caused by loose ice.
According to a third aspect, there is provided a re-
tractable thruster for a swimming vessel. The retracta-
ble thruster comprises a propeller and a lifting and
lowering arrangement. The lifting and lowering arrange-
ment is configured to move the propeller in the verti-
cal direction between a retracted position and an
ejected position. In the retracted position the propel-
ler is substantially inside a bottom well of the swim-
ming vessel and in the ejected position the propeller
is substantially outside the bottom well. Further, the
retractable thruster comprises a water-permeable pro-
tective element configured to be located inside the
bottom well above the propeller and configured to ver-
tically move with the propeller. In the ejected posi-
tion the water-permeable protective element is config-
ured to prevent ice from entering the bottom well
through the water-permeable protective element. Thus,
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the water-permeable protective element prevents jamming
of the lifting and lowering arrangement caused by loose
ice.
According to a fourth aspect, there is provided a re-
tractable thruster for a swimming vessel. The retracta-
ble thruster comprises a moving support structure, a
propeller below the moving support structure and a
lifting and lowering arrangement. The lifting and low-
ering arrangement is configured to move the propeller
with the moving support structure in the vertical di-
rection between a retracted position and an ejected po-
sition. In the retracted position the propeller is sub-
stantially inside a bottom well of the swimming vessel
and in the ejected position the propeller is substan-
tially outside the bottom well. Further, the retracta-
ble thruster comprises a water-permeable protective el-
ement configured to be located inside the bottom well
between the propeller and the moving support structure
and configured to vertically move with the propeller.
In the ejected position the water-permeable protective
element is configured to substantially prevent loose
ice from drifting inside the bottom well through the
water-permeable protective element and when the propel-
ler is moved from the retracted position to the ejected
position, the water-permeable protective element is
configured to push ice out of the bottom well. Thus,
the water-permeable protective element prevents jamming
of the lifting and lowering arrangement caused by loose
ice.
In one embodiment, in the ejected position, the water-
permeable protective element is at a lower end of the
bottom well. In one embodiment, in the ejected posi-
tion, the water-permeable protective element is in
proximity to a lower end of the bottom well. The tech-
nical effect is that the water-permeable protective el-
CA 02949013 2016-11-18
ement prevents loose ice or ice blocks from entering
the bottom well through the water-permeable protective
element. "In proximity to a lower end" may mean a loca-
tion of the water-permeable protective element being at
5 a maximum distance of approximately 200mm from the wa-
terside opening towards the bottom well.
In one embodiment, in the ejected position, the water-
permeable protective element substantially covers a wa-
terside opening of the bottom well. In one embodiment,
in the ejected position, the entry of ice into the bot-
tom well is prevented in a portion of the area of the
waterside opening which is at least 95% of the area of
the waterside opening of the bottom well. The technical
effect is that the water-permeable protective element
limits the possible area of the opening in a way that
no or only a minor portion of ice or substantially
small ice blocks are permitted to go into the bottom
well past or through the water-permeable protective el-
ement. "Substantially covers a waterside opening" may
mean that, together with the structures of the lifting
and lowering arrangement, the water-permeable protec-
tive element covers at least around 95% of the area of
the waterside opening.
In one embodiment, the water-permeable protective ele-
ment comprises at least one perforated plate. The tech-
nical effect is that the water is permitted to go
through holes in the perforated plate when the propel-
ler is retracted or ejected, thereby lowering the re-
sistance of the water and lowering the force needed to
move the propeller in the vertical direction.
In one embodiment, the water-permeable protective ele-
ment comprises at least one detachable plate part. In
one embodiment, the water-permeable protective element
comprises at least two detachable plate parts. The
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technical effect is that assembling of the retractable
thruster and servicing the retractable thruster is eas-
ier because at least one of the plate parts may be de-
tached and the detachable plate part, bottom well and
the part of the retractable thruster inside the bottom
well can be inspected.
In one embodiment, the water-permeable protective ele-
ment comprises mesh. The technical effect is that the
water is permitted to go through the mesh when the pro-
peller is retracted or ejected, thereby lowering the
resistance of the water and lowering the force needed
to move the propeller in the vertical direction.
In one embodiment, the water-permeable protective ele-
ment comprises a combination of a perforated plate and
mesh. The technical effect is that when mesh is in-
stalled into larger holes of the perforated plate,
smaller holes are less needed, thus improving the manu-
facturability, and the mesh also permits only very
small ice blocks to go through the water-permeable pro-
tective element. Further, when the water-permeable pro-
tective element comprises a larger portion of the plate
than mesh, the stiffness of the structure may be im-
proved comparing to a water-permeable protective ele-
ment made completely from mesh.
In one embodiment, the water-permeable protective ele-
ment comprises a combination of a pipe structure and
mesh. The technical effect is that the structure of the
water-permeable protective element may be lighter com-
pared to a metal plate when it is made of a hollow
pipe.
In one embodiment, the water-permeable protective ele-
ment comprises a combination of a support structure and
mesh. The technical effect is that the support struc-
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ture improves the stiffness of the water-permeable pro-
tective element.
In one embodiment, the lifting and lowering arrangement
comprises a stationary support structure comprising a
guiding element and a lead-through hole. Further, the
lifting and lowering arrangement comprises a non-
pivoting tube configured through the lead-through hole,
wherein a lower end of the non-pivoting tube is config-
ured to be connected to the propeller enabling to slid-
ably connect the propeller to the guiding element and
enabling the propeller to be moved vertically. Further,
the lifting and lowering arrangement comprises an actu-
ator arrangement configured to be connected between the
non-pivoting tube and the bottom well in such a way
that when the propeller is moved to the retracted posi-
tion, the actuator arrangement is configured to lift
the propeller substantially inside the bottom well by
sliding the non-pivoting tube inside the guiding ele-
ment and correspondingly when the propeller is moved to
the ejected position, the actuator arrangement is con-
figured to lower the propeller substantially outside
the bottom well by sliding the non-pivoting tube inside
the guiding element. In one embodiment, the guiding el-
ement is a bearing. In one embodiment, the non-pivoting
tube is a guide bar. The technical effect is that the
retractable thruster may be mounted in place with the
stationary support structure and the propeller may be
lifted or lowered with the lifting and lowering ar-
rangement in a controlled and reliable manner.
In one embodiment, the lifting and lowering arrangement
comprises at least two hydraulic cylinders. In one em-
bodiment, the actuator arrangement comprises at least
two hydraulic cylinders. In one embodiment, each hy-
draulic cylinder comprises a piston which is hollow al-
lowing a hydraulic fluid connection line connected to
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the at least two hydraulic cylinders to be placed to a
location inside the bottom well, which is out of the
reach of water. The technical effect is that, by means
of the hydraulic cylinders, the lifting and lowering of
the propeller may be done reliably as the hydraulic
cylinders share the load of the propeller, thereby bal-
ancing the lifting and lowering manoeuvre. Further, the
hydraulic cylinder usually performs reliable linear
movement even in hard environmental conditions.
In one embodiment, the lifting and lowering arrangement
comprises a manual lifting and lowering mechanism.
In one embodiment, the lifting and lowering arrangement
comprises a moving support structure fixed to the non-
pivoting tube, wherein a piston of each hydraulic cyl-
inder is configured to be connected to the non-pivoting
tube via the moving support structure and a cylinder
housing of each hydraulic cylinder is configured to be
connected to the bottom well. The technical effect is
that the propeller may be steadily moved by the pistons
which are connected to the moving support structure,
and the cylinder housing of each hydraulic cylinder may
be secured in place to the bottom well, enabling relia-
ble push force of the pistons.
In one embodiment, the retractable thruster comprises
at least one stopper configured to stop the movement of
the propeller to the ejected position. In one embodi-
ment, the at least one stopper is connected to the sta-
tionary support structure between the stationary sup-
port structure and the moving support structure. The
technical effect is that the propeller may be smoothly
stopped in the ejected position and the stopper pre-
vents the moving support structure from strongly col-
liding against the stationary support structure.
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In one embodiment, the water-permeable protective ele-
ment is configured to prevent jamming of the lifting
and lowering arrangement caused by freezing of loose
ice. The technical effect is that it is possible to
move the propeller in the vertical direction even in
ice conditions.
In one embodiment, the propeller is configured to be
pivotable for 360 degrees around a vertical axis of the
retractable thruster. In one embodiment, the retracta-
ble thruster is an azimuth thruster. The technical ef-
fect of the pivotable feature of the azimuth thruster
is that it makes a rudder unnecessary and gives the re-
tractable thruster better maneuverability than a fixed
propeller and rudder system.
According to a fifth aspect, there is provided a method
for retracting and ejecting a propeller of a retracta-
ble thruster for a swimming vessel, wherein the propel-
ler is retracted and ejected by:
- connecting a water-permeable protective element to
the retractable thruster above the propeller inside a
bottom well of the swimming vessel;
- preventing, with the water-permeable protective ele-
ment, loose ice from passing through the water-
permeable protective element to the inside of the bot-
tom well when the propeller is in an ejected position;
- pushing ice out of the bottom well when the propeller
is moved from a retracted position to the ejected posi-
tion.
According to a sixth aspect, there is provided a swim-
ming vessel comprising a bottom well, a retractable
thruster, and a power pack for supplying power for mov-
ing a propeller of the retractable thruster in the ver-
tical direction. The retractable thruster comprises the
propeller, a lifting and lowering arrangement config-
CA 02949013 2016-11-18
ured to move the propeller in the vertical direction
between a retracted position and an ejected position,
wherein in the retracted position the propeller is sub-
stantially inside the bottom well and in the ejected
5 position the propeller is substantially outside the
bottom well. Further, the retractable thruster compris-
es a water-permeable protective element located inside
the bottom well above the propeller and configured to
vertically move with the propeller. In the ejected po-
10 sition the water-permeable protective element is con-
figured to substantially prevent loose ice from drift-
ing inside the bottom well through the water-permeable
protective element and when the retractable thruster is
moved from the retracted position to the ejected posi-
tion, the water-permeable protective element is config-
ured to push ice out of the bottom well.
According to a seventh aspect, there is provided a
swimming vessel comprising a bottom well, a retractable
thruster according to the first aspect, and a power
pack for supplying power for moving a propeller of the
retractable thruster in the vertical direction.
In one embodiment of the swimming vessel, the propeller
is configured to be pivotable for 360 degrees around a
vertical axis of the retractable thruster. In one em-
bodiment of the swimming vessel, the retractable
thruster is an azimuth thruster. The technical effect
of the pivotable feature of the azimuth thruster is
that it makes a rudder unnecessary and gives the swim-
ming vessel better maneuverability than a fixed propel-
ler and rudder system.
The retractable thruster described herein has many ad-
vantages. The water-permeable protective element ena-
bles shipping in ice or arctic conditions. The struc-
ture of the water-permeable protective element enables
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the prevention of jamming of the movement of the re-
tractable thruster by substantially preventing loose
ice from entering the bottom well through the water-
permeable protective element when the propeller is in
the ejected position. This may also enable preventing
of unexpected shutdowns of the retractable thruster
caused by ice jamming the lifting and lowering arrange-
ment. The water-permeable protective element also ena-
bles the blocking of many other types of objects in the
water such as sunken logs and other waste material that
could damage the structures of the retractable thruster
inside the bottom well.
The simple and robust construction of the retractable
thruster provides high operational reliability even in
ice conditions. The mechanism of the retractable
thruster is simple, which may bring savings in mainte-
nance costs. The construction is strong-built and can
push large blocks of ice out of the bottom well. In one
embodiment of the retractable thruster, hydraulics pro-
vides the needed amount of force in order to lift the
propeller reliably and safely. In the hydraulic solu-
tion of the lifting and lowering arrangement it is pos-
sible to equip the hydraulic system with suitable
valves for securing the system of the lifting and low-
ering arrangement against a possible overload or mal-
function incident. As the propeller is very heavy, hy-
draulic valves provide safe lowering of the propeller
to the ejected position.
In an azimuth thruster the propeller pivots 360 around
the vertical axis, so the unit provides propulsion,
steering and positioning thrust even in ice conditions.
The design of the retractable thruster has been devel-
oped in response to market requirements, whereby the
design of the thruster may be adapted to suit many
types of applications. The simple and robust construc-
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tion provides high operational reliability together
with simple maintenance.
In one embodiment, the structure of the retractable
thruster enables the retractable thruster to be in-
spected by detaching at least one part of the water-
permeable protective element. This feature is advanta-
geous because it makes the maintenance of the retracta-
ble thruster easier, which may provide cost savings.
The retractable thrusters do not have any parts that
can be external to the bottom well except the propel-
ler, whereby there are no parts outside the bottom well
except the propeller that in course of time may break
or wear and may have to be replaced by new parts. For
example, external structures outside the bottom well
for limiting the ice blocks require space under the
hull of the swimming vessel and increase the draft of
the hull and are sensitive to impacts. These external
structures have a risk of colliding against underwater
obstacles at the bottom of the body of water such as
rocks. These external structures may reduce the minimum
depth of water that a ship or boat requires to safely
navigate. Further, these types of external structures
may collect extensive amounts of waste material or oth-
er obstacles from the passing water and may have to be
cleaned on a regular basis.
The embodiments described herein may be used in any
combination with each other. Several or at least two of
the embodiments may be combined together to form a fur-
ther embodiment. A method or a device may comprise at
least one of the embodiments described hereinbefore.
It is to be understood that any of the above embodi-
ments or modifications can be applied singly or in com-
bination to the respective aspects to which they refer,
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unless they are explicitly stated as excluding alterna-
tives.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to pro-
vide a further understanding and constitute a part of
this specification, illustrate various embodiments and
together with the description help to explain the prin-
ciples of the embodiments. In the drawings:
Figure 1A is a side illustration of an embodiment of a
retractable thruster in an ejected position;
Figure 1B is a front side illustration of an embodiment
of a retractable thruster in an ejected position;
Figure 2 is an illustration of an embodiment of a wa-
ter-permeable protective element;
Figure 3A is a sectional view V-V of the embodiment of
the retractable thruster of Figure 1A;
Figure 3B is a sectional view VI-VI of the embodiment
of the retractable thruster of Figure 3A, where the re-
tractable thruster is in the ejected position;
Figure 3C is a sectional view of the embodiment of the
retractable thruster of Figure 3B, where the retracta-
ble thruster is in a retracted position;
Figure 4A is an illustration of an embodiment of a re-
tractable thruster in an ejected position; and
Figure 4B is an illustration of an embodiment of a re-
tractable thruster as seen obliquely from below in an
ejected position.
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Figure 4C is a simplified sectional view of the embodi-
ment of the retractable thruster of Figure 4A in an
ejected position.
Figure 4D is a detail view of the retractable thruster
of Figure 4A.
Figure 4E is another detail view of the retractable
thruster of Figure 4A.
Figure 5 is a sectional view IV-IV of the embodiment of
the retractable thruster of Figure 1A;
Figure 6 is a sectional view VII-VII of the embodiment
of the retractable thruster of Figure IA;
Figure 7A is a partial section view of an embodiment of
a retractable thruster in an ejected position;
Figure 7B is a partial section view of the embodiment
of the retractable thruster of Fig. 7A in a retracted
position;
Figure 8 is another illustration of a water-permeable
protective element;
Figure 9 is another illustration of a water-permeable
protective element;
Figure 10 is another illustration of a water-permeable
protective element; and
Figure 11 is another illustration of a water-permeable
protective element.
. CA 02949013 2016-11-18
DETAILED DESCRIPTION
Reference will now be made in detail to the embodi-
ments, examples of which are illustrated in the accom-
panying drawings.
5
A retractable thruster is a thruster where a propeller
of the thruster can be retracted substantially inside a
hull of a swimming vessel. In one embodiment, the re-
tractable thruster may be adapted for horizontal drive
10 with an automatic drive shaft disconnection system or
for vertical drive. In one embodiment, lifting and low-
ering of the propeller can be activated by a remote
control system, for example with a push button on the
bridge of the swimming vessel. In one embodiment, en-
15 gagement of a drive shaft coupling for the retractable
thruster can be automatic.
Figure lA is a side illustration of an embodiment of a
retractable thruster in an ejected position. Figure 1B
is a front side illustration of an embodiment of the
retractable thruster in the ejected position. The re-
tractable thruster comprises a propeller 3 comprising a
lower gear 301 inside a lower gear housing 302. The de-
tailed operation of the propeller 3 is not described in
detail herein as it is well known to a man skilled in
the art.
The retractable thruster comprises a lifting and lower-
ing arrangement 4 configured to move the propeller 3 in
the vertical direction between a retracted position and
an ejected position. The retracted position is de-
scribed in more detail below, for example with refer-
ence to Figure 3C. In the ejected position the propel-
ler 3 is substantially outside a bottom well 5, for ex-
ample fully outside the bottom well 5 as illustrated in
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Figs. lA and 1B. The bottom well 5 is located at the
bottom of the hull 6 of the swimming vessel 2.
A water-permeable protective element 7 is connected to
the retractable thruster above the propeller 3 and its
lower gear housing 302. In the embodiment of Figs. lA
and 1B the water-permeable protective element 7 com-
prises at least one perforated plate. The water-
permeable protective element 7 in Figs. lA and 1B is
formed of two sections, which are a first and a second
perforated plate 71, 72. The perforated plates 71, 72
are lifted and lowered with the propeller 3 when the
propeller 3 is moved vertically. In the ejected posi-
tion, the water-permeable protective element 7 is in
proximity to a lower end 9 of the bottom well 5. For
example, in the ejected position, the water-permeable
protective element 7 may be at a maximum distance of
approximately 200mm from the lower end 9 towards the
inside of the bottom well 5 or exactly at the level of
the lower end 9. When the retractable thruster is in
the ejected position, the perforated plates 71, 72 are
in proximity to the lower end 9, in which case loose
ice cannot drift inside the bottom well 5 through the
water-permeable protective element 7. Thus, the water-
permeable protective element 7 substantially prevents
ice from getting into the bottom well 5 through the wa-
ter-permeable protective element 7 when the propeller 3
is in the ejected position. This can be accomplished by
the structure of the perforated plates 71, 72 and the
location of the perforated plates 71, 72 in the re-
tractable thruster.
Figure 2 is an illustration of an embodiment of the wa-
ter-permeable protective element 7. Figure 2 illus-
trates the water-permeable protective element 7 from
the top. Figure 2 shows that most of the area Al of a
water-side opening 8 of the bottom well 5 is substan-
CA 02949013 2016-11-18
17
tially covered by the water-permeable perforated plate
7. The water-permeable protective element 7 is split in
the middle into sections, which are the perforated
plates 71, 72. The perforated plates 71, 72 may be made
out of metal. The first perforated plate 71 comprises a
first opening 25a and the second perforated plate 72
comprises a second opening 25b designed to leave space
for an actuator arrangement of the lifting and lowering
arrangement, which actuator arrangement supplies the
force for the linear movement of the retractable
thruster. Because of the shape of the openings 25a,
25b, the surface of the perforated plates 71, 72 resem-
bles a shell-like shape. The actuator arrangement may
comprise, for example, cylinders and structures or
brackets that are needed in order to mount the cylin-
ders. The cylinders are explained below with reference
to Figures 3B, 3C, 4A and 4B.
The water-permeable protective element 7 comprises a
plurality of holes 23, the size and amount of which are
determined according to the size of the retractable
thruster. The size of the bottom well 5 and the amount
of water in the bottom well 5 affect the size and
amount of the holes 23. The size and amount of the
holes also have an effect on the force that is needed
when the propeller 3 is retracted, and on the ejecting
speed of the propeller 3. The purpose of the holes 23
is to permit water to penetrate through the holes 23
when the propeller is retracted. A minor amount of wa-
ter is also pushed through a clearance 30 between the
water-permeable protective element 7 and the bottom
well 5 when the propeller is retracted.
When the propeller 3 is in the ejected position, the
openings 25a, 25b are substantially covered by the ac-
tuator arrangement, such as cylinders and structures or
brackets that are needed in order to mount the cylin-
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ders. While retracting and ejecting the propeller, the
cylinders are inside the openings 25a, 25b. One cylin-
der and its mounting part are fitted inside each open-
ing 25a, 25b when the propeller 3 is in the ejected po-
sition. Because the water-permeable protective element
7 substantially covers the waterside opening 8 in the
ejected position, ice blocks that are larger than the
largest hole 32 are prevented from entering the bottom
well 5 through the water-permeable protective element 7
and are forced to stay below the water-permeable pro-
tective element 7. The diameter 132 of the water-
permeable protective element 7 may be so large that the
water permeable protective element 7 covers at least
95% of the area Al of the waterside opening 8.
A hole pattern of an attachment interface 31 of the wa-
ter-permeable protective element 7 is illustrated with
dash-dot lines around a lead-through opening 26 of the
water permeable protective element 7. The attachment
interface 31 is used to connect the water-permeable
protective element 7 to the rest of the structure of
the retractable thruster. Because the perforated plates
71, 72 are detachable, they improve the maintenance of
the retractable thruster as one or both of the perfo-
rated plates 71, 72 may be detached at the time of
maintenance or inspection. The mounting of the water-
permeable protective element 7 is also easier as the
mounting of the heavy water-permeable protective ele-
ment 7 can be made in two phases.
Figure 3A is a sectional view V-V of the embodiment of
the retractable thruster of Figure 1A. Figure 3A illus-
trates the retractable thruster from the top and the
position of the cut-out VI-VI which is illustrated in
Figure 3B. Figure 3B is a sectional view VI-VI of the
embodiment of the retractable thruster of Figure 3A,
where the retractable thruster is in the ejected posi-
CA 02949013 2016-11-18
19
tion. Figure 3C is a sectional view of the embodiment
of the retractable thruster of Figure 3B, where the re-
tractable thruster is in a retracted position.
Figures 3B and 30 illustrate that the water-permeable
protective element 7 substantially prevents loose ice
from passing inside the bottom well 5 through the wa-
ter-permeable protective element 7, when the propeller
3 is in the ejected position and when the propeller 3
is moved from the retracted position to the ejected po-
sition, the water-permeable protective element 7 pushes
ice out of the bottom well 5.
The structure of the retractable thruster enables the
possibility to use the retractable thruster in ice con-
ditions. The water-permeable protective element 7 pro-
tects the bottom well 5 from the ice, whereby it is
possible to retract the propeller 3 without the ice in-
terfering or preventing the retracting maneuver. The
solution prevents loose ice from permanently accumulat-
ing inside the bottom well 5 in such a way that the
vertical movement of the propeller 3 will be jammed. In
ice conditions when the propeller 3 is in the ejected
position, there is a risk that loose ice permanently
fills the bottom well 5, whereby the retraction of the
propeller 3 is not possible because the ice jams the
retracting/lifting operation.
The lifting and lowering arrangement 4 comprises a sta-
tionary support structure 11 located, for example, at
least partially inside the bottom well 5 and comprising
a guiding element 12. Further, the lifting and lowering
arrangement 4 comprises a non-pivoting tube 13 for
slidably connecting the propeller 3 to the guiding ele-
ment 12 and an actuator arrangement 17 connected be-
tween the non-pivoting tube 13 and the bottom well 5.
The non-pivoting tube 13 goes through a lead-through
hole in the stationary support structure 11. This lead-
CA 02949013 2016-11-18
through hole 35 is illustrated in Figure 4B. The non-
pivoting tube 13 is connected to the propeller 3 ena-
bling the propeller 3 to be moved vertically. When the
propeller 3 is moved to the retracted position, the ac-
5 tuator arrangement 17 lifts the propeller 3 substan-
tially inside the bottom well 5 by sliding the non-
pivoting tube 13 inside the guiding element 12. Corre-
spondingly, when the propeller 3 is moved to the eject-
ed position, the actuator arrangement 17 is configured
10 to lower the propeller 3 substantially outside the bot-
tom well 5 by sliding the non-pivoting tube 13 inside
the guiding element 12.
The actuator arrangement 17 may be, for example, two
15 hydraulic cylinders 14a, 14b. By means of the hydraulic
cylinders 14a, 14b the lifting and lowering of the pro-
peller 3 may be done reliably as the hydraulic cylin-
ders 14a, 14b share the load of the propeller 3, there-
by balancing the lifting and lowering manoeuvre. As the
20 propeller 3 is very heavy, the hydraulic cylinders 14a,
14b enable keeping of the propeller 3 and parts con-
nected to the propeller 3 steady in such a way that,
during normal operation of the retractable thruster,
there is no possibility of jamming of the lifting oper-
ation caused by the heavy load. The first hydraulic
cylinder 14a is illustrated in Figures 3B and 3C and
the second hydraulic cylinder may be located on the op-
posite side of the first hydraulic cylinder 14a. The
position of the hydraulic cylinders 14a, 14b in rela-
tion to each other is also illustrated in Figure 1B.
Each hydraulic cylinder 14a, 14b comprises a cylinder
housing 16a, 16b and a piston 19a, 19b as illustrated
in Figure 1B. The pistons 16a, 16b may be hollow as il-
lustrated in Figure 3B and 3C.
The lifting and lowering arrangement 4 comprises a mov-
ing support structure 15 fixed to the non-pivoting tube
CA 02949013 2016-11-18
21
13. The moving support structure 15 can be, for exam-
ple, welded to the non-pivoting tube 13 or detachably
attached to the non-pivoting tube 13 with screws or
similar types of accessories. The piston 19a, 19b of
each hydraulic cylinder 14a, 14b is connected to the
non-pivoting tube 13 via the moving support structure
15. Each piston 14a, 14b may comprise a fixing flange
36 which is used to connect the piston 14a, 14b to the
moving support structure 15. There is one piston 19a,
19b on both sides of the moving support structure 15
for enabling a steady and reliable lifting maneuver.
The cylinder housings 16a, 16b are attached to the bot-
tom well 5 and thereby remain stationary.
The swimming vessel may comprise a power pack 20 for
supplying power for moving the propeller 3 in the ver-
tical direction. The power pack 20 is used to supply
hydraulic fluid to the hydraulic cylinders 14a, 14b.
Two hydraulic fluid connection lines may be needed to
connect the power pack 20 to the hydraulic cylinders
14a, 14b, or one main hydraulic connection line may be
used, which is divided into two hydraulic fluid connec-
tion lines near inlets 40a, 40b of the hydraulic cylin-
ders 14a, 14b. One hydraulic fluid connection line 54
may be arranged for each cylinder 14a, 14b. A hydraulic
fluid connection line 54 connected to a chamber 21 in-
side a first cylinder housing 16a of the first hydrau-
lic cylinder 14a via the hollow interior of the piston
19a is illustrated with a dashed line in Figure 3B. The
hydraulic fluid connection line 54 may be connected to
an inlet 40a, 40b, which is structured into the moving
support structure 15. One inlet 40a, 40b may be ar-
ranged for each of the hydraulic cylinder 14a, 14b. The
inlet 40a, 40b is arranged through the moving support
structure 15 to the inside of the piston 14a, 14b. The
inlet 40a, 40b may be connected to the hydraulic fluid
connection line 54 with a suitable fitting. The inlet
CA 02949013 2016-11-18
22
40a, 40b is used to supply the hydraulic fluid inside
the hydraulic cylinders 14a, 14b.
When the retractable thruster is assembled, air may be
trapped in the hydraulic circuit. After the startup, it
may be important to remove the air from the hydraulic
circuit. If the trapped air is not removed, it will be
mixed to the hydraulic fluid which may lead to malfunc-
tion as the air is compressible. This may be prevented
by arranging an air venting connection 53, which is
connected to the chamber 21. This air venting connec-
tion 53 may be, during normal operation, sealed, for
example, with a plug. When the venting of air is needed
to be done, the plug is removed or untightened so that
the air is removed from the cylinders 14a, 14b. The air
venting connection 53 may be arranged into the moving
support structure 15 where it is connected to the cham-
ber 21 via the hollow interior of the piston 19a, 19b.
Each hydraulic cylinder 14a, 14b may be connected to
one air venting connection 53. As the air venting con-
nection 53 may be connected to the highest point in the
hydraulic cylinder 14a, 14b, the air may be removed ef-
ficiently.
The hydraulic fluid is pumped from the power pack 20
inside the hydraulic cylinders 14a, 14b. The hydraulic
fluid is pumped inside the first piston 19a and from
there into the chamber 21. Simultaneously, the hydrau-
lic fluid is supplied inside the second piston 19b.
When the pistons 19a, 19b are ejected, the pistons 19a,
19b together with the moving support structure 15 lift
the propeller 3 upwards by sliding the non-pivoting
tube 13 inside the guiding element 12. The water inside
the bottom well 5 flows through the holes in the water-
permeable protective element 7. Thus, lifting of the
propeller 3 with a lifting force F to the retracted po-
CA 02949013 2016-11-18
23
sition is enabled. A stroke L of the retractable
thruster is illustrated in Figure 30.
In the retracted position, loose ice is permitted to
enter the bottom well 5. When the propeller 3 is moved
from the retracted position to the ejected position,
the water-permeable protective element 7 pushes ice out
of the bottom well 5. In the embodiment of the re-
tractable thruster in Figures 3B and 30, the hydraulic
cylinders 14a, 14b are single acting cylinders. The
propeller 3 is ejected/lowered by its own weight. The
ejecting speed is determined by the size of the propel-
ler 3, the size of the bottom well 5, the amount and
size of the holes 23 in the perforated plates 71, 72
and by whether valves are used to throttle the flow of
the hydraulic fluid out from the hydraulic cylinders
14a, 14b.
Finally, the movement of the propeller 3 may be stopped
by stoppers 18. In the embodiment of the retractable
thruster in Figures 3B and 30 there are four stoppers
18 connected to the upper surface 37 of the stationary
support structure 11. One stopper 18 is not visible in
Figures 3B and 30 because it is opposite the stopper 18
in the middle of the stationary support structure 11.
These stoppers 18 are located between the stationary
support structure 11 and the moving support structure
15, thereby stopping the movement of the moving support
structure 15 when the propeller 3 is ejected to the
ejected position. The propeller 3 is intended to be
moved slowly in the vertical direction, thereby avoid-
ing possible bumps or collision caused by the heavy
load tending to continue its movement after the stop.
The stoppers 18 can be, for example, adjustable rods
which have a thread and can be threaded onto threads in
the stationary support structure 11. The thread enables
the adjustable rods to be lifted or lowered in order to
CA 02949013 2016-11-18
24
find the right stop position, for example in a start-up
phase of the retractable thruster. At the end of the
adjustable rods there may be a rubber, plastic or other
type of elastic part. The height to which the adjusta-
ble rods are threaded determines the stop position of
the propeller 3. The adjustable rods may be made out of
metal. Another solution for the stoppers 18 may be to
use correct length shock absorbers comprising gas
springs instead of the adjustable rods (not illustrat-
ed). In this solution, there may be possible to arrange
only one a larger shock absorber into the stationary
support structure 11 instead of four adjustable thread
rods (not illustrated).
The hydraulic fluid exiting from the inside of each hy-
draulic cylinder 14a, 14b may be restricted by using
hydraulic valves. Depending on the size of the re-
tractable thruster and the propeller 3, the hydraulic
valves may be, for example, throttle valves or counter-
balance valves. The purpose of these above-mentioned
valves is to ensure that the propeller 3 will not fall
down in an uncontrolled manner, colliding strongly
against the stoppers 18. Also, the amount of hydraulic
fluid supplied from a pump in the power pack 20 to the
hydraulic cylinders 14a, 14b may be adjusted with a hy-
draulic valve in order to set the correct lift-
ing/retracting speed. Summarizing, the purpose of the
hydraulic valves is to control the flow out from and
possibly also the flow into the hydraulic cylinders
14a, 14b, thereby improving the reliability and control
of the hydraulic system.
It is also possible to equip the hydraulic cylinders
14a, 14b with an integrated end dampening structure
which will smoothly slow down the speed of the pistons
19a, 19b when the pistons 19a, 19b are retracted. An-
other solution is to use conventional double-acting hy-
CA 02949013 2016-11-18
draulic cylinders with a separate piston inside the
cylinder housing and a piston rod connected to the sep-
arate piston instead of the single-acting hydraulic
cylinders 14a, 14b. In this solution the double-acting
5 cylinder is used as a single-acting cylinder. In this
solution, air must be exhausted from a piston rod side
chamber, for example with suitable breathers.
The location of the hydraulic valves may preferably be
10 in the power pack 20. In this way the hydraulic valves
are protected from the corrosive conditions inside the
bottom well 5. Another solution is to locate the hy-
draulic valves inside a manifold connected to the inlet
40a, 40b of each hydraulic cylinder 14a, 14b. In this
15 solution the manifold may have to be protected from
corrosion. It may also be possible to connect the mani-
fold comprising the hydraulic valves outside the bottom
well 5 between the hydraulic cylinders 14a, 14b and the
power pack 20 in the hydraulic fluid connection line 54
20 by using suitable connectors and piping.
Another solution may be to arrange mechanically actuat-
ed cylinders to provide the linear movement (not illus-
trated) instead of hydraulic cylinders 14a, 14b. These
25 mechanically actuated cylinders would have a gearbox
and an electric motor, and rotational movement would be
transformed into linear movement by the gearbox (not
illustrated). Suitable protection for the electric mo-
tor and for other electric parts may have to be provid-
ed in order to have reliable operation in sea condi-
tions.
The propeller 3 of the retractable thruster in Figure
3C is in the retracted position. In the retracted posi-
tion, the propeller 3 is substantially inside the bot-
tom well 5. In the embodiment of the retractable
thruster, the propeller may be, for example, approxi-
CA 02949013 2016-11-18
26
mately for 85% inside the bottom well 5. Only a portion
34 of a conical housing 33 of the propeller 3 is out-
side the bottom well 5.
Another solution is to fully retract the propeller 3
inside the bottom well 5, thereby enabling full removal
of the drag of the propeller (not illustrated). In this
solution the stroke L of the retractable thruster and
the stroke of the hydraulic cylinders 14a, 14b may have
to be longer than in Figures 3B and 3C, and also the
bottom well 5 may have to be deeper.
A method for retracting and ejecting the propeller 3 of
the retractable thruster for the swimming vessel 2 may
be performed in Figures 3B and 3C by the following
steps:
- connecting a water-permeable protective element 7 to
the retractable thruster above the propeller 3 inside
the bottom well 5 of the swimming vessel 2;
- preventing, with the water-permeable protective ele-
ment 7, loose ice from passing through the water-
permeable protective element 7 to the inside of the
bottom well 5 when the propeller is in the ejected po-
sition according to Figure 3B;
- pushing, with the water-permeable protective element
7 ice out of the bottom well 5 when the propeller 3 is
moved from the retracted position according to Figure
3C to the ejected position according to Figure 3B.
Figure 4A is an illustration of an embodiment of a re-
tractable thruster in an ejected position. Figure 4B
illustrates the retractable thruster obliquely from be-
low. Figures 4A and 4E illustrate that one hydraulic
cylinder 14a, 14b goes through each opening 25a, 25b in
the perforated plates 71, 72. Thus, a first cylinder
housing 16a of the first hydraulic cylinder 14a goes
through the first opening 25a of the first perforated
plate 71 and a second cylinder housing 16b of the sec-
CA 02949013 2016-11-18
27
ond hydraulic cylinder 14b goes through the second
opening 25b of the second perforated plate 72. The
first cylinder housing 16a is connected to a first con-
nection element 39a and the second cylinder housing 16b
is connected to a second connection element 39b. These
connection elements 39a, 39b are used to connect the
lower end of the cylinder housings 16a, 16b to the in-
ner surface of the bottom well. In fact, the shape of
the openings 25a, 25b may be designed according to the
connection elements 39a, 39b. As seen from Figures 3C,
3B and 4B, the housings 16a, 16b of the hydraulic cyl-
inders 14a, 14b go through the stationary support
structure 11. The upper ends of the hydraulic cylinders
14a, 14b may be secured to the stationary support
structure 11 in order to improve the stability of the
hydraulic cylinders 14a, 14b.
For example, the non-pivoting tube 13 can be a stem
tube, which functions as a guide bar having a sliding
surface in an outer surface of the stem tube. The guid-
ing element 12 may comprise a suitable bearing and/or a
sliding surface and a seal fitted around the stem tube.
The guiding element 12 may comprise, for example, a me-
chanical seal, which enables the sliding of the outer
surface of stem tube inside the guiding element 12.
Figure 4B illustrates that the non-pivoting tube 13
goes through a lead-through hole 35 in the stationary
support structure 11. The guiding element 12 is con-
nected around the lead-through hole 35 of the station-
ary support structure 11 and thereby remains station-
ary. The moving support structure 15 is connected to
the upper end of the non-pivoting tube 13. The connec-
tion between the upper end of the non-pivoting tube 13
and the moving support structure 15 may be done, for
example, by welding or with a tight fit in order to
firmly connect them together. The non-pivoting tube 13
is fitted inside the guiding element 12. The non-
CA 02949013 2016-11-18
28
pivoting tube 13 moves vertically inside the guiding
element 12 when the pistons 19a, 19b move the moving
support structure 15 in a reciprocating manner, thus
retracting or ejecting the propeller 3. Figure 4A also
illustrates the position of the inlet 40a, 40b of each
hydraulic cylinder 14a, 14b, which may be located near
the upper end of the piston 19a, 19b.
The retractable thruster may comprise guide bars 38a,
38b. One guide bar 38a may be for each hydraulic cylin-
der 14a, 14b. The purpose of the guide bars 38a, 38b is
to support the retractable thruster into a wall and/or
to ceiling structures inside an engine room of the
swimming vessel. One example of additional attachment
structures 41 to the wall(s) and/or to the ceiling are
illustrated with dashed lines in Figure 4A. These guide
bars 38a, 38b may be configured through the moving sup-
port structure 15 with similar type of structure as the
guiding element 12. Each guide bar 38a, 38b may be con-
figured inside a guiding element 381a, 381b of the mov-
ing support structure 15. Each guiding element 381a,
381b may comprise a mechanical seal enabling the slid-
ing of the outer surface of the guide bar 38a, 38b in-
side the guiding element 381a, 381b. The guide bars
38a, 38b may be hollow pipes, which are attached into
the stationary support structure 11 from a lower end of
the guide bar 38a, 38b.
An upper end of the guide bar 38a, 38b is attached to
the wall(s) and/or ceiling of the engine room with the
additional support structures 41. The moving support
structure 15 slides up and down along the guide bars
38a, 38b, when the pistons 19a, 19b reciprocate. At the
upper end of the guide bars 38a, 38b, the retractable
thruster may comprise a locking device 52, which locks
the retractable thruster to the retracted position.
This locking device 52 may be needed because there may
CA 02949013 2016-11-18
29
be internal leaks in the hydraulic cylinders 14a, 14b
or in the hydraulic system, whereby it may be possible
that over time, the propeller 3 is unwantedly low-
ered/ejected. This unwanted movement may be marginal,
but in the long term, it may have an unwanted impact on
the operation of the retractable thruster and particu-
larly when the retractable thruster is in the retracted
position where it has been unused for some time.
The retractable thruster may comprise a drive lead-
through channel 42. The drive from the engine or motor
is led to the lower gear 301 through this drive lead-
through channel 42.
The propeller 3 may be pivotable for 360 degrees around
a vertical axis 43 of the retractable thruster. This
movement is illustrated with arrows 28 in Figure 4A.
Figure 4B illustrates that the retractable thruster may
comprise a bearing 29 which enables the rotation of the
propeller 3 around its vertical axis 43. Figure 4B also
illustrates that a lower end 24 of the non-pivoting
tube 13 is connected to the propeller 3. A second at-
tachment interface 49 of the retractable thruster be-
tween a pivoting tube 50, which is inside the non-
pivoting tube 13, and the propeller 3 is illustrated in
Figure 4B. The pivoting tube 50 is pivotable connected
to the lower end bearing 29 enabling the propeller 3 to
be pivoted for 360 degrees around the vertical axis 43
of the retractable thruster. A third attachment inter-
face 51 of the retractable thruster may be between a
support 27 of the lifting and lowering arrangement 4
and the non-pivoting tube 13. This third attachment in-
terface 51 is described in more detail below, for exam-
ple with reference to Figures 4C, 4D and 6.
Figure 4C is a simplified sectional view of the embodi-
ment of the retractable thruster of Fig. 4A in an
CA 02949013 2016-11-18
ejected position. Figure 4C illustrates that the non-
pivoting tube 13 is outside the pivoting tube 50 and
therefore functions as a stem tube. The bearing 29 is
configured between the non-pivoting tube 13 and the
5 pivoting tube 50 enabling the pivoting of the propeller
3 around the vertical axis 43. The bearing 29 is repre-
sented with two rectangles filled with mesh-like hatch.
The bearing 29 allows the pivoting of the pivoting tube
50 without the pivoting of the non-pivoting tube 13. A
10 drive element (not illustrated) may be led to the lower
gear 301 of the propeller 3 via the lead-through chan-
nel 42 of the pivoting tube 50. The drive element is
used to drive/rotate the propeller 3 to achieve the
thrust of the retractable thruster.
Figure 4D is a detail view of the retractable thruster
of Figure 4A. Figure 413 discloses how the support 27 is
connected to the lower end 24 of the non-pivoting tube
13 with the third attachment interface 51. The third
attachment interface 51 is described in more detail be-
low, for example with reference to Figure 6. The sup-
port 27 is described in more detail below, for example
with reference to Figure 5.
An azimuth thruster is an embodiment of a marine pro-
peller that can be pivoted to any horizontal angle (az-
imuth), making a rudder unnecessary. Azimuth thrusters
give swimming vessels better maneuverability than a
fixed propeller and rudder system.
By pivoting the propeller of the azimuth thruster for
360 , the full propulsive power may be used for manoeu-
vring of the swimming vessel. The retractable thruster
can be adapted for different types of drives, for exam-
ple a diesel or an electric drive.
CA 02949013 2016-11-18
31
Figure 4E is another detail view of the retractable
thruster of Figure 4A. Figure 4E describes one suitable
installation point for the inlets 40a, 40b of the hy-
draulic cylinders 14a, 14b. Also the location of the
air venting connection 53 is illustrated in Figure 4E.
As seen from Figure 4E, the inlet 40a leads the hydrau-
lic fluid from the hydraulic fluid connection line 54
to the inside of the piston 19a of the hydraulic cylin-
der 14a. This feature is advantageous, because the hy-
draulic connection line 54, such as hydraulic hoses,
pipes and/or fittings, may be connected to the moving
support structure 15 so there may be no need to arrange
any hydraulic hoses, pipes and/or fittings on the water
side opening portion of the well. This feature may pre-
vent corrosion of the hoses, pipes or fittings connect-
ed to the inlets 40a, 40, because the hoses, pipes
and/or fittings may be kept out of reach of the water
inside the well.
Figure 5 is a sectional view IV-IV of the embodiment of
the retractable thruster of Figure 1A. Figure 5 illus-
trates a sectional view of the retractable thruster
from the top of the retractable thruster. The area Al
of the cross-section of the bottom well 5 is referenced
with an indication Al and has a diameter Dl. An area A2
of the water-permeable protective element 7 including
the area of the connection elements 39a, 39b is refer-
enced with an indication A2 and has a diameter D2. The
Area A2 may cover 95% of the area Al, or even 98-99%.
The suitable percentage may be determined according to
the clearance 30 needed for the retracting/ejecting to
work properly in such a way that the water-permeable
protective element 7 does not collide against the inner
surface of the bottom well 5 at any position along its
movement. Some clearance 30 must be left between the
inner surface of the bottom well 5 and an outer edge of
CA 02949013 2016-11-18
32
the water-permeable protective element 7 in order to
reliably move the water-permeable protective element 7.
The connection elements 39a, 39b may be welding brack-
ets as illustrated in Figure 5. The welding brackets
are welded to the inner surface of the bottom well 5.
These welds are referenced with an indication 22 in
Figure 5. The welds are not too sensitive to corrosion
as they can be painted over. Another attachment solu-
tion would naturally be to use bolts to connect the
connection elements 39a, 39b to suitable threads in the
bottom well 5. In this case, adequate protection must
be provided for this bolt type attachment in order to
prevent corrosion.
The lifting and lowering arrangement 4 may comprise a
support 27. The support 27 may be, for example, a
plate. The purpose of the support 27 is to connect the
cylinder housings 16a, 16b to each other and to an out-
er surface of a lower end of the non-pivoting tube 13
in order to provide extra support. As the propeller is
very heavy, this feature improves stability in a lower
portion of the lifting and lowering arrangement 4. With
the support 27 it is also possible to connect the first
perforated plate 71 and the second perforated plate 72
together to form the water-permeable protective element
7. The water-permeable protective element 7 is connect-
ed to the support 27 from the attachment interface 31.
In Figure 5 the attachment interface 31 is under the
support 27 and thereby only partially illustrated with
dashed lines. The support 27 may be a thick triangular-
like plate. Each cylinder housing 16a, 16b goes through
a hole 44 in the support 27 located in proximity to two
of the tips of the triangular-like shape. The support
27 is connected to the lower end of the non-pivoting
tube 13 and thereby moves with the non-pivoting tube
13. When the water-permeable protective element 7 moves
CA 02949013 2016-11-18
33
in the vertical direction with the propeller 3, the
cylinder housings 16a, 16b function as bearing surfaces
enabling the support 27 to move along the outer surface
of the cylinder housings 16a, 16b.
Figure 6 is a sectional view VII-VII of the embodiment
of the retractable thruster of Figure 1A. Figure 6 il-
lustrates how the water-permeable protective element 7
is connected to the rest of the structure in the re-
tractable thruster. The support 27 may be connected to
the lower end 24 of the non-pivoting tube 13 with the
third attachment interface 51. As seen also from Figure
4D, the lead-through opening 26 of the water-permeable
protective element 7 may have a larger diameter than a
lead-trough opening 55 of the support 27. This feature
enables the support 27 to be connected to the lower end
24 of the non-pivoting tube 13 with the third attach-
ment interface 51, for example, by bolting. The water-
permeable protective element 7 is on the other hand
connected to the support 27 from the attachment inter-
face 31.
Figure 7A is a partial section view of an embodiment of
a retractable thruster in an ejected position. Figure
7B is a partial section view of the embodiment of the
retractable thruster of Fig. 7A in a retracted posi-
tion. The retractable thruster may comprise a water-
permeable protective element 7a according to Figures 7A
and 7B. The water-permeable protective element 7a com-
prises mesh 73a with a suitable mesh size. The mesh 73a
may me made out of two parts: a lower mesh 71a and an
upper mesh 72a. The meshes 71a, 72a may be designed to
have a curved shape. When the meshes 71a, 72a are
brought together, the shape may bring more strength for
the water-permeable protective element 7a. The water-
permeable protective element 7a may be connected to the
lower end 24 of the non-pivoting tube 13. The operation
CA 02949013 2016-11-18
34
of the retractable thruster in Figures 7A and 7B is
similar to the retractable thruster in Figures 1-6 and
is not explained again herein.
Figure 8 is another illustration of a water-permeable
protective element 7b. The water-permeable protective
element 7b comprises a combination of a perforated
plate 71b, 72b and mesh 73b. Each perforated plate 71b,
72b comprises three mesh structures. The water permea-
ble protective element 7b comprises several cut-out
openings 23b that are manufactured into the perforated
plates 71b, 72b. The meshes 73b are connected on top of
or inside the cut-out openings, for example by welding
or with screws or other suitable accessories. In this
solution there may be less drilling to do, and thereby
costs may be reduced in the manufacturing phase of the
water-permeable protective element 7. The water permea-
ble protective element 7b is similarly connected to the
support as the water-permeable protective element 7 in
Figures 1-6.
Figure 9 is another illustration of a water-permeable
protective element 7c. The water-permeable protective
element 7c comprises a combination of a pipe structure
10 and mesh 73c. The pipe structure 10 may be made out
of several pipe parts. A frame of the water-permeable
protective element 7c may be made out of bent pipes
101, 102, 103, 104, 105 which are, for example, welded
together. The frame may be welded together with a lead-
through part 46c with welds 45. The structure of the
water-permeable protective element 7c may be strength-
ened with straight pipes 106, 107, 108, 109, 110, 111
which are connected between the frame and the lead-
through part 46c. The straight pipes 106, 107, 108,
109, 110, 111 may be connected inside holes 47 in the
frame and in the lead-through part 46c. The straight
pipes 106, 107, 108, 109, 110, 111 may also be welded
CA 02949013 2016-11-18
to the frame and to the lead-through part 46c. The non-
pivoting tube is arranged through the lead-through part
46c. The water-permeable protective element 7c may be
connected to the lower end of the non-pivoting tube
5 with the support. The structure of the water-permeable
protective element 7c may enable the making of the re-
tractable thruster lighter as the pipes are hollow and
most of the area of the water-permeable protective ele-
ment is mesh 73c.
Figure 10 is another illustration of a water-permeable
protective element 7d. The water-permeable protective
element 7d comprises mesh 73d. The water-permeable pro-
tective element 7d comprises a combination of a support
structure 48d and mesh 73d. The support structure 48d
comprises support arms 111d, 112d, 113d, 114d, 115d,
116d, 117d, 118d and a lead through part 46d. The
structure of the water-permeable protective element 7d
may be strengthened with the support arms 111d, 112d,
113d, 114d, 115d, 116d, 117d, 118d. The support arms
111d, 112d, 113d, 114d, 115d, 116d, 117d, 118d are con-
nected between an outer edge 47d of the mesh 73d and
the lead-through part 46d, for example by welding. The
support arms may be, for example, made out of a metal
plate. They can also be standard steel parts such as
metal profiles or beams. The non-pivoting tube is ar-
ranged through the lead-through part 46d. The water-
permeable protective element 7d may be connected to the
lower end of the non-pivoting tube with the support.
Figure 11 is another illustration of a water-permeable
protective element 7e. The water-permeable protective
element 7e is arranged inside a square-shaped bottom
well 5e. Thus, also the water-permeable protective ele-
ment 7e is designed square-shaped. Another difference
between the water-permeable protective element 7e in
Figure 11 and the water-permeable protective element 7
CA 02949013 2016-11-18
36
in Figure 2 is that a perforated plate 71e of the wa-
ter-permeable protective element 7e is made out of a
single part. Otherwise, the water-permeable protective
element 7e is similar to the water-permeable protective
element 7 in Figure 2.
Although in the embodiments the water-permeable protec-
tive element 7, 7a, 7b, 7c, 7d, 7e is disclosed as a
substantially circular or a square-like structure, the
water-permeable protective element may also be another
type of a shape, for example oval, triangular, or any
type of a shape which is made according to the bottom
well. The water-permeable protective element can be im-
plemented in various types of shapes, and the number,
shape and amount of holes or the mesh size may vary.
The water-permeable protective element 7, 7a, 7b, 7c,
7d, 7e substantially prevents loose ice from drifting
inside the bottom well 5, 5e when the propeller 3 is in
the ejected position. This enables prevention or at
least reduction of the possibility that the lifting and
lowering arrangement 4 is jammed because of the loose
ice jamming the linear movement and possibly even
freezing inside the bottom well 5, 5e. Thus, it is pos-
sible to use the retractable thruster in ice condi-
tions.
Although Figures 1A to 11 describe the retractable
thruster with the water-permeable protective element 7,
7a, 7b, 7c, 7d, 7e to be used in ice conditions, the
water-permeable protective element 7, 7a, 7b, 7c, 7d,
7e may be adapted to block many different types of ob-
jects in the water. For example, with the structure of
the retractable thruster disclosed above it is possible
to gain protection against other solid material that
may damage the structures of the retractable thruster,
for example sunken logs and other waste material.
CA 02949013 2016-11-18
37
It is obvious to a person skilled in the art that with
the advancement of technology, the basic idea may be
implemented in various ways. The solution and its em-
bodiments are thus not limited to the examples de-
scribed above; instead they may vary within the scope
of the claims.
The embodiments described herein may be used in any
combination with each other. Several or at least two of
the embodiments may be combined together to form a fur-
ther embodiment. A method or a device may comprise at
least one of the embodiments described hereinbefore.
It is to be understood that any of the above embodi-
ments or modifications can be applied singly or in com-
bination to the respective aspects to which they refer,
unless they are explicitly stated as excluding alterna-
tives.
