EP3551532A1 - A method of and a device for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster - Google Patents

A method of and a device for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster

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Publication number
EP3551532A1
EP3551532A1 EP17829133.2A EP17829133A EP3551532A1 EP 3551532 A1 EP3551532 A1 EP 3551532A1 EP 17829133 A EP17829133 A EP 17829133A EP 3551532 A1 EP3551532 A1 EP 3551532A1
Authority
EP
European Patent Office
Prior art keywords
fins
pod housing
pod
distance
fin
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP17829133.2A
Other languages
German (de)
French (fr)
Other versions
EP3551532B1 (en
Inventor
Anders LOBELL
Rikard Johansson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kongsberg Maritime Sweden AB
Original Assignee
Kongsberg Maritime Sweden AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kongsberg Maritime Sweden AB filed Critical Kongsberg Maritime Sweden AB
Publication of EP3551532A1 publication Critical patent/EP3551532A1/en
Application granted granted Critical
Publication of EP3551532B1 publication Critical patent/EP3551532B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H5/00—Arrangements on vessels of propulsion elements directly acting on water
    • B63H5/07—Arrangements on vessels of propulsion elements directly acting on water of propellers
    • B63H5/125—Arrangements on vessels of propulsion elements directly acting on water of propellers movably mounted with respect to hull, e.g. adjustable in direction, e.g. podded azimuthing thrusters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
    • B63B1/32—Other means for varying the inherent hydrodynamic characteristics of hulls
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H1/00—Propulsive elements directly acting on water
    • B63H1/02—Propulsive elements directly acting on water of rotary type
    • B63H1/12—Propulsive elements directly acting on water of rotary type with rotation axis substantially in propulsive direction
    • B63H1/14—Propellers
    • B63H1/28—Other means for improving propeller efficiency

Definitions

  • the present invention relates to a method of reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster having a rotary pod housing with a substantially vertical slewing axis and a downwardly directed fin means carried by the pod housing abaft the slewing axis.
  • It also relates to a device for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster having a rotary pod housing with a substantially vertical slewing axis and a downwardly directed fin means carried by the pod housing abaft the slewing axis.
  • the azimuthal torque around the slewing axis of a pod unit or azimuthal thruster has to be handled by an installed steering machine for all combinations of steering angles, propeller speeds and ship speeds.
  • the main causes of the azimuthal torque are:
  • a common way of reducing the azimuthal torque for pod units and azimuth thrusters is to place a fin with a wing profile abaft the slewing axis.
  • the fin creates a lateral force due to the angle of attack, especially at turning of the pod unit.
  • the lateral force gives rise to a torque that acts in a direction opposite to the sum of other torque contributions and therefore it reduces the maximum azimuthal torque.
  • a fin with a wing profile placed in the slip stream of a propeller may generate a forward directed force, which is greater than the total drag on the fin that acts in the opposite direction. Thereby, this regain of the rotational energy in the slip stream will give a positive thrust contribution that increases the efficiency of the pod unit.
  • the distance between the slewing axis and a center of the lateral forces acting on the fin forms a second arm of the lever.
  • JP 2009214650 (A) (Universal Shipbuilding Corp.) discloses a pod type propulsion unit capable of reducing propulsion resistance, wherein rectangular-plate vanes (current plates) are fixed to the side surface of the pod body so as to be disposed parallel to the axial direction of the pod body and in the direction normal to (the same as the radial direction of) the side surface of the pod body.
  • the amount of projection of the vane is 40 % or smaller of the radius of the propeller, i.e. the projection is extremely small compared to conventional known fins and therefore may not provide sufficient capability.
  • POD arrangements having a plurality of fins, but not for the purpose of reducing torque or reducing resistance, but to improve cooling and recover swirl, respectively.
  • the object of the present invention is to improve in comparison to that for a pod unit or azimuth thruster having a conventional downward extending fin.
  • a further advantage that may be achieved with the invention is that the risk of grounding may be made lower than for a design using a single fin, since the two fins may be positioned to protrude a smaller distance below the POD
  • Fig. 1 is a side view of a preferred embodiment of a pod unit or azimuth thruster
  • Fig. 2 is a side view and a view from behind respectively of a mounted, two fins design according to the invention
  • Fig. 3 is a side view and a view from behind respectively of a mounted, conventional single fin design according to prior art
  • Fig. 4 is a side view presenting pressure characteristics appearing on the front part of a mounted, two fins design according to the invention and a conventional single fin design according to prior art, respectively,
  • Fig. 5 presents a diagram showing test results regarding steering torque at different steering angles for a POD unit without any fin, equipped with a conventional single fin and equipped with a two fins design according to the invention, respectively,
  • Fig. 6 presents a diagram showing test results regarding efficiency at different fin axis intersection positions for a POD unit equipped with a two fins design according to the invention.
  • Fig. 1 shows a pulling pod unit or azimuth thruster 1 having a rotary neck 2.
  • a pod housing 4 having a central axis 3B extending generally horizontal.
  • the rotary neck 2 provides a substantially vertical slewing axis 3A, around which the pod unit 1 or azimuth thruster may be rotated.
  • a pulling propeller 7, having a radius R.
  • the slewing axis 3A may be positioned at different locations, as exemplified according to this embodiment, it may be positioned a distance x in front of the vertical center line 5 of the pod housing 4.
  • the pod housing carries two fixed, generally downwardly directed fins 6.
  • the fins 6 are positioned on the aft part 40 of the POD housing 4, at a first axial distance r (to a front attachment part of the fin) from the slewing axis 3 A, which distance r may vary, but that in some applications preferably is greater than the radius R of the propeller 7.
  • the end surface 41 of the aft part 40 of the POD housing 4 is positioned at second axial distance L a from the slewing axis 3 A which second axial distance is larger than the first axial distance r.
  • the aft end 65 of the fins 6 preferably terminate in line with or at a distance Y frontwardly from the aft part end 41.
  • the first axial distance r i.e. between the POD azimuth rotation axis 3A, and the fins 6 should preferably be 10% to 85%, even more preferred 50%> to 70%>, of the second axial distance L a between the slewing axis 3 A and the aft part end 41.
  • the fins 6 are positioned and extend on one side each in relation to a vertical longitudinal plane 30 of the pod housing 4.
  • the fins 6 comprise one starboard fin 6A, positioned on the starboard side of the aft part 40 in relation to the slewing axis 3, and one port fin 6B, positioned on the port side of it in relation to the slewing axis 3A.
  • the two fins 6 are preferably identically shaped and symmetrically positioned in relation to the vertical longitudinal plane 30 of the pod housing 4 and extend downwardly below the lower edge 42 of the pod housing, such that both fin tips 63 are positioned below the lower edge 42 of the pod housing.
  • the fins 6 extend substantially radially to present an angle ⁇ them between, which preferably is in the range of 0° ⁇ ⁇ ⁇ 90°, more preferred ⁇ ⁇ 70°, even more preferred ⁇ ⁇ 50°.
  • the distance ⁇ between the inner portions of the centre plane 65 of the fins 6 shall advantagely be smaller than the diameter Dp of the POD housing 4, preferably 0,1 Dp ⁇ ⁇ ⁇ 0,7 Dp, more preferred 0,2 Dp ⁇ ⁇ ⁇ 0,4 Dp and preferably ⁇ is such that the crossing point of the center lines 65 of the fins 6 will cross at a point above the horizontal center plane of the pod housing 4.
  • Both fins are preferably in form of streamlined wing profiles having a largest thickness t and presenting a side area A, projected along the vertical longitudinal plane 30.
  • the fin span Sf should preferably be about 40% to 100%, even more preferred 60%> to 95%, of the radius R of the propeller 7.
  • the fins 6 will protrude a vertical distance Ld from the lowest surface 42 of the POD housing 4, wherein preferably 0,1 Sf ⁇ Ld ⁇ 0,7 Sf, more preferred 0,3 Sf ⁇ Ld ⁇ 0,6 Sf.
  • the fins 6 have a front portion 61 that protrude downwards and abaft presenting an angle a in relation to a vertical axis, which angle a preferably is in the range of 0-80°, more preferred 30-60°.
  • the aft portions 62 protrude downwards and abaft presenting an angle ⁇ in relation to the vertical axis, which preferably is smaller than the angle a (in any direction in relation to the vertical) of the front portion 61, preferably in the range of 0-70°, more preferred 20-50°. Thanks to this design, a larger fin area may be exposed (compared to non-angled) within a vertical space limited by a desired depth level, e.g. Ld.
  • Fig. 4 there are shown schematic views of fins 6 presenting results from analysis of low pressure zones at 7,5° steering angle for an arrangement according to the invention in the left hand side of Fig. 4 and for a single fin in the right hand side.
  • the width 61 of the cavitating part of a double fin 6 is significantly smaller than that 61 ' of a single fin. Thanks to this result a larger cavitation free steering angle is easily achieved.
  • a part of the superior cavitation performance can also be traded to further increase the gain in hydrodynamic unit efficiency by making the fins relatively thinner, i.e.
  • the diameter D of the propeller is preferably in the range of 1 meter - 10 meter, most preferred 1,5 meters to 8 meters.
  • the horizontal span C is preferably in the range such that C/R is from 0,4 to 0,8.
  • the diameter Dp of the pod housing 4 is in the range of 0,4 R - 1,2 R, more preferred 0,5 R - R.
  • the pod neck 2 itself and/or the transition zone between the pod housing 4 and the neck 2 may preferably be designed to achieve a further reduction of the azimuthal torque by presenting further areas and/or a kind of vane located along the upper part of the pod housing 4, whereby the unit efficiency will be slightly further improved.
  • Fig. 6 presents a diagram showing test results regarding efficiency at different fin axis intersection positions for a POD unit equipped with the two fins design according to the invention.
  • the fins 6 intersecting at a point above the horizontal center plane (including the centre line 3B) of the pod housing 4 and to use fins that are thin.
  • Three different arrangements have been tested, including two different fin designs, a first fin design, graphs a) and c), having a first fin thickness tl and a second fin design b) having a second fin thickness t2, wherein t2 is larger than tl .
  • the fin designs are the same.
  • graph c presents an arrangement where the POD housing has irregularities (e.g.
  • the intersecting point A, B, C of the center lines 65 of the fins 6 is positioned between 0,1 to 0,7 times the diameter Dp of the POD housing 4 above the horizontal center plane of the pod housing 4, preferably 0,2-0,5 times the diameter Dp.
  • the fin may be bent or twisted to meet the flow in a way to improve efficiency at low steering angles.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • Ocean & Marine Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)
  • Movable Scaffolding (AREA)
  • Wind Motors (AREA)
  • Earth Drilling (AREA)

Abstract

This invention relates to a device and method), of reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster (1) having a rotary pod housing (4) with a substantially vertical slewing axis (3A), a pulling propeller (7), and two downwardly directed fins (6) carried by the pod housing (4) abaft the slewing axis (3) adjacent the rear end (41) of the pod housing (4) and positioning said two downwardly directed fins (6) a distance (δ) apart, one on each side of a longitudinal plane (30) through the slewing axis (3A) on an aft part (40) of the pod housing (4) to extend substantially radially out from the pod housing (4), wherein said fins (6) are positioned to have their center planes (65) presenting a sharp angle (β) between the two fins (6) wherein the intersecting point of the center lines (65) of the fins (6) will intersect at a point above a horizontal center plane of the pod housing (4).

Description

A METHOD OF AND A DEVICE FOR REDUCING THE AZIMUTHAL TORQUE ACTING ON A PULLING POD UNIT OR AZIMUTH THRUSTER
TECHNICAL FIELD
The present invention relates to a method of reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster having a rotary pod housing with a substantially vertical slewing axis and a downwardly directed fin means carried by the pod housing abaft the slewing axis.
It also relates to a device for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster having a rotary pod housing with a substantially vertical slewing axis and a downwardly directed fin means carried by the pod housing abaft the slewing axis.
BACKGROUND ART
The azimuthal torque around the slewing axis of a pod unit or azimuthal thruster has to be handled by an installed steering machine for all combinations of steering angles, propeller speeds and ship speeds.
The main causes of the azimuthal torque are:
• The lateral force that is created due to an oblique flow toward the propeller together with the distance between the propeller and the vertical slewing axis. This distance forms one arm of a lever that is pivotal around the slewing axis. · At turning an oblique flow to the propeller blades will give a varying angle of attack over a complete turn at a given radius. This variation causes a torque that affects the total azimuthal torque.
• The distance between the load center, due to hydrodynamic forces, of the pod housing and the vertical slewing axis will together with the resulting lateral force give a torque that affects the total steering torque.
A common way of reducing the azimuthal torque for pod units and azimuth thrusters is to place a fin with a wing profile abaft the slewing axis. The fin creates a lateral force due to the angle of attack, especially at turning of the pod unit. The lateral force gives rise to a torque that acts in a direction opposite to the sum of other torque contributions and therefore it reduces the maximum azimuthal torque. At certain operating conditions, a fin with a wing profile placed in the slip stream of a propeller may generate a forward directed force, which is greater than the total drag on the fin that acts in the opposite direction. Thereby, this regain of the rotational energy in the slip stream will give a positive thrust contribution that increases the efficiency of the pod unit. The distance between the slewing axis and a center of the lateral forces acting on the fin forms a second arm of the lever.
The use of such a fin is disclosed in WO 2005/012075 Al (Rolls-Royce Marine AS) and JP 2004090841 (A) (Kawasaki Heavy Ind. Ltd.), for example.
JP 2009214650 (A) (Universal Shipbuilding Corp.) discloses a pod type propulsion unit capable of reducing propulsion resistance, wherein rectangular-plate vanes (current plates) are fixed to the side surface of the pod body so as to be disposed parallel to the axial direction of the pod body and in the direction normal to (the same as the radial direction of) the side surface of the pod body. The amount of projection of the vane is 40 % or smaller of the radius of the propeller, i.e. the projection is extremely small compared to conventional known fins and therefore may not provide sufficient capability. Further, from WO 01/54973 and JP2010221975 there are known POD arrangements having a plurality of fins, but not for the purpose of reducing torque or reducing resistance, but to improve cooling and recover swirl, respectively.
SUMMARY OF THE INVENTION
The object of the present invention is to improve in comparison to that for a pod unit or azimuth thruster having a conventional downward extending fin.
This object is achieved in accordance with the present invention by means of the novel concept as defined in the independent claims.
Thanks to the use of a two fins configuration according to the invention significant performance advantages may be gained compared to a single fin configuration. Inter alia a better cavitation performance may be achieved, resulting in the advantage that a larger cavitation free steering angle is easily obtained. Moreover, it has shown that it is possible to recover more of the rotational propeller flow losses, compared to a single fin configuration, i.e. to increase the hydrodynamic unit efficiency. According to an additional aspect a part of the superior cavitation performance may also be traded to further increase the gain in hydrodynamic unit efficiency by making the fins relatively thinner, i.e. designing the fins having a thickness t that is relatively smaller in relation to the flow length C compared to a conventional single fin, wherein preferably the total thickness of the two fins is smaller than the thickness of one fin. tt,f /
A further advantage that may be achieved with the invention is that the risk of grounding may be made lower than for a design using a single fin, since the two fins may be positioned to protrude a smaller distance below the POD
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention will be described in more detail with reference to preferred embodiments and the appended drawings.
Fig. 1 is a side view of a preferred embodiment of a pod unit or azimuth thruster
according to the present invention, and,
Fig. 2 is a side view and a view from behind respectively of a mounted, two fins design according to the invention,
Fig. 3 is a side view and a view from behind respectively of a mounted, conventional single fin design according to prior art,
Fig. 4 is a side view presenting pressure characteristics appearing on the front part of a mounted, two fins design according to the invention and a conventional single fin design according to prior art, respectively,
Fig. 5 presents a diagram showing test results regarding steering torque at different steering angles for a POD unit without any fin, equipped with a conventional single fin and equipped with a two fins design according to the invention, respectively,
Fig. 6 presents a diagram showing test results regarding efficiency at different fin axis intersection positions for a POD unit equipped with a two fins design according to the invention.
DETAILED DESCRIPTION
Fig. 1 shows a pulling pod unit or azimuth thruster 1 having a rotary neck 2. At the lower end of the neck 2 there is arranged a pod housing 4 having a central axis 3B extending generally horizontal. The rotary neck 2 provides a substantially vertical slewing axis 3A, around which the pod unit 1 or azimuth thruster may be rotated. At the front of the pod housing 4 there is arranged a pulling propeller 7, having a radius R. The slewing axis 3A may be positioned at different locations, as exemplified according to this embodiment, it may be positioned a distance x in front of the vertical center line 5 of the pod housing 4. Abaft the slewing axis 3 A, the pod housing carries two fixed, generally downwardly directed fins 6. The fins 6 are positioned on the aft part 40 of the POD housing 4, at a first axial distance r (to a front attachment part of the fin) from the slewing axis 3 A, which distance r may vary, but that in some applications preferably is greater than the radius R of the propeller 7. The end surface 41 of the aft part 40 of the POD housing 4 is positioned at second axial distance La from the slewing axis 3 A which second axial distance is larger than the first axial distance r. The aft end 65 of the fins 6 preferably terminate in line with or at a distance Y frontwardly from the aft part end 41. The first axial distance r, i.e. between the POD azimuth rotation axis 3A, and the fins 6 should preferably be 10% to 85%, even more preferred 50%> to 70%>, of the second axial distance La between the slewing axis 3 A and the aft part end 41. As shown in Fig 2 the fins 6 are positioned and extend on one side each in relation to a vertical longitudinal plane 30 of the pod housing 4. The fins 6 comprise one starboard fin 6A, positioned on the starboard side of the aft part 40 in relation to the slewing axis 3, and one port fin 6B, positioned on the port side of it in relation to the slewing axis 3A.
In accordance with the invention, the two fins 6 are preferably identically shaped and symmetrically positioned in relation to the vertical longitudinal plane 30 of the pod housing 4 and extend downwardly below the lower edge 42 of the pod housing, such that both fin tips 63 are positioned below the lower edge 42 of the pod housing. The fins 6 extend substantially radially to present an angle β them between, which preferably is in the range of 0° < β < 90°, more preferred β < 70°, even more preferred β < 50°. As is evident for the skilled person the fins 6 may extend in different angles β, to fulfil the purpose of the invention, e.g. even in parallel β = 0°, with each other. Test indicate that it is an advantage to have β > 0°, and to have the fins 6 relatively close to each other to form a kind of flow tunnel in the space between the two fins 6, which will cause a synergetic effect regarding the flow of water passing around the fins 6. Hence, the distance δ between the inner portions of the centre plane 65 of the fins 6 shall advantagely be smaller than the diameter Dp of the POD housing 4, preferably 0,1 Dp < δ < 0,7 Dp, more preferred 0,2 Dp < δ < 0,4 Dp and preferably β is such that the crossing point of the center lines 65 of the fins 6 will cross at a point above the horizontal center plane of the pod housing 4. Both fins are preferably in form of streamlined wing profiles having a largest thickness t and presenting a side area A, projected along the vertical longitudinal plane 30. The fin span Sf should preferably be about 40% to 100%, even more preferred 60%> to 95%, of the radius R of the propeller 7. The fins 6 will protrude a vertical distance Ld from the lowest surface 42 of the POD housing 4, wherein preferably 0,1 Sf < Ld < 0,7 Sf, more preferred 0,3 Sf < Ld < 0,6 Sf.
According to the preferred shown embodiment in Figs. 1 and 2 the fins 6 have a front portion 61 that protrude downwards and abaft presenting an angle a in relation to a vertical axis, which angle a preferably is in the range of 0-80°, more preferred 30-60°. Also, the aft portions 62 protrude downwards and abaft presenting an angle γ in relation to the vertical axis, which preferably is smaller than the angle a (in any direction in relation to the vertical) of the front portion 61, preferably in the range of 0-70°, more preferred 20-50°. Thanks to this design, a larger fin area may be exposed (compared to non-angled) within a vertical space limited by a desired depth level, e.g. Ld.
Thanks to the invention there is an advantageous influence on the POD steering torque, i.e. by having a twin fin arrangement in the aft part of the POD unit. A larger total fin area Atot, is projected along the longitudinal vertical plane 30, compared to a
conventional single fin configuration (see fig. 3). In general terms Atot = 2 x A, implying that a much larger surface Atot can be active in comparison with a single fin.
Furthermore, that larger area Atot may be achieved at the same time as they 6 protrude a vertical distance Ld that is significantly smaller than with a single fin.
In Fig. 4 there are shown schematic views of fins 6 presenting results from analysis of low pressure zones at 7,5° steering angle for an arrangement according to the invention in the left hand side of Fig. 4 and for a single fin in the right hand side. There are shown five cavitation zones 61a-61e (from stronger to weaker). It is clear from this figure that the cavitation performance is better with a design according to the invention. The width 61 of the cavitating part of a double fin 6 is significantly smaller than that 61 ' of a single fin. Thanks to this result a larger cavitation free steering angle is easily achieved.
A part of the superior cavitation performance can also be traded to further increase the gain in hydrodynamic unit efficiency by making the fins relatively thinner, i.e.
designing the fins 6 having a thickness t that is relatively smaller in relation to the flow length C compared to a conventional single fin, wherein preferably t/C is in the range of 0,05- 0,3, more preferred 0,1-0,2. In fig. 5 there is presented a diagram showing test results regarding steering torque at different steering angles for a POD unit without any fin (curve A), equipped with a conventional single fin (curve B) and equipped with a two fins design according to the invention (curve C), respectively. As is evident a much better effect is achieved by means of the invention. It is shown significant differences, e.g. it should be noted that using a POD having no fin as reference for torque, i.e. a maximum of 1, a POD with one fin presents a maximum of 0,5, whereas according to the invention it merely is 0,3.
The diameter D of the propeller is preferably in the range of 1 meter - 10 meter, most preferred 1,5 meters to 8 meters.
The horizontal span C is preferably in the range such that C/R is from 0,4 to 0,8.
The diameter Dp of the pod housing 4 according to a preferred embodiment is in the range of 0,4 R - 1,2 R, more preferred 0,5 R - R.
Further, the pod neck 2 itself and/or the transition zone between the pod housing 4 and the neck 2, may preferably be designed to achieve a further reduction of the azimuthal torque by presenting further areas and/or a kind of vane located along the upper part of the pod housing 4, whereby the unit efficiency will be slightly further improved.
Fig. 6 presents a diagram showing test results regarding efficiency at different fin axis intersection positions for a POD unit equipped with the two fins design according to the invention. As is evident from the diagram it is an advantage to have the fins 6 intersecting at a point above the horizontal center plane (including the centre line 3B) of the pod housing 4 and to use fins that are thin. Three different arrangements have been tested, including two different fin designs, a first fin design, graphs a) and c), having a first fin thickness tl and a second fin design b) having a second fin thickness t2, wherein t2 is larger than tl . In other aspects, the fin designs are the same. Further, graph c), presents an arrangement where the POD housing has irregularities (e.g. screw heads) near by the fins, which causes extra turbulence. All three arrangements, a), b) and c), were tested having their intersecting point A (see Fig. 2) of the center lines 65 at said centre plane, and at a point B that intersects 0,3 Dp above said centre plane,
respectively. Further two of the fins sets, a) and b), were tested having their intersecting point C of the center lines 65 at 0,6 Dp above said centre plane. It is evident from the tests that the efficiency is better when the intersecting point is above said centre plane, and best when the intersecting point is at about 0,3 Dp above said centre plane. Further, it is evident from the tests (cf. graph a) and b)) that the efficiency is better when there is used thinner fins. Finally, the tests indicate (see graph c)) that the efficiency is even more improved when the POD housing has irregularities to use a positioning of the fins, such that their intersecting point is above said centre plane (cf. point A and B).
Preferably, the intersecting point A, B, C of the center lines 65 of the fins 6 is positioned between 0,1 to 0,7 times the diameter Dp of the POD housing 4 above the horizontal center plane of the pod housing 4, preferably 0,2-0,5 times the diameter Dp.
The invention is not limited by what that is described above but may be varied within the scope of the claims. For instance, it is evident that the skilled person knows that there is a big variety of different materials that can be used to fulfill the function of the fin 6, but that metal, e.g. steel, will often be preferred. Furthermore, in some
applications, the fin may be bent or twisted to meet the flow in a way to improve efficiency at low steering angles.

Claims

A method of reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster (1) having a rotary pod housing (4) with a substantially vertical slewing axis (3 A), a pulling propeller (7), and two downwardly directed fins (6) carried by the pod housing (4) abaft the slewing axis (3) adjacent the rear end (41) of the pod housing (4) and positioning said two downwardly directed fins (6) a distance (δ) apart, one on each side of a longitudinal plane (30) through the slewing axis (3 A) on an aft part (40) of the pod housing (4) to extend substantially radially out from the pod housing (4), characterized by positioning said fins (6) to have their center planes (65) presenting a sharp angle (β) between the two fins (6) wherein the intersecting point of the center lines (65) of the fins (6) will intersect at a point above a horizontal center plane of the pod housing (4).
A method as claimed in claim 1, characterized by positioning said fins (6) extending downwardly below the lower edge (42) of the pod housing, such that both fin tips (63) are positioned below the lower edge (42) of the pod housing.
A method as claimed in claim 1 or 2, characterized by positioning said fins (6) to extend substantially radially out from the pod housing (4) to have their center planes (65) presenting an angle (β) between fins (6) in the range of 0° < β < 90°, preferably β < 70° and even more preferred β < 50°.
A method as claimed in claim 1,2 or 3, characterized by arranging the intersecting point (A, B, C) of the center lines (65) of the fins (6) between 0,1 to 0,7 times the diameter (Dp) of the POD housing (4) above the horizontal center plane of the pod housing (4), preferably 0,2-0,5 times the diameter (Dp).
A method as claimed in claim 1,2, 3 or 4, characterized by positioning said fins (6) a distance (δ) apart regarding the inner portions of the centre planes (65) of the fins (6) that is smaller than the diameter (Dp) of the POD housing (4), preferably the distance (δ) is in the range 0,1 Dp < δ < 0,7 Dp.
A method as claimed in any preceding claim, characterized by positioning said fins (6) to protrude substantially radially a maximum vertical distance (Ld) from the lowest surface (42) of the POD housing (4) in the range of 0,1 Sf < Ld < 0,7 Sf, preferably 0,3 Sf < Ld < 0,6 Sf, wherein Sf is the radial span of a fin (6).
7. A method as claimed in any preceding claim, characterized by positioning said fins (6) such that the axial distance (r), between the slewing axis (3 A, and the front part of the fins (6) is in the range of 10% to 85% of a second axial distance (La), preferably 50%> to 70%> of said second axial distance (La), wherein said second axial distance (La) is the distance between the slewing axis (3 A) and the aft part end
(41) of the POD housing (4).
8. A pod unit or azimuth thruster having a fin arrangement for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster (1) having a rotary pod housing (4) with a substantially vertical slewing axis (3 A), a pulling propeller (7), and two downwardly directed fins (6) carried by the pod housing (4) abaft the slewing axis (3) adjacent the rear end (41) of the pod housing (4), wherein said two downwardly directed fins (6) are positioned, one on each side on an aft part (40) of the pod housing (4) and at a distance (δ) apart in relation to a longitudinal plane (30) including the slewing axis (3 A) ) and said two fins (6) extending substantially radially out from the pod housing, characterized in that the center planes (65) of said two fins (6) present a sharp angle (β) between fins (6), wherein the intersecting point of the center lines (65) of the fins (6) will intersect at a point above a horizontal center plane of the pod housing (4).
9. A fin arrangement as claimed in claim, characterized in that said fins (6) are arranged to extend downwardly below the lower edge (42) of the pod housing, such that both fin tips (63) are positioned below the lower edge (42) of the pod housing.
10. A fin arrangement as claimed in claim 8 or 9, characterized in that said fins (6) are arranged to extend radially out from the pod housing (4) to have their center planes (65) presenting an angle (β) between fins (6) in the range of 0° < β < 90°, preferably β < 70° and even more preferred β < 50°.
11. A fin arrangement as claimed in claim 8, 9 or 10, characterized in that the intersecting point (A, B, C) of the center lines (65) of the fins (6) is positioned between 0,1 to 0,7 times the diameter (Dp) of the POD housing (4) above the horizontal center plane of the pod housing (4), preferably 0,2-0,5 times the diameter (Dp).
12. A fin arrangement as claimed in any of claims 8-11, characterized in that the inner portions of the centre planes (65) of said fins (6) are a distance (δ) apart that is smaller than the diameter (Dp) of the POD housing (4), preferably the distance (δ) is in the range of 0,1 Dp < δ < 0,7 Dp.
13. A fin arrangement as claimed in any of claims 8-12, characterized in
that said fins (6) are arranged to protrude radially a maximum vertical distance (Ld) from the lowest surface (42) of the POD housing (4) in the range of 0,1 Sf < Ld < 0,7 Sf, preferably 0,3 Sf < Ld < 0,6 Sf, wherein Sf is the radial span of a fin (6).
14. A fin arrangement as claimed in any of claims 8-13, characterized in
that that the axial distance (r) between the front part of said fins (6) and the slewing axis (3 A), is in the range of 10% to 85% of a second axial distance (La), preferably 50% to 70% of said second axial distance (La), wherein said second axial distance (La) is the distance between the slewing axis (3 A) and the aft part end (41) of the POD housing (4).
EP17829133.2A 2016-12-07 2017-12-07 A method of and a device for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster Active EP3551532B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE1651610A SE542122C2 (en) 2016-12-07 2016-12-07 A pod unit or azimuth thruster having a fin arrangement for reducing the azimuthal torque
PCT/EP2017/081773 WO2018104420A1 (en) 2016-12-07 2017-12-07 A method of and a device for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster

Publications (2)

Publication Number Publication Date
EP3551532A1 true EP3551532A1 (en) 2019-10-16
EP3551532B1 EP3551532B1 (en) 2021-07-28

Family

ID=60972169

Family Applications (1)

Application Number Title Priority Date Filing Date
EP17829133.2A Active EP3551532B1 (en) 2016-12-07 2017-12-07 A method of and a device for reducing the azimuthal torque acting on a pulling pod unit or azimuth thruster

Country Status (4)

Country Link
EP (1) EP3551532B1 (en)
RU (1) RU2747323C2 (en)
SE (1) SE542122C2 (en)
WO (1) WO2018104420A1 (en)

Family Cites Families (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07196085A (en) * 1994-01-06 1995-08-01 Kawasaki Heavy Ind Ltd Propulsion device of ship
RU2128126C1 (en) * 1998-03-04 1999-03-27 Центральный научно-исследовательский институт им.акад.А.Н.Крылова Shipboard screw-propeller for motion and maneuvering of ship under ice conditions
FI115042B (en) 2000-01-28 2005-02-28 Abb Oy Engine unit for ships
JP4301748B2 (en) * 2001-06-29 2009-07-22 三菱重工業株式会社 Ship propulsion device
JP3842189B2 (en) * 2002-09-03 2006-11-08 川崎重工業株式会社 Pod propeller
NO324501B1 (en) 2003-08-01 2007-11-05 Rolls Royce Marine As Device for increasing the transmission stability of ships
JP2009214650A (en) 2008-03-10 2009-09-24 Universal Shipbuilding Corp Pod type propulsion unit and vessel
RU2384457C2 (en) * 2008-04-25 2010-03-20 Василий Николаевич Храмушин Active stabiliser of pitching and rolling motion of ship - stormy emergency propeller
DE202008011699U1 (en) * 2008-09-03 2008-11-06 Dl Fischer Gmbh Motorized propeller drive for a watercraft
JP5360887B2 (en) * 2009-03-25 2013-12-04 株式会社Ｉｈｉ Pod propeller
JP5294265B2 (en) * 2009-03-25 2013-09-18 株式会社Ｉｈｉ Pod propeller
JP5388184B2 (en) * 2009-03-25 2014-01-15 株式会社Ｉｈｉ Pod propeller
KR102095421B1 (en) * 2013-11-05 2020-03-31 대우조선해양 주식회사 Azimuth thruster

Also Published As

Publication number Publication date
SE542122C2 (en) 2020-02-25
WO2018104420A1 (en) 2018-06-14
EP3551532B1 (en) 2021-07-28
RU2019118777A3 (en) 2021-03-15
RU2019118777A (en) 2021-01-11
RU2747323C2 (en) 2021-05-04
SE1651610A1 (en) 2018-06-08

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