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.

Landscapes

• 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)
• Earth Drilling (AREA)
• Wind Motors (AREA)
• Movable Scaffolding (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=60972169

Family Applications (1)

Country Status (4)

Family Cites Families (13)

• 2016
  • 2016-12-07 SE SE1651610A patent/SE542122C2/en unknown
• 2017
  • 2017-12-07 WO PCT/EP2017/081773 patent/WO2018104420A1/en active Application Filing
  • 2017-12-07 EP EP17829133.2A patent/EP3551532B1/de active Active
  • 2017-12-07 RU RU2019118777A patent/RU2747323C2/ru active

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