Azimuth Thruster Two-Fin Configuration Torque Reduction
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Solution Overview
Problem
Existing designs for pulling pod units and azimuth thrusters with conventional single fins are insufficient in reducing azimuthal torque and improving hydrodynamic efficiency, particularly at varying steering angles and propeller speeds, and may not provide sufficient protection against grounding risks.
Innovation Solution
A configuration of two downwardly directed fins, positioned aft of the slewing axis, with a thinner profile compared to conventional designs, which are symmetrically arranged and extend radially to form a flow tunnel, enhancing cavitation performance and reducing steering torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single fin is used, then the structure is simple, but the azimuthal torque reduction capability is insufficient
Solution Approach 1:
The single fin is divided into two separate fins positioned symmetrically on opposite sides of the pod unit. This segmentation allows each fin to generate lateral force independently, creating opposing torques that collectively reduce the total azimuthal torque more effectively than a single fin could achieve alone.
Solution Approach 2:
The two fins are positioned to create counteracting lateral forces that balance each other. By placing fins symmetrically on opposite sides, the design uses the counterweight principle to neutralize azimuthal torque through opposing force vectors, reducing the net steering torque required.
2Reliability
If a conventional single fin is used, then the grounding risk is higher, but the two-fin configuration protrudes further below the POD
Solution Approach 1:
The grounding protection function is segmented between two fins rather than relying on one long fin. Each fin can be shorter while collectively providing adequate protection, as they are positioned symmetrically to cover different angular sectors during pod rotation.
Solution Approach 2:
Instead of extending one fin further out in a single direction, the design uses two fins positioned at different angular locations. This dimensional redistribution allows grounding protection to be achieved through spatial distribution rather than increased protrusion length in one direction.
3Strength
If the fin thickness is increased, then the structural strength is improved, but the cavitation performance deteriorates
Solution Approach 1:
The structural strength requirement is distributed across two thinner fins rather than concentrated in one thick fin. Each fin can be optimized with reduced thickness to minimize cavitation, while the combined structure of both fins provides adequate overall strength and stiffness.
Solution Approach 2:
The fin thickness parameter is changed from a single thick fin to two thinner fins. This parameter modification reduces the local thickness-to-chord ratio, delaying flow separation and reducing cavitation inception while maintaining acceptable structural integrity through the dual-fin configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The two-fin configuration significantly reduces azimuthal torque, increases cavitation-free steering angles, and enhances hydrodynamic efficiency by recovering rotational propeller flow losses, while minimizing the risk of grounding by protruding a smaller distance below the POD unit.
Implementation Method 1
The fin creates a lateral force due to the angle of attack, especially at turning of the pod unit
Implementation Method 2
The lateral force that is created due to an oblique flow toward the propeller
Implementation Method 3
this regain of the rotational energy in the slip stream will give a positive thrust contribution that increases the efficiency of the pod unit
Implementation Method 4
a better cavitation performance may be achieved, resulting in the advantage that a larger cavitation free steering angle is easily obtained
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
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).