Azimuthing Tractor Drive Ship with Symmetric Rear Skegs
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Solution Overview
Problem
Azimuthing tractor drive tugs experience instability in course due to asymmetric flow against central skegs and changing flow conditions around side stabilizing skegs, leading to unpredictable steering behavior, which compromises safety in ship handling.
Innovation Solution
The use of two rear skegs positioned symmetrically on either side of the centerline, extending deep into the water, with a profiled shape to generate a predictable and symmetrical flow, improving resistance and stability during straight sailing and small steering angles, and supported by struts for docking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a central rear skeg is used for course stabilizing, then the ship gains course stability, but asymmetric flow against the skeg generates steering torque that counteracts propulsion forces, leading to instability in course
Solution Approach 1:
The single central skeg is divided into two separate rear skegs positioned symmetrically on either side of the centerline. This segmentation eliminates the asymmetric flow problem by distributing the flow symmetrically across both skegs, preventing the generation of destabilizing steering torque while maintaining course stabilizing capabilities.
Solution Approach 2:
The invention uses symmetric positioning of two skegs rather than a single central skeg. By placing skegs at equal distances from the centerline, the design creates symmetry in the flow pattern, ensuring that forces on both sides balance each other and do not generate net steering torque.
2Stability of the object's composition
If stabilizing skegs are located on both sides of the centreline, then the ship gains course stabilizing capability, but changing flow conditions around the skegs during arched paths lead to unstable flows and unpredictable steering behavior
Solution Approach 1:
The skegs are positioned at specific locations behind the propellers where the flow conditions are more stable and predictable. By optimizing the longitudinal position of the skegs, the design ensures that they operate in a region where flow angles remain relatively constant during maneuvering, providing consistent stabilizing forces.
Solution Approach 2:
The skegs are pre-positioned in optimal locations during ship design to anticipate and counteract flow changes during maneuvering. The fixed positioning ensures that regardless of the arching path taken, the skegs always experience flow at predictable angles, providing consistent steering characteristics.
3Stability of the object's composition
If the skegs are positioned to provide course stability, then the ship gains stability, but the skegs create flow resistance that affects ship performance
Solution Approach 1:
The skeg design incorporates optimized cross-sectional shapes and dimensions that adapt to the flow conditions. The skegs are sized and shaped to provide maximum stabilizing effect at minimum drag, balancing the need for course keeping stability with the need to minimize energy loss from flow resistance.
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
This configuration provides predictable steering characteristics, enhances course-keeping stability, and reduces flow resistance, ensuring stable and safe maneuvering of the ship.
Implementation Method 1
the rear skegs extend sufficient deep in the water so that a lateral movement of the hull creates lateral resistance on the rear skegs to improve the course keeping stability of the ship
Implementation Method 2
the propulsion jets create a symmetrical flow on both sides of the rear skegs, which improves the resistance against disturbances
Data Source
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AI summary
The invention concerns a ship (1) comprising a hull (8) and a length that is less than 3.0 times and preferably less than 2.5 times a beam of the hull, located forward of the amidships two propulsion and steering units (6) with a propulsion drive for rotating propellers around a propeller axis (5) and a steering drive for positioning the propeller axis at a steering angle relative to a centreline (20) of the hull, and rearward of the amidships stationary course stabilising skegs (9) located symmetrically on both sides of a centreline (20) of the hull. The distance between the fronts of the stabilising skegs is between 30% and 70% of the beam and preferably between 30% and 70% of the beam.