Experimental Low-speed Positioning System with VecTwin Rudder for Automatic Docking (Berthing)

TL;DR

This paper presents an experimental VecTwin rudder-based low-speed positioning system (VTPS) for ships, enabling precise docking and berthing without full actuation, using linearized hydrodynamic models and PID control.

Contribution

Introduction of a novel VTPS that achieves low-speed ship positioning without full actuation, based on linear hydrodynamic modeling and PID control.

Findings

Successful automatic docking and position-keeping in experiments.

Potential for practical low-speed ship positioning applications.

Promising results with room for further improvements.

Abstract

A VecTwin rudder system comprises twin fishtail rudders with reaction fins to increase its performance. With a constant propeller revolution number, the vessel can execute special low-speed maneuvers like hover, crabbing, reverse, and rotation. Such low-speed maneuvers are termed dynamic positioning (DP), and a DP vessel should be fully/overly actuated with several thrusters. This article introduces a novel and experimental VecTwin positioning system (VTPS) without making the ship fully/overly actuated. Unlike the usual dynamic positioning system (DPS), the VTPS is developed for low-speed operations in a calm harbor area. It is designed upon an assumption that the forces due to the interaction between the rudders, the propeller, and the hull are linear with the rudder angles within a range around the hover rudder angle. The linear relationship is obtained through linear regression of the results from several CFD simulations. The VTPS implements a PID controller that regulates the actuator forces to achieve the given low-speed positioning objective. It was tested in combined automatic docking and position-keeping experiments where disturbances from the environment exist. It shows promising potential for a practical application but with further improvements.