Powering extrapolation approaches of ship model tests with the gate rudder system

This study evaluates several approaches to extrapolate the model test-based powering results to the full-scale for two coastal ships with the Gate Rudder System (GRS) using their model test results and sea trials data. Ship model resistance and self-propulsion tests were conducted in the Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University (ITU) for a 450 TEU and 2400 GT container ship (SHIGENOBU) and a 7241 DWT multi-purpose dry-cargo ship (M/V ERGE) both fitted with the GRS. The model test-based powering results were extrapolated by implementing three approaches, including the standard ITTC 1978 performance prediction method and its two variations. In the first variation (Method I), the GRS blades with the propeller were treated as a single propulsor unit, similar to the treatment of the ducted propulsors, due to the inherent similarities between the GRS blades and a typical accelerating duct. In contrast, the second variation (Method II) treated the GRS blades as the appendage, like a conventional rudder, but with a pragmatic approach for the full-scale wake correction based on the limited experience of ships with the GRS. The effectiveness of the three methods was evaluated based on the validations of the sea trials data for the two ships. While the evaluations clearly supported the appendage treatment of the GRS blades, Method II was the most favourable approach in spite of some overestimations of the sea trials data for both ships, hence requiring further investigations and full-scale data for ships with the GRS.