The Effect of Propeller Scaling Methodology on the Performance Prediction

Stephan Helma,Jan Richter,Heinrich Streckwall

doi:10.3390/jmse6020060

Abstract

In common model testing practise, the measured values of the self propulsion test are split into the characteristics of the hull, the propeller and into the interaction factors. These coefficients are scaled separately to the respective full scale values and subsequently reassembled to give the power prediction. The accuracy of this power prediction depends inter alia on the accuracy of the measured values and the scaling procedure. An inherent problem of this approach is that it is virtually impossible to verify each single step, because of the complex nature of the underlying problem. In recent years the scaling of the open-water characteristics of propeller model tests attracted a renewed interest, fuelled by competitive tests, which became the norm due to requests of the customer. This paper shows the influence of different scaling procedures on the predicted power. The prediction is compared to the measured trials data and the quality of the prediction is judged. The procedures examined are the standard ITTC 1978 procedure plus derivatives of it, the Meyne method, the strip method developed by the Hamburgische Schiffbau-Versuchsanstalt (HSVA) and the β i -method by Helma.

Highlights

The International Towing Tank Conference ITTC established the “1978 ITTC Performance Prediction Method” (ITTC 1978) [1], which is widely used to extrapolate the data collected during model test to full scale performance for trial or service condition
Most authors believe that these deviations between prediction and measured performance is due to the scaling method for the open-water performance, which is needed by the ITTC 1978 power prediction method
The scaling methods which do not scale down to the Reynolds number of the self-propulsion test typically perform better than the same method using the scaled down open-water characteristics to analyse the self-propulsion test (B–A, D–C, F–E, H–G, J–I, O–N, Q–P, U–T and W–V, but not S–R)

Summary

Introduction

The International Towing Tank Conference ITTC established the “1978 ITTC Performance Prediction Method” (ITTC 1978) [1], which is widely used to extrapolate the data collected during model test to full scale performance for trial or service condition. In recent years, it was suggested by more and more people—mainly designers of unconventional propellers—that the predictions made using this method often do not reflect the performance measured during ship trials, see for example Brown et al [2]. It mentions that the final validation should be done by comparing predicted with measured performance data, which is the topic of this paper

Methods

Results

Discussion

Conclusion