NÚMERO 5: ABRIL 2016
Ingeniería Naval Académica. ISSN: 2340-4779
Scale effects in open water test results for performance prediction of conventional and unconventional propellers
ITTC’78 Performance Prediction Method is the only existing standard procedure approved by ITTC to carry out predictions of ship performance based in model tests results. It has been successfully applied from 1978 by towing tanks directly or introducing some variations. But it has been explicitly recognized by ITTC that this method must be only applied to conventional propellers and cannot be applied to Unconventional Tip Shape propellers.
This kind of propellers is one of the best options to save energy in marine propulsion. However, as at model scale these improvements are not clearly shown, the lack of a standard procedure to be applicable to this type of propellers reduces in many projects the possibilities to implement energy saving propellers.
In this study a new procedure will be explained in detail going a step deeper in the basic principles of viscous effects depending of the local section Reynolds number.
The validation work here presented confirms that ITTC’78-PPM is not useful to predict propulsion characteristics of unconventional tip shape propellers and that present proposed method predicts with reasonable accuracy propulsion characteristics of conventional and unconventional propellers, monoblock or CPP type and it is repetitive and easy to implement.
Keywords: Propellers, performance prediction, open-water tests, model to ship extrapolation, unconventional tip blade shape.