Technical report | Calm Water Resistance of a 1:25 Scale Model of the Armidale Class Patrol Boat

Abstract

 DSTO has recently joined the International collaborative consortium FAST3.JIP with the aim to develop a numerical capability for the prediction and analysis of the resistance, seakeeping and seaway loads of high speed semi-planing hullforms. As part of this research program DSTO, in collaboration with DNPS, have undertaken a series of calm water resistance scaled model tests on the Armidale Class Patrol Boat, (ACPB). The data obtained from this model test program will be utilised to validate the numerical tools within the FAST3.JIP. Once fully validated these tools can be utilised to increase the understanding of any potential fuel saving strategies for the ACPB's and the through life structural management of the platform. The results will also be utilised to provide stern flap position advice to the Royal Australian Navy for minimisation of fuel consumption at various displacements and ship speeds. This report presents the data from the experimental test series.

Executive Summary

The Armidale Class Patrol Boats, ACPBs, are a semi-planing hullform which has significant differences in the resistance, manoeuvring and seakeeping capabilities when compared to other RAN platforms. The Australian Defence Science and Technology Organisation, DSTO, has recently joined the International Collaboration, FAST3 Joint Industry Program, which is aimed at developing more advanced numerical tools to accurately predict the non linear motions, resistance, manoeuvring and wave induced loads of these semi-planing hull forms.

As part of the development of these numerical tools an extensive validation study is required. DSTO, in collaboration with the Directorate of Naval Platform Systems, DNPS, has recently undertaken a series of calm water resistance tests on a scaled model of the ACPB to obtain a database set for these validation studies. This experimental program included studying the effect that speed, displacement and the angle of the stern flaps had on the resistance of the hull. Three trim tab settings were studied: (1) retracted by 6.4 degree from the neutral, (2) tab parallel to the baseline along the neutral line and (3) the trim tab extended by 6.4 degree from the neutral.

Outcomes from this study showed that, for all load conditions tested, when the speed of the vessel was less than 15 knots, the lowest resistance was recorded when the trim tab was in the retracted position. For speeds greater than 15 knots, an extended trim tab resulted in the lowest resistance.

It was observed that the dynamic trim of the vessel was influenced by the angle at which the trim tab was set. When the trim tab was in the retracted position, the ACPB always had a stern down trim across the entire speed range tested. When the trim tab was set in the neutral position, the ACPB had a bow down trim for speeds less than 15 knots and a stern down trim for speeds greater than 15 knots. When the trim tab was extended, the speed at which the ACPB changed from a bow down trim to a stern down trim increased to between 17.5 and 20 knots.

For all load conditions and speeds tested, the rise of the vessel increased as the angle of the trim changed from retracted to extended.

For speeds greater than 15 knots, the effective power was higher when the trim tabs were set in the retracted position when compared to the neutral position which in turn was higher than for the extended setting. For speeds lower than 15 knots there is very little difference in the effective power for all the trim tab settings studied. Throughout this lower speed range the trim tabs could be operated in the fully retracted position as there is no benefit in terms of effective power when operating with them extended.

The data from this study will now be used as a validation dataset for the numerical tools being developed within the FAST3 Joint Industry Program. Once fully validated, these tools will provide the Australian Department of Defence with a capability to enhance their understanding of the operational performance of these semi-planing platforms. This is important for the ACPB's through life management, including fuel saving studies and the life of type structural fatigue studies. These tools are also applicable to support any future acquisition programs that may utilise semi-planing craft