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Title: The Use of Manned Models in the Development of New Concepts

Author: John C Lewthwaite, IMAA Ltd, UK

Abstract: Over the past 15 years, IMAA in the UK has been developing techniques for evaluating new types of fast landing craft. In response to upcoming requirements of the UK MoD, the company has devised several novel types including the PACSCAT and HOVCAT concepts. Large manned sea-going models of such designs have been built and tested in local sea areas.

The advantages of such a technique are the ability to test new concepts on all relative headings in correctly simulated environmental conditions not only relating to evaluating performance and behaviour in scale sea conditions but also to investigating manoeuvring and beaching techniques.

Measurements of waves in coastal areas have demonstrated that such seas are a close representation of the steepness and multi-directionality of larger waves in more exposed sea areas. This is in comparison with waves in model towing tanks which are unidirectional and appear less steep. Significant differences have been found in the added resistance scaled from tank models compared with those from larger sea-going models. The scaling of the sea-keeping results from manned model tests should be more reliable due to the reduced scale factor effects.

The manned models were of course fitted with motion recording systems and their propulsion arrangements (water-jets on the PACSCAT and ducted air props on the amphibious HOVCAT) were calibrated to measure the thrust and hence to deduce the resistance of the craft. An IMAA WAVETECTOR2 wave buoy was used to measure and record the sea state.

It has been found that the overall cost of manned model testing is similar to that of testing smaller models in towing tanks, since tank hiring costs are significant and the sea, of course, is free to use.