Measurement of bottom pressures on planing craft

The knowledge of the pressures on the bottom of vessels sailing at high speeds is essential for the design bottom plate and its scantlings. However, only a few semi-empirical methods based on scarce full or model scale experimental results can be found in the open literature. The shortage of measured data is partly due to the complexity of the measurements. This kind of data is valuable for validating the proposed analytical methods and for providing background to the rules issued by the classification societies. Two methods are reviewed in this paper to measure the pressure distribution on the bottom of fast ships. In the former, membrane-type pressure sensors are fitted on a grid of points on the bottom of the vessel, while in the latter Pitot-tubes are connected to digital pressure transducer through a 48-channel fluid switch wafer. The pros and cons of both methods, which were tested in the Towing Tank of the Laboratory for Ship and Marine Hydrodynamics of the National Technical University of Athens, are presented and discussed.