International audienceA performance prediction program dedicated to merchant ships was developed to assess fuel saving abilities of a kite. The solving of the parameterization presented led to kite velocities and tethers tensions prediction continuously along a flight path within the wind window, including especially wind gradient and ship velocity. Both static and dynamic flight cases were considered regarding optimization strategy for kite tow efficiency. For dynamic flight case azimuth, elevation and orientation of the trajectory are continuously optimized in the present algorithm. Magnitude orders of towing forces induced by the kite were compared to those obtained in the literature. Especially in upwind conditions, which are the most frequent point of sail for fast vessels, results are dramatically improved. Finally, using a 320 m2 kite on a 50,000 dwt tanker, the fuel saving predicted is about 10% for a wind velocity of 9.77 m s−1 (Beaufort 5) and reaches more than 50% for a wind velocity of 15.68 m s−1 (Beaufort 7)
A tool dedicated to assess fuel economy induced by kite propulsion has been developed. To produce reliable results, computations must be performed on a period over several years, for several routes and for several ships. In order to accurately represent the impact of meteorological trends variations on the exploitability of the kite towing concept, a time domain approach of the problem has been used. This tool is based on the weather database provided by the ECMWF. Two sailing strategies can be selected for assessing the performance of the kite system. For a given kite area, the simulation can be run either at constant speed or at constant engine power. A validation has been made, showing that predicted consumption is close from in-situ measurement. It shows an underestimation of 11.9% of the mean fuel consumption mainly due to auxiliary consumption and added resistance in waves that were not taken into account. To conclude, a case study is performed on a 2200 TEU container ship equipped with an 800m² kite on a transatlantic route between Halifax and Le Havre. Round trip simulations, performed over 5 years of navigation, show that the total economy predicted is of around 12% at a speed of 16 knots and around 6.5% at a speed of 19 knots.
In prawn-trawling operations, otter boards provide the horizontal force required to maintain net openings, and are typically low aspect ratio (∼0.5) flat plates operating on the seabed at high angles of attack (AOA; 35–40°). Such characteristics cause otter boards to account for up to 30% of the total trawling resistance, including that from the vessel. A recent innovation is the batwing otter board, which is designed to spread trawls with substantially less towing resistance and benthic impacts. A key design feature is the use of a sail, instead of a flat plate, as the hydrodynamic foil. The superior drag and benthic performance of the batwing is achieved by (i) successful operation at an AOA of ∼20° and (ii) having the heavy sea floor contact shoe in line with the direction of tow. This study investigated the hydrodynamic characteristics of a generic sail by varying its twist and camber, to identify optimal settings for maximum spreading efficiency and stability. Loads in six degrees of freedom were measured at AOAs between 0 and 40° in a flume tank at a constant flow velocity, and with five combinations of twist and camber. The results showed that for the studied sail, the design AOA (20°) provides a suitable compromise between greater efficiency (occurring at lower AOAs) and greater effectiveness (occurring at higher AOAs). At optimum settings (20°, medium camber and twist), a lift-to-drag ratio >3 was achieved, which is ∼3 times more than that of contemporary prawn-trawling otter boards. Such a result implies relative drag reductions of 10–20% for trawling systems, depending on the rig configuration.
This paper presents sea trials on a 6-m boat specifically designed for kite propulsion. The kite control was automatic or manual, dynamic or static, depending on the point of sailing. The measurement system recorded boat motion and load generated by the kite. A particular attention was paid to wind measurement with several fixed and mobile locations directly on the kiteboat or in the vicinity. A high resolution weather modelling showed that a classical power law, describing the wind gradient, was not satisfactory to get the wind at kite location. 5-min measurement phases were systematically recorded. In the end, 101 runs were carried out. Data were processed with the phase-averaging method in order to produce reliable and accurate results.
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