The seakeeping behaviour of naval ships is an important factor for its operational effectiveness, as vessels with good seakeeping abilities are able to go to sea and successfully execute their missions despite possible adverse weather conditions. Hence, it is not surprising that
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The seakeeping behaviour of naval ships is an important factor for its operational effectiveness, as vessels with good seakeeping abilities are able to go to sea and successfully execute their missions despite possible adverse weather conditions. Hence, it is not surprising that the hydrodynamic assessment of a new frigate type hull forms is often based on motion levels and related motion phenomena like sustained speed in waves and deck wetness. One of the design concepts that has been quite successful on all of these hydrodynamic aspects is the is the so-called AXE Bow concept. This concept has already been applied on many (smaller) fast vessels, like Fast Crew Suppliers and Offshore Patrol Vessels, and it is featured by a strong modification of the bow which has deep, almost vertical V-shape sections. The largest AXE Bow designs build today are approximate 70 meters in length, so it has not been applied to a vessel the size of a frigate. Though, previous studies indicated that the AXE bow application on a frigate type hull has quite a number of hydrodynamic benefits (Eefsen, et al. 2004); (Keuning and Van Terwisga 2015). In the current study a more detail hydrodynamic comparison is made between a conventional frigate and the AXE Bow frigate in calm water and in regular and irregular head waves using a combination of both CFD calculations and model experiments. The hull of the convention frigate was initially designed by the Defence Material Organisation of the Ministry of Defence of the Netherlands and this model is used as a parent design and benchmark in the current study. The AXE Bow version of the frigate has been developed by the Delft University of Technology with a special attention to keep the functionally of the two combatants the same as much as possible. The models were tested in different configurations in the towing tank of the Delft University of Technology, both in a more traditional towed configuration in which the models were directly connected to the towing carriage in a way that the model is free to heave and pitch but retrained in all other modes of motion; and in a free sailing configuration in which the models were remote controlled an kept on course using autopilot steering. Special attention is paid to the differences in motions and added resistance between these two test configurations. The CFD calculations were performed and these numerical results are compared to the experimental results with a particular interest in how well the calculations of the added resistance in waves correlate to the experimental results. The results show that the calm water resistance of the AXE Bow frigate is about 9% lower at the design speed of the ship. Moreover, the AXE frigate outperforms the conventional frigate on all hydrodynamic aspects in waves; lower heave and pitch motions are seen and it has significantly lower added resistance in waves particularly at cruising speed. The above conclusions are confirmed by both the numerical and experimental results.@en
