During some time now the application of the so called AXE Bow has proven very successful. Typical applications so far have been as Fast Crew Suppliers in the Offshore industry, as Patrol Boats with Coast Guards and SAR boats all in the range of 50 till 20 meter length overall and speeds ranging from 25 to 35 knots. Applying the AXE Bow Concept on smaller boats than 15 meter length overall is a challenge, because minimal stability requirements generally ask for a smaller L/B ratio and so beamier ships. On the other end application on frigate type hulls, which have generally a rather high L/B ratio and already fine bow could be considered less advantageous because high vertical accelerations, bow slamming and added resistance in head waves are already relatively small. In an earlier study commissioned by the Netherlands, Italian and Danish navies some 10 years ago (the THALES Project reported in Ref [1]) the application of the Enlarged Ship Concept and the AXE Bow Concept on a frigate type hull were already considered but only on a limited scale.
Over the last decade a large amount of design information has been gathered from the experience gained from full scale measurements on board of real AXE Bow ships. This refers amongst others to increased directional stability particular in following waves by applying fixed skegs and so reduced rudder motions to be applied, the possibility to vary and increase the maneuverability at wish by making these skegs retractable (Ref [2]), a reduced added resistance in waves and considerably less shipping of green water when sailing in head waves.
All these aspects led to the question raised when the replacement of the presently employed “M Frigate” of the Royal Netherlands Navy came in sight whether the application of the AXE Bow Concept on the new frigate would be a desirable and feasible option. The main question to be addressed by the present research was How does the Conventional Frigate hull type compare to the AXE Bow hull with respect to: the calm water resistance, taking on green water, the behavior in stern quartering waves, and the maneuverability.
These research questions were formulated and the project commissioned by the DAMEN Shipyard at Gorinchem, Damen Schelde Naval Shipbuilding and the Defense Material Organization from the Ministry of Defense of the Netherlands to the Ship Hydromechanics Department of the Delft University of Technology.
An extensive research plan including a large test program has been set up to investigate the behavior of both designs, both in the towing tank of the Delft University and from MARIN at Wageningen and also on open water on an estuary in the south with radio controlled models. Part of the measurements were conducted on open water to be able to carry out turning circles at various forward speeds and rudder angles. Also for the tests in following and stern quartering waves the addition of open water tests seemed essential to gather sufficient statistically reliable results on rarely occurring events such as broaching. The main results of this research project will be reported in this paper.
