Axe bow

Comparison between an axe bow (442) and a conventional bow (441)

The axe bow is a wave-piercing type of a ship's bow, characterised by a vertical stem and a relatively long and narrow entry (front hull). The forefoot is deep and the freeboard relatively high, with little flare, so that the bow profile resembles an axe. The bow cuts through the water, and is less affected by passing through waves than a bow with more flare, making this bow type much less susceptible to pitching. Because the deep forefoot does not generally rise above the water level, it is less susceptible to slamming. The axe bow moves the centre of lateral area forwards and the vessel may need considerably more rudder motion to hold its course, and this increases with the wave steepness.[1]

A vertical prow is not unique; they were common in the early steam era. The innovation of the axe bow is combined with a lengthened bow of the ship. This concept was developed in the Netherlands by Lex Keuning of Delft University of Technology,[1] Damen Shipyards Group, Marin (Maritime Research Institute Netherlands), the Royal Netherlands Sea Rescue Institution, the Royal Netherlands Navy, Damen Schelde Naval Shipbuilding and the United States Coast Guard.

Ax-Box

This is a bulbous bow with a wave-deflecting axe-shape at the top of the prow. It was developed by NKK of Japan, and first noted in the early 2000s. It offers an advantage of several percent in added resistance by incident waves over the ordinary bow shape.[2][3]

LEADGE-bow

The LEADGE (or LEAding eDGE) bow is a non-bulbous bow that fills in between the bulb and the Ax to form a straight and vertical bow, slightly higher than normal prow to ensure wave deflection. It was first described by K, Hirota et al in 2005. It offers an advantage of about 5% over the Ax-box and a further similar amount over the ordinary bow from incident wave resistance.[2][3]

This bow has been adopted for the intended Royal New Zealand Navy replenishment ship (replacing HMNZS Endeavour (A11) in 2020), in what is called the "Enviroship" design by Hyundai Heavy Industries.[4][5]

See also

References

  1. 1 2 J.A.Keuning, J. Pinkster and F. van Walree: Further Investigation into the Hydrodynamic Performance of the AXE Bow Concept Archived October 21, 2013, at the Wayback Machine.
  2. 1 2 Development of Bow Shape to Reduce the Added Resistance due to Waves and Verification on Full Scale Measurement, Hirota, K., Matsumoto, K., Takagishi, K., Yamasaki, K., Orihara, H. & Yoshida, H., 2005, accessed 2016-12-22
  3. 1 2 Optimization of Bow Shape for Large, Slow Ships, S7.3, Daniel E. Nordås, Norwegian University of Science and Technology (NTNU), June 2012, accessed 2016-12-22
  4. ↑ New Navy tanker to cost $493 million, Claire Trevett, New Zealand Herald, 18 July 2016, accessed 2016-12-22
  5. ↑ Rolls-Royce designs HHI’s first naval Environship, Green4Sea.com, 21 September 2016, accessed 2016-12-22
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