Confederation Marine Modellers
Nautical lore - Take a bow.
The 'eagle eye' of Peter recently spotted an unusual ship in Hamilton harbour. It interested Peter because it was smaller than the ships we usually see in the harbour. What turned out to be more interesting was the shape of its bow. The ship is the VikingBank and it was built by Ferus Smit at one of their shipyards in Groningen and Leer (Germany). The only information they give out about the bow design is: Special bow form with vertical stem profile and sharp waterlines without bulb results in less resistance at moderate speeds while having more displacement and cargo hold volume. Sharp entrance angles and less bow flare reduce speed loss in seaway." Pictures 1 to 3.
This is not the only bow shape that differs from what we are used to on our model boats.
A bow is the forward most part of the ship’s hull which helps in reducing the resistance as the ship cuts through the waves. Bow designs have been modified several times in the past in order to improve ship’s efficiency and stability in sea water. The type of bow design used depends on the characteristics of the vessel, area of operation, and purpose of the ship.
X -bow is a unique bow design which was introduced by the Ulstein Group of Norway in 2006. According to comparative tests done by Ulstein, the X bow design with its sharp hull does not generate a spray as it cuts through the waves. As the ship parts the waves efficiently, the wave energy transfer is less and the loss in vessel speed is negligible. Moreover, as the X bow cuts through the waves instead of pitching over them, there is considerably less amount of green water on the ship’s deck as compared to the ships with conventional hulls. This also implies that there is almost negligible bow flare and slamming resulting from the same in the front part of the ship.
The X bow hull design ships provides smoother movement of the ship with less slamming, which also makes living and working environment on the vessel better and reduces the chances of cargo shifting. According to a study, X bow design reduces the movement of the ship by almost 20% even in the roughest seas. A ship with an X bow design can thus easily sail through heavy waves with better speed and less movement. Opinions taken from seafarers who have worked with X Bow reflect much better living and operating conditions. Some of the officers even mentioned that unlike in ships with conventional bows, speed in X bow ships didn’t require to be reduced when facing rough sea weather.
Pictures 4 and 5.
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 vessel may need considerably more rudder motion to hold its course, and this increases with the wave steepness.
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, 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. Picture 6.
Information from www.marineexecutive.com, www.marineinsight.com, and wikipedia