Performance-enhancing bow designs can turn conventional thinking on its head, save fuel and increase the overall efficiency of ship operations.
In ship design, the bow plays an important part in that it influences the flow of water past the rest of the hull, affecting the vessel's hull resistance and performance.
Over the centuries different approaches to this part of the ship have evolved for several reasons.
In ancient times and the Victorian era, the ram bow developed as an offensive weapon; bluff bows were often seen on wooden sailing vessels; and in the 20th century the bulbous bow emerged as a very effective and popular performance enhancer. There are a number of other designs adopted in the recent past – or are now emerging as significant developments.
V-shape: The Maierform bow
The Maierform bow was designed by Austrian engineer Fritz Maier who, during his studies at the Technical University in Vienna from 1865-1870, realised the importance of an improved hull form for good sea keeping and economic efficiency of ship operations.
Maier’s design used a pronounced V-shape hull to produce a very even flow around the fore and aft body to reduce frictional resistance. Wave resistance too would improve because of the significant cutting away of the bow and stern.
With this design, the power required for a certain speed in smooth water reduced by 8-10% compared with a conventional hull shape. Sea keeping improved with the increasing reserve buoyancy causing pitching movements to be greatly reduced. Propeller immersion improved with less loss of performance in harsh weather.
Maier's son took up his father’s design and founded Maierform GmbH in Bremen in 1927 for the purpose of realising and marketing the concept. Initially, three fishing boats were built with Maierform bows in 1928, and by 1931 there were 26 ships with the bow design – rising to over 900 vessels in service by the end of World War 2.
Bow design is not just about improving performance below water by reducing resistance, it also affects seaworthiness above water.
The so-called Atlantic bow was designed in the late 1930s to overcome a problem that had emerged in the seakeeping qualities of some major German warships. These vessels were built with a relatively low fore end which proved very wet except in a calm seaway. The answer was to adopt a raised bow with noticeable shear and flare that kept the foc’sle much drier than before and made weaponry nearby easier to operate.
Ships that had to be upgraded with an Atlantic bow included the battlecruisers Scharnhorst and Gneisenau, and the pocket battleships Deutschland/Lützow and Admiral Scheer.
It is interesting to note that the UK's last battleship, HMS Vanguard, had what might be termed a normal raked bow yet was very seaworthy. This was highlighted in 1953 during exercises with the battleship USS Iowa which had seakeeping qualities described as good, but not outstanding. The long fine bow and sudden widening of the hull in front of the foremost turret contributed to the ships being wet for their size, and Iowa experienced water all over her decks in the severe weather during the exercise compared with Vanguard.
Unconventional design: X-BOW and Axe bow
In the last few years, two new concepts have been developed for all-round performance improvement. The most unusual is the X-BOW which turns conventional thinking on its head.
Introduced in 2005 by the Ulstein shipyard in Norway, X-BOW is an inverted design concept that has redefined marine engineering. The result is a bow that has a wave-piercing effect at small wave heights, and reduces pitching and bow impact loads in bigger seas having been evaluated in tough weather conditions. It is also said to reduce noise.
Instead of just rising on the waves and then dropping, the X-BOW is able to distribute the force more evenly across its surface, enabling the ship to remain more stable during poor weather conditions, increasing comfort for passengers and crew alike and, because it uses less fuel to get through the waves, it also helps to save energy. First tried and tested in the offshore sector in the design of supply ships, it has now found favour in a wide range of ship types.
The Axe bow is a wave-piercing design, developed by Dutch shipbuilding group Damen, and is characterised by a hull with a vertical stem and relatively long and narrow entry. 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 waves than a bow with more flare, making it much less susceptible to pitching and slamming because the deep forefoot does not usually rise above the waterline.
John Barnes is a former editor of Engineering Review and a freelance journalist.