Is it possible for ships to sail faster through rough water and keep the safety of the crew a priority? Lex Keuning, Associate Professor at the Technical University (TU) Delft, asked himself this question after he had broken both of his kneecaps in a speeding incident at sea.
In cooperation with Jaap Gelling, Managing Director High-Speed Craft at Damen Shipyards Group, Keuning introduced a new type of hull that could withstand more speed: the ‘axe bow’.
During the lecture in the Maritime Museum in Rotterdam, Keuning and Gelling told the audience about this success story of naval engineering.
Gelling started the lecture by emphasising the big difference between the automotive and shipbuilding industries: “As a result of large scale production since the twentieth century, the technology of cars has developed more rapidly than those of ships.” But there were some major innovations, like the axe bow. The two explained the audience how the special bow was developed.
Lex Keuning pointed out the danger ships are exposed to when they speed in rough water: “The faster ships are sailing over waves, the stronger the movements of the ship become. When a ship hits a wave, the ship usually slows and accelerates again. During these movements, however, the G-forces on board also increase and can even endanger the crew.”
In 1980, his knees collapsed due to a boost in G-forces during a ship speeding test. In this experiment, the crew experienced 6.5 G, which means that they had become six and half times heavier. For Keuning, this incident was a wake-up call – from now on the comfort and safety of the crew was the main focus of his research regarding the speed of ships.
In Keuning’s further quest to safely expand the speed, he focused on the peak accelerations of ships and the subsequent reactions of the crew: “Peak accelerations appear when the vertical movement of a ship increases (positive) or decreases (negative) in a short amount of time. When the pounding of a ship becomes too heavy, the crew can only do one thing: reduce speed.”
The choice to reduce speed is actually necessary to ensure the crew’s safety – that is how overwhelming the pound movements of ships can become.
Keuning was the first to develop a mathematical method to estimate the vertical movements of ships. At the TU Delft, he analysed how he could reduce the pound movement of ships and in which way this affected the hull of the ship.
Keuning concluded that the removal of flare, the minimisation of the V-shape of the bow and a deeper keel line sufficiently reduced the pound movement of a ship. However, because of the removal of flare and the minimisation of the V-shape, the bow loses a lot of ‘volume.’ This volume is nonetheless crucial to keep the front of the ship above the water.
As a solution, Keuning added extra buoyancy. As a result, the shape of the bow became similar to an axe bow. Thus, the ‘axe bow’ was born.
Gelling told the audience at the Maritime Museum in Rotterdam how he already knew Lex Keuning when he studied at the TU Delft, where Lex was a researcher.
On a personal as well as a business level, there was a good connection between the two. At the beginning of this century, they worked together with the Royal Navy, Maritime Research Institute Netherlands (MARIN) and the US Coast Guard to investigate the axe bow as a new type of hull. Keuning’s earlier research was also confirmed by the outcome of these investigations. Due to the application of the axe bow, the number of peak accelerations was decreased by 80 per cent, and as a bonus, the axe bow also contributed to 10 to 20 per cent fuel use reduction.
Since 2006, Damen Shipyards has been constructing ships with axe bows for the professional market. So far, Damen has sold over 150 different types of ships with the axe bow technology.
Due to this success, the parties involved agreed to set aside a small part of the profit for collective research by the TU Delft and Damen.
This success, however, also had a negative side. Just like in the automotive sector, ship builders copy each other’s technologies. As a result, there are ships in the waters of France, Australia and Bangladesh, to name a few, with hulls that look like bow axes even though they are not produced by Damen.
Nevertheless, those are just lookalikes, since the special characteristic of the bow axe is located under the water level – and that technology is patented by Damen.
Source: worldmaritimenews.com This article was previously published in Maritime Holland edition #3 – 2017.