Bulbous bow optimisation for P-Type
In the past two years, Spliethoff took over 10 multipurpose, heavy lift vessels - the Spliethoff P8 and P14 series. With our operational profile differing significantly from the one used for the original design, a study of the large bulbous bow was undertaken to improve the operational performance and environmental impact.
A bulbous bow is the protruding part of the bow just below the waterline The wave generated by this bulbous bow interferes with the wave system created by the hull, resulting in lower resistance. However, this will only happen when the vessels sail at the speed and draught range for which the bulbous bow was designed. Reviewing the operational profile of the vessels, the average draught was much lower than the design draught, as we mainly operate the vessels as project carriers, which do not require maximum deadweight. We also intend to operate the vessels at a lower speed than the design speed, as this is very effective in reducing the environmental impact and improves operational efficiency. To better understand the differences, a variety of operational profile model tests were performed by HSVA in Hamburg. By changing the draught, trim and speed we obtained insights into the waves generated by the bulbous bow and the impact these had on the resistance of the vessel.
The next step was to ask the maritime research institute MARIN to design a new bulbous bow for our intended operational profile. However, with a worldwide operation, we wanted this design to optimise the performance both in calm water and in (head) waves. MARIN studied and optimised three different bulbous bow shapes and looked at how they would perform, taking 10 years of global weather statistics into account. The bulbous bow with the best overall performance was chosen for the vessel. It was significantly flatter than the bulbous bow designed for calm water. To validate the results, additional model tests were performed at HSVA with the new bulb design. Following the results we took the decision to retrofit the bulbous bow. The bulbous bow’s three sub-sections were prefabricated in Dalian, China and the Pauwgracht was the first P-Type vessel to get a ‘nose job’. Currently, we are evaluating the results, but this will require some long-term monitoring. However, the first results look promising.