Energy-saving retrofits are relatively commonplace on large cargo vessels and cruise ships. But can they also make a significant difference on a small passenger vessel? Swiss ship owner CGN, which operates a fleet of 19 passenger ships on Lake Geneva, decided to find out and reports that the answer is a resounding yes.
As a test case, they chose the 30m passenger vessel Valais, which was built in 2008, and that services its N3 line, connecting Yvoire in France and Nyon in Switzerland, making up to 40 crossings a day. Before starting the retrofit, CGN commissioned a ship optimisation study by utilising Computational Fluid Dynamics software, comparing several possible hydrodynamic improvements at an operating speed of 25km/h.
In the study, the benchmark hull, which has a trim wedge, was compared to various retrofit alternatives for the stern, such as ducktail extensions, interceptors and a Hull Vane, a hydrodynamic wing-shaped stern appendage which converts the energy of the stern wave and of the ship’s motions into forward thrust. Irwin Gafner, technical director of CGN, explains: “This is a rather novel solution and can be described as a ‘spoiler for ships’. It was the best alternative to come out of this optimisation process, promising a resistance reduction of 15%. Furthermore we also decided to optimise a bulbous bow for the ship.”
After the hydrodynamic study, CGN ordered the Hull Vane from the Dutch company, Hull Vane BV, and the bulbous bow from a local subcontractor. Lake trials were performed before drydocking, throughout which accurate measurements were made of the ship’s fuel consumption. During the scheduled drydock period, at the company’s own facilities in Lausanne, both devices were installed, and the main engines were replaced with new common- rail V8 MAN engines. After launching of the vessel, ballast was added in the bow to bring the ship to the appropriate draught.
Gafner says: “In spite of the significant amount of added weight, including the Hull Vane, bulbous bow construction and ballast, the results showed that the fuel consumption of the vessel was reduced by 24%.” Noise measurements onboard also showed that the improved efficiency, lower rpm and new engines made the vessel quieter, with noise levels reduced by 2dB(A) in the wheelhouse and by 6dB(A) in the passenger lounge. The vessel now also makes significantly less waves, while the added weight and additional submerged surfaces also improve the stability and seakeeping of the vessel.
Bruno Bouckaert, sales director of Hull Vane BV, suggests that other, similar ships might also benefit from this retrofit. He says: “There are a lot of small passenger ships ranging from 20 to 100m in use worldwide, on rivers, lakes and servicing islands. Because of their length and displacement, they often operate at speeds that are excellent to optimise Hull Vane’s effectiveness, making a retrofit very worthwhile.”
CGN says it is extremely pleased with the results of this retrofit. It calculates that it will reduce CO2 emissions by 129tonnes per year and diesel particle and NOx emissions by 24%. Last but not least, the return on investment is said to be excellent.