RPA 8 shows exceptional efficiency at river trials

Nov 8, 2017

Shipyard Kooiman conducted river trials this week on the RPA 8, the new patrol vessel of the Port of Rotterdam. The 25 m boat marks a big step in naval architecture for such vessels, combining Van Oossanen Naval Architects’ Fast Displacement Hull Form (FDHF) with an underwater spoiler, called Hull Vane®. The ship will consume less than 60% of her predecessors to carry out the same tasks.

Niels Moerke, managing director of Van Oossanen and Hull Vane BV: “Fast vessels need some form of lift in the aft ship to be efficient at high speeds. You can generate this lift with the hull, by creating a hard chine planing hull form, or with hull appendages such as interceptors and trim wedges. In our experience however, the most efficient way to create this lift is with a submerged wing at the transom. This allows us to design the vessel to be much more efficient at the cruising speed of 20 km/h, while still achieving a maximum speed of 35 km/h.” The stern-mounted wing is basically a hydrofoil for displacement ships, a patented product called Hull Vane® and on the market since 2014. It reduces the stern wave and develops forward thrust. Model tests at Marin showed that the Hull Vane® saves over 20% in fuel consumption from 20 to 35 km/h on RPA 8.

What is most striking onboard is that there is no noticeable difference between sailing at 15, 25 or 35 km/h. Due to its FDHF hull shape and the Hull Vane® there is no “hump speed”, and the speed can be chosen freely depending on the need. There is also a very minimal generated wave pattern at all speeds. Due to her efficiency and a number of noise-reducing measures, RPA 8 is an exceptionally quiet boat. She has 40% less engine power than her colleagues RPA 1 and RPA 2. At 95% power, the measured noise level in the wheelhouse was only 49 dB(A), which is what you normally experience at home. The fuel consumption at 20 km/h is only 26 litres per hour.

Manouvring trials were done, showing that RPA 8 is extremely manoeuvrable. For slow-speed manouvring, she is helped by her controllable pitch propellers, her rudders with a maximum angle of 60 degrees and a powerful bow thruster. RPA 8 has a hybrid propulsion installation, allowing her to run both propellers and all electrical consumers from just one – properly loaded – main engine during patrolling.

Niels Moerke: “RPA 8 is a good example of what can be achieved when a ship is designed for efficiency over the entire operational profile. We congratulate Shipyard Kooiman on building such a quality vessel and the Port of Rotterdam for their courage to embrace new technology, which will massively reduce CO2 emissions. We hope to retrofit a Hull Vane® also to similar existing ships.” RPA 8 is the eighth vessel to be equipped with a Hull Vane®, and ten other ships which will have a Hull Vane® are currently under construction.

Wave profile at maximum speed