Tech Talk

WORKING PRINCIPLES

The fuel-saving effect of the Hull Vane® is due to four distinct aspects:

Thrust

The Hull Vane® is able to recover energy from the ascending water flow near the stern of the ship. The lift force that is generated by the Hull Vane® has a component facing forward. When the foil’s own resistance is less than this forward thrust, the net result is a push in the back of the ship.

Wave reduction

By accelerating the water over the top of the Hull Vane®, the stern wave of a ship is reduced, much like a bulbous bow reduces the bow wave. The wave pattern generated by a ship is energy spent by the propulsion engines. Reducing the stern wave therefore reduces the fuel consumption.

Trim correction

Many ships sailing in the higher displacement range benefit from a trim correction at higher speed. The upward lift generated by the Hull Vane® reduces the running trim and keeps the ship at even keel at higher speeds.

Reduced pitching

Moving a large horizontal plane vertically through the water requires a lot of force. The same goes for the Hull Vane®. This effect significantly reduces the pitching and heaving motions of the ship in waves, which in turn reduces the added resistance caused by these motions. Added benefits are an increased level of comfort for passengers and crew onboard, and a reduced probability of cargo damage in heavy weather.

Effectiveness

The Hull Vane® is most effective on ships which are relatively heavy and relatively fast. We look mainly at the speed-to-length ratio. In naval architectural terms, this means Froude numbers between 0.2 and 0.7, in combination with a maximum speed of about 30 knots. For a 25 m vessel, this means a speed range from 6 to 21 knots, for a 50 m vessel from 8 to 30 knots, for a 100 m vessel from 12 to 30 knots, and for a 200 m vessel from 17 to 30 knots. Ships corresponding with these characteristics are a.o. yachts, naval and coastguard vessels, passenger ships and roro vessels, and several types of offshore vessels.

The Hull Vane® is particularly effective on ships with a wide speed range, which have a high top speed combined with a lot of sailing at intermediate speeds, such as patrol vessels. In this case, savings of 10 to 20% are common. On large container vessels or cruise ships, the savings percentage is usually much lower, but it can still result in a very short payback period due to the high power installed and the many sailing hours. When sailing in waves, the Hull Vane® reduces also the added resistance, often increasing the savings percentage. The dampening of ship motions such as pitching and yawing increases the operability of the vessel and the comfort onboard. If you wonder whether your ship is in the applicable range for application of a Hull Vane®, do not hesitate to contact us.

Design process

Just like a bulbous bow, each Hull Vane® is different and custom designed for a specific ship. An optimisation of the Hull Vane® using Computational Fluid Dynamics (CFD) is the starting point. Such a Hull Vane® study indicates how much the ship’s resistance is reduced with the addition of a Hull Vane® – either for a single speed or for a wider operational profile.

Based on the results of this study, a cost-benefit analysis can be made and a go or no-go can be given for the further development of a Hull Vane® for this ship. In the following phase, we conduct a Finite Element Analysis and vibration analysis to ensure sufficient strength of the Hull Vane® for a lifetime of trouble-free operations. Hull Vane BV builds the Hull Vane® in The Netherlands with certified welders and a high degree of finish and accuracy.

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