Numéro : 2784 - Year : 2022
Efficiency of trim-wedge appendage versus HULLVANNE® in different range of the Froude number and scale effects
Thierry CHAMBENOIS, Joseph CHERRORET, Paul BUNEL, David BELLEVRE - Direction Générale de l’Armement – Val de Reuil (France)
Appendages designed to reduce the pitch angle of the ship at high Froude numbers have been widely used in naval architecture for decades. Trim-wedges, interceptors and flaps are designed by naval architects to reduce ship resistance at maximal specified speed, thus reducing the power to be installed on board. They may even reduce the ship’s consumption all along its life.
More recently, Hull Vane BV, a dutch company, has been offering a patent for a lifting appendage integrated to the stern of the ship, which seems to offer power gains far superior to those provided by the regular aforementioned appendages, and on a wide range of Froude numbers, including for transit or economical speeds, which is the weakness of regular appendages.
Hence, DGA TH had to test this Hull Vane®, to assess the resistance gains advertised by the company, and to compare with those provided by a trim-wedge configuration. Risk reduction studies on the French new generation aircraft carrier have created an opportunity to set up several comparative studies at DGA TH between trim-wedges and Hull Vane®.
The objective of these DGA TH studies were to evaluate the scale effects on the performance of a trim-wedge type appendage, and on those of a Hull Vane®-inspired appendage, designed at DGA TH. These scale effects are well known by naval architects. Towing tank tests at model scale are pessimistic, and shipyards rely on first-hand experience of sea trials on a great number of ships, which they compare to the predictions they issue from towing tank tests to adjust model predictions. The process proposed in the present article combines CFD at model and full scale, supported by towing tank model tests, and can provide a relevant assessment of these scale effects.
Our studies point out that trimwedges can be very efficient at a high speed, while still being neutral at transit speed. The Hull Vane® designed by DGA TH is indeed superior to the trim-wedge on the resistance reduction level, even at lower Froude numbers. Both types of appendages slightly increase hull efficiency. Final gains should thus be evaluated through CFD studies and model tests, both using propellers.
Compared to trim reducing systems, there are very few appendages reducing the vertical dynamic of the ship in head waves. Considering the shape and the location of the Hull Vane®, one can expect a reduction of the pitch motion and thus, the added resistance in waves. Due to its large span, the Hull Vane®® can efficiently reduce the roll motion as well.
DGA TH has performed model tests in head waves in order to measure the effect of the Hull Vane® on vertical motions and the added resistance in waves. A significant reduction in the pitch has been observed for transit and high speeds, whereas the effect on the added resistance in waves seems very low or non-existent. For bigger ships, CFD computations show that the gains of the Hull Vane® on the pitch motion would be much lower, due to a lower Froude number. This kind of appendage is then fitter for fast displacement ships.