| With the commissioning of the Norwegian Voith Water Tractor "BAUT" of the Norwegian shipping company Bukser og Berging, the improved characteristics of the new VSP blades were impressively demonstrated in December 2003. The bollard pull could be improved by 9%, while the input power remains unchanged. Measurements of the bollard pull were carried out under the supervision of the Norwegian classification company DNV.
Voith Schneider Propellers and especially Voith Water Tractors (VWT) are renowned in marine circles for precise, efficient and safe ship assistance. The VSP allows accurate, stepless and extremely swift thrust variations in accordance with XY coordinates. In order to improve the hydrodynamic characteristics of the VSP even further, a new generation of blades has been developed. The basis for the successful development is the numeric simulation of the fluid dynamics (CFD = Computational Fluid Dynamics). The CFD method initially serves to optimize the shape of the propeller blade; it also provides the exact loads for the structural and mechanical optimization by using the Finite Element Method (FEM).
Fig. 1 shows a CAD illustration of the new VSP size 36R6/255-2 with a propeller input power of 3380 kW.
Fig. 2 shows the Voith Water Tractor "BAUT" of the Norwegian shipping company "Bukser og Berging".
The new blade generation distinguishes itself by the following characteristics:
- Improved propeller blade profile
- Increased, uniform profile thickness along the entire blade length
- Reduced weight due to hollow drills
- Rectangular blade geometry with optimized end plates
Which hydrodynamic effects are associated with the new blade generation?
The new blade profile is based on the renowned HSVA 73 profile, while significant modifications were carried out at the leading edge and at the trailing edge. The new profile distinguishes itself by an increased lift drag ratio in the relevant range and incidence angles. Additionally, the hydrodynamic characteristics at high angles of attack have been considerably improved. The modifications increase the efficiency of the VSP; the propeller also stands out because of its reduced vibrations and low noise emission. Especially during extreme manoeuvring situations, such as direct stops of ships that are being handled or during crash stops, larges forces can be generated safely and in a controlled manner.
The uniform optimum profile thickness along the entire blade length, the rectangular blade shape and the end plates result in a uniform load distribution as a function of the blade length. Consequently, losses caused by the induced resistance are extremely low.
In order to minimize the centrifugal forces, the blades have hollow drills. Compared to the thinner blades of the previous generation, their weight is therefore reduced.
Fig. 3 shows the blade blanks at the Voith works premises after delivery by the relevant drop forging company.
Afterwards, the blades are mechanically machined, using a high-performance 5-axis milling machine and a special Voith machine for shaft turning. Finally the blade surface is being ground to achieve a fine surface quality.
Fig. 4 shows a VSP blade of the latest generation at the Voith production department. The blade has been drop-forged from high-quality chrome-nickel steel.
The machined blade is shown in Fig. 5. The Voith production department guarantees highest quality. This has a lasting effect on the hydrodynamic characteristics and the long service life of the Voith Schneider Propeller.
The new size 36R6/255-2 blades of the VSP represent an important step towards the further improvement of the hydromechanics of Voith Schneider Propellers.
For new propellers, the new profiles will be a standard feature; any further improvements can be realized with immediate effect. |
