BAUT excels with new VS propeller

Voith Water Tractor demonstrates the capability of the new Voith Schneider Propeller (VSP) blades with increased bollard pull for the same input power.

With the commissioning of the Voith Water Tractor Baut owned by the Norwegian towage company Bukser og Berging (B&B), the improved characteristics of the new Voith Schneider Propeller (VSP) blades were impressively demonstrated in December last year. The bollard pull was found to be improved by 9%, while the input power remained unchanged. Measurements of the bollard pull

were carried out under the supervision of DNV.

The new 40.55 metre long tug was built at the Norwegian shipyard of Moen Slip, located in Kolvereid, some 300 km north of Trondheim. This yard has, since 1994, delivered five tugs for the same owner and this latest unit represents their largest to date. B&B undertook the design in-house while the yard prepared the body lines and production drawings. A slightly modified sister ship is planned to be built for the Snoehvit Melkoya gas terminal in northern Norway.

Power train

As is common with most Voith tractor tugs, the power train is diesel mechanical via a Voith hydraulic turbo coupling. The main engine plant consists of two 3,440kW Deutz SBV 16M628 medium speed diesels each driving a Voith 36R6/255-2 propulsor. Auxiliary engines are two 380kW Deutz BF8M1015MC diesel gensets. Towing equipment comprises of a Karmoy winch with a pull of 170 tonnes and a braking capacity of 300 tonnes.

Ship assistance

VSP and, especially, Voith Water Tractors (VWT) are well known 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 ?computational fluid dynamics? (CFD). The CFD method initially serves to optimise the shape of the propeller blade while it also provides the exact loads for the structural and mechanical optimisation by using the ?finite element method? (FEM).

The new blade generation distinguishes itself by the improved propeller blade profile, increased uniform profile thickness along the entire blade length, reduced weight due to hollow spaces in the blades and rectangular blade geometry with optimised

end plates.

The new size 36R6/255-2 blades of the VSP represents an important step towards the further improvement of the hydromechanics of the propellers and, although the new profiles will be a standard feature, any further improvements will be able to be realized immediately.

Blade profile

Based on the well-established HSVA 73 profile, the new blade profile underwent significant modifications both to the leading and trailing edge. The new profile distinguishes itself by an increased lift-resistance ratio in the relevant angle of attack. Additionally, the hydrodynamic characteristics at high angles of attack have been considerably improved.

The modifications increase the efficiency of the VSP and the propeller also stands out because of its reduced vibrations and low noise emission. This is especially apparent during extreme manoeuvring situations, such as bringing ships to a stop or during crash stops when large forces have to be generated safely and in a controlled manner.

Hollow spaces

In order to minimize the centrifugal forces, the blades have been drilled out to create hollow spaces and as a result, compared to the thinner blades of the previous generation, have a lower weight.

The blades are then mechanically machined using a high-performance 5-axis milling machine along with a

special Voith machine for shaft

turning after which the blade surface is polished to achieve a fine surface

quality.

Principle Particulars

Gross tonnage 741gt

Deadweight 585 dwt

Length overall 40.55 m

Length b.p. 38.93 m

Breadth 14.30 m

Draught (escort conditions) 5.70 m

Main engines 2 x Deutz SBV 16 M 628 output 3,440kW each

Auxiliaries 2 x Deutz BF8M1015MC output 380kW each

Propulsors 2 x Voith 36R6/255-2

Service speed (ahead/astern) 15.5/15 knots

Bollard pull 95 tonnes

Steering pull 160 tonnes