Berg wins chemical tanker orders

(Aug 14 2009)

Berg Propulsion is to deliver the first examples of the new Berg Controllable Pitch Propeller (BCP) with feathering capability to two 100 m chemical tankers, plus a ferry.
The company said that the inherent flexibility, redundancy and better manoeuvrability claimed by twin screw operations when compared to single screw solutions have increasingly been accepted across the shipping industry.

A single engine driving a single propeller achieves maximum efficiency at a fixed level in the design condition. At lower power, whether working in combination with fixed pitch or controllable pitch propellers, engine working pressure decreases and engine efficiency is lost.
Greater flexibility can be achieved by operating two smaller engines driving two propellers because, at lower speeds, the ship’s master has the option to operate on one engine alone, working at its optimum efficiency.

Furthermore, the greater propulsion area covered by two smaller propellers is calculated to equate to about a 10% efficiency gain when compared to a single screw solution.
The concept of feathering one of two propellers at lower speeds, so that the other can run at higher output, closer to optimum efficiency, is by no means new.

Developed as a more efficient alternative to locking or clutching out an unneeded shaft line, ‘feathering’ sees the propeller blades rotated through 90 deg so that they are in parallel to flow.
Putting a propeller in the feathered position during an emergency, or at low speed, minimises drag, with consequent fuel savings, Berg said.

However, feathering techniques to date have featured a complex and often cumbersome mechanical solution, or hubs that cannot offer astern pitch due to their internal mechanical limits. Thus the attractions of feathered hubs have been limited to ships operating within complicated mission profiles.

Berg claimed that its new BCP design offers the capability to feather propeller blades within its standard hydraulic hub. The result is an expansion in the propeller’s operating pitch range. A patent application on this aspect of the design is currently pending.
The tankers, under construction at the Dingheng (Jiangsu) Shipbuilding in China, will be constructed to Germanischer Lloyd Ice Class E3 and will each feature two 3,600 mm diameter, BCP950 propellers, driven by 1,600kW engines at 136.1 rev/min.

Berg Propulsion said that the feathering option is now available across its complete range of BCP hubs.