August 12, 2009
U.S.-built ferry to have innovative Berg propellers
An 85.5 m ferry being built at Eastern Shipbuilding Group, of Panama City, Florida, will be one of the first three vessels to be equipped with a new design of Berg Controllable Pitch Propeller (BCP) that has a feathering capability.
The ferry is on order for the Government of New Brunswick, Canada, which signed a $65 million contract with Eastern for the 82 car ferry in March, after Eastern beat out four competitors. Delivery is set for 2011.
The two other vessels being equipped with the new Berg propeller are two 100 m chemical tankers under construction at the Dingheng (Jiangsu) Shipbuilding Co, in China.
The ferry and the two tankers have twin engine, twin screw propulsion systems.
The New Brunswick ferry will be built to Lloyd's Register Ice Class 1D, and will incorporate 2,600mm, BCP760 propellers, driven by 2,240kW engines operating at 277.7rpm
The Chinese-built tankers will be constructed to Germanischer Lloyd Ice Class E3, and will feature two 3,600mm diameter, BCP950 propellers apiece, driven by 1,600kW engines at 136.1rpm.
Berg says that the concept of feathering one of two twin 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 degrees so that they are in parallel to flow. Putting a propeller in the feathered position during an emergency or at low speed minimizes drag, with consequent fuel savings.
Until now, though, feathering techniques 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 says 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.
"We saw it as critical that we developed a solution that could match Berg's hub core standards for performance, efficiency and reliability," said Linus Ideskog, Berg Propulsion Technology product manager. "Using the Berg BCP Feathering hub means that pitch can range from full astern, via full ahead, to full feathering. For the ship owner, this means that the feathering concept can fit in with any type of ship operating with more than one propeller that demands flexibility in the driving mode, while also bringing fuel savings and environmental benefits."