High fuel costs have strengthened sales of the Propeller Boss Cap Fins (PBCF) jointly developed by Mitsui OSK Lines, the West Japan Fluid Engineering Laboratory and Mikado Propeller (which makes the fins). First applied in 1987, the propulsive efficiency-enhancing system has now logged over 1,350 reference installations, split roughly 50:50 between newbuilding and retrofit projects and serving a wide range of coastal and deepsea tonnage.
Applicable to fixed pitch or CP propellers, the PBCF system exploits a boss cap with fins that rectify the propeller hub vortex and recover rotational energy otherwise lost in the slipstream. Propeller thrust is reportedly increased by over 1 per cent and propeller torque reduced by more than 3 per cent, thereby underwriting fuel savings of up to 5 per cent.
A ship speed gain of 2 per cent can be delivered with the same engine output. Apart from enhancing propulsive efficiency, the PBCF system is said to reduce stern vibrations and propeller noise, and resolve a number of rudder erosion problems.
No shaft design reviews are required by classification societies when replacing conventional propeller boss caps with the PBCF, no maintenance is called for and replacement is simple, the designers assert.
Some 160 sets were sold last year, large container ships providing good business along with car carriers, roro vessels, ferries, bulk carriers and tankers. Most of the references – with propeller input powers ranging from around 1,500kW to over 66MW – involve fixed pitch propeller applications.
PBCF sales are handled by Tokyo-based Mitsui OSK Techno-Trade (MOTech), which advises potential customers of the anticipated benefits for a given ship project. MP