The Client
Ledcor Resources and Transportation – Marine Division owns a fleet of tugs and barges that serve natural resource and industrial customers in Southwest British Columbia. They operate along the coast of the mainland and Vancouver Island and in the Fraser River. They provide ship assist, towing services and haul woodchips, gravel, fuel, and other cargoes.
The Brief
Ledcor Marine Division had the tug Paul C. Ledcor out of the water for maintenance on the propeller nozzles. The main propulsion engines had recently been updated with higher horsepower engines and, knowing that the nozzles would need complete replacement in the near future, Ledcor requested CMDL to advise on whether installing larger propellers and nozzles would allow them to increase their bollard pull, thrust, and vessel speed.
The Design
The Paul C. Ledcor is a 63 ft. long tug designed by A.G. McIlwain Ltd. The propulsion system was originally twin Caterpillar D346 (480 BHP @ 1800 rpm) engines with reduction gearboxes driving Kaplan-type fixed pitch propellers in Kort nozzles. New Caterpillar 3412E engines had been installed at 720 BHP @ 1800 rpm each (B rating – Heavy Duty) with the existing shafting, propellers and nozzles.
The original design had maximized the size of the nozzle, which touched the bottom shell at it’s leading edge. Therefore, any increase in propeller diameter would require the addition of a partial tunnel in the bottom shell impacting fuel oil tanks, keel cooling, rudder stock bearing housings, and steering gear.
Using propeller curves and NavCad software, it was determined that additional pitch could be used with the existing propeller diameter to absorb the additional power from the new propulsion engines while keeping cavitation within acceptable levels. Excellent support from Osborne Propellers revealed that not all of the required pitch could be added to the existing propellers, but new propellers could be cast with the full required pitch. Using ABS Rules, it was determined that the existing shafts remained suitable for the additional power and the existing rudder stocks would be sufficient for the expected increase in speed due to the new propeller.
CMDL provided this advice to Ledcor Marine Division so they could be fully informed to make decisions about their vessel maintenance into the future.