The design of a bulk carrier propulsion system

Abstract

Competitive ships must be designed to survive challenges of a globalized market, increase of speed, increase of cargo capacity, minimum fuel consumption and maximizing maneuverability are among them, in consequence, lots of efforts are being placed to overcome mentioned ideas. Regarding propulsion systems, our aim is to develop designs to give maximum propulsive efficiency without noise and vibration.

The objective of this master thesis is to design a bulk carrier propulsion system; fundamental of the design is the selection and integration of the main components (prime mover, transmission and propulsor) into a functional system. For the propulsion system of the ship it was decided to use a low speed diesel engine with directly driven fixed pitch propeller.

As stated before, propulsion systems consist of three components, engine, transmission, and propeller. Engine will be selected by its power (MCR) to overcome ship resistance accounting for losses, shaft line will be design using GL rules for its dimensioning, and propeller development will be divided in three stages, preliminary design, detailed design and analysis.

Determination of the required propulsion power and engine sizing requires previous knowledge of the quasi-propulsive coefficient. At initial point, propeller diameter was estimated by considering ship draught in ballast condition, to avoid air drawing; Wageningen B Series data was used to obtain optimum propeller velocity of rotation rpm for maximum open water efficiency; once engine brake power was obtained, selection of engine was performed.

Because main engine influences the propeller through the propeller rpm and delivered power, new propeller diameter for maximum efficiency was computed satisfying required clearance; also, propeller was designed to absorb a given delivered power (15% sea margin and 10 % engine margin taken into consideration). Main results of this stage are diameter D, number of blades z, expanded area ratio and propeller mean pitch ratio P/D.

Second stage in propeller design procedure is to find the blade geometry for a specified distribution of blade loading over the radius. To achieve this goal, a wake adapted propeller was designed using an in-house code for lifting line theory with lifting surface corrections.

Finally, propeller geometry was used as input data to start the third and last stage of propeller design, called analysis, where we perform numerical analysis of the open water characteristics and hydrodynamic performances of the wake adapted propeller. Primordial objective of this stage are the calculation of open water characteristics, calculations of pressure distribution on propeller blades and calculation of the unsteady forces and moments acting on propeller shaft. If satisfactory results are obtained at this stage, the design of the propeller is concluded, if not, an iterative design cycle will take place with a changed propeller geometry.