Impact of Propulsion Plant Choice On Maintenance
Maintenance is one of the keys to profitability in shipping. In fact, the maintenance of machinery is often a top design priority from the initial stages of most projects. In 1993, Deltamarin of Finland completed a case study, in preparation for the TT-Line passenger ferry project, that evaluated and quantified the level of annual expenses attributed to maintenance and repair (M&R) of diesel engines. One of the primary concerns of the study was whether the machinery choice would have any significant impact on expected maintenance costs. The study indicated that the conventional diesel machinery would have somewhat lower aquisition cost, but the diesel-electric solution was superior in possibilities for novel machinery arrangement, offering a chance for larger cargo space and efficient lower cargo hold operations. Although many other factors play a part in machinery selection, the M&R aspects are a key element in the buying decision.
Machinery concept related differences were evaluated by comparing the M&R costs between dieselelectric concept (D-E) and dieselmechanical concept (D-M). Two alternative machinery concepts were presented; and in an effort to remain consistent, engines by the same manufacturer were selected. Total installed main engine power was about 18 MW for both models. Deltamarin found that the D-E machinery was the favorable option, based upon an 18 percent difference in service hours, spare parts costs and total costs. In terms of the complexity of installation and also on the number of separate devices needed to run the systems, M&R costs were found to be lower for systems with less equipment. Less machinery equals a lesser demand for repairs. On a D-E ship, there are no separate engines for propulsion and ship electric production; therefore, the ancillary systems are simpler and less expensive.
These conclusions are based on figures which calculated the scheduled M&R costs for machineries and corresponding ancillary systems. All data was based on supplier's manuals and information for scheduled maintenance and spares for a machinery operating according to a specified profile. Actual operation profile and corresponding engine loading and running hours were calculated for a period of eight years in order to get a true figure of the differences under long term operation. Annual increase in M&R costs due to inflation was ignored. In addition to machinery related concepts, fuel choice related consequences were also examined. All comparisons between MDO burning and HFO burning were made between two similar D-E machineries. Deltamarin's study concluded that HFO would cause a 29 percent increase in engine spare parts costs due to the increased complexity of the fuel system. As determined earlier in the discussion on machinery, fewer system complications generally indicate a more modest budget.
Overall, HFO systems tallied costs equaling 19 percent more thanthis scenario, the study concluded that HFO is therefore less cost-effective.
In a real-case scenario set up by Deltamarin, use of HFO instead of MDO forecasted a 54 percent cost differential between the options. After manning, M&R is usually the largest item among operating cost of a ship.
The cost implications of damage or unscheduled repairs are largely unquantifiable, but as demonstrated by Deltamarin's study, it is possible to project maintenance costs by examining factors such as machinery and fuel burning. Other maintenance factors not looked at in this particular study include drydocking, tank cleaning and coating, boilers, hull, piping system, electric, external and internal cleaning and painting.
One of the most difficult operating costs to evaluate and quantify is the level of annual expenses attributed to M&R. Deltamarin's study showed that machinery and fuel choice have a demonstrated impact on M&R costs, and therefore equipped the TT-Line passenger ferry ships with diesel-electric propulsion and MDO burning engines.
This information was excerpted from Deltamarin's study, "Impact of Propulsion Plant Choice on Maintenance.