22 February 2009

Monitoring Hull Performance

Hull performance is critical for both fuel economy and fuel emissions control. The ability to accurately monitor fuel economy and emissions was the subject of a presentation, “Hull Performance Monitoring: A Tool for Fuel/Emissions Management,”by Daniel Kane, Propulsion Dynamics,also given at the Marine Coatings Conference.
The speaker presented a monitoring system that has been in use for about five years. The system gives a precise speed-through-water analysis and the corresponding fuel consumption. The factors affecting hull performance are :

  • age of ship/ time out of dock;
  • time in port;
  • service speed;
  • water temperature;
  • fouling; and
  • loading conditions.
All ships have “performance monitoring systems,” and all owners say they are aware of their fuel consumption per day. The factors affecting consumption that owners can control are coating selection during newbuilding, drydocking interval, hull pre-treatment and coating at drydocking and a maintenance program. The speed log, however, isn’t measured relative to the water conditions. Wind, and, to a certain extent, the fuel itself and the loading conditions are all parameters that influence the sailing characteristics. By making use of the hydrodynamic technique in the proprietary monitoring system, these and variables like trim and fouling can be monitored. The problem is then correcting the performance data into actual speed through the water. For example, 60% power can lead to anything between 19 and 26 knots.
By using the performance-monitoring program, examples were given to show :
  • how polishing the propeller can reduce drag by up to ten percentage points;
  • that cleaning the hull led to reducing the fuel consumption from 190 to 170 tons a day in one instance;
  • that a ship that anchored for four weeks used up nine tons a day more than before anchoring; and
  • different antifouling coatings can be compared for effectiveness.
By analyzing all the operational variables for a vessel, an accurate picture of hull performance (drag) can be obtained, and the optimum cleaning/coating cycle can be predicted to give maximum fuel savings and minimum emissions. It has been calculated that typical average fuel savings in the merchant fleets worldwide are about 5–15 tons a day.

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