A system for analysing vessel efficiency and times for hull and propeller maintenance, based on standard vessel voyage reports
MARINTEK has developed a new tool called SOPRANweb™ (Ship Operation Analysis), which analyses the sailing efficiency of a vessel in terms of its consumption of time and bunkers and follows up trends in the condition of its propeller and underwater hull. Such trends can be utilised as a decision-support tool for determining the most suitable point in time for the next round of maintenance or docking operation, and to determine the effects of maintenance once this has been carried out. SOPRAN can also estimate bunkers consumption for future voyages.
For route planning purposes and when voyage contracts are being signed, it is important to be able to estimate future speed/consumption relationships as accurately as possible. When a vessel’s consumption of bunkers and time varies, often increasing over a period of time, it is important to identify the underlying causes and how they contribute to rising bunkers consumption and lost time.
The shipping company Bergesen d.y. has installed the first version of SOPRAN and will trial the system on its whole fleet, using data that has been gathered electronically since 1986.
In the course of time, all vessels develop roughness and fouling on their propellers and hulls. Fouling starts out as a coating of slime and gradually develops into an ever heavier growth of algae, which in extreme cases provide a base for the growth of seaweeds, barnacles and shellfish. These gradually reduce the sailing efficiency of the vessel. In order to bring the ship back to its original level of efficiency its hull and propeller need to be cleaned at regular intervals. Although several methods exist for scrubbing hulls and propellers at sea, vessels still need to be docked at certain intervals for partial or full renovation of the hull and treatment with antifouling paint.
For several years, MARINTEK has been studying problems associated with loss of speed caused by fouling. We are now in a position to offer a new service whereby, with the assistance of SOPRAN, we can help ship-owners to actively follow up the sailing efficiency of their vessels. SOPRAN is installed at a shipping company as a web service and is used in connection with a standard web browser. The system is based on vessels’ own daily reports of voyage data to company headquarters. Operational data, including time, distance sailed, propeller revolutions, bunkers consumption, currents, wind and wave conditions are all logged. SOPRAN requires voyage data in electronic format, and these data are transmitted directly via the Internet in a standard XML format, either by email or as file transfer. SOPRAN analyses the data to generate infor-mation that describes the current condition of the vessel. The point of departure for the analysis is relevant information about the ship’s “as new” condition, concerning speed and consumption, which are usually available from its sea-trials data. The reference data is gradually and automatically improved via systematic analysis of new voyage data as these are added to the database.
Figure 1 shows a typical SOPRAN screen image of a log of trends in the sailing efficiency of a vessel. The as-new condition of the hull is defined as 100%. A one-percent reduction in hull condition corresponds to a reduction in speed of one percent compared with the speed of the vessel when it was new.
As the curves in the figure fall off the ship-owner needs to decide when it is time to do something about hull and propeller fouling. Measurement uncertainty and other uncontrollable variations in the measurements are smoothed out by SOPRAN in order to bring out the overall trends.
Experience to date shows that this overview of trends provides a very accurate view of the state of the hull and propeller.
The effects of measures taken to reduce hull and propeller fouling can also be clearly documented. SOPRAN might be useful for evaluation of the effect of TBT free paint.
Contact at MARINTEK: Harald Sleire
(This is an article presented in MARINTEK Review No 3-June-2003)