On-line system for monitoring and forecast of ship resistance in ice, supporting winter navigation in the Baltic Sea

Abstract

The winter navigation occurs mostly in ice channels, which icebreakers break into the fast or drift ice. Every ship proceeding in such an ice channel experiences the ice resistance, which influences the ship speed and navigational capabilities. Maritime safety in ice conditions is first task brought up in order to ensure smooth and optimized winter traffic at the sea. As different risk analysis and management tools well exist and are capable to give general advices for organisation of navigation in ice, then lack of operational tools capable to monitor and forecast ice navigation conditions in local sea area are practically absent. We propose an online system to monitor and forecast the ship resistance in ice, supporting wintertime navigation in local, ship's scales. Firstly we introduce the technology for in situ estimation of the ship resistance in ice, based on measurements of shiphull vibrations. The measurement technology was based on the understanding that in different ice conditions the interaction of ice with the ship hull results in a vibration of the ship hull of different intensity. The vibration could be taken as a measure of ship resistance in ice, bigger the vibration intensity is, more ice resistance ship encounters. The icebreaker of the Estonain Maritime Administration EVA-316 was instrumented and vibrations of the ship hull were recorded by means of acceleration sensors in 3 directions. The acceleration data and ship position were transferred in real time to FTP server of the Marine Systems Institute. Next, after a preliminary analysis of data, the ice resistance index was defined and calculated. The comparison of the acquired ship hull vibration data and ice conditions information from satellite ice images showed that the obtained data well distinguish the open water and ice conditions of different severity. An successful attempt was made to relate the ice resistance index to relevant forcing parameters like wind speed and direction. We concluded that the wind direction and especially the angle between the wind direction and ship course was an important factor determining the ship resistance in ice channel. The recorded data on the ship hull vibrations together with the ship speed and course form a dataset which enables to assign a specific rank for the severity of ice conditions for the ice channel where ships operate. In order to supply the system with forecasting skill, a fuzzy logic relational scheme was defined, applied and validated. The on-line system to show the in-situ ice resistance and its forecast was designed and realised for the fairway into Pärnu Port, Gulf of Riga, the Baltic Sea.