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Configuring a speed range in an Area of Interest (AOI) allows a user to view AIS-transmitting vessels on the map that are traveling at a targeted speed or speed range for a specified time or distance.
There are several reasons you may want to generate this event:
To monitor vessels traveling above a speed where they are in danger of fatally striking large mammals (e.g. Right Whale migration along the east coast of the United States).
To monitor vessels that are unlikely to be on “innocent passage” through an area.
To monitor speed range events you must first create an area of interest and configure the speed range event in the AOI.
Area Size Limits
Areas larger than 1,000,000 sq km cannot be configured for speed range events - if your area is larger than this limit we recommend breaking the area up into smaller sections (e.g. northern half, southern half)
Speed Range Configurations
To prevent showing vessels that are anchored, speed ranges have a minimum speed of 1 knot. Although the time duration for a speed range can be set as low as 1 minute, we suggest setting the time at a minimum of 20 minutes to avoid multiple speed events that are only a few minutes apart.
Distance can be configured with nautical miles, kilometers, or miles.
Once configured, the system will start to monitor speed ranges within a few minutes. When a vessel meets the criteria of the speed range, it will be displayed on the map as an event.
Duration of Events
The event will continue for as long as the vessel's speed continues within the range. For example, if the range is defined as 13-60 km for 3 nautical miles and the vessel travels for 16 then 14 then 15 km for 3 nautical miles, then the speed icon is displayed on the map. If the vessel continues at 13-60 km for an additional nautical mile, it will still be counted as a single event. The speed range event ends when the vessel’s AIS transmission indicates it is no longer traveling 13-60 km. A second speed event will occur when the vessel’s AIS transmissions again indicate it is traveling 13-60 km for 3 nm. The same is true for time. If the range is defined as 10-14 km for 1 hour, the event displays on the map after the vessel travels 10-14 km for 1 hour. If the vessel continues traveling 10-14 beyond 1 hour, then the event will continue.
Skylight uses speed over ground (SOG) to measure the vessel’s speed.
The duration of the event is measured with a simple calculation of (event end time) - (event start time). In other words, duration is the time/distance from when AIS transmissions first detect the vessel started traveling at the designated speed to when AIS transmissions indicate the vessel is no longer traveling at the designated speed. For example, if the range is defined as 10-14 km for 1 hour, after 1 hour of the vessel traveling 10-14 km/hour the event will display on the map and the duration will be "1 hour". On the vessel details screen duration for all speed events, even those defined by distanced are displayed in time. This allows users to see the duration for all events in the same units for easy comparison.
There may be instances when the average speed for an event is slightly outside of the configured range. Typically this is due to the vessel accelerating or decelerating at the end of a segment.