Offshore Unit Dimensions
- The purpose of this message is to supplement AIS message 5 (ITU-R M.1371-5, Annex 8, § 3.3.3) and AIS symbols (IMO SN/Circ.243 - True Scale Outline) related to offshore platforms or similar units.
- Offshore Support Vessels travel to offshore platforms, but must not touch them. The awareness of the dimensions and facilities of platforms increases the platform and navigation safety.
- In order to support previous plan and real time approach, this message should be transmitted in the same rate of Message 5 of offshore unit and be displayed on ECDIS or ECS of support vessels.
- This content intends to represent features of the unit, like the edge, flare truss and auxiliary circles, besides cranes range and facilities points, to aid the approach of navigational watches.
- The Restiction Area is the circle where the navigation should be avoided. Auxiliary Circle could represent a rounded unit, the helideck, the mooring turret, the unit ramble around the turret or other feature.
- The Approaching Aid Points could be used to represent unit facilities to improve the approach safety. Its use increase the message size from 2 AIS slots to 3 (up to 16 points) or 4 (up to 32 points) slots.
- ECDIS or ECS of support vessels should have the ability to use VRM (Variable Range Marker) and EBL (Electronic Bearing Line) dynamically to approaching aid points, according to IEC 62288.
- The display of this message on ECDIS or ECS of support vessels should be as the following:
8.1. The IMO SN/Circ.243 symbol of unit (AIS Target - True Scale Outline) should be superseded to this content. The AIS triangle symbol should be added at the reference point to clarify the true heading.
8.2. The offsets of edge unit and others features should be located relative to reported position of AIS Message 1. The unit edge and features should be oriented along the true heading of AIS Message 1.
8.3. The offshore unit representation on ECDIS or ECS of support vessels should be refreshed and redisplayed at the same rate as AIS Message 1 reporting intervals.
8.4. The colors, styles, weights and labels of the unit outline should be equivalent to IEC 62288. The display should not confuse with others standard symbols. Circles and polygons should be hollow.
8.5. The Restriction Area should be represented in all scales as a circle or a point. The offshore unit edge, flare truss and auxiliary circle should be represented on scales up to 1:12000.
8.6. The Flare truss could represent the horizontal projection of flare truss or the derrick base of an drilling unit. The derrick base should be represented as a square with diagonals (as an gray "X").
8.7. The crane circle could represent the operational range of the crane on scales up to 1:4000. It should be represented as a gray circle (lighter than others lines) and its center as a gray point.
8.8. The Approaching Aid Points should be represented on scales up to 1:4000. They should be seen even if they overlap the lines (edges, circles and flare truss).
8.9. The origin of Set approaching aid points should not be displayed. If Transverse distance = Longitudinal distance = 0 of an specific approaching aid point, do not display the specific point.
8.10. The Label of Approaching Aid Points should be represented on scales up to 1:4000. The ECDIS / ECS of support vessels should have the ability to display or hide all labels by using a unique command.
8.11. The font of Approaching Aid Points labels should not be larger than the AIS default label font (MMSI, vessel name). The label of a specific point should be placed in order to avoid conflicts.