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Naming convention for describing objects relative to the vessel's heading




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What is the issue?
When navigating a vessel it is important that direction from which objects appear can be efficiently and effectively communicated. Having a single clear sectorial naming convention for the surrounding sea areas with reference to the various relative points of the vessel delivers this.

Why address this?
To be able to communicate the relative position and movement of a vessel or object is vital for safety of navigation. Moreover, the ability to further use this as a reference to judge the relative motion, that is, to be able to judge the changing distance and bearing between the moving vessel and a stationary object or another vessel is an important ability for all mariners to develop.

This is no better exemplified than with a constant bearing, decreasing range (CBDR) bearing, the term used to indicate some object, usually another vessel viewed from the one's own vessel, is getting closer but maintaining the same relative bearing. If this should continue, the vessels will collide.

How to address this?
The six point naming convention for sectors in which an object can be described as appearing relative your craft's forward direction are set out below.


Sector definitions for object areas relative to the vessel's heading
Image: Michael Harpur


The above sector definitions, augmented by 'port' and 'starboard' as appropriate, e.g fpo provides adequate detail for most recreational sailing. But where more precision is needed there are two other options:

Relative Bearing The direction of an object from a vessel relative to the vessel's heading. The relative bearing of an object is the clockwise angle from the heading of the vessel to a straight line drawn from the observation station on the vessel to the object. Typically, the relative bearing is given as a horizontal angle measured clockwise from 000° (dead ahead) through 359°.

For example, an object relative bearing of 0° would be dead ahead; an object relative bearing 180° would be behind. It can also be given in points, an interval of 111° as in 'two points off the starboard bow. Likewise it can be express as the clock face, with an object appearing directly on the starboard beam being at 3 o'clock.

Absolute Bearing The absolute bearing refers to the angle between the magnetic north, magnetic bearing, or true north, true bearing, and an object. For example, an object to the East would have an absolute bearing of 90°.

Some people are able to develop a sailor's eye much better than others but time at sea helps.

Other Spatial Orientation Terms

Other seagoing terms that provide succinct definitions for spatial orientation in a marine environment, or a location on a vessel, that are usefull to understand are as follows:

Abaft (preposition): at or toward the stern of a vessel, or further back from a location, e.g. the mizzen mast is abaft the main mast.
Aboard: onto or within a vessel, or in a group.
Above: a higher deck of the vessel.
Aft (adjective): toward the stern (rear) of a vessel.
Adrift: floating in the water without propulsion.
Aground: resting on the shore or wedged against the sea floor.
Ahull: with sails furled and helm lashed alee.
Alee: on or toward the lee (the downwind side).
Aloft: the stacks, masts, rigging, or other area above the highest solid structure.
Amidships: near the middle part of a vessel.
Aport: toward the port side of a vessel.
Ashore: on or towards the shore or land.
Astarboard: toward the starboard side of a vessel.
Astern (adjective): toward the rear of a vessel (opposite of "forward").
Athwartships: toward the sides of a vessel.
Aweather: toward the weather or windward side of a vessel.
Aweigh: just clear of the sea floor, as with an anchor.
Below: a lower deck of the vessel.
Belowdecks: inside or into a vessel, or down to a lower deck.
Bilge: the underwater part of a vessel between the flat of the bottom and the vertical topsides.
Bottom: the lowest part of the vessel's hull.
Bow: front of a vessel (opposite of "stern").
Centerline or centreline: an imaginary, central line drawn from the bow to the stern.
Fore or forward: at or toward the front of a vessel or further ahead of a location (opposite of "aft").
Inboard: attached inside the vessel.
Keel: the bottom structure of a vessel's hull.
Leeward: side or direction away from the wind (opposite of "windward").
On deck: to an outside or muster deck (as "all hands on deck").
On board: on, onto, or within the vessel.
Onboard: somewhere on or in the vessel.
Outboard: attached outside the vessel.
Port: the left side of the vessel, when facing forward (opposite of "starboard").
Starboard: the right side of the vessel, when facing forward (opposite of "port").
Stern: the rear of a vessel (opposite of "bow").
Topside: the top portion of the outer surface of a vessel on each side above the waterline.
Underdeck: a lower deck of a vessel.
Yardarm: an end of a yard spar below a sail.
Waterline: where the water surface meets the vessel's hull.
Weather: side or direction from which wind blows (same as "windward").
Windward: side or direction from which wind blows (opposite of "leeward").

With thanks to:
Michael Harpur
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