One or more relatively small objects of characteristic shape or colour (or both), placed on top of a navigation mark (or buoy) to identify it. (Figs. 65 and 66)
Note 1: A topmark may be
- a. Simple
- b. Composite, viz. made up of two or three individual topmarks.
Note 2: The following characteristic apparent shapes of topmarks are internationally recognised for the lateral system of marking (or buoyage):
- St. George's Cross
A broom topmark has the appearance of a circular broomhead and has two forms "Broom, point upwards" (in German, "mit Besen abwarts") and "Broom, point downwards" (in German, "mit Besen aufwarts").
Note 3: The following characteristic apparent shapes of topmarks are internationally recognised for the cardinal system of marking (or buoyage):
- Two cones, point upwards
- Two cones, point downwards
- Two cones, point to point
- Two cones, base to base
Note 4: Other forms (e.g. St. Andrew's Cross) are used, for example, as landfall marks.
Note 5: In the U.S.A. the word Daymark is often used for a topmark.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
acceleration due to gravity (m/s2)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM