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A shape fitted above a mark's body.
Also known as: Topmark shape, Daymark topmark
The IALA convention of fitting a distinguishing shape above a buoy so that its meaning survives at distance and in silhouette.
Fits a distinguishing shape above a buoy's body to carry its meaning at distance.
Contexts: Navigation
Works in silhouette, so it remains readable against a bright sky or at a range where colour has already failed, which is why it exists at all.
Contexts: Navigation
A small shape — a cone, a can, a sphere or a cross — mounted on a short staff above the body of the mark.