Rule 28

Vessels Constrained by their Draft.

A vessel constrained by her draft may, in addition to the lights prescribed for power driven vessels in Rule 23, exhibit where they can best be seen three all-round red lights in a vertical line, or a cylinder.

This rule is simplicity itself, but has been found to frequently cause confusion.  The lights prescribed are usually confused with a vessel aground, which shows a completely separate set of lights and shapes, of which more later, in Rule 30.

Additionally, it is always assumed that a vessel that is CBD is a large vessel.  This is not always the case and relatively small vessels may be CBD, as the rule governing the definition relates directly to the available depth and width of navigable water.  Therefore a vessel less than 50 metres in length could be CBD.

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Rule-29