What is the minimum size of the shape that indicates a vessel constrained by her draught?

The minimum size of the shape that indicates a vessel constrained by her draught is specified in the COLREGs regulations. A vessel that is constrained by her draught must display a specific day shape to signal her condition to others. The correct minimum size for this shape, which is a cylinder, is 0.6 meters in length.

This requirement is set to ensure visibility and clarity, allowing other vessels to recognize the constraints of the vessel's maneuverability due to her draft. The size of 0.6 meters is considered adequate for the day shape to be easily identifiable, enhancing navigational safety by alerting other mariners of potential limitations in the vessel's ability to navigate freely in shallow waters.

Other sizes listed do not meet the standard outlined in the COLREGs, hence they are not valid options for indicating the day shape for a vessel constrained by her draught. The emphasis on this minimum size is crucial in maritime navigation, promoting awareness and caution in congested or restricted waterways.