What is the minimum height for the lowest light on a vessel of 20 metres in length in the Great Lakes?

The minimum height for the lowest light on a vessel of 20 metres in length is 4 metres above the hull. This requirement is based on the regulations set forth to ensure proper visibility of navigation lights from a distance, especially in congested or busy waters like the Great Lakes. The elevation helps to prevent the lights from being obscured by the vessel's structure or other elements that could obstruct visibility.

In this case, the height of 4 metres is specified to ensure that the light is adequately positioned above any part of the vessel that could otherwise block it when viewed from various angles, including from other vessels or shore observers. Properly positioned lights are crucial for maintaining safety at sea and for allowing other vessels to discern the type and orientation of the vessel.

Other heights suggested, such as 2 metres, 3 metres, or 5 metres, do not comply with the established standards for vessels of this size. A height of less than 4 metres may not provide sufficient visibility, while a height of 5 metres exceeds the minimum requirement but is not the required standard. Therefore, 4 metres is the appropriate and required height for the lowest light on a 20-metre vessel in this environment.