What is the key requirement for the placement of sidelights on a vessel of 20 meters or more in length?

For a vessel that is 20 meters or more in length, the correct requirement regarding the placement of sidelights is that they should be installed not higher than the aft masthead light. This positioning ensures that the sidelights are visible from a distance and conform to the regulations regarding visibility angles for navigational lights.

The placement ensures that the sidelights, which indicate the port (red) and starboard (green) sides of the vessel, are effective in communicating the vessel's orientation and direction of travel to other vessels, especially at night or in low visibility conditions. If the sidelights were positioned higher than the aft masthead light, it could create confusion about the vessel's heading and increase the risk of collisions.

Other options may refer to different scenarios or placements that do not align with the specific requirements set forth in the COLREGs for vessels of this size. By adhering to the specification of placement relative to the aft masthead light, vessels maintain compliance with safety standards and enhance their visibility to others on the water.