Final answer:
Sailing vessels over 20 meters in length must show a red light to port, a green light to starboard, and a white stern light visible up to 2 miles at night; during the day, shapes like a cone with apex downwards indicate both sail and power propulsion.
Step-by-step explanation:
The lights and shapes for a sailing vessel over 20 metres in length adhere to international maritime regulations for the safety and communication between ships at sea. According to the International Regulations for Preventing Collisions at Sea (COLREGs), a sailing vessel of this size must exhibit specific lights at night: a red light to port and a green light to starboard, both visible at a range of at least 2 miles, and a white stern light visible over the same distance. During the day, sailing vessels over 20 meters must display shapes, such as a cone with apex downwards if under sail and power simultaneously. It's essential for mariners to understand these visual signals to navigate safely and avoid collisions.