Final answer:
In a nighttime crossing situation, the stand on boat is typically the sailboat if it is under sail alone. The powerboat must yield to the sailboat, altering its course to avoid collision according to navigation rules.
Step-by-step explanation:
In marine navigation, the stand on boat is the vessel that has the right-of-way and should maintain its course and speed, while the other boat is termed as the give way or burdened vessel, which must take early and substantial action to avoid a collision. At night, the responsibilities do not change and the nature of the vessels is determined by the navigation lights they exhibit. In the case of a crossing situation between a sailboat and a powerboat, the generally accepted rule, according to the International Regulations for Preventing Collisions at Sea (COLREGs), is that the powerboat should give way to the sailboat if the latter is under sail alone. This is because sailboats are typically less maneuverable under sail power than powerboats.The COLREGs dictate the action of vessels in a crossing situation at night by assessing the aspect of each other's navigation lights. The sailboat, provided it is not under power but under sail alone, displays a red light to port and a green light to starboard. A powerboat is likely to have a white masthead light that can be seen ahead and sidelights. If the powerboat sees the red light of the sailboat on its starboard side, it means the sailboat is the stand on vessel and the powerboat must yield, altering course to pass behind the sailboat.In conclusion, during a crossing situation at night, the stand on vessel is typically the sailboat if it is under sail because it is less maneuverable, and the powerboat should take action to avoid collision by giving way.