Final answer:
The correct answer is option a, which signifies that while underway, every vessel must maintain a proper lookout.
Step-by-step explanation:
The correct answer is option a. proper lookout.
When underway, it is crucial for a vessel to proceed at a safe speed for the prevailing conditions. In addition, a proper lookout by sight and hearing, as well as by all available means appropriate in the prevailing circumstances and conditions, is essential for ensuring the safety of the vessel and to make full appraisal of the situation and the risk of collision, stranding and other dangers to navigation. While maintaining a straight course may be part of navigational practice, it is not mentioned in navigational rules as a requirement like proper lookout. A constant engine watch may also be important for the operation of the vessel, but it is not specified as a requirement when underway in the same manner as maintaining a safe speed and proper lookout are.
When underway, every vessel must proceed at a safe speed and maintain a proper lookout, a constant engine watch, and a straight course.
A safe speed ensures that the vessel can maneuver effectively and avoid collisions. A proper lookout involves keeping a watch for other vessels, obstacles, and potential hazards. A constant engine watch ensures that the engine is functioning properly and can be adjusted as needed. Finally, a straight course helps maintain the vessel's intended path and reduces the risk of accidents.