For the purpose of the Rules, what does the term "vessel" include?

The term "vessel," as defined by the Rules of the Road, encompasses a broad range of watercraft, which includes seaplanes. This recognition stems from the fact that any means of transportation used on water qualifies as a vessel under maritime regulations. Seaplanes, while primarily aircraft, often operate on the water and are used for various purposes such as transporting passengers or cargo, thus they fall under the same regulatory framework.

The other options have limitations in their definitions. Power-driven vessels and sailing vessels are specific classifications of vessels but do not represent the entirety of what is defined as a vessel under the Rules. Navigational aids, on the other hand, are devices used to aid navigation and do not fall into the category of vessels, as they do not function as means of transportation themselves. By understanding the broader definition that includes seaplanes, one can appreciate how the Rules of the Road apply across various types of water-related activities.