Parallel sailing is a term often used in the context of sailing and navigation. Essentially, it refers to a path or course that is parallel to another. However, if you are looking for synonyms to use in place of "parallel sailing", there are several options available. For example, you could use the term "concurrent navigation" to describe the idea of two ships or boats traveling alongside each other. Alternatively, you might use the phrase "simultaneous course" to convey a similar meaning. Other possible synonyms include "coextensive voyage," "corresponding sailing," and "equivalent trajectory." Ultimately, the choice of synonym will depend on the context and intended meaning.