The phrase "puts to sea" simply means to set sail or embark on a sea journey. There are numerous synonyms that can be used interchangeably with this phrase, including "sets off," "launches," "departs," "casts off," "moves out," "heads out," and "commences a voyage." Depending on the context, other synonyms that can be utilized include "starts a sea journey," "begins a naval expedition," "embarks on a cruise," "dives into the ocean," "explores the high seas," and "ventures into the open water." Regardless of the synonym used, all carry the same sense of setting forth on a journey across the sea.