A seafarer is a person who works at sea, either on a merchant vessel or a recreational boat such as a yacht. Seafarers include a wide range of professions, including deckhands, engineers, officers, and other specialists who work on ships and boats.
A seaman is a specific type of seafarer who works on a merchant vessel, typically in a deck or engineering capacity. A seaman may be a member of the deck crew or engineering department, and may be responsible for tasks such as navigating the vessel, maintaining the hull and machinery, and loading and unloading cargo.
In general, the term "seafarer" is used to refer to anyone who works at sea, while the term "seaman" specifically refers to someone who works on a merchant vessel. However, the terms are often used interchangeably, and some people may use the term "seaman" to refer to any worker at sea, regardless of whether they are on a merchant vessel or a recreational boat.