The term “seaworthy” is used to describe a boat or ship which is considered fit for the conditions which it may encounter while underway. At a minimum, a craft is seaworthy if it won't sink, but seaworthiness can get very complex, and it can depend on a number of factors. For passengers, it is understandable to want to know whether or not a craft is seaworthy, but shippers, insurance companies, and the owners of the ship also need to know how prepared it is for a journey.
Seaworthiness encompasses the obvious physical condition of a ship and its fittings, along with the number of crew on board, and the loading of the cargo. A ship can be in excellent physical condition with working equipment and still be unseaworthy because it is overladen, or because the crew is not big enough or experienced enough. Physical design is also an issue, as some configurations are more seaworthy than others.
Another consideration is the type of trip the ship is making. Navigating a river is obviously very different than making one's way across the open ocean, and therefore the conditions which the ship may encounter should be considered. A sailboat fit for conditions in the Caribbean may not be prepared for icy arctic waters, and likewise, a riverboat may not be safe for use on the Great Lakes.
One of the standards which is often used to determine if a ship is seaworthy is considering whether or not the owner of the ship would allow it to sail as-is. If the owner would express doubts or a desire to remedy certain issues on board, the ship is not seaworthy. Insurance companies, which do not want to rely on the owner alone, may send out an assessor to establish seaworthiness before providing insurance to the ship's owner or the company which has a contract for use of the ship.
In addition to boats, the term is also sometimes applied to members of the crew. People who are not fully trained for their positions are not seaworthy, and the same holds true for injured, sick, or severely disabled sailors who are not capable of doing their jobs. For this reason, many seamen are required to receive medical examinations and certificates indicating that they can safely do their jobs. The same requirement is made of pilots, with the goal of ensuring the safety of craft, cargo, and passengers.