Technically, the hull, turbine, electric power, outfitting, lifesaving, staffing, living facilities and other aspects must meet the requirements of solas Convention and STCW78-95 Convention, and meet the requirements of the port country where the ship needs to sail (for example, the United States has requirements for crew living facilities, although these do not affect the seaworthiness of the ship, but have an impact on the operation), and obtain corresponding certificates, and pass.
From the insurance point of view, the seaworthiness of the ship is somewhat different from the above. I have forgotten what the concept is. If you need this, please fill in the questions. I'll turn to the book later.