Ordinary seaman
An ordinary seaman (OS) is a member of the deck department of a ship. The position is an apprenticeship to become an able seaman, and has been for centuries. In modern times, an OS is required to work on a ship for a specific amount of time, gaining what is referred to as "sea time". For centuries, the term ordinary seaman was used to refer to a seaman with between one and two years' experience at sea, who showed enough seamanship to be so rated by their captain. Historically in some navies and the merchant marine a sailor  with less experience was called a landsman. An OS is generally not required to stand watch, but must pass examinations on watchstanding skills such as performing lookout duty and being a helmsman. Thus an OS will often be found on a ship's bridge after working hours taking a turn at the ship's wheel or being familiarized with bridge equipment. During the apprenticeship, an OS performs a variety of duties concerned with the operation and upkeep of deck department areas and equipment. These duties vary with the type of ship, the type of voyage, the number of crewmembers, the  weather, the supervisor, and any number of other variables. However, in most cases, one can expect an ordinary seaman to clean, to perform maintenance, to work with deck equipment, and to undergo on-the-job-training under the supervision of senior deck department members. Duties. As an ordinary seaman, one's duties may include the following: On specialized vessels, an OS may have unique duties. For example, on research vessels, an OS may rig and operate hydrographic and other specialty winches; handle and stow oceanographic explosives; and stage and stow beach support equipment. Advancement. United States. The next step on  the career ladder for the ordinary seaman is to become an able seaman. This advancement is based on a number of factors laid out in the Code of Federal Regulations. Training. The Code of Federal Regulations establishes in 46 CFR 12.05 four categories of able seaman for the United States Merchant Marine: Time served in certain training programs and school ships may be substituted for the time of service listed above. Special certificates of service are available for "Able Seaman, Great Lakes—18 months service"; "Able Seaman, Any waters—12 months"; "Able Seaman, Tugs and towboats—any waters"; "Able Seaman, Bays and  sounds—12 months, vessels 500 gross tons or less not carrying passengers"; and "Able Seaman, Seagoing barges—12 months". Examination requirements. For the United States Merchant Marine, the Code of Federal Regulations establishes in 46 CFR 12.05 examination requirements for the certification of able seamen, which includes: