Captain
The title of Captain is the title given to an individual in control of a ship at sea, and tend to be the strongest members of their crew. Anyone can attain the rank of captaincy out of pure leadership, as a founding member or voted by other crew members. All major decisions are made by them, though they may be usually advised and influenced by other members.
First Mate
The First Mate a major officer on a ship that answers directly to the Captain. Their general position is oftentimes something important on the crew such as a doctor or shipwright, but some captains have their second strongest fighter as their First Mate.
Second Mate
The Second Mate on a crew is customarily the Navigator in charge of charting the route of the ship. Their job is to take on the work load of the First Mate if they are absent and perform the duties of watchkeeping. In some cases, the position can also be filled in by the third strongest member of a crew.
Boatswain
A boatswain or bosun, is the senior of the deck department and is responsible for the components of a ship's hull. The boatswain supervises the other members of the ship's deck department, except on vessels with small crews. Additional duties vary depending upon ship, crew, and circumstances.
Cook
A cook, or chef, is a person who prepares food for passengers or crew mates on ships. A cook must have knowledge of nutritional values and know how to cook a variety of things while out at sea into something edible.
Doctor
The doctor is someone who studies medicine and treats injuries. While out at sea it is important for a doctor to be well versed in worldly knowledge of diseases in the seas that their crew will be swimming in. As well, they need to be able to treat virtually any sickness or wound inflicted on a member of the crew, if possible. Without a doctor, a single mishap could spell the end even for for an entire crew of incredibly powerful sailors.
Navigator
A navigator is the person on board a ship responsible for the navigation of the vessel. The navigator's responsibilities includes planning the journey, advising the captain, and ensuring that hazards or obstacles, climatic or otherwise, are avoided.
Shipwright
A shipwright is a person who is responsible for the design, construction, and/or repair of ships, boats, and other marine vessels. They are responsible for the building and the repair of the ship; similar to how a ship's Doctor is responsible for the health of its crew, the Shipwright is responsible for the well being and seaworthiness of the ship itself. Often this position is shared with a Boatswain who would tend to the sails or other parts of the ship that do not directly deal with the foundation of a vessel.
Sniper
A sniper is a person adept at utilizing as well as maintaining ranged weaponry both on and off of a ship. Their duties usually involve maintaining the cannons, firearms, and other ranged weaponry a ship may contain. Sometimes, if one is present on a crew, a sniper may task the duties of being cannoneer, or gunner, to the Commando of the crew.
Archaeologist
An Archaeologist is a type of Scientist that goes out and studies the ancient history of cultures or ruins. They have knowledge of the past and possibly some locations that may no longer be written on up-to-date maps. Their knowledge may also stem far enough back, or they've performed studies of, to understand Poneglyphs.
Assassin
Assassins are trained killers that are often powerful and stealthy fighters. They are normally hired to assassinate other individuals, gather or steal information, and perform clandestine operations.
Barber
The Barber is in charge of maintaining the healthiness of the crew by tending to their hair. They can give the crew distinct haircuts or help them disguise themselves using some supplies involving extensions or specific hairstyles. A Barber is often also known to be one of the more fashionable members of the crew, able to gather information in crowds and gossip easier than most of their crew due to their status.
Beast Tamer
A Beast Tamer, or Pet Tamer, is someone on a crew who often handles the animals brought on board for the duration of the travel. These animals could be trained specifically for amusement, combat situations, or otherwise.
Blacksmith
The Blacksmith attends to all of the armor, ammunition, and weapons on the ship. It is their job to polish, repair, and maintain the efficiency of weapons, primarily those wielded by Martial Artists and Swordsmen on the crew.
Cabin Mate
The Cabin Mate is often the maintenance worker of the ship handling menial tasks on board of a ship. Scrubbing decks, performing duties the Boatswain, Cook, or Shipwright would perform in small increments to teach the crew mate how to live among the sea.
Helmsman
A helmsman is someone who steers the ship and maintains course. While this position can be covered by anyone on the ship, a helmsman will have far better control of a ship than those with a different general position.
Instructor
A knowledgeable, and sometimes powerful individual whose main job is to share their worldly knowledge. Many instructors on a crew train them physically, in Haki, or something that they were specifically assigned. Most instructors are older people who wish to hand over their reigns to the next generation, or those who wish to pass on knowledge that only they know.
Lookout
The crew member who rests in the Crow's Nest is called a Lookout. Their job is to use instruments to check the weather and see faraway objects before reporting down to the First Mate or Navigator with their findings. The Crow's Nest becomes a small, secondary bed for the crew member assigned to this duty who can personalize it however they wish.
Quartermaster
The member of the ship responsible for providing quarters, rations, clothing, and other supplies. Their main duty outside of that is to maintain the ship's treasure and quota when shopping for supplies. They often work together with many other members of the crew before making any major decision involving the wealth of the crew.
Martial Artist
Normally powerful individuals who have mastered some type of physical combat. Their main job on the crew is to train the Infantry and those who cannot defend themselves on the ship self-defense. This can sometimes lead to other members of the crew becoming stronger than they appear making them more useful if they originally were in a non-combative position.
Merchant
The right hand of the Quartermaster and the one who actually performs the task of spending, bargaining, and trading among the crew. Commonly a very sly individual, they are able to get better prices than most folks and knows how to haggle. This individual can also be useful for scoping out a port town beforehand by sending them ahead to gather supplies rather than waiting to dock at port first.
Musician
A musician is great to have on long voyages. Most crews while out at sea will eventually become bored, so it never hurts to have some enlightening musical talent on board the ship for entertainment. Most musicians have little to no fighting capabilities though it is not unheard of for a musician to also be a powerful member of one's crew.
Scientist
The Scientist of a crew is a very rare position that is ever filled. When it is filled, however, it gives a crew access to someone with enough intellect to make the Blacksmith, Commando, and Shipwright dangerous individuals. Scientists can invent new armor, gadgets, or weapons for the crew to utilize that world has never seen before.
Swashbuckler
A member of the crew that is a jack-of-all-trades who is expertly skilled two of the following three positions: Martial Artist, Sniper, or Swordsman. They are incredibly versatile, and can handle most situations the positions they cover require with ease. Commonly, powerful Captains will take up this position, and most stories tell tall tales of these Captains comparing them to "Heroes".
Swordsman
A member of the crew that fights using pure swordsmanship. Whether they are a Power-type or Speed-type swordsman, commonly their strength puts them right next to the Captain in terms of power. There will often be plenty of swordsmen or swordswomen on a crew, and are known to be a competitive group of folks.
Tailor
A member of the crew that is tasked with handling and mending the clothes of the crew. While some are simply craftsman, some can use their skills to disguise members of the crew with their personal creations. They oftentimes work hand-in-hand with the crew's Barber when it comes to disguises and can commonly be found below deck.