Navigation
The chief mate kept the ship's log while at sea. Though the captain checked entries for accuracy, the responsibility for recording wind and weather conditions, distance and daily readings belonged to the chief mate. At noon each day, the chief mate and the captain came on deck with navigation instruments, called sextants, to measure the position of the ship. When the sun passed the meridian, they took readings, recording them in the ship's log. From these readings, the captain could determine the position and course of the ship.
Supervising the Crew
The chief mate took orders from the captain and relayed them to the crew when setting sail and anchoring. Once at sea, he became the commanding officer, directing the crew in the execution of their duties. The chief mate knew every seaman's job, but as an officer, did not engage in physical labor himself. He inspected the condition of the ship and the chains and ropes that controlled the sails, called the rigging and reported problems to the captain. He ensured supplies and tools were prepared for the daily work and for emergencies at sea.
Standing Watch
Watches divided the day into four-hour periods when at sea. The second mate supervised the starboard watch while the chief mate commanded the port, or larboard, watch. When all hands were on deck during the day, the chief mate was always the officer in charge and gave orders to the men from either watch. If only the starboard crew was on deck, however, the chief mate did not interfere with the orders of the second mate.
Duties in Port
In port, the chief mate took command of the ship while the captain was ashore. In addition to overseeing the daily work and repair to the sails and rigging, the chief mate supervised the loading, unloading and stowing of cargo. Standing on the gangway, he supervised the movement of cargo onto and off the ship and kept an accurate account for the ship's records, issuing receipts when necessary.
Accountability
The chief mate's position, in relationship to the captain, was different from the second mate's position. The owners, insurers and shippers demanded special duties and qualifications from the chief mate, so he could not be removed from his position by the captain except under special circumstances and with just cause. The chief mate knew navigation as well as seamanship. If the captain died or was unable to perform his duties, the chief mate was prepared to take command and continue the voyage.