Shipwrights throughout the ages were influenced not only by individual and regional preferences, but also their own tolerances for innovation. As a result, there are countless variations in ship design, and it's nearly impossible to point to a single vessel as the definitive example of a ship in a particular era of history.
Given that disclaimer, here are a few general characteristics to look for in distinguishing between ships of various centuries. Remember, these are generalizations, not absolutes. No doubt you can find exceptions to the loose descriptions below.
Also, I have chosen to focus on the largest class of vessel of the period—the capital ship or "man o' war." The distinctions between smaller craft throughout the ages is a study in and of itself, which I'll leave to someone else. :)
Sail Plan: Ships of the 16th century often used a mast aft of the mizzen, known as the "bonaventure." By the early part of the 17th century, the bonaventure had disappeared, and most warships carried three masts thereafter.
In the 16th and 17th centuries, most large ships used one or two "spritsails," smallish square sails that were rigged from the bowsprit. Then a triangular fore-and-aft sail, the "jib," was introduced in 1715. Jib sails are perhaps the most telling sign of an 18th-century or post-18th-century ship.
Ships of the 18th century also used fore-and-aft staysails, so known because they were rigged on the stays that held the masts in place. Staysails were known on smaller boats much earlier, but did not start to be used on capital ships until 1660.
Hull design: In general, ships became less top-heavy through the centuries. The high forecastle of the 15th-century gave way to a less prominent foredeck. Similarly, the imposing, highly ornamented sterns disappeared over time, and by the end of the 18th-century, ship design favored low, sleek hulls with sparsely decorated sterns.
Steering gear: 16th- and 17th-century ships were steered by way of a whipstaff, a bar connected to the tiller. The ship's wheel was introduced at the beginning of the 18th century. Initially located just fore of the mizzen mast, it was gradually moved aft, and by the 19th century, the ship's wheel was placed as far aft as possible.
Mast Top: The medieval mast top, a round, flat platform used when handling yard and sail, had sides sturdy enough to support mounted weapons and provide protection for archers and crossbowmen. But once gunpowder was introduced and projectile weaponry grew to oak-smashing power, the advantages of a built-up mast top dwindled.
Over time, the sides were lowered and the area increased. A replica in the Mary Rose Museum depicts the top of Henry VIII's flagship with sides only about as high as a man's knee. Mast tops of 17th-century ships were shaped like saucers with shallow rims. By the early 18th century, the main top had developed into a square, flat platform with no sides—the "fighting top," where sharpshooters were positioned to pick off personnel aboard enemy ships.
The "crow's nest" was a deep, cup-shaped platform developed by 19th-century whalers, who recognized the advantages of the design for protecting seamen sent aloft to watch for whales. "Crow's nest" should not be used to refer to the mast top on ships of earlier design.
16th-century ship: The Great Harry
, flagship of Henry VIII, launched in 1546.
17th-century ship: Dutch man o' war. From a 1630 painting by Hendrik Vroom.
18th-century ship: The Friendship
, built in Salem, Massachusetts in 1797. From an 1820 painting by George Ropes, Jr.
Hough, Richard (1969).
Fighting Ships. New York: G.P. Putnam's Sons.
Giltaij, Jeroen, Kelch Jan, Museum Boymans-Van Beuningen (1977).
Praise of Ships and the Sea : The Dutch Marine Painters of the 17th Century.
Rotterdam: Museum Boijmns Van Beuningen.
Mondfeld, Wolfram zu (1985).
Historic Ship Models. Argus Books Limited.
Peabody Essex Museum