The Writer’s Guide to the Technology of Ships

Most people look at a sailing ship and don’t think of it as a piece of technology. But technology is “the application of scientific knowledge for practical purposes,” according to the dictionary. Ship sails and hulls are the product of millennia of practical scientific application. If a hull has an incorrect shape, the ship won’t be buoyant. If a sail is an incorrect shape, it won’t catch the optimal amount of wind. Here are the basics of the physics of ships.

As always, magic is the exception to the rule. Because magic.

Hull

The shape of the hull is important because it creates enough buoyancy for the ship to float. The earliest boats had simple rounded hulls, such as canoes. But ship builders experimented with different shapes. Most ship hulls throughout history and up to the modern day are wide on the sides before curving down to the keel.

Most hulls taper toward the bow and stern, with the widest section in the center. This reduces drag and allows the hull to slip through the water. The surface is made as smooth as possible to further reduce drag.

Hull shapes break down into several subcategories. Hard chined hulls have flat planes that meet at sharp angles. Moulded, round bilged, or soft chined hulls have smooth curves and are the most common today. [3] Some hulls are designed primarily for displacement, while others are constructed for high speed and planing across the surface of the water.

There are pros and cons to each shape. For example, flat-bottomed hulls are more stable but have high drag, so the vessel is slower. A severely tapered hull can be fast but can also be unstable, leading to the danger of heeling, or leaning far to one size, and capsizing.

Sails

The sails are used to catch the wind coming from the back of the ship and pull the vessel along the surface of the water. The sails act as an airfoil and provide lift, although only to a certain point before drag asserts itself. [2] There is an incredible amount of physics behind a ship’s sail.

Most ships can adjust the placement of their sails so they can catch wind coming from different directions. This is known as trimming and is achieved by adjusting the running rigging. Sails can use wind coming from the sides and the back. Ships can use wind coming from the front by tacking or zigzagging back and forth to fill the sails from the side.

There are three general sail shapes that have been used throughout history.

Square sails are exactly what they sound like. This shape is the one that most people think of when they picture a sailing ship. The sails are suspended from a yard attached to the mast. There are paintings of ancient Egyptian ships with square sails from as early as 3200 BCE. [1]

The crab claw rig is a sail spread between two spars which meet at one end. This style of sail was used extensively in the Pacific Ocean by the people of Micronesia, Polynesia, and Madagascar. It enabled them to sail vast distances of open ocean and is mostly used on catamarans and outriggers. [4]

Lateen sails are triangular and suspended from a canted yard. They were used extensively in the Mediterranean, beginning in the 2^nd century CE. [5] This style is believed to be a variation of the crab claw sail that developed from contact with Southeast Asian Austronesian trading ships in the Indian Ocean. [6] Lateen sails have better upwind performance than square sails, especially on smaller vessels, and beginning in the 15^th century, became the most common for ships sailing rivers and the Mediterranean. [7] However, square sails were still the standard for trans-Atlantic and North Sea sailing.

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[1] John Coleman Darnell (2006). “The Wadi of the Horus Qa-a: A Tableau of Royal Ritual Power in the Theban Western Desert”. Yale. Archived from the original on 2011-02-01. Retrieved 2010-08-24.
[2] Batchelor, G.K. (1967), An Introduction to Fluid Dynamics, Cambridge University Press, pp. 14–15, ISBN 978-0-521-66396-0
[3] Zeilen: Van beginner tot gevorderde by Karel Heijnen
[4] Doran, Edwin Jr. (1974). “Outrigger Ages”. The Journal of the Polynesian Society. 83 (2): 130–140.
[5] I. C. Campbell, “The Lateen Sail in World History” Archived 2016-08-04 at the Wayback Machine, Journal of World History (University of Hawaii), 6.1 (Spring 1995), p. 1–23
[6] Hourani, George Fadlo (1951). Arab Seafaring in the Indian Ocean in Ancient and Early Medieval Times. New Jersey: Princeton University Press.
[7] Chatterton, Edward Keble (1912). Fore and aft. London: J. B. Lippincott. p. 203. OCLC 651733391. fore and aft rig schooner.