Characteristics
In their heyday, square-rigged vessels ranged in size from small boats to full rigged ships. But this rig fell from favour to fore-and-aft gaff rigs and bermuda rigs after the development of steam power and new materials. Ocean going sailing ships stayed mostly square rigged.
Square rigs allowed the fitting of many small sails to create a large total sail area to drive large ships. Fore-and-aft could be sailed with less crew and were efficient working to windward or reaching, but creating a large total sail area required large sails, which could cause the sails and cordage to break more easily under the wind. Despite the large overall sail areas, and even when sailing on their best points of sail, large warships were slow, for example 6–8 knots. Some clipper ships that had square rigs and for whom speed was critical could be much faster; for example Cutty Sark could make 17 knots. The late windjammers were as fast as the clippers, being much bigger.
Not only could a smaller sail be managed by a smaller crew but also these smaller sails constrained the impact of weapons on them. A hole from a cannonball affected only one sail's area, whilst a hole in a large sail would eventually tear the whole larger area and reduce more of the vessel's motive power.
With the development of more advanced fittings, equipment and cordage, particularly geared winches, high loads on an individual line (or rope) became less of an issue, and the focus moved to minimising the number of lines and so the size of the crew needed to handle them. This reduced running costs and also enlarged the space available in the ship for profitable cargoes.
New materials also changed sail designs, particularly on hybrid vessels carrying some square-rigged sails. The low aspect ratio of square rigged sails (usually 1/2 to 1/3) produces much drag for the lift (motive power) produced, so they have poor performance to windward compared to modern yachts, and they cannot sail as close to the wind. The Bermuda rig is the (nearly) undisputed champion of windward performance in soft sails, due to its very low drag and high lift-to-drag ratio. One advantage of square rigs is that they are more efficient when running, where the high lift to drag is irrelevant and the total drag is the most important issue. Square rigged sails are also less prone to broaching when running than Bermuda rigs. Ocean going vessels take advantage of e.g. the trade winds and the westerlies and are thus mostly running.
On a square rigged mast the sails had names which indicated their vertical position on the mast. The lowest square sail was the course, the next sail up the mast was called the topsail, the next the topgallant sail. Many vessels shipped a fourth sail called the royal, above the other three, some even more on trades with light winds. Sometimes a vessel might put out studding sails which would be fixed outboard of these sails along the yards. Beginning in the mid-nineteenth century, the topsails and topgallants were each split into upper and lower sails; this allowed smaller crews to tend the sails and provided captains with a greater set of options in choosing which sails to set.
Sails are referred to by their mast and then name, e.g., "the fore mast topgallant sail", often shortened to "fore t'gallant", or historically "fore t'gar'ns'l". Where no mast is specified, the main mast is implied.
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