Square Rig Ships

Square rig is a generic type of
sail and rigging arrangement in
which the primary driving sails
are carried on horizontal spars
which are perpendicular to the
keel of the ship and the masts.
These spars are called yards,
the tips of which, beyond the last
stay, are called the yardarms.
Square rig was the main design
in the age of sail, (1571—1863).
A ship at least partially so rigged
is called a square rigger.

It can also describe individual
four-cornered sails suspended
from the horizontal yards, and
carried on either a square rigged or a mainly fore-and-aft rigged vessel, such as one with either a bermuda rigged or gaff rigged mainsail.

The term is also used for the uniform of a rating in the Royal Navy from 1857 onwards. It is slang and refers to anyone wearing the non-peaked cap worn by Petty Officers and Officers this 'rig' includes the famous blue bib on the shoulders and bell-bottomed trousers. This name perhaps reflects the fact that it was these men who managed the square rigged sails.

A mast is considered square rigged if its lowest sail or course is square rigged, but normally if this is the case it will have a complete set of square rigged sails. If the course is fore-and-aft, square topsails can still be carried in front of the mast.

Even square rigged masts may also have staysails that are deployed fore and aft between masts.

Characteristics Of Square Rig

In their heyday square rigged vessels ranged in size from small boats to full rigged ships, however, today this rig has fallen from favour and the rig in common use today is one form or another of fore-and-aft gaff rigs and bermuda rigs. The reason for this change are the development of two technologies, steam and new materials. For larger ships it was only possible to drive large tonnages using multiple sails until steam arrived and made sails unnecessary, although hybrids existed for a while.

Also, the strains imposed on cordage and sails in the Age of Sail meant that a large number of sails were necessary to get the surface area necessary for larger ships. Fewer larger sails would not have survived the rigours of the larger commercial and military ships and required more men to manage. Therefore, in order to get the large number of sails to effectively collect wind and provide motive power they had to be square to the hull. There were no examples of the more efficient fore and aft rigs on larger vessels for this reason. Despite the large overall sail areas, and even when sailing on their best points of sail, it was sometimes the case that large warships could only make 6-8 knots, however some of the faster clippers for whom speed was critical could make much faster speeds, e.g. Cutty Sark which could make 17 knots.

The square rig breaks up the sail area into many smaller sails, each of which can be individually handled by a small team hauling by hand on their controlling lines. Having many smaller sails also allowed warships to manage the impact of weapons upon them. Instead of losing one very large sail to a hole from a cannonball, which would then tear, the damage was constrained to a much smaller sail area and therefore less impact on the motive power of the vessel. 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 hence the size of the crew needed to handle them - a situation that favoured a few large sails instead of many small ones. However since the smallest ships, such as sloops were always fore and aft rigged this in many ways did not change the situation, the change was that large ships moved from square rig to steam.

It is particularly in the area of hybrid vessels carrying some square-rigged sails that changes due to materials are noticeable. The low aspect ratio of square rigged sails (usually 1/2 to 1/3) produce large amounts of drag for the lift they produce, and thus give very poor performance to windward. This means that 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. Square rigs do have their advantages, however; 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 less prone to broaching when running than Bermuda rigs.

On a square rigged mast the sails had names which indicated their position on the mast. The lowest square sail was the course or mainsail, the next sail up the mast was called the topsail, the next the topgallant sail. If the ship were a large one it would have a fourth sail called the royal above the other three. Sometimes in lighter winds a ship, so equipped, would put out studding sails which would be fixed outboard of the sail on both sides of it. These studding sails were principally used on the higher sails only and were relatively small and time consuming to attach and detach. In some ships, especially commercial vessels, the topsail and topgallants were each split into upper and lower sails again to minimise the strain on the rigging and crew. Sails are referred to by their mast and then name so, for example, the fore topgallant sail often shortened to fore t'gallant.

Sail Characteristics

A square rigged sail is not in fact square, but more nearly trapezoidal, being symmetrical but longer in the foot than the head. Like all sails it is three-dimensional, and its curve or belly means that its foot (lower edge) is not a straight line at all. It is fixed to a spar (the yard) along its head, and its clews (bottom corners) are controlled by sheets, often run to blocks on the spar immediately below the sail. The lower sails, without a spar below them, may also have tacks.

Modern square rigged ships are still used for training, tourism and ceremonial purposes.



Mainmast of the Prince William, from aft. Sails set are (from the top) main-royal, main-topgallant, main-upper-topsail and main-lower-topsail. The main-course is stowed, as is the spanker.Photo by Pete Verdon - Click To Enlarge