Crosstrees are the two horizontal spars at the upper ends of the topmasts of sailing ships that are used to anchor the shrouds from the topgallant mast. They may also be mounted at the upper end of the topgallant to anchor the shrouds from the royal mast (if fitted). Similar transverse spars remain on steamship and motor vessel masts to secure wire antennae or signal flag halyards. [1]
Any vertical structure like a mast is subject to dynamic swaying stress from wind, which levers immense force at the base of the mast. Such stress is countered through guy ropes which are diagonally supporting ropes from mast top to its base. These ropes share the load on the mast tops and communicate that force to the base structure.
The taller the mast, the wider a base is required for the guy-wires so as to form an appropriate angular support against the sway the mast is exposed to, yet ships are fixed in their beam (width) and hence only a limited angle is possible for the guy-ropes to support very high masts. Thereby, the taller the ship's mast, the more narrow and unfeasible would be the angle between its support wires and its top. This is where a simple innovation like the crosstree helps to overcome such limitation.
The crosstree serves as a fresh base to spread the next level of supporting guy ropes, thereby providing a stable height extension to the masts. Without the crosstree, the ship's mast would have been severely limited in height, in relation to the beam of the ship.
Each crosstree serves to spread another level of holding ropes on a fresh wider spar so as to provide support to the next mast top section. Effectively, the crosstree allows to extend the height, mount yet another layer of sail shrouds and option more wind power to the ships. The crosstree also serves to spread the shroud tops.
Media related to Crosstrees at Wikimedia Commons
Rigging comprises the system of ropes, cables and chains, which support a sailing ship or sail boat's masts—standing rigging, including shrouds and stays—and which adjust the position of the vessel's sails and spars to which they are attached—the running rigging, including halyards, braces, sheets and vangs.
A sailing ship is a sea-going vessel that uses sails mounted on masts to harness the power of wind and propel the vessel. There is a variety of sail plans that propel sailing ships, employing square-rigged or fore-and-aft sails. Some ships carry square sails on each mast—the brig and full-rigged ship, said to be "ship-rigged" when there are three or more masts. Others carry only fore-and-aft sails on each mast, for instance some schooners. Still others employ a combination of square and fore-and-aft sails, including the barque, barquentine, and brigantine.
A sailing vessel's rig is its arrangement of masts, sails and rigging. Examples include a schooner rig, cutter rig, junk rig, etc. A rig may be broadly categorized as "fore-and-aft", "square", or a combination of both. Within the fore-and-aft category there is a variety of triangular and quadrilateral sail shapes. Spars or battens may be used to help shape a given kind of sail. Each rig may be described with a sail plan—formally, a drawing of a vessel, viewed from the side.
On a sailing boat, the shrouds are pieces of standing rigging which hold the mast up from side to side. There is frequently more than one shroud on each side of the boat.
Standing rigging comprises the fixed lines, wires, or rods, which support each mast or bowsprit on a sailing vessel and reinforce those spars against wind loads transferred from the sails. This term is used in contrast to running rigging, which represents the moveable elements of rigging which adjust the position and shape of the sails.
Boat building is the design and construction of boats and their systems. This includes at a minimum a hull, with propulsion, mechanical, navigation, safety and other systems as a craft requires.
A guyed mast or guyed tower is a tall thin vertical structure that depends on guy lines for stability. The mast itself has the compressive strength to support its own weight, but does not have the shear strength to stand unsupported. It requires guy lines to stay upright and to resist lateral forces such as wind loads. Guy lines are usually spaced at equal angles about the structure's base.
The mast of a sailing vessel is a tall spar, or arrangement of spars, erected more or less vertically on the centre-line of a ship or boat. Its purposes include carrying sails, spars, and derricks, giving necessary height to a navigation light, look-out position, signal yard, control position, radio aerial or signal lamp. Large ships have several masts, with the size and configuration depending on the style of ship. Nearly all sailing masts are guyed.
A yard is a spar on a mast from which sails are set. It may be constructed of timber or steel or from more modern materials such as aluminium or carbon fibre. Although some types of fore and aft rigs have yards, the term is usually used to describe the horizontal spars used on square rigged sails. In addition, for some decades after square sails were generally dispensed with, some yards were retained for deploying wireless (radio) aerials and signal flags.
This glossary of nautical terms is an alphabetical listing of terms and expressions connected with ships, shipping, seamanship and navigation on water. Some remain current, while many date from the 17th to 19th centuries. The word nautical derives from the Latin nauticus, from Greek nautikos, from nautēs: "sailor", from naus: "ship".
A guy-wire, guy-line, guy-rope, down guy, or stay, also called simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly for ship masts, radio masts, wind turbines, utility poles, and tents. A thin vertical mast supported by guy wires is called a guyed mast. Structures that support antennas are frequently of a lattice construction and are called "towers". One end of the guy is attached to the structure, and the other is anchored to the ground at some distance from the mast or tower base. The tension in the diagonal guy-wire, combined with the compression and buckling strength of the structure, allows the structure to withstand lateral loads such as wind or the weight of cantilevered structures. They are installed radially, usually at equal angles about the structure, in trios and quads. As the tower leans a bit due to the wind force, the increased guy tension is resolved into a compression force in the tower or mast and a lateral force that resists the wind load. For example, antenna masts are often held up by three guy-wires at 120° angles. Structures with predictable lateral loads, such as electrical utility poles, may require only a single guy-wire to offset the lateral pull of the electrical wires, at a spot where the wires change direction.
A derrick is a lifting device composed at minimum of one guyed mast, as in a gin pole, which may be articulated over a load by adjusting its guys. Most derricks have at least two components, either a guyed mast or self-supporting tower, and a boom hinged at its base to provide articulation, as in a stiffleg derrick. The most basic type of derrick is controlled by three or four lines connected to the top of the mast, which allow it both to move laterally and cant up and down. To lift a load, a separate line runs up and over the mast with a hook on its free end, as with a crane.
Radio masts and towers are typically tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the tallest human-made structures. Masts are often named after the broadcasting organizations that originally built them or currently use them.
The top on a traditional square rigged ship is the platform at the upper end of each (lower) mast. This is not the masthead "crow's nest" of the popular imagination – above the mainmast is the main-topmast, main-topgallant-mast and main-royal-mast, so that the top is actually about 1/4 to 1/3 of the way up the mast as a whole.
The masts of traditional sailing ships were not single spars, but were constructed of separate sections or masts, each with its own rigging. The topmast is one of these.
The spritsail is a four-sided, fore-and-aft sail that is supported at its highest points by the mast and a diagonally running spar known as the sprit. The foot of the sail can be stretched by a boom or held loose-footed just by its sheets. A spritsail has four corners: the throat, peak, clew, and tack. The Spritsail can also be used to describe a rig that uses a spritsail.
A spreader is a spar on a sailing boat used to deflect the shrouds to allow them to better support the mast. The spreader or spreaders serve much the same purpose as the crosstrees and tops in a traditional sailing vessel.
Literally, the word pinisi refers to a type of rigging of Indonesian sailing vessels. A pinisi carries seven to eight sails on two masts, arranged like a gaff-ketch with what is called 'standing gaffs' — i.e., unlike most Western ships using such a rig, the two main sails are not opened by raising the spars they are attached to, but the sails are 'pulled out' like curtains along the gaffs which are fixed at around the centre of the masts.
The following outline is provided as an overview of and topical guide to sailing:
This glossary of nautical terms is an alphabetical listing of terms and expressions connected with ships, shipping, seamanship and navigation on water. Some remain current, while many date from the 17th to 19th centuries. The word nautical derives from the Latin nauticus, from Greek nautikos, from nautēs: "sailor", from naus: "ship".