Masts

Boom jaws are various pieces of iron that attach a boom or gaff to the mast providing an ability to change the angle of a sail. These boom jaws would be used in conjunction with standing rigging.

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 width (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.

A mast coat is a covering either of painted canvas or of rubber, secured round the foot of a mast and to the deck around it, which prevents water running below through the opening in the deck where the masts goes down to its step in the keelson. It is mainly used in sailing vessels where the masts have to be allowed a certain amount of play as they go through the openings in the deck so as to absorb the pressure of wind on the sails.

A mast cap is a strong, thick block of wood, used to confine two masts together, when the one is erected at the head of the other, in order to lengthen it. It is for this purpose furnished with two holes perpendicular to it's length and breadth, and parallel to it's thickness; one of these is square, and the other round; the former being solidly fixed upon the upper-end of the lower-mast, whilst the latter receives the mast employed to lengthen it, and secures it in this position.

The principal caps of a ship are those of the lower-masts, which are fitted with a strong eye-bolt on each side, wherein to hook the block by which the top-mast is drawn up through the cap.

The breadth of all caps is equal to twice the diameter of the top-mast, and the length to twice the breadth. The thickness of the main and forecaps is half the diameter of their breadths; the mizen-cap three-sevenths, and the top-mast-caps two-fifths of their respective breadths.

In the same manner as the top-mast slides up through the cap of the lower-mast, the top-gallant-mast slides up through the cap of the top-mast.

Parrels are an element of sailing rigging, usually deployed at the jaws of a gaff. It is a sliding ring or collar of rope loop, wood (known as a truck), or metal that confines a yard, spar or the jaws of a gaff to the mast allowing for vertical movement.