Spars are the wooden and nowadays mostly steel or even aluminium round poles, on which sails are hoisted. Depending on their function a spar has the following names: mast, yard, boom, gaff or bowsprit.

Mast

The upright poles on a sailing ship are called masts. A vessel can have one or more masts depending on her size. The first ships had a mast made out of one piece of wood. By the end of the 15th century the required length of the mast became longer than the available lengths of wooden trunks. To solve this problem mast were built up from more sections. Gradually the number of sections increased up to three and even four sections. In order of rising height: lower-mast or mast; top-mast; topgallant-mast and if applied royal-mast. For lights, radio-equipment or radar a pole-mast might be added.

The sections are connected semi-permanent to allow bridge-passage (the sections can be lowered to the required clearing). The sections are connected on the lower end of the upper section by a bracing platform mounted on the masttop called: crosstree to which the shrouds of the upper section are connected and at the upper-end of the lower section by the cap(of the mast).

Since the introduction of steel masts, mast-sections were no longer required for length reasons. Therefor the lower- and topmast are generally made of one piece. Although this is now one piece, the mast is still named as two parts with a masttop in the middle. The topgallant-mast remained separated to be able to pass bridges. German built ships (like the Kruzenstern) have lower- and topmasts of one piece with a length allowing passage of the Kiel Canal, the separated topgallant-mast can be lowered.

Of the tall-ships sailing today, the maximum number of sections is three i.e. mast; topmast and topgallantmast. With some ships these mast are still fully separated (Lehmkuhl, Cisne Branco, Stad Amsterdam) Most of the vessels however have only separated topgallant-masts.

For three-masted ships the mast are called from bow to stern:

Foremast, with sections: Fore-mast (lower); Fore top-mast and Fore topgallant-mast.
Mainmast, with sections: Main-mast (lower), Main top-mast, Main topgallant-mast and (if fitted) Royal-mast.
Mizzenmast, with sections: Mizzen-mast (lower), Mizzen top-mast and Mizzen topgallant-mast.

For ships with more than three masts, the aft-most mast is called:
Jiggermast with sections: Jigger-mast (lower), Jigger top-mast and Jigger topgallant-mast.

For ships with more than four masts the remaining masts have no fixed name.

References

Wikepedia: en.wikipedia.org/wiki/Mast_(sailing)
Globalsecurity: www.globalsecurity.org/military/systems/ship/sail-masts.htm

Yards position
Yards

The horizontal spar to which square sails are set is called yard. A yard is named after the (section of the) mast it is mounted on, i.e.: main-yard to mainmast; fore topgallant-yard to fore topgallant-mast. Most ships have two yards mounted to the topmast, the naming of these yards is preceded by lower or upper for instance lower main top-mast yard and upper main top-mast yard.
On the topgallant-mast either two or three yards are mounted. Three combinations of naming are possible:

  1. lower main topgallant yard; upper main topgallant yard, or
  2. main topgallant yard; royal yard, or
  3. lower main topgallant yard; upper main topgallant yard; royal yard.

Yards can be rotated around the mast to enable setting to the wind. When running downwind the yards are set perpendicular to the ships center line. When the wind comes from starboard (right) the yards are moved anti-clockwise, comes the wind from port (left) the yards will be moved clockwise.

When a ship, due to the force of the wind heels over, the yards are not horizontal resulting in less efficiency. To re-establish maximum efficiency, the yards can be tilted to be set horizontal again.

Wooden or steel yards are a considerable weight height above the ships center of gravity. To increase stability of the ship, especially in rough weather, some yards can be lowered when not in use.

References

Wikepedia: en.wikipedia.org/wiki/Yard_(sailing)
Globalsecurity: www.globalsecurity.org/military/systems/ship/sail-yards.htm

Boom gaff

A gaffsail is set between a boom at the foot (lower end) and a gaff at the head (upper end) of a sail. All large sailing ships have at least one gaffsail at the aft-most mast. This sail is called spanker, hence the corresponding boom and gaff are called spankerboom and spankergaff.
A splitted spanker is called a german-spanker has a gaff in the middle and a monkey-gaff above.

Schooners and barquentines have more gaffsails and therefore more booms and gaffs. The naming convention for boom and gaff on other masts than the aft-mast is as follows:

  1. The gaffsail on the foremast (only hoisted on schooners) is called Schoonersail, thus schoonerboom and schoonergaff.
  2. The gaffsail on the mainmast is called mainsail. Thus mainboom and maingaff.
  3. For four-mast schooners or barquentines, the third sail is called mizzensail i.e. mizzenboom and mizzengaff.

References

Wikepedia: en.wikipedia.org/wiki/Gaff_rig
The Cheap Pages: www.thecheappages.com/boat/cob/COB_sea-boat.html

Bowsprit

A spar projected forward from the bow of a ship is called a bowsprit. It provides an anchor-point for the forestays. A bowsprit might be extended with a jibboom or even an additional flying jibboom.

The bowsprit (and jibboom) are secured with stays and guys. At the outer-end of the bowsprit (in case a jibboom is provided) or approximately two-third from the outer end (when no jibboom is mounted), a vertical spar called dolphinstriker projects downward to support the martingale-stays.

Some ships have small spars called whiskers mounted horizontal on each side of the bowsprit (jibboom) to support jibguys.

References

Wikepedia: en.wikipedia.org/wiki/Bowsprit
Wikepedia: en.wikipedia.org/wiki/Jibboom