A jibboom (also spelled jib-boom) is a spar used to extend the length of a bowsprit on sailing ships.^[1] It can itself be extended further by a flying jib-boom.^[1] The heel (i.e. rear and lower) end of the flying jib-boom is attached to the jib-boom, and the heel of the jib-boom to the bowsprit. The point (i.e. higher and fore end) of the flying jib-boom is generally the fore-most extent of a ship. The jib- and flying jib- booms carry the tacks of the jib and flying jib sails, respectively, and the stay for the fore topgallant mast and the royal stay.

In yachts it is a boom attached to the foot of the jib, to keep the shape of the sail in different wind angles and to allow self tacking.

The jib-boom is—as the name suggests—the boom for the jib, extending its foot.^[1] On smaller, merchant, sailing ships, it is commonly attached to the bowsprit by a cap and a saddle, either lashed down or secured with a crupper chain.^[1][2][3] Alternatively, it can be attached by a boom iron and a cap, or even by two boom irons.^[3] The cap and saddle allow it to be withdrawn aft along the bowsprit as a ship enters harbour, reducing the opportunity for passing ships to glance against it and snap it off from the bowsprit.^[3]

It is octagonal in cross-section at its heel end.^[4] If secured by a chain to the bowsprit, it is iron-scored at the heel.^[4] At its point it is also (partly) octagonal in cross-section, the same as is the boom iron that secures the flying jib-boom to it.^[4] The flying jib-boom lies against the upper starboard side of the octagon.^[4]

The stay of the fore topgallant mast is attached to the jib-boom at the extremity of its point.^[1][4][5] The stay for the jib sail is attached to the shouldering at its heel.^[4] Just as the bowsprit has bobstays, in order to counteract the upward force from the jib and fore topgallant stays a martingale hangs down from the point of the jib-boom to a dolphin striker, pulling downwards on the jib-boom.^[6]

The flying jib-boom is secured, at its heel end, to the jib-boom by a boom iron and lashing.^[1] At its point, it has a sheave for the royal stay.^[4][5] Another sheave at the heel is for a heel rope.^[4] It is to the point that the tack of the flying jib sail is drawn out.^[3]

• Biddlecombe, George (1925). "Martingale". The Art of Rigging. Dover Maritime Series (reprinted 1990 by Courier Dover Publications ed.). Salem, Massachusetts: The Marine Research Society. ISBN 978-0-486-26343-4.
• Boyd, John M'Neill (1857). A manual for naval cadets (3rd ed.). London: Longman, Brown, Green, Longmans & Roberts. OL 23468580M.
• Jamieson, Alexander (1829). "Jib-Boom". A dictionary of mechanical science, arts, manufactures, and miscellaneous knowledge. Vol. 1. London: H. Fisher, Son & Co.
• Moore, J. J. (1801). "Stay". The British mariner's vocabulary: or universal dictionary of technical terms and sea phrases used in the construction, equipment, management and military operations of a ship. London: Hurst.
• Nares, George Strong (1868). Seamanship (4th ed.). Portsmouth: James Griffin and Co.
• Smyth, William Henry (2008). "JIB-BOOM". In Belcher, Edward (ed.). The Sailor's Word: A Complete Dictionary of Nautical Terms from the Napoleonic and Victorian Navies. Fireship Press. ISBN 978-1-934757-41-3.

• Lees, James (1979). "Rigging to the flying jibboom". The masting and rigging of English ships of war, 1625–1860. Naval Institute Press. pp. 52 et seq. ISBN 978-0-87021-847-7.