The Irish galley was a vessel in use in the West of Ireland down to the seventeenth century, and was propelled both by oars and sail. In fundamental respects it resembled the Scottish galley or bìrlinn, their mutual ancestor being the Viking longship. Both the Irish and Scottish versions were colloquially known as "longa fada" (longships). The Irish galley was commonly an eight or twelve-oared vessel and was used for both warfare and trade. It was notable for its speed when rowed.
No archeological remains have been found which would enable a detailed reconstruction of the Irish galley. There are, however, illustrations on Irish maps of the Elizabethan period  (though of contested reliability), and these are supplemented by written accounts. There is also a carving in the old Cistercian monastery on Clare Ireland (Oileán Chliara), home of the seafaring O'Malleys. The carving, though very simple, shows a vessel remarkably similar to images of its Scottish equivalent, being an oared, single-masted ship with a yard for a single square sail.
Cartographic images of the later sixteenth century, however, show interesting differences from the vessel shown in the carving. This may reflect foreign influences, since Irish galleys traded to Spain and Portugal. An image from a 1657 map of Ireland shows an oared vessel with a round stern and a raked stem. There is a raised deck over the latter, and a cabin with a curved roof considerably aft of the mast. The mast is placed forward and carries a single sail, possible a lugsail. There are stays visible and lifts with a block.
Images on a map of Ulster by Francis Jobson show three Irish galleys, each with eight oars and a vertically striped square sail. Rudders are visible, along with stays, braces and crow's-nests. The forestay descends to a beak, with a round-roofed cabin aft.
There is pictorial evidence that by the end of the sixteenth century similar influences may have affected the design of the Scottish galley. A carving made at Arasaig in 1641 shows a vessel with a lowered stem and stern. An English map of north-east Ireland made no later than 1603 shows "fleetes of the Redshanks [Highlanders] of Cantyre" with a square sail mounted on a sloping yard arm and a small cabin at the stern projecting backwards. Two Clanranald seals attached to documents dated 1572 show a birlinn with raised decks at stem and stern, a motif repeated in later heraldic devices. If such changes occurred, they would reflect (as in Ireland) influences from the south-east and ultimately from the Mediterranean.
It is reasonable to assume that galleys in both Western Scotland and the West of Ireland were built in accordance with well-established shipwrights' techniques of north-west Europe, of which the Norse were major exponents. There was extensive Norse settlement both on the west coast of Scotland and around the coasts of Ireland. Norse shipwrights would attach both the stem and stern to the keel with scarfed joints, the hull itself being clinker-built with iron nails. Ribs would be attached to the strakes with cords or trenails, and thwarts installed. The mast would then be inserted in the mast step. The stem and stern posts would have notches to receive the ends of planks, and knees would secure the thwarts.
Images of Scottish ships appear to show vessels built in accordance with these techniques. They were clinker-built, open-decked amidships, single-masted and oared, the major difference being that, unlike Norse ships of the classical period, they had a rudder attached to a steep transom. From the evidence available, it is likely that Irish galleys resembled their Scottish equivalents in their construction, rigging, steering and means of propulsion.
References are found in the Annals of the Four Masters to Irish fleets of the period in which the galley was dominant. In 1413, for example, Tuathal Ó Máille, a member of the O'Malley family, was returning to Mayo from Ulster when his fleet of seven ships was overtaken by "anfadh na mara" (a sea tempest) and driven northwards to Scotland. Only Tuathal survived.
The O'Malleys and the O'Flahertys, lords of west Connacht, were the main users of galleys, which they used for plundering or for transporting the troops of other chieftains. In the sixteenth century the Crown made a determined attempt to suppress the Irish fleets with its own ships. In December 1559 the following was recorded in the English State Papers:
- "There are three very good galleys with Tibbot ne Longe, sone to Grany O’Malley, his brother and O’Malley that will carry 300 men apiece. These, if employed by Her Majesty, would do much good in the north, and the O’Malleys are much feared everywhere by sea. There are no galleys in Ireland but these."
Grany O’Malley or Grace O'Malley (Irish: Gráinne Ní Mháille) was the most famous of the seafaring chieftains. The Governor of Connacht, Sir Richard Bingham, wrote of her in 1591 that she had twenty ships, though it is uncertain whether this was her usual complement. She, like her father before her, was a notable merchant by sea.
These ships were used for the export of salted and pickled fish, linen, wool, hides and tallow. From Spain and Portugal they would import copper, silk, wine, figs, pomegranates, cumin, cinnamon and saffron.
The English State Papers of 1599 record that Grace O'Malley's son "Tibbot ne Longe" (Irish: Tiobóid na Long - Theobald of the Ships), had three very good ships, each able to carry 300 men. It is likely, however, that such ships were not as large as the English galleon. They were certainly vulnerable to cannon fire (their light construction meant they could carry no great guns themselves), though they could easily hold their own with English craft of a similar size.
- Ireland in Schools:‘Grace O’Malley, Granuaile: Chieftain, trader, pirate: ships’: www.iisresource.org/Documents/0A4_Grace_Fleet.ppt
- Map of Ulster (1591), Francis Jobson, TCD MS 1209/17.
- From the Dartmouth Collection of the British National Maritime Museum.
- Rixson (1988)
- Greenhill (1976), p 234.
- Greenhill (1976), p 234.
- Rixson (1998), p 138.
- M1413.3 Annals of the Four Masters 1413.
- Rixson (1998), p 42.
- Ireland in Schools: 'Grace O’Malley, Granuaile: Chieftain, trader, pirate: ships’: www.iisresource.org/Documents/0A4_Grace_Fleet.ppt
- Rixson (1998), p 44
- 1593 Petition of Grace O'Malley to Queen Elizabeth, State Papers Relating to Ireland (microfilm: original in the Office of Public Records, London) SP 63/171/18
- Ireland in Schools: ‘Grace O’Malley, Granuaile: Chieftain, trader, pirate: ships’: www.iisresource.org/Documents/0A4_Grace_Fleet.ppt
- Chambers (1998), p 24, quoting from Knox H.T. (1908), History of the County Mayo, Dublin, p 250.
- Rixson (1998), p 50, quoting from an account by Captain Plessington of the warship Tramontana, which captured an Irish galley between Teelin and Killbegs in Donegal in July 1601: Not withstanding she rowed with thirty oars and had on board ready to defend her a hundred good shots which entertained a skirmish with my boat for most of an hour and had put her to the worst. Coming up with my ship to the rescue, I quickly, with my great shot made an end to the fray. This galley comes out of Connaught and belongs to Grany O’Malley whereof a base son of hers is captain.
- Chambers, Anne (1998). Granuaile: The Life and Times of Grace O'Malley c. 1550 - 1603. Wolfhound Press. ISBN 0-86327-631-8
- Greenhill, Basil (eag.) (1976). Archaeology of the Boat: A new introductory study . London: Adam and Charles Black. ISBN 0-7136-1645-8
- Rixson, Denis (1998). The West Highland Galley. Edinburgh: Birling. ISBN 1-874744-86-6