For up to 4,500 years, sunken dug-out canoes have been lying on the bottom of Lough Corrib in County Galway, in the far west of Ireland. The lake's shores and its hundreds of islands are speckled with known archaeological sites, but until recently few had explored beneath its surface.
     Thanks to a project to produce up-to-date navigation charts of the lake's relatively shallow waters, sonar highlighted a number of previously undetected sites. It was the appearance of a long, slender anomaly that prompted marine surveyor Trevor Northage to contact Ireland's National Monuments Service.
     A dive team headed by Karl Brady was sent to investigate that feature, as well as around 20 other suspected sites, over half of which have proven to be the remains of boats of various ages. Five log boats have been securely dated so far.
     The oldest and largest vessel yet identified is a 12 metre long dugout, found near Annaghkeen, and radiocarbon dated to 2500 BCE. The craft is so well preserved that a distinctive spine 2 to 3 centimetres tall can still be seen running the length of its floor. Four cross-ridges extend from this at right angles, dividing the boat into sections. The boat's size suggests it would have required a crew of perhaps 10 to 12 persons.
     One vessel reveals traces of Bronze Age construction techniques: ancient repairs performed on a 3,400-year-old log boat discovered off Lee's Island show signs of experimentation with methods that were only just beginning to arrive in Ireland during this period. Although only the base and lower parts of the hull remain, details of its construction have survived, including a series of cleats - wooden loops set into its floor, anchoring the slender rods that held two sections of the hull together - the earliest known example of this technique being used in Ireland.
     A later Bronze Age vessel was found near Killbeg. Only the craft's base remains, but within the boat the team found a socketed bronze spearhead containing fragments of wood that were radiocarbon dated to the 9th century BCE, as well as a complete spear carved from yew, which lay beside the hull.
     Spears have proven a common feature of several of the log boats: two iron spearheads were recovered from the 11th-century CE wreck, while a vessel found near Rabbit Island produced four.
     The presence of weapons could indicate that the boats sank while on active service, although spears are sometimes associated with wrecks where a vessel at the end of its life has been ritually 'killed'.
     The boat which gives the clearest insights into its construction is the 11th-century CE Carrowmoreknock boat. This craft is remarkably well preserved, its sides rising almost to full height around over three quarters of the hull, while four of its five thwarts - seats made from planks - are still in place. Unlike the Bronze Age craft, this boat was not paddled, but rowed, as evidenced by the remains of four pairs of thole-pin holes, which would have held the oars.
     "This is probably among the best-preserved logboats ever found in Britain and Ireland, designed for travelling around the lake at speed," Brady said. "It is just beautifully crafted, probably made for a high-status individual."
     The discovery of weapons inside the boat, including three battle axes, an iron work-axe, two iron spearheads, and a curious piece of metal provisionally interpreted as a copper-alloy dagger pommel, suggests the crew were also warriors. One blade is so large, its owner would likely have needed both hands to wield it. Sections of all three axes' cherrywood handles have also survived, and the complete haft of the largest axe is 80 centimetres long. These are classic Viking-style weapons, Brady says, though by the 11th century they are more likely to have been in the hands of Irish warriors than Norse raiders.

Edited from Current Archaeology (23 June 2014)