The riddle of the stones transported by boats

Current World Archaeology October issue, has a news report on the subject of megalithic stones being transported by boat – coracles in fact. Franscesco Benozza of the University of Bologna, whose field of study is the continuity of old words into recent languages as a means of understanding aspects of ancient societies. In the European Archaeologist he reports on research near the Portuguese megalithic site of Almendes where megalithic stones are known as ventrecurgo = belly + boat. In Brittany they are called Bronbag, meaning breast + boat. Interestingly, it is not the Brittany word for boat that has passed into British languages – but the Portuguese. Curgo is related to the Celtic word for boat which became Irish currach, Welsh cwrgw, and English coracle and it is now being suggested that by translating such words this is proof that megalithic people sometimes transported large slabs of stone slung underneath the belly, or breast of skin covered boats. Quarrymen in Ireland, apparently as late as the 19th century, transported stone in just this way – as stone weighs less beneath the water line. The stones were taken to a tidal river, rolled onto the mudflats at low tide and lashed to the bottom of a boat. When the tide came in the boat and its cargo floated. The question now is – how far were stones carried and would they have been able to coastal hop from Prescelly to Wiltshire? Would they have been able to transport them up a narrow river such as the Avon?