While there is a Claudy in Scotland, it is not particularly close to the Clyde (of which Claudy could possibly be a corruption). The song does not seem very Scottish in style though. After much searching through gazetteers, the likeliest I could come up with was the river Cleddau (Milford Haven, Pembrokeshire) in "the little England on the further side of Wales, which does at least have a signifcant seafaring tradition.