Lorcan (InOBU) was a key player in building our currachs here in New London and is shown in the group photo (in the hat).
I suspect the earliest of the currach/coracle family may very well have been roundish and used in relatively calmer waters. The current (as in, for the last few centuries) currachs in Ireland are the long ones with the up-curved prow. The round ones are traditionally associated with Wales, as coracles (apparently a Latinized diminutive of the same word), used by one boater on a river or lake. A 7th century reconstruction would be likely to have a good deal of overlap though since the political boundaries were not fixed at that time and the earlier form of the boat would be the reasonable expectation.
Julius Caesar did describe the currachs of the Gaels, though, covered in ox-hide as they were up until around the turn of the last century when tarred canvas replaced the hide.