What was Ben Gunn's type of homemade boat?

From the text:

I had not then seen a coracle, such as the ancient Britons made, but I have seen one since, and I can give you no fairer idea of Ben Gunn's boat than by saying it was like the first and the worst coracle ever made by man. But the great advantage of the coracle it certainly possessed, for it was exceedingly light and portable.