"A needleboat is a skiff-like boat (Oxford/Cambridge race), canotto in Italian, the same poem in Italian is "Osservando i canottieri a San Sabba," he writes.
It seems that the word originally signified a quill, hence its use to describe a racing shell.
So that's cleared up. I would have put a nice picture of a canotta here, but searches in Flickr and Photobucket only turned up photos featuring the canotto pneumatico, or inflatable boat. In fact, all the pictures are of scantily dressed young people playing in the surf with rubber dinghies, which is very nice but not what I was looking for (honestly, Constable).