Timber augers came in a lot of sizes. Post&beam framing, shipbuilding; two more possibilities for needing a hole that size.
Aside from the one spiral auger here, scroll down for the picture of boat building tools (on a smaller scale).
http://www.gutenberg.org/files/16277...mages/069s.jpg
http://www.gutenberg.org/files/16277...he_boatbuilder
Cheers
GC