The Turtle Backs are a great lakes boat that is unique to the waters.
They look almost like a hull with another turned upside down on top of it. The Dutch shoe boat that Joe described is almost certainly a TurtleBack. Doors on the sides of the boat, about midships would open and nets and trawls could be hauled abourd where the crew could work the fish out of the weather. Built this way they could withstand some heavy weather and wave action.

And anyone who thinks "They are just lakes, what kind of weather can they have" can stand on the wall at Oswego, NY when its blowing forty from Toronto. The North Atlantic has nothing to show us that the Great Lakes hasn't already seen.

Don