Paul--I found that same paddle shape in Fabulous Folbot Holidays by J. Kissner. The book is more than a little bit of self promotion, but there are pictures going back to the 1930's which show the square tipped spoon bladed paddles. Possibly this was just an easy shape to manufacturer. I've paddled a Folbot with those paddles, not knowing that other paddles existed, and they worked fine.

As an aside, the book describes a trip from Grand Central Station, NYC, by train to Falls Village, CT with 75 Folboats and 150 paddlers. They paddled 20-some miles down the Housatonic River. Although I've paddled a significant portion of the Housatonic, I never paddled that section, some of which is used for WW slalom racing.

Mike