Shaper Pattern Question

I'm rereading my copy of Classic American Runabouts:Wood Boats 1915-1965. Drive-by warm fuzzy, got it in a used book store for $6. On pages 34 and 35, they've got a piece titled: Building The Runabouts. Page 35 has a picture taken in the Chris-Craft factory, undated, but prabaly the late 20s, early 30s, described thusly: Chris-Craft boats were assembled with precut parts. Here, workmen are producing parts from dressed lumber clamped in patterns and cut on large shapers.
The picture is two workmen and a large shaper, the bit looks about 6" tall and as big around as your fist. The pattern and lumber look to be at least 10' long, maybe longer, hard to tell.
It looks to me like the pattern in the bottom piece. Then short cross pieces holding up, or spacing, two pieces of lumber being shapped. It looks like the pieces being shaped are held by three holes drilled along the length, then some type of bolt coming thru, passing thru a crosswise piece of wood, and tightened by what looks like some type of bolt about 6' high. OK, I can understand all that. I saw someting on the Lyman Boat company making repairs from patterns of all the types of boas they ever made - they saved ALL the patterns - and the wood was held to the patterns with holes drilled, and bolts. But, looking at the picture, I can't see any sign of a bearing, either top or botto of the bit, to follow the pattern.
The only possible way I can think of for this to work, would be if there is a fixed shield around the bit, with a section out on one side, wo allow the wood to be shaped by the bit. Anyone know if this is the how it was being done? Or what? I've seen a lot of varied tools, but never a shaper.
JOAT I do things I don't know how to do, so that I might learn how to do them. - Picasso

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