here's a site with a picture in the water and a text description of how they're made:
http://www.northcarolinasportsman.com/details.php?id=283
He tied the wing to a concrete anchor buried in the sand 30 yards away from the blind. If the wing had remained in place, waves would have banged it against the curtain.
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The upwind section of the wing measured 16 x16 feet and extensions on each side of the blind measured 5x8. It was built in detachable sections for boat transportation. There was enough distance between the 1x4-inch boards for Austin to step between them.
A classic curtain blind has two parts: a base of concrete and concrete block and a classic curtain of Atlantic white cedar planks, a native wood that withstands rot, covered with an outer cloak of waterproof fabric ( traditionally canvas). But modern materials have made curtain blinds more durable as well as more waterproof.
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So finding a location for building a curtain blind is as important as building the blind. Tide ranges along the oceanfront may be as great as 6 feet in North Carolina. But in the state’s sounds, it decreases substantially.
A section of 2x4 lumber is attached to each inside corner. A hole is drilled in the bottom of each 2x4 where they extend below the cedar framework. Ropes are attached to the top of the concrete box and threaded through the hole. Inside the blind the ropes are wrapped around boat cleats set on each 2x4. Shortening or lengthening the ropes raises and lowers the curtain.
Each corner can only be raised or lowered an inch or two in sequence to adjust the height of the curtain because of the tight fit between the wooden framework and the concrete box and because of the ropes holding the other three corners.
Waterproof fabric is attached to the top of the wooden framework and to the top of the concrete box. The flexibility of the fabric allows the wooden framework to be raised and lowered like one section of an accordion or an old time Kodak camera’s focusing device — while keeping out water.
The bottom of the fabric is sealed with a gasket compressed between wood planks and the concrete by tightening nuts on the bolts extending from the concrete.
Couple of pictures here too:
http://www.ocracokeduckhunting.com/gallery.html