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sailquik said..
I actually like the idea of the water filled plastic tube. I can see it might be feasible to construct it using ultasonic welding and a huge roll of PVC.
The inherent problem with such a structure is that it is water filled, and therefore has the same density as the water it sits in, with the exception of the actual plastic film. This means it need to be anchored to the bottom securely. Not an insurmountable problem, but a complication nonetheless. because, wherever there is strong wind, the surface water will be moving with it, trying to drag you barrier as well.
It has to stick above the water, so there will be a little bit of downforce. But the wind and water will push it downwind. They had some problems with that during the first year. The tube held without problems in 15-20 knots, but started moving when it picked up to 30 knots. They fixed it by adding more anchors. One every 15 ft worked for 30 knots; for 40 knots, you might need more or heavier anchors. Seems solvable, though. And if you curve the tarp a bit to get a deep downwind angle towards the end, most of the anchors will be needed near the front.
If you set up at a place with long shallow areas, the barrier "reef" does not need to be very long, since an approach at decent speed is possible through moderate chop. At the GPS trial in Cervantes, the length of the speed strip was less than 150 m, with sizable chop at the approach and noticeable wind shadow after the first 50 m or so. The spit at Lake George is about 400 m before the trees. A 500 m reef with a 300 m approach through 2 ft water may be too short for official 500 m records, but should be good enough for 50 knot 10-second runs.