Tidalenergy, thanks for adding the graphic and extra information as requested, it makes things clearer for the reader. However, you have still not addressed the fundamental issue regarding a claim of efficiency of "3 times higher then the Betz Limit of 59.3%". Noone here has contested that a shroud can lead to 3-4 times higher energy extraction than a similar sized turbine. The problem I still have is that you are using the word efficiency and implying 180% efficiency - a value over 100%. As I'm sure you know, energy efficiency can never go over 100%, see energy conversion efficiency for exactly why. If you replace the words efficiency with energy extraction I will be happy.