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 times higher then the betz limit of noone here has contested that a shroud can lead to times higher energy extraction than a similar sized turbine the problem i still have is that you are using the word efficiency and implying efficiency a value over as i'm sure you know energy efficiency can never go over see energy conversion efficiency for exactly why if you replace the words efficiency with energy extraction i will be happy