Arnulf Knittel says: Dear John Armstrong,

Brilliant! And a few great steps beyond the potentially very unbehaving single-rotor configuration you display on the website. I trust you are right to pursue the multi-rotor option in this, and to rely on stochastics and to keep loads levelled out...

I appreciate your in-depth answers, and I would like to hear your opinion about the prospects of this technology for regions where tidal streams are not plentyful as in the UK and around NW Europe:

(i) What role does, on your view, cavitation play, and could cavitation not be pushed to higher tip speeds by increasing the hydrostatic pressure, in other words the depth of installation? Is a certain depth required, or can you operate the array near the surface?

(ii) What can you say about deploying such a turbine in 'blue water', e.g. near the surface in a thermal current without flow reversal, say the Gulf Stream? Is the length of the tether incompatible with the catamaran concept? Can you, economically, rate the turbine down to achieve a higher capacity factor in moderate speeds? Can annual average mean speeds vary as much as for wind turbines with a more or less 'one-size-fits-all' rating?

I look forward to your answers, and I hope this idea (it seems a bit more mature than that) will receive prime attention and the fostering it doubtlessly deserves.