Lee-Bow..... Windsurfers...etc (Dons tin hat)

Yes, very elegant. The basic principle is the same as the pendulum though. It's using the energy of the flow to push itself across the river whilst attached to a bank.  

I mean, it looks nice, but it's basically no different than a yacht swinging on it's mooring when the tide changes. It's using the differential between the ground and the water to move it in relation to the ground. 

The energy source is the water moving relative to the land. A sailing dinghy the energy source is the air moving relative to the water. The sailing dinghy has no contact with the land and therefore it can't access that energy, which is why bringing it up is so insane and irrelevant.   

The pendulum crossing / reaction ferry are attached to the bank via a rope and are using the flow of the river to drag / swing them across. The ferry is far more elegant, but it is using a rope to shore to 'pull' them through the water. 

What this even has to do flow over foils in a boat not attached to shore is the real question. The information being presented is disparate and so irrelevant that the conclusions you're all drawing from them are not even wrong. They can't even be described as an argument.

I like you Sam, you seem genuine. Are you trying to say what if instead of a rope to shore, you have sails that are pushing you along through the water instead? Well, the rope will always pull you in the same direction, no matter how you the steer the boat. The wind and drive in your sails will not.  If you had a rope pulling you towards the windward mark, then yeah, sure, head up and point straight at the mark and cross tide will push you there. But, we don't. The wind isn't an ever present driving force like a rope to a bank. It demands we align our sails correctly and sailing the correct VMG angle. If you head up, the sails will stall and you'll lose way. You'll be floating around in the tide.  So that is why the rope to shore argument is laughably bad. It's like it's come from your mate who's never been sailing... you know the one... why can't we just sail straight at the mark?

As I said I'm not taking a stance on the LBE thing, just trying to find an explanation for the effect GarethT observed.

Never come across Tom Scott before but, yes, it is a brilliant video. Will look for more from him.

No, actually I'm arguing the opposite (I think, not maybe getting the correct words), not that the flow over the foils is altered by the current but that there is some kind of explanation to why GarethT saw what he saw, just think of it as an interesting puzzle that I'm curious to solve.