A Moth?

Unbelievable. And the speed it was going was unbelievable. How the "yachtsman" got on and off is a complete mystery since we only saw him shooting backwards and forwards. I think that this is a Moth Class hydrofoil. and/ or possibly a "Bladerider" or a "Wazsp". Briefly  (obs I had to Google this) "A sailing hydrofoil, hydrofoil sailboat, or hydrosail is a sailboat with wing-like foils mounted under the hull. As the craft increases its speed the hydrofoils lift the hull up and out of the water, greatly reducing wetted area, resulting in decreased drag and increased speed. A sailing hydrofoil can achieve speeds exceeding double and in some cases triple the wind speed."
You can read all about it here: https://en.m.wikipedia.org/wiki/Sailing_hydrofoil
I was quite proud to have captured this action shot, vaguely in focus with my trusty Samsung!