Hi Tony - good to see you at The White Horse last night....in answer to your questions, the event is indeed on 8th August, part of Dover Town Council's Horticultural Event in Pencester Gardens. You don't have to make the boats yourself, which is good news for the origamically challenged amongst us (like me!) and the participation involved amounts to parting with your £50.00 note (well, you are a wealthy man!) and standing on the bank of the River Dour throwing missiles at the opposition's flotilla. Oops, I mean cheering your boat on to glorious victory!
(Except one of mine is going to win.

)