Tall Ship Festival.
As Chris pointed out the festival is pretty spread out over a series of sites between Greenwich and Woolwich, some boats on moorings and others in the old docks.
So it would take all day to visit all sites and go on-board as many ships as possible. There were all sorts of packages to go for sails, from VIP hospitality to joining them on the leg from Falmouth to London.
I took the easy option for one still not feeling his best, namely the Thames Clipper river bus. One ticket taking me all the way there in three hops: from Putney to Embankment, then Embankment to Greenwich to pick up the last leg through the Thames Barrier to Woolwich.