(Photos: Feadship Fanclub)
Feadship is a Dutch yachtbuilding company. It recently sent this massive ship out of its shipyard. At 333 feet long, Symphony is the largest yacht Feadship has ever built. Here it is traveling down the Gouwe canal, which crosses over the A12 road from Arnhem to The Hague.
It squeezed through one lock with only inches to spare on either side. As a result, the standard protective fenders were too thick to use on the Symphony. The crew had to use boards covered with carpet instead. You can see more photos at Super Yacht World.
-via Twisted Sifter
This doesn't work if...
a) The boat is rubbing along the bottom. If it ain't afloat then all bets are off.
b) The water level rises. It's a canal, so the sections between locks have a finite volume. Displacing some by dropping a boat in it will cause the level to rise locally until it can flow away - probably over a weir somewhere downstream.
And yes - I do already know the answer, but it's a good one to ask kids who're doing physics at school.