Which are the largest LEGO ships that actually float? My kids are frantic about LEGO ships, and I was wondering which are largest ships ever made.

Of course, they need to be actually able to float in a pool.
The largest LEGO ship that officially floats in water is the Cargo Ship that comes in 7994-1 LEGO City Harbor:



It is the only set which contains the 74 x 18 x 7 Boat Hull, which is the largest boat hull LEGO has made.