Circumstantial evidence (the settlement of Australia) points to boats being invented about 40,000 years ago. The oldest physical evidence of boats are logboats from 7,000 to 10,000 years ago.
people never know but: The U-Boat, or undersea boat, was first created by Cornelius Drebbel in the 1500's or by John Holland in the 1800's. The more popular U-Boat used in World War 2 was invented by...