Allure of the Seas Aquatheater
The scale of this ship is absolutely MASSIVE! Currently, the MS Allure of the Seas is still the largest passenger ship the world had ever seen. There's another ship being built in the Oasis Class coming 2016, but I can't see it being much larger since it's in the same class. Due to welding and assembly, the Allure of the Seas is ~2 inches longer than the preceding Oasis of the Seas.
By displacement, the Oasis Class displaces twice as much water as the RMS Titanic, carries more than twice the number of passengers and also holds more than twice the amount of crew on top of that.
Propeller technology has also come a long way, the latest and greatest passenger cruise ships all run on 360 degree rotating Azipods instead of the old drive shaft and propeller technology. These things can move sideways and has no need for tug boats to maneuver into a port.