The biggest Superyacht is now Azzam owned by the Emirati Royal Family specifically Sheikh Khalifa bin Zayed al-Nayan launched in April of this year and costing at around 390 million pounds. Its length is 590ft, this is Mega yachting at is largest. This You Tube clip by CNN is amusingly presented so wanted to share this with you. I am sure we will be seeing this yacht out and about as it will be hard to miss, more of a Mega Ship really.
Above is a bit of a somber You Tube clip of Azzam but provides some info.
More information can be found here Azzam World's Largest Mega Yacht