Why settle for 8% ?
The rule of 72 would see (72 divided by

your invested amount requiring 9 years to double, then 9 years to double again and so forth.
Safe stocks like Amazon, E.A, Activision, Facebook, TakeTwo (Rockstar) etc would double in half that time if their current trend continues.
Hell, buy AMD shares and you might double it in just 12 months from now.
Do your own investing.