Question about speed.

My first time on the sub, please tell me if I'm breaking the rules. You guys seem way smarter than me and I have a question.

I am by no means a smart man, so this may sound dumb but I was thinking one day while sitting in my car. If you were to build a massive boat that traveled at 100mph and then a huge car that drove on the boat that went 100mph and then flew a jet inside the car at 400mph would you be traveling at 600 mph? To add to that, could you stack this and eventually go infinitely fast?