How can I make a player become a Vehicle?

I want the player to be able to jump on in this case a boat and become a child of the boat so that the player rocks and moves with the boat as they are apart of the same object BUT I also want the player to have free form movement on said vehicle and the ability to interact with objects on the boat (Such as approaching say the wheel and hitting "E" key to take control of the vehicle)

Best way I can describe what I mean is what they did with "Guns of Icarus"

Click Here for Video Example

To note I am not looking to clone this game in anyway.. just this game houses a unique feature which I intend to include in my project!