Custom entity can't control boats

Hi ! I'm here because i have a problem that i'm not able to solve alone. I want to make an entity that is able to use a boat to go somewhere, but when my entity enter a boat, it can't move anymore. It can move when it isn't in the boat but when it enter in it stuck. I tried to make a code that can move the boat instead of my entity inside but it doesn't work : the boat don't move.
It's important for me i realy need that my entity can ride a Minecraft vanilla boat and not a custom "boat" entity.
So, can someone help me to make my entity control the boat ?
Thanks !