[Pago]

I think it could be possible, but you'd have to hard code it into the game (or maybe not, we'll see). Anyway, it could be a system where a player can move all he wants on the NPC, but he'd be moving at the same rate as the NPC:

if(playerenters){
istrans(width of transport,height}

This would tell the game engine that the NPC is a mode of transportation, and the player would be able to move in the given area. Of course, you'd still need to set a timeout and a variable for the X and Y movement, but this tag would allow the player's movement on the boat to mimic the Law of Momentum.