Velocity and Ice

I'm trying to edit the velocity of a boat while moving on ice with a player but i have two problems:

1. The function getVelocity() returns 0.0,0.0,0.0 from the boat and the player on ice my solution for this is that (i don't know if it's perfect but it works)
   
   Code:

   public void onMove(PlayerMoveEvent e) {
       double vx = e.getTo().getX() - e.getFrom().getX();
       double vz = e.getTo().getZ() - e.getFrom().getZ();
   }

2. When I edit the boat's velocity sometimes the boat stop for no reason, i don't know why.
   Code:

   boat.setVelocity(new Vector( 2D*boat.getLocation().getDirection().getX() , 0D, 2D*boat.getLocation().getDirection().getZ()));

If you can help me.

 

https://hub.spigotmc.org/javadocs/bukkit/org/bukkit/entity/Boat.html

As you can see setMaxSpeed(double speed), setOccupiedDeceleration(double rate),
setUnoccupiedDeceleration(double rate)

I think that the lower the Deceleration, the faster the boat can go (also setMaxSpeed).
If this isn't what you want NMS is the only other option.