Having trouble with a custom entity boat

Code:

package podmain;

import org.bukkit.craftbukkit.v1_12_R1.CraftWorld;

import net.minecraft.server.v1_12_R1.EntityBoat;

public class CustomBoat extends EntityBoat{
    public CustomBoat(org.bukkit.World world) {
        super(((CraftWorld)world).getHandle());
        this.maxSpeed = 3.9D;
        this.occupiedDeceleration = 0.2D;
        this.unoccupiedDeceleration = -1.0D;
        this.landBoats = true;
        this.setSize(1.5F, 0.6F);
    }
}

I'm able to spawn the custom boat in place of the regular boat, but its speed stays the same. I've tried changing both the boat and the players' velocities but to no avail. The method to change the max speed is deprecated so I can't do it that way and I've been forced to create a custom entity, but it still doesn't respond to me changing the max speed of the new entity. Could anyone help me out? Thanks in advance.