Am i violating oop rules

[socialite]

I have an interface that requires my vehicles to have a engine power and break power. My abstract class of boat has a

static final brake

but every type of boat(sub-classes) has its own engine power. My abstract car class leaves it up to the subclasses how much brake power they have. Is the boat abstract class wrong
heres so code to help clear it up

[code]
interface IVehicule{
    double EnginePower = null;
    double BreakPower = null;
    double Decelerate(double speed, int gear, double brake);
    double Accelerate(int gear, double EnginePower);
    int IncGear();
    int DecGear();
}


abstract class Boats implements IVehicule
{    
    private static final double Brake = 5;
    protected double speed;
    protected int gear;
    public double Decelerate (double speed, int gear, double brake)
    {
        return this.speed=speed/brake+(gear/2);
    }

    public int DecGear ()
    {
        return this.gear--;
    }
    public int IncGear ()
    {
        return this.gear++;
    }
    public double Accelerate (int gear, double EnginePower)
    {        
        return gear*EnginePower;
    }    
}

class SpeedBoat extends Boats implements IVehicule{    
    public static double EnginePower = 20.0;                    
    public void decelerate(double speed,int gear,double brake){
        Decelerate(speed, gear, brake);
    }
    public void accelerate(int gear){
        Accelerate(gear, EnginePower);
    }
    public void incgear(){
        IncGear();
    }
    public void decgear(){
        DecGear();
    }
    
}/*      does this class need to 
**      implement its own field 
**      decleration for brake or 
**      is it fine in the abstract class? */
[/code]