Physics, Force, Racing, and (Fixed)Update.

This may be quite a loaded question, and I'll do my best to comment the code in order to get across clearly what I am trying to accomplish.

This code here is supposed to drive my Ship forward. This project will become a mobile racing game that will eventually support Multiplayer. The problems I am having are as follows:

1) Choppy Force movement. I've messed with Update vs. FixedUpdate and neither have been able to supply me with a smooth fluid forward movement. I swear when I quit last night it was practically perfect, but this morning it is choppy and nasty. It steps forward regardless of FixedUpdate or Update. I have tried changing the FixedUpdate interval from .02 to .005 even.

2) The movement becomes ULTRA fluid once I remove my fingers from the screen, aka when there is no force being added to the ship.

3) Any wisdom on using Update vs. FixedUpdate for racing? I feel like FixedUpdate is necessary because the Update function will allow faster mobile devices to travel quicker, right?

 using UnityEngine;
 using System.Collections;
 
 public class ShipController : MonoBehaviour {
     public float basePower = 60.0F;
     public float baseBoostSpeed = 100.0F;
     public float baseBrakeSpeed = 25.0F;
     public float baseBrakeDrag = 1.35F;
     public float baseDrag = 0.75F;
     public float baseHandling = 50.0F;
     public GameObject Ship;
     float regionWidth = Screen.width / 2;
     Vector3 still = Vector3.zero;
     bool first = true;
     float[] throttleCoords = new float[4];
     float brakeTime = 0.0F;
     float speed = Mathf.Clamp(0.0F, 0, Mathf.Infinity);
     
     
     
     void FixedUpdate(){
           int fingers = Input.touchCount; // cache touchCount in q
         Vector3 movement = Ship.rigidbody.GetPointVelocity(transform.position);
           if (fingers == 1){ // if one finger only...
             speed = basePower;
             print(speed);
             float touchPoint = Input.mousePosition.x;
             if (touchPoint < regionWidth & movement == still) { // rotate left
                 clearDriveData(fingers, speed);
                   turnShip("left");
             }
             else if (touchPoint < (regionWidth * 2) & movement == still){ // rotate right 
                 clearDriveData(fingers, speed);
                   turnShip("right");
             }
             else if (touchPoint < regionWidth) { //carry force into left turn
                 clearDriveData(fingers, speed);
                 turnShip("left");
                 moveShip("turn", speed);
             }
             else if (touchPoint < regionWidth * 2) { //carry force into right turn
                 clearDriveData(fingers, speed);
                 turnShip("right");
                 moveShip("turn", speed);
             }
           }
           if (fingers > 1){ // if two fingers, move the ship forward
             speed = basePower;
             speed = boostCheck(speed);
             moveShip(null, speed);
             if (first) {
                 createThrottleCoords();
             }
           }
         if (fingers == 0) {
             speed = basePower;
             clearDriveData(fingers, speed);
         }
         
     }
     
     void turnShip(string direction) {
         if (direction.Equals("right")) {
             Ship.transform.Rotate(Vector3.up * baseHandling * Time.deltaTime);
         }
         if (direction.Equals("left")) {
             Ship.transform.Rotate(Vector3.up * -baseHandling * Time.deltaTime);
         }
     }
 
     void moveShip(string instructions, float speed){
         if (instructions == null) {
             Ship.rigidbody.AddForce(transform.forward * speed);
         }
         else if (instructions.Equals("turn")) { //cut speed for turning
             Ship.rigidbody.AddForce(transform.forward * (speed / 3));
         }
     }
     
     void createThrottleCoords() { // creates a set of coordinates used to determine boost or braking mechanism
         float firstFinger = Input.GetTouch(0).position.y;
         float secondFinger = Input.GetTouch(1).position.y;
         throttleCoords[0] = firstFinger;
         throttleCoords[1] = secondFinger;
         first = false;
         print(firstFinger);
         print(secondFinger);
         foreach (object x in throttleCoords) {
             print(x);
         }
     }
     
     void clearDriveData(int fingers, float speed) { //reset values
         float[] throttleCoords = new float[4];
         if (fingers != 2) {
             resetSpeed(speed);
         }
         first = true;
     }
     
     void resetSpeed(float speed) {
         speed = basePower;
         Ship.rigidbody.drag = baseDrag;
     }
     
     float boostCheck(float speed) {
         float newFirstFinger = Input.GetTouch(0).position.y;
         float newSecondFinger = Input.GetTouch(1).position.y;
         throttleCoords[2] = newFirstFinger;
         throttleCoords[3] = newSecondFinger;
         float boostSetA = throttleCoords[2] - throttleCoords[0];
         float boostSetB = throttleCoords[3] - throttleCoords[1];
         float brakeSetA = throttleCoords[0] - throttleCoords[2];
         float brakeSetB = throttleCoords[1] - throttleCoords[3];
         if (boostSetA > 75 & boostSetB > 75) {
             print("BOOOOOSTING");
             speed = baseBoostSpeed;
             print(speed);
             return speed;
         }
         else if (brakeSetA > 25 & brakeSetB > 25) {
             Ship.rigidbody.drag = baseBrakeDrag;
             brakeTime += Time.fixedDeltaTime;
             print(brakeTime);
             float brakeStrength = (brakeSetA + brakeSetB)/2;
             print("Braking");
             speed = Mathf.Clamp(speed - (brakeStrength * brakeTime), 0, Mathf.Infinity);
             print(speed);
             return speed;
         }
         
         else {
             brakeTime = 0.0F;
             resetSpeed(speed);
             print("Nope");
             return speed;
         }
     }
 }