public static void createBoat(String type){
		
		switch(type){
		case RACE_MODE:
			instance = new RaceBoat();
			break;
		case STATION_KEEPING_MODE:
			instance = new StationKeepingBoat();
			break;
		default:
			System.out.println("Cannot set boat mode : unknown mode " + type);
			if(instance == null){
				System.out.println("Program will quit now.");
				System.exit(0);
			}
		}
		
	}