Once you get started with the classes and the studying it is important to keep chipping away at your certs and furthering your knowledge in water. It is more likely that you will be successful if you are repetitiously studying and taking exams than to take a break in between, ESPECIALLY if you do not pass. Do not get discouraged, Keep Going! And do not think you should settle for a cert/license that is required for your position and not chase after the one that is required of your supervisor, you would only be shorting yourself a future opportunity or advancement!
There is only one way to make a better living for yourself in this industry and that is to get your certs, education and some great experiences.... This ultimately makes you more valuable and your journey more fulfilling!