i am currently serving on a 164 westport of 496 gross ton and just under 8000hp. i want to eventually work my way to chief engineer i just dont know what is required to get a QMED. any advice/ help is much appreciated
I’m a deckie so won’t have much on the technical side, but begin here. Find your closest Regional Exam Center and when you have time at least drop by and say hello. Make sure you meet the qualifications to get a MMC “Merchant Mariners Credential” and TWIC if you don’t have those already. While you may not need it right away, shoot for getting STCW endorsements (starting with RFPEW) so your not restricted on areas of service.
Download and look over the course approval list. It’s a big list, but get through it so you can find some schools offering approved classes near you. Then stop by so you know the place and can find out schedules for any required or desired courses.
go to the national maritime center’s website. You will find all the checklists required.
You need 180 eight hour days of service in the engine room to qualify for a qmed. There are a few different ratings.
To get all ratings (off of the top of my head I think they condensed them to five) you will need to take a test for each.
If you only want to get one rating, qmed-oiler is a good place to start. You can either buy your own study material and take the test at the REC, or do a uscg approved course. There are a few out there but they are pretty expensive. Good thing about doing a course is you will get more than one rating probably and if you are short on sea time you may get some sea time credit.
To be marketable and as competitive as you can be, you’ll need to get STCW along with your QMED. You’ll need basic training, able seafarer-engine and rating forming part of an engineering watch like rmurphy said. You will need to find courses for those and it will be pretty expensive. You may be able to get assessments by an engine officer depending on where you work. Get to it you have lots of research to do 
by the way, the horsepower and tonnage isn’t that important for the qmed but it will definately be good for if and when you end up making your way to a chief or assistant’s license.
Not sure how much sea time you have but you could bypass being a qmed and jump right to a DDE license. look for the checklists on those as well when you get to the NMC’s site.
See 46 CFR 12.501 and 12.503. Generally, it’s 6 months service in the engine department and complete a test for each QMED endorsement you are applying for.
I’d start with these checklists:
http://www.dco.uscg.mil/Portals/9/NMC/pdfs/checklists/mcp_fm_nmc5_221_web.pdf?
http://www.dco.uscg.mil/Portals/9/NMC/pdfs/checklists/mcp_fm_nmc5_222_web.pdf?
http://www.dco.uscg.mil/Portals/9/NMC/pdfs/checklists/mcp_fm_nmc5_227_web.pdf?
In the right most column, it will give other referencs (NVIC 07-14, etc.). I’d read those to find all the little details about EXACTLY what service is creditable, who can sign what, what you need signed, etc.
Good luck