I am applying to Mechanical Engineering PhD programs. The weakest part of my application is my GPA, which I explain in my statement of purpose was due to being a three-sport, Division I athlete (yes I know I should've spent more time on studying because it's my future and athletics is not, I know, I know).
Prof 1: Been in four of his mechanical engineering classes, told me he would give his highest recommendation for me in the letter. This one is a #1 keeper for all my applications.
Prof 2: Adviser for a senior design project and was in his mechanical engineering class. Also a very good recommendation, my #2.
Coach: Confirm long practice time and commitment to team, varsity 4 years, captain 1 year. (Do grad schools even care about this?)
Boss: Industry work consisted mostly of 3D modeling and engineering design but we also gathered data about our process and analyzed it to improve it and make it more efficient. Am slightly worried about his writing skills/this being his first letter. I gave him heavy notes on how to write the letter and suggested a lot of content but he is adamantly and engineer and openly knows he is not great with writing etiquette.
For applications that ask for 2 letters: I will include the two professors. Should I include, as supplementary, the one from my coach, or boss, or both?
For applications that ask for 3 letters: I will include the two professors. Which should be the 3rd? Should the 4th be supplementary?
Thank you in advance.