PS: make up a male-to-female that to go to your boatside inlet, do NOT make a male-to-male cord (called “a death cord”) that energizes the boat thru a 15a receptacle.
Use 10ga flex cord (12ga is acceptable for a short length.)
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@ Porch
120vac, 30a Shore power cords’ form factor are indeed NEMA L5-30P (plug) and L5-30R (receptacle) Not to be confused w/ L6-30 which is 30a 230vac. Scamazon and Big box stores carry them if you need to make up a shorter cord. But the non-Marinco brands (Leviton, Legrange, etc.) are brass not chrome prongs.
I have a short Marinco plug for my cable end in my Scamazon cart because the weather cover on the shore receptacle won't close over my “current” (ugghh) long Marinco plug end.