First time hear about maritime security being equipped with HMGs. Had an acquaintance here in Europe that worked as guard on merchant ships, they would be equipped with mix of semiautomatic rifles, really anything from converted long barreled AKs to Benelli hunting selfloaders. One useful thing to have along with weapon was high power visible laser pointers, those would be routinely used to dissuade random small vessels from approaching the guarded ship, not talking about actual pirates, but fishermen and other randos, whom you dont want to blast unless there is no other option.
Quality of the weapons varied, some of them were used, some new, but specifically there were no machine guns or any heavy ordnance that could be conspicious and would require mounting or altering structure of the vessel. Every cruise the company provided new weapons and basic protective gear like vests and helmets, As you wrote, they were shipped after the vessel arrived into international waters, but guards would enter the ship along with the crew, in port. Granted it was few years ago and security company was located in Europe, so no shady mercenary cowboy Blackwater stuff going on.
All in all he wouldnt recommend it : lots of cerificates that required quite an initial investment, no guarantee of getting job in reasonable time and salaries were goind down after the companies began hiring Ukrainians and pajeets. Also boredom, because unless there is a drill time, you basically spending your shift glued to binoculars and NVGs or sitting beside radar and listening to music.