DefenseNews reports the Brits have seen the need for a shipboard machine gun simulator. Considering how many 7.62mm and .50 cal machinegun mounts the Coast Guard uses–certainly more than the Royal Navy, it might be worth considering.
Chuck Hill's CG Blog
Chuck Hill's CG Blog 
“””””The simulator does not include motion, but the projected image can reproduce varying factors such as sea states, solar glare, surface reflections and sea spray.””””
From my limited experience with machineguns at sea the motion is the hardest part. Trying to keep it on target when the ship rolls and pitches is hard. Though I have seen some experienced gunners doing pretty good, even they get some wild shots.
Though “sea states, solar glare, surface reflections and sea spray” are also a problem. So this should help, even if it just gives some more practice, since actual shooting is often very limited
The need for a full motion platform is worth considering since most of our machine guns are mounted on relatively small vessels.
In those unlikely events where our small boats are going to use their machineguns in anger, there is likely a possibility that stray rounds might cause collateral damage, so all the more reason we might need this, and it might include judgement training as well as procedural and marksmanship training.