Greetings,
I love sailing, I love beer, and I love home brewing.
I should probably preface these comments that one of my nicknames at work is “the wet blanket.”
There are a few technological hurdles to overcome here. First: I don’t use secondary fermenters so the lees settle to the bottom of the keg. The first half pint of a keg is usually cloudy and then all is well. Unless I move a keg to a party at a friends house. Then it is all stirred up and cloudy looking. So rack the beer an extra time or two into secondary fermenters. Possibly get a filtering system. Otherwise motion of the boat will cause cloudiness.
Second: you must pressurize the keg with gas. You could use air like rental kegs but it’ll go stale after a couple days. So, unless the combined thirst of the crew is sufficient for this, you are probably looking at CO2 or nitrogen. You want enough pressure to force carbonate the beer but still be able to dispense without having a full pint of froth. Trouble is that rocking and rolling on the ocean will knock these gasses out of suspension. (Shaking up the coke bottle) and again a glass of froth.
For the serious Brewer sailor we must devise a gimballed keg system. For me though I’ll just buy some delicious canned beer and go sailing with it.