Not sure stylistically what you would call that..."hooch" maybe? ;-)
The dividing line for what is practical aboard a boat is between brewing something really basic and brewing something more complex, sylistically accurate, and in larger volumes.
I think most cruisers are interested in just brewing something simple. So, some suggestions below on how to approach it aboard a boat.
Sanitation is critical to brewing to avoid undesireable critters growing in that nice sugar rich liquid you just made. Everything that comes into contact with your brew needs to be cleaned and sanitized first. There are lots of sophisticated cleaning
and sanitizing products made for the brewing industry, but you wont find those in most cruising grounds. Bleach is readily available almost everywhere and good for brewing sanitation if used properly. First, you don't need much, about 1 tablespoon per gallon of water
makes an effective sanitizing solution. Do not use on aluminium and time limit exposure on stainless. Rinse thuroughly because chlorine and create off flavors.
Temperature control is also critical to brewing. Going with all extract brewing (more below) greatly reduces the temp control requirements for the "hot side" of brewing, but yeast need to work with in certain temp ranges or they may produce off flavors. Exact temp ranges vary by strain of yeast, but keeping your ferminting brew at around 65F will keep most yeast strains happy enough. Higher temps are more likely to produce off flavors. Store in as cool and dark a place as you can manage on the boat. Temp stability is important too...big fluctuations can stress the yeast and cause them to create off flavors. For rudimentary temp control, I would go with a gallon or less container wrapped in a damp towel and stored securely in a locker.
Volume. Regarless of what you want to brew go small. This simplifies everything else.
Yeast. To really nail a brew stylistically you need a specific strain of yeast, but given that most cruisers don't care about that, bread yeast will work fine for rudimentary brewing and can be found almost anywhere.
Beer. If I were to brew beer aboard. I would go with 1 gallon all extract. Ideally a pre-hopped extract and then you do not need to boil. You will have to import
this or be in a developed country where you might find it. Be aware that LME (liquid malt extract) does not have an indefinate shelf life, it will first start to darken and then develop off flavors as it ages. Especially true if stored in less than ideal conditions as is likely on a boat. DME (dry malt extract) tends to have a better shelf life if properly stored (vaccum bagged, cool, dry), but it immediately aborbs moisture (including humidity) so you need a way to re seal it. . A vaccum bagger like used for food
works fine and has other uses aboard. If it is not sealed air tight it will form into rock like chunks and spoil much faster. Malt extracts are also used by the food
industry so you might be able to find some from a commercial
food ingredients distributor.
Mead. In many ways basic mead is simpler to brew than beer. The ingredients for a basic traditional mead are just honey and water. And you are much more likely to find honey locally than malt extract. If brewed using bread yeast it is likely to finish quite sweet because of the low alcohol tolerance of bread yeast. For ingredients availability in remote
locations mead wins out easily over beer.
If you want to learn more about brewing then pick up one of the many excellent learn to brew texts like John Palmer's How to Brew. An older version of it is legitimately available on line at http://www.howtobrew.com/intro.html