OK guys, now this is something I know about and is dear to (the layers of self induced fat around) my heart.
Many cruisers home brew and some cant wait more than 2 weeks to drink the stuff. Their stuff was horrible, mine was gooooood!
Ok - I decided that it had to be simple or it wasnt worth it. I used plastic bottles as they were light weight and you can store more/ volume than glass.
Clean the fermenter and the bottles as per manufacturers recomendations, (as the guys in previous posts say); use tap water and dont worry about high temperatures or specific gravities etc. At the end of 6 or 7 days (when calm enough), bottle the stuff.
We cruised the tropics for almost 3 years. Some brews were a little average, most were great. BUT allow it to sit second fermenting in the bottle (in the dark) for 3 months. In order to do this, I had 4 brews running (120 bottles) so that each could sit for 3 months or longer before I touched it. I had 4 plastic boxes, each held one brew. They sat in a single bunk in the aft cabin with the lee sheet up and a sheet or towel over the top (reduce the light). The temperature in that cabin was fairly consistant as the water temp stays consistant.
As to the tap water, we usually had to return somewhere about every 3-5 weeks for fresh food, and would top up with fuel and water etc. Thats when I would use tap (filtered) water.
If you keep it simple, and follow the instructions it will work just perfectly.