While on a cruise, you want to use the smallest amount of gear possible, to give your body a break yet maintain your muscle. Your ideal compound is test, at the lowest dose you can use and still feel ok and function normally. I wouldn't use anymore than 200mg EW. If you can use less, I feel you'll be better off. 100mg every 5 days is a good place to be, IMO.

Gaining muscle is still a possibility while you are on a cruise. For the most part, you are mimicing your natural levels of test. You just have to remember that gains are going to be slow compared to when you are "on". In this phase, you need to focus even more on your diet and training, making sure you do everything right and get enough rest. limited gains can be made, for a time, while on gear, without knowing what you're doing, but if you are at all advanced, it's going to take hard work and learning your body's needs well, if you want to keep moving forward during a cruise.