The standard 18-55mm kit lens that the camera came with is a very standard range. You can capture most things that you could capture with basically any general purpose camera would. The 55-250mm lens is quite a large zoom, allowing you to capture things farther away, and the range of this even further extends what you can do. If you were set on capturing birds on your cruise for example, 250mm might be too short - but this is just an example. If you are planning on capturing the interiors of the cruise ship rooms - 18mm might be not wide enough - but this is just an example. We can't tell you what to buy, because you don't tell us anything about what you plan to shoot or what you are limited by.
I will say that both of the lenses that you own do not have very wide apertures. You may struggle to capture a scene with great bokeh, and you may struggle to capture very low light scenes with action. f/3.5 is your widest aperture and that is only when zoomed out with the 18-55mm. If you don't quite understand this yet, I would recommend learning your camera and this limitation before you just go out and purchase something.
What lens should I buy? - No lenses. Go take pictures!