New Online Form - Country Visited box

Good Evening All,

I am new to the form and I apologise if I have posted this in the wrong section.
I have been trying to fill in the new online form to apply for british citizenship. Filling the form is quite straightforward I think but I have a problem with the Absences section.
There is a "country visited" box that I have to fill for every absence I enter. the box only accepts entries from a drop down menu containing every country in the world. the box does not allow any other entry and the system does not let you save if you leave it empty or if you try to type your own text in it. Unfortunately most of my absences are related to trips on boats, leaving from a UK port and returning to a UK port, mainly working in UK waters outside the 12miles from the coast (therefore these periods are to be counted as absences). I didn't really visit any other country (Once or twice I got off abroad and returned by flying, but that is not the norm). What should I do? I thought about entering "united kingdom" in the box (which is allowed by the system) but that's not strictly abroad. I am confused. would you be able to help me?

Francesco