I'm preparing to work on a constructed language for a fictional culture that exists primarily at sea. I haven't yet determined if it will be a pidgin/creole or a separate language all it's own, but I am wondering how the sea/ocean itself will affect its phonology. If high altitudes encourage the use of ejectives (3), are there any particular sounds that low altitude and high humidity would encourage or discourage?
After a quick look to WALS, my initial impression is that the number of unusual features in world languages tends to increase with historical isolation. Geographical proximity and language contact may result in the formation of Sprachbünde, or areas of linguistic convergence, which favors the use of common features instead of unusual ones. Influential languages may become sources for loanwords and cause spelling irregularities and sound changes.
Edit: Also, standardization, which occurs in advanced literate societies for languages with hundreds of thousands of speakers, also aims to remove much of the unwanted or redundant complexity, creating a prestige dialect that will be taught at schools and spoken by most people.
Assuming that your sea-faring fictional culture has a rich merchant tradition and interacts with many other cultures, I think that it should have a fairly typical language. 5-6 vowels, not too many consonants, lack of complex consonant clusters. A quite typical syllable structure is (consonant)(glide)vowel(consonant).