"I am big. The ship is little."
Translation:jItIn. mach Duj.
No. tIn is a verb and so it MUST have the proper verb prefix. To say that "I" am doing something and there is nothing specific person or thing that I am doing it to, I need to use the prefix jI-. I can say, jItIn jIH, but the jIH is redundant and not needed since the prefix already includes that information.
In English, our adjectives are not verbs, so if you want to connect a person or thing to an adjective, you must add a verb to the sentence. So in English we say, "I am big". But in Klingon we just say, jItIn. For nouns, in Klingon, we use the pronoun as a connector, so you would say tlhIngan jIH and we think of the jIH as acting like a verb meaning "I am". But with English adjectives, the Klingon words are already verbs. The verb tIn means, "to be big". So in jItIn jIH, the jIH only means "I" and the "am" is instead included in the tIn (which still needs the proper prefix).
Humans can be big and humans can be tall. Sometimes people use the word "big" to refer to tall humans, but sometimes a human is big without necessarily being tall. I wonder if there were additional considerations in the other sentence you mention. Maybe it would be good if you could find it again and comment in the sentence discussion so we can point out what is different about it.