This exercise is actually wrong, proceed with caution. The correct/standard answer should be "These boats are fortunate". For "fortunate boats" we'd normally have to invert "lōgra" and "biariar". Word order, however flexible, does matter!
No! How do you all think this?!
First, it could never be "these boats", because kesi doesn't agree with lōgra in gender. So any answer with "these boats" will always, always be wrong.
Second, there's absolutely nothing wrong with lōgra biariar. The noun is nominative plural aquatic; the adjective is nominative plural aquatic. They agree perfectly. Furthermore, adjectives can follow the nouns they modify.
Finally, for those being confused about the order, remember that kesi is a pronoun. Kesi means "these ones". It's nominative plural. It's the plural of kesy. As a pronoun, it only agrees in animacy with its referent. Boats are not animate, so it's not bisi, it's kesi. It doesn't matter that lōgra is aquatic, as the pronouns don't agree in gender, just animacy. Since there is an overt subject nominal, the order of the adjective and noun of the complement is important—doubly so since biariar could, again, never modify kesi. Kesi is lunar nominative plural; biariar is aquatic/terrestrial nominative plural.
If this wasn't clear in the notes provided for this section, please let me know, but I would have thought by this skill the rules of noun-adjective concord and word order would have been quite clear.
Thanks, had that as my answer, was rejected. Reported it