My question stems from a task of comprehension from the exercises for Lingua Latina Per Se Illustrata Familia Romana.
What is the grammatical class of "nāuigantī" in the following excerpt and what role does it play?
Italicised words were blank spaces to be filled.
Exercitia Latina Chapter 16, Exercise 6, item 8:
Nautae ad occidentem nāuigantī merīdiēs ā sinistrā est, ā dextrā septentriōnēs, oriēns ā tergō.