“It utterly trails on excursion when you have ladies with you who are thinking all the tune of their dress than of the trip.” Why does the narrator feel so?

Jerome is lamenting about ladies in their boating costumes making such a fuss about their dresses and getting wet that they do not enjoy the trip. He complains that women, or the ones he knew, were not up for sporting activities. Instead they treated a boating trip like a fashion show.