PARIS — Karl Lagerfeld certainly knows how to work a theme. He showed Chanel’s cruise collection on a Parisian riverboat on Wednesday evening, for example, and, naturally, he used the opportunity to explore classic nautical style. His crested navy blazers were just the starting point for light-handed looks that also referenced schoolgirl uniforms, Ivy League style and even tennis players circa 1920. Here, one of his stylish navy numbers, worn with a blouse and slim skirt. For more on Chanel and the season, see Coming Attractions.