I seem to have a minority viewpoint regarding Mrs. Clay's statements about sailors. I don't see her knowledge as being derived from, shall we say, unladylike behavior, or anything suspicious. We know that Jane Austen has a great amount of respect for the Navy, the chosen career of two of her brothers. I think that the author wants to give credit to sailors, but who is the best character to do it? It couldn't be Sir Walter or Elizabeth - too snobby; it can't be Anne because her family would not listen to her for that many sentences together. The choices are Mrs. Clay, Mr. Shepherd, or Lady Russell. While any of them will do, Mrs. Clay makes the most sense IMHO for setting up her character and the rest of the story.