Place rinsed Navy beans in a large lidded stock pot and add salt. Cover with water about 2 inches over the level of the beans. Stir, cover, and cook on low heat for 4-5 hours, stirring occassionally. If the beans get too dry, boil some water and add as needed. If the beans are too juicy, remove the lid and continue cooking until they reach the desired thickness. About an hour before the beans are done, tear the bacon in small pieces and add to beans. Add the pepper and onion (and the carrot and celery, if desired). Stir, and continue cooking until the vegetables are tender.