Frank B. Gilbreth Jr., 81, coauthor of "Cheaper by the Dozen" and its sequel, "Belles on Their Toes." In South Carolina, Gilbreth was known for his popular column "Doing the Charleston," which he wrote under the pen name Ashley Cooper from the late 1940s to 1993, in the Charleston Post and Courier. But his wider reputation was based on his many humorous books, particularly the two he wrote with his sister, Ernestine Gilbreth Carey, about their family's 12 children and efficiency-expert parents. Clifton Webb and Myrna Loy starred as the eccentric but loving Gilbreth parents in the first film in 1950, and Loy starred as the widowed mother operating the family engineering firm in the 1952 sequel. The books and films mirrored reality: Gilbreth's mother had continued to operate the family construction engineering business, Gilbreth Inc., after her husband's death in 1924. Frank Gilbreth was a decorated naval officer in the South Pacific during World War II. On Sunday in Charleston.