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A064509 Marks (in fathoms) on lead line used by ships on the Mississippi River. 0
2, 3, 5, 7, 10, 13, 15, 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Certain depths have (or had) a visual and tactile indicator at positions on the lead line. All depths with such attachments are "marks". All others are "deeps." A leadsman measuring 12 feet of water calls "by the mark two (or twain)." If the depth on the lead is 36 feet (6 fathoms) he would call "by the deep six!".
Samuel Clemens chose the nom de plume Mark Twain because, for a riverboat skipper on the Mississippi, when the water was 12 feet deep, it was safe sailing for those boats.
REFERENCES
Bowditch, The American Practical Navigator, 1931 edition.
Postings to newsgroup rec.org.sca, circa Oct 22, 1994 by djheydt(AT)uclink.berkeley.edu (Dorothy J. Heydt), Jeff Suzuki (jeffs(AT)math.bu.EDU) and Hal Ravn.
LINKS
FORMULA
For n >= 9, a(n) = 5(n-5).
CROSSREFS
Sequence in context: A117952 A090420 A162999 * A096221 A258084 A120367
KEYWORD
nonn,nice
AUTHOR
Peter Shor, Oct 06 2001
EXTENSIONS
a(55)-a(56) corrected by Sean A. Irvine, Jul 14 2023
STATUS
approved

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Last modified February 29 10:20 EST 2024. Contains 370418 sequences. (Running on oeis4.)