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A064509 Marks (in fathoms) on lead line used by ships on Mississippi. 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, 260, 265 (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, as 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

Table of n, a(n) for n=1..56.

Mark S. Harris, Period measures and cautions for recipes

FORMULA

For n >= 9, a(n) = 5(n-5).

CROSSREFS

Sequence in context: A117952 A090420 A162999 * A096221 A258084 A120367

Adjacent sequences:  A064506 A064507 A064508 * A064510 A064511 A064512

KEYWORD

nonn,nice

AUTHOR

Peter Shor, Oct 06 2001

STATUS

approved

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Last modified July 23 20:32 EDT 2019. Contains 325264 sequences. (Running on oeis4.)