Ground Speed? How is it calculated? - Page 2 - SailNet Community
Old 07-16-2007
A little less cheek

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Tea-Rex, you still have one of those things? I haven't seen one of those since I sold it in 1972.

Ground speed is calculated by dropping a bouhyied line and timing how many knots you've tied into the line at 6 fathom intervals transverse through your hands during a sandglass timed interval of 3 minutes. This is a modern feature added as an extra on new Catalinas, Beneteaus and Hunters. All the rest of us (particularly at my age) don't really care how fast we're going, just that we're still going

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Old 07-16-2007
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Ian-

IIRC, using a chip knot log... will tell you the boat speed relative to the water, but not the speed over ground, since it doesn't account for whatever current set and drift may be occurring at the time.

Quote:
Originally Posted by ianhlnd
Ground speed is calculated by dropping a bouhyied line and timing how many knots you've tied into the line at 6 fathom intervals transverse through your hands during a sandglass timed interval of 3 minutes. This is a modern feature added as an extra on new Catalinas, Beneteaus and Hunters. All the rest of us (particularly at my age) don't really care how fast we're going, just that we're still going

Sailingdog

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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
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her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 07-16-2007
A little less cheek

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saildog:
Quote:
IIRC, using a chip knot log... will tell you the boat speed relative to the water, but not the speed over ground, since it doesn't account for whatever current set and drift may be occurring at the time.
So whats your point? It's not going to make any difference, you'll get there when you get there

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Old 07-16-2007
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LOL... very true Ian...but the OP was asking specifically for SOG...

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New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 07-16-2007
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Very informative, gentlemen.

Since I was taught that SOG meant Sailing off Greece.......
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Old 07-16-2007
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Plotting frequent positions on the chart, ascertained by the most reliable methods available, is the best method of determining set and drift. It is a navigational axiom that one should do upon the chart as much as possible. Using formulas and calculations one is apt to make the dreaded math error. Plotting on the chart is much less error prone as each conclusion must "look right". Besides, doing all that math, when a simple fix will do, keeps one too long in the chart room and not on watch where one belongs.

“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.
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Old 07-17-2007
A little less cheek

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Sorry NoDoubt, got caught in a glass of merlot. After reading all this stuff, suggest you look at: Who are the real subject matter experts here?

maybe that would help

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Old 07-17-2007
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Quote:
Originally Posted by ianhlnd
Tea-Rex, you still have one of those things? I haven't seen one of those since I sold it in 1972.
i guess i do, since i inherited my dad's navigation toolbox. i haven't had the courage to open it yet, though.
dad passed away last fall after 40+ years as a master mariner and 12 years retirement.
Tea-Rex is offline
Old 07-17-2007
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make sure you look up and peer around periodically while you are doing all this math....
tenuki is offline

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