# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Practical difficulties
From: Patrick Goold
Date: 2011 May 13, 14:43 -0400
Dear Fred,
Three perpendicular axes define the space you are moving through.  You can move ALONG one or more of these dimensions, changing your x,y,z coordinates.  You could instead remain fixed along these dimensions, say fixed at the orgin, and yet rotate  AROUND one or more of the axes.   This would be an angular movement rather than a translation along the axes.  Roll, pitch and yaw are the rotational movements.  Surge, heave and sway are one set of names for the movements along.

I am not an engineer.  I may be misusing the phrase "degrees of freedom".  It is a phrase Bill Morris used in explaining to me how to mount the mirror on my artificial horizon.  It seems like a useful notion in thinking about sailing.

Best regards,
Patrick

On Fri, May 13, 2011 at 1:56 PM, Fred Hebard wrote:
Patrick,

For my edification, why do your refer to six degrees of freedom for boat motion rather than three?  I can imagine roll, pitch and yaw.  I guess one could add bobbing up and down.  T

Thanks for the report; I like sea stories.

Fred

On Fri, May 13, 2011 at 12:46 PM, Patrick Goold <goold@vwc.edu> wrote:

> (4)        The next day the sky was clear all day.  But now we were on a broad reach with a steep and substantial quartering swell.  The boat was moving quickly through all six degrees of freedom.  I am not especially prone to seasickness but this kind of tack is the one most likely to bring it on.  Even if I have had a few days to get my sea legs (which I hadn't in this case), when the boat is yawing, swaying and surging in addition to pitching, rolling and heaving, I need to keep one eye on the horizon or go green.  The sextant never left the case.  Even had I taken a full set of sights, reducing and plotting them would have been beyond me.
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> These were not storm conditions.  It was a rather typical spring day on the Chesapeake Bay.  The wind was NE at 15 knots.  The swell was no more than three or four feet but short and steep.
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> Patrick
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--
Dr. Patrick Goold
Department of Philosophy
Virginia Wesleyan College
Norfolk, VA 23502
757 455 3357

Charles Olson: "Love the World -- and stay inside it."

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