Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: Silicon Sea: Leg 80
    From: Dan Hogan
    Date: 2001 Oct 17, 9:12 AM

    On 17 Oct 2001, at 8:35, Noyce, Bill wrote:
    > > OK, but Great Circle is not of much use since on a small sailboat it
    > is just about impossible to sail it. But you have an idea of how many days to
    > go. Try using Mercator/Rhumbline calculations, the distance is a bit far for
    > accuracy  from Mid-Latitude.
    > Here's an attempt at Mercator sailing.  I used a spherical
    > approximation, not an ellipsoid:  MP = 7915.7 * log10( tan( Lat/2 + 45d ) )
    > From   4d  9.6' N   MP =  250.2       111d 34' W
    > To    19d 30.0' N   MP = 1193.6       154d 45' W
    >   dLat = 920.4' N  dMP =  943.4 N  dLo = 2591' W
    > TC = atan(dLo/dMP)  =  290.0d
    > Dist = dLat/cos(TC) = 2690.1 nmi
    > Compared to the GC distance of 2687.4, I'll agree it's not worth the
    > aggravation to try to save 3 miles.  I assume this is because we're
    > at a fairly low latitude.
    Also we are on a "northerly" course.
    > If we were far enough from the equator for it to make a difference,
    > I get the impression that the normal approach is to plot a few
    > waypoints along the GC course, then sail the rhumbline from point to
    > point.  With waypoints plotted a day or two apart, we would get
    > essentially all the benefit of the shorter distance, while still
    > being able to sail a "constant" compass course for long stretches.
    > And we'd be adjusting our heading based on new fixes from time to
    > time anyway. I assume a wobbly approximation to a GC course is still
    > shorter than an equally wobbly approximation to the rhumbline...
    The big problem for a sailboat is the wind and current. That makes it very
    hard to follow a Great Circle and many times a non-GC route is faster.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site