Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: The Mapmakers--I need more!
    From: Trevor Kenchington
    Date: 2002 Dec 7, 16:18 -0400

    Some time back, Rodney Myrvaagnes wrote:
    
    > It would be interesting to see something about charting procedures in
    > the 18th C as well. I remember going to the WInter Antiques Show at
    > Park Ave Armory about 25 years ago and seeing an admiralty chart from
    > about 1770 for Nantucket Sound. It was surprisingly modern in many
    > respects. Somebody had done a lotr of soundings.
    >
    > One thing really shocked me. There were instructions for piloting from
    > Nomans Land to the corner of Chappaquiddick by sighting on the corner
    > of land itself, there being no light house there at the time. The tidal
    > currents around there would make this exceedingly hazardous in an 18th
    > C frigate or the like.
    >
    > I wanted that chart very badly, but not enough to part with the $4000
    > he wanted for it. Maybe I was wrong.
    
    
    That chart was likely from the "American Neptune", the result of
    DesBarres' surveys. There are quite a number of bound copies of the
    Neptune around, plus many loose charts. Although a lot of them are held
    by public institutions, others are in private hands and appear on the
    market from time to time. The great prize is often considered to be
    Desbarres' chart of Sable Island, though it is some 8 feet long, which
    makes it a bit hard to display!
    
    A couple of years back, I ran into a history student who was writing a
    PhD thesis on DesBarres and his survey methods. He claimed, though I do
    not know how seriously, that DesBarres trained Cook in surveying, which
    would have to be counted quite an achievement even if Cook went on to
    exceed his mentor's capabilities.
    
    DesBarres was a military engineer, of Swiss origins, who was trained in
    mathematics and engineering at Woolwich in the early 1750s. His first
    chart, based on French materials captured in Louisbourg, was prepared in
    1759 and covered the St.Lawrence. Thus, along with Cook, he made
    possible the conquest of Quebec and New France by providing the English
    fleet with the information needed if it was to work up the river. Since
    the great flowering of hydrographic surveying dates from about that
    time, I have supposed (without much supporting evidence) that its
    origins lay in the terrestrial survey methods which DesBarres and other
    engineers took to sea. If so, those methods had been developed early in
    the 17th century, when the increasing firepower of artillery drove
    fortress builders to a new level of sophisticated, mathematical design
    and their opponents to a matching level of sophistication in the layout
    of siege works.
    
    As to the methods actually used: DesBarres left one account of his own
    methods, with comments on measuring out a baseline on shore, then using
    theodolites and plane tables to map the coastline. Copies of that were
    provided to a sloop (i.e. a small warship, not a sloop-rigged boat)
    which beat on and off the shore to a distance of ten miles or so, taking
    soundings, to a "shallop" which did the same around headlands and
    islands, and to "boats" which worked the "indraught" to the heads of the
    bays. He did not remark on the instruments used on the sloop, shallop
    and boats but I'd guess a leadline and quadrants used for horizontal
    angles. They apparently also laid a 100-fathom line taught across the
    bottom to give themselves a measured baseline in the water.
    
    Where his crews took the time to get it right, DesBarres surveys are
    about as accurate (though not as detailed) as mid-20th century ones.
    However, I know of points on the Nova Scotian coast where the complexity
    of the rocky shoreline seems to have overwhelmed the survey parties,
    resulting in substantial errors such as an entire headland being missed
    and the coves on either side run together.
    
    One further point: The Admiralty commissioned the surveys of the
    American coastline, so far as I can tell, before much of England was
    properly charted. Why? My guess is that they had traditionally-trained
    pilots who knew the English coast without needing charts, whereas ships'
    Masters needed to navigate along American coasts that they had never
    seen before and without the aid of people who knew every rock and
    channel by heart. Hence, modern concepts of paper-based navigation were
    needed on the unknown coast, in place of the memory-based pilotage that
    had served mankind for millenia.
    
    
    Trevor Kenchington
    
    
    
    --
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
    
                         Science Serving the Fisheries
                          http://home.istar.ca/~gadus
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    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