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: Longitude by Time Sight...good enough at sea?
    From: Michael Bradley
    Date: 2012 Nov 29, 11:52 -0800


    Welcome to the 'Do It The Easy Way' section of NavList.
    In the British Merchant Marine a common development of the Time Sight was to plot an LOP using the 'Longitude by Chronometer' from the Time Sight, the chosen Latitude, and a separately calculated/looked up Azimuth. So you can use the Time Sight in LOP navigation if you wish ( see last paragraph).

    Frank is absolutely correct about the past practice of avoiding any marks on the chart at all, this particularly applied in the days when the cost of a chart was considered a capital matter - an interesting contrast with today's times when the culture of entitlement (i.e. the expectation of free charts ) is in full operation.

    One of the problems of avoiding marks on the chart is that of calculating and expressing usefully the DR/EP having steamed/sailed through perhaps 12 hours of darkness between the evening (time?) sight and the morning (time?) sight. Traverse Tables allow this to be done on a notepad rather than drawing on the chart. But drawing lines can makes the results of any navigational calculation slips scream out at you - a major advantage. Navigators were and are taught to construct their own plotting sheets on a jotter pad to avoid the cost of bought in sheets. It's very easy to do: admittedly that rich professional Bowditch calls this an 'emergency navigation' technique. That said, there are freeware universal plotting sheets out there on the Wild Word Web.

    I've written a piece of Windows software, almanac built in, tested on XP Service Pack3, which reduces sights in three ways to provide three ways of plotting the same LOP from a single sight for comparison:
    Marq St Hilaire Intercept and Azimuth from the EP ( or AP) as is usual nowadays.
    Longitude by Chronometer and Azimuth from the nearest whole number Latitude,
    as referred to in the first paragraph.
    'Ex Meridian' Latitude and Azimuth from the nearest whole number Longitude.
    My favourite is my 'Ex Meridian' Latitude and Azimuth which gets a position line on the chart/universal plotting sheet faster than any other (for most sights). The Time Sight method comes second.

    I'm hoping to find a practising navigator on NavList who has a varied set of recorded real sights and is willing to try out the software and compare the three methods. Please get in touch by 'Reply to Author'.

    Good navigating

    Michael B
    55 North

    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com

    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