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: Wartime (WW2) navigation
    From: George Huxtable
    Date: 2010 Feb 2, 00:32 -0000

    Trevor Bell wrote, about the sinking of Rangitane in 1940-
    
    "I agree - this is getting interesting. I acknowledge that the first 
    waypoint was nowhere near the great circle - that was the intention of the 
    naval control service routings - to sail off the normal direct routes but 
    what the calculations have shown is that the total distance using the 
    different methods varies by only a very small percentage.
    
    Having re-read the 1941 inquiry into the Rangitane sinking I can confirm 
    that the waypoint coordinates I have given are correct but I realise that 
    there was another error in my previous post: I said that the NCS told the 
    captain to sail a great circle route between waypoints. This is wrong - he 
    was told Mercator but the captain said at the inquiry that he may have 
    sailed great circle. From various other enquiries I have made I understand 
    that it was virtually impossible to sail a great circle because of 
    continuous changes in heading so the great circle was broken up into a 
    series of rhumblines. If he had sailed an approximated great circle, this 
    makes the position of sinking (see previous post 11695) much more acceptable 
    at about 35nm, but still off course.
    
    Just to lay another issue to rest - there has been some discussion in other 
    posts about me using the term 'whole circle' instead of 'great circle' - 
    sorry about that, it comes from my background as a civil engineer in which 
    we use the term 'whole circle bearing'."
    
    ================
    
    If she was commanded to sail a rhumbline (Mercator) course to waypoint 1, 
    that would have been at a course of 93.3º. When she reached the longitude 
    where the sinking occurred, at W175º 22', the latitude would be S36º50'. In 
    fact, she sank at a latitude of S36º58', just 8 miles further South. That 
    would be exactly compatible with the ship steering that Mercator course of 
    93.3º, but getting deflected a bit to the South by the South-East going 
    current of 5 to 10 miles per day. We can conclude, then, that she was doing 
    exactly what she had been instructed to do. (In practice, courses would be 
    rounded to the nearest whole degree).
    
    Was that sensible, though? In the absence of any wartime dangers, from 
    Cuvier (not Curvier) Island, she would be expected to take a great-circle 
    path to Panama, which was 6352 miles at an initial course of 92.4º, which 
    would later be adjusted throughout the passage, at intervals. Note that this 
    initial course was only 1º from the course that was actually specified, as a 
    supposedly anti-interception measure! So she had been instructed to set out 
    in almost exactly the same direction that an enemy vessel would be expecting 
    to find her! Presumably, the most dangerous parts of such a passage were 
    near the beginning and near the end, when vessels would be concentrated, 
    scattering from the departure point and converging on the destination at 
    Panama. It would seem most sensible for a ship to diverge from the 
    great-circle, to one side or the other, immediately after leaving port. But 
    it seems that no such divergence was programmed until later in the Pacific 
    crossing.
    
    If Rangitane had simply followed that great circle, by the time she reached 
    the longitude of W175º22, where the sinking occurred, she would have been at 
    a latitude of S36º23'. She was sunk at S36º58', only 36 miles further South 
    than that. Indeed, she may have been intercepted at a much earlier time, and 
    followed, which would have been easy to do, as her speed from Cuvier seems 
    to have been no more than about 10.5 knots. Why so, for a 16-knot vessel?
    
    This analysis appears to raise more questions than it answers.
    
    George
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 
    
    
    
    
    

       
    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