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
    Name or NavList Code:
    Email:
       
    Reply
    Re: Titanic vs Endurance
    From: Howard G
    Date: 2022 Mar 12, 10:39 +0000

    Hi Frank

     

    I let your reply smoulder a little – wanting to digest your comments about Worsley which seem a little harsh – can you explain your reasoning.

     

    I have read the exploits of Shackleton - though a while ago – simply because exploring always interested me on how they survived and how they navigated.

    However, I was under the impression that Worsley (and his exploits not including his skill as a navigator and ship’s captain and not only assisting in getting all to Elephant Island and then navigating and partaking in the passage of the James Caird to South Georgia) was somewhat overshadowed by Shackleton’s colourful character and exploits.

     

    However, Worsley was an author and I have just downloaded to kindle from Amazon -  Endurance – An Epic Voyage – by Worsley – to refresh my knowledge.

     

    Frank your definition of a navigator seems a bit skewed to only include (the maritime flavour) – however an aeronautical navigator does navigate the ocean of air – perhaps – however I do believe that a navigator or its implied skillset is one that can find ones location, know how you got there and get you wherever you want to go (broadly speaking a compressed definition) – it is a complete skillset.

     

    A navigator has all the skillset – not just part of the skillset – i.e. just because a farmer can suture the skin wound of an animal using local anaesthetic (as most farmers can do) does not maketh a skilled surgeon. Farmers can calve cows, and do a lot of things a veterinary surgeon can do but would never say they were a veterinarian – actually illegal.

     

    A navigator is a skilled surgeon of a refined art – maritime/aeronautical

     

    I was a military navigator – RNZAF GD(N)  = General Duty Navigator –  we were qualified as navigators – then we had to do a conversion onto a type of aircraft – undoubtedly I would imagine as would a maritime navigation officer.

     

    Just my opinion – others may disagree.

     

    Regards Howard G

     

     

    From: NavList@fer3.com <NavList@fer3.com> On Behalf Of Frank Reed
    Sent: Saturday, 12 March 2022 10:15
    To: Howard George <HHG@raptorbusinessservices.com.au>
    Subject: [NavList] Re: Titanic vs Endurance

     

    David C, you wrote:
    "Worsley used lunar occulations of stars to determine time. Would typical marine navigators of the time know anything about such things? It is something that a land surveyor would have learned. I note that there was a physicist on board the Endurance.  Did the ship have a good library of surveying/astronomical/navigation books that they could spend a year studying? Should the physicist share some of Worsley's kudos"

    Yes, the "physicist" (name please?) contributed to the success of the occultation work, too. Typical marine navigators mostly would have no idea what an occultation was. This was certainly a land-based method almost exclusively, and since they were nearly motionless on the ice, the Shackleton team could apply methods more suited to land exploration. 

    The 'kudos' heaped on Worsley is over-done. He did his job, and he did it competently. Most importantly, he continued to work competently under deteriorating conditions that might have caused many navigator to become despondent and careless. Also, when people say Worsley was a "great navigator", I think it's important to remember that the word "navigator" has two somewhat different definitions. A navigator can be someone who 'navigates' an ocean, or in other words a skilled professional mariner. A navigator (and this is the sense for most of us) can be someone who has the skills to determine a vessel's position (and also speed, but often that's a given).

    "Is a lunar occulation of a star a special case of a lunar i.e.  lunar distance=0?"

    In principle, yes. The key principle in lunars and occultations, too, is that the Moon moves relative to the background stars (ignoring parallax effects for the moment) at an average speed of half a degree per hour, which is equal to half a minute or arc per minute, which is also equal to half a second of arc per second of time. The math used to work occultations is significantly different from the math for lunar distances, but in my opinion that should be seen as a "mere technicality". The big difference between lunars and occultations is the method of observation. For lunars, we measure angles with sextants, and it's not possible to do better than 5-10 arcseconds even under the best circumstances with excellent instruments. Occultations on the other hand are visually timed. It's certainly possible to time an occultation to the nearest second of time, and on land they can be reasonably timed to the nearest quarter of a second. Timing an occultation to the nearest second of time is comparable to measuring a lunar distance to the nearest half a second of arc, which is ten or twenty times better than the capabilities of manual sextant observations. Unfortunately there are some interesting problems that arise when we get down to seconds of arc, so it's not a foolproof improvement.

    Note that the only reason Worsley et al. needed occultations was to test the chronometer(s). With that done, and under the assumption that the chronometer did not change its rate in the months after the occultations observations, the rest is really just common celestial navigation and dead reckoning analysis. They saw Endurance drop through the ice on a cloudy day. They knew how far they were from that spot. The next day Worsley took Sun sights which, properly done, could fix the camp's position to the usual accuracies of celestial navigation, which would be on the order of one mile. The most important catch in this analysis was that the camp was migrating. They were shooting sights on a moving ice floe, much like the condition of a vessel adrift and becalmed. Sights have to be adjusted for motion, like in a running fix, and assumptions have to be made to extrapolate that motion backwards to the time when Endurance began the last two miles of its voyage ...straight down.

    What's missing in all the media coverage is that the team that found Endurance, and all of us riding along virtually with them, got very lucky. It easily could have happened that the motion of the ice overnight back in 1915 was less predictable and even at one knot in some odd direction could have misplaced the calculated position by over 20 nautical miles. We don't actually know where they found Endurance. So far they're keeping that secret. And even if they tell me, which they might, I can't tell all of you! Was it 4 miles from Worsley's position, which we have been calling the "Endurance Memorial Position" (given with added and indefensible precision, a bit like listing the time of a patient's death to the exact minute)? Was it 8 miles? But we do know, I think, that it wasn't 20 miles even though that could have resulted just from random and unpredictable motions of the ice.

    Frank Reed

    Frank Reed

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

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

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

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

    Email Settings

    NavList ID 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