Page 10 of 10 FirstFirst ... 5678910
Results 91 to 99 of 99
  1. #91
    Join Date
    Jul 2008
    Location
    East coast UK. Mostly. Sometimes the Philippines
    Posts
    10,131

    Default Re: Call yourself a navigator?'

    Quote Originally Posted by AntarcticPilot View Post
    Reading about the voyage to Svalbard reminds me of my own early career - I helped to produce one of the earliest accurate maps of NordAustlandet, and worked on Svalbard through the 80s - my first trip there was in 1972!
    Did you re-survey Hecla Cove? I ask because I particularly recall the legend "Surveyed by Lt Parry, RN, 1827" on the chart we used. It was quite something to anchor in Parry's cove, named after his ship, and to do so using his chart!

  2. #92
    Join Date
    Dec 2008
    Location
    tayvallich
    Posts
    3,007

    Default Re: Call yourself a navigator?'

    Quote Originally Posted by Minn View Post
    I most certainly have seen a small(ish) boat navigated accurately with a sextant, a deck watch, a Walker Excelsior log and a lead line, for several thousand miles including little known coastlines.

    https://comlay.net/tilman/voyages/1974-spitzbergen/
    Excellent! Thanks

  3. #93
    Join Date
    May 2007
    Location
    Cambridge, UK
    Posts
    6,203

    Default Re: Call yourself a navigator?'

    Quote Originally Posted by Minn View Post
    Did you re-survey Hecla Cove? I ask because I particularly recall the legend "Surveyed by Lt Parry, RN, 1827" on the chart we used. It was quite something to anchor in Parry's cove, named after his ship, and to do so using his chart!
    No, we didn't - the main island, Vest Spitzbergen, was well mapped (by Arctic standards!) by the Norsk PolarInstitutt. They didn't have aerial cover of NordAustlandet, where we were going to carry out geophysical surveys. That was the impetus for our mapping.

  4. #94
    Join Date
    Jul 2008
    Location
    East coast UK. Mostly. Sometimes the Philippines
    Posts
    10,131

    Default Re: Call yourself a navigator?'

    A Norsk PolarInstitutt vessel which I would describe as a slightly glorified sealer, much like the Sysselman’s yacht, but with two small choppers on the after deck (it was too small for them to land or take off from - they must have been put over the side with a derrick) came into Hecla Cove whilst we were there but they didn’t seem to be surveying anything. Anyway, Parry’s work was good enough (by Arctic standards!).

  5. #95
    Join Date
    Nov 2016
    Posts
    2,731

    Default Re: Call yourself a navigator?'

    I remain intrigued by the techniques used by then-Major Ewen Southby-Tailyour RM when he surveyed the coves and inlets around much of The Falkland Islands in about 1979.
    His notes formed the basis of his pilotage book 'Falkland Islands Shores', with an important supplement by Peter and Annie Hill.

  6. #96
    Join Date
    Feb 2007
    Location
    West London
    Posts
    3,163

    Default Re: Call yourself a navigator?'

    Quote Originally Posted by davidjackson View Post
    Use what ever you like. I hadn't done a night entry for several years so preferred the added reassurance of ticking off the laterals and cardinals from the fairway buoy.
    Easier to just stay in the white sectors, no need to tick off anything.

  7. #97
    Join Date
    Jun 2019
    Location
    Lowestoft
    Posts
    825

    Default Re: Call yourself a navigator?'

    Quote Originally Posted by zoidberg View Post
    I remain intrigued by the techniques used by then-Major Ewen Southby-Tailyour RM when he surveyed the coves and inlets around much of The Falkland Islands in about 1979.
    His notes formed the basis of his pilotage book 'Falkland Islands Shores', with an important supplement by Peter and Annie Hill.
    The Hills' supplement is a free download from the RCC Pilotage Foundation, and E S-T writes that he did his surveying from a dinghy, a warship, a yacht.. and by swimming!

  8. #98
    Join Date
    May 2007
    Location
    Cambridge, UK
    Posts
    6,203

    Default Re: Call yourself a navigator?'

    Quote Originally Posted by Minn View Post
    Did you re-survey Hecla Cove? I ask because I particularly recall the legend "Surveyed by Lt Parry, RN, 1827" on the chart we used. It was quite something to anchor in Parry's cove, named after his ship, and to do so using his chart!
    Just to expand on my brief earlier answer. In remote regions, it is most unlikely that terrestrial topographic mapping would be done by ground parties; it simply isn't cost-effective. What happens (and this was our procedure in the Antarctic) is that once an area has been identified as requiring mapping, the first part would be to obtain a number of ground control points (GCPs) - these days, by sending a field party out with a survey-grade GPS; in past times (pre 1980s - Transit was used before GPS; we used Transit in 1983!) this would be a trigonometric survey tied either to a pre-existing survey network or to astronomical fixes. In parallel, there would be an airborne photographic survey acquiring photographs with sufficient overlap for photogrammetry (at least 50%; usually more). The map would then be made using photogrammetric techniques to measure elevation and plan position - these days (since 2000) it would be done using a suitably equipped PC; in days of old by using a specialized photogrammetric plotter. The number of ground control points required isn't all that high; the main criterion is that they be on points readily identified on aerial photos. The point is that GCPs need not be on points such as peaks that are identifiable at great distances horizontally as in conventional survey, so the GCPs for aerial photography can be acquired without heroic efforts to scale inaccessible peaks etc.

    To the best of my knowledge most of the rocky islands of Svalbard have been mapped using these techniques; NordAustlandet and Kvitoya are the exceptions because photogrammetry doesn't work on uniform snow-covered surfaces such as the icecaps of those two islands. These days satellite techniques are used, which don't work so well on the steeper terrain of the other islands.

    Using this technique means that large areas can be mapped without excessive investment in field parties - a few hours flying time can map hundreds of square kilometres of ground, and most of the work takes place in a nice warm office! And the ground party can usually do it's work in a few days of workable weather, rather than months.

    Hydrographic survey is most unlikely to happen at all in such areas except on an opportunistic basis by expeditions such as Parry's. There simply isn't any impetus for routine surveying of remote areas; commercial or naval vesssels don't go there, and people such as Tilman are presumed to go at their own risk! However, Tilman should have had access to perfectly adequate topographic maps of everywhere except NordAustlandet, and HinlopenStretet was also pretty well mapped - it was the parts of NordAustlandet further east that were not well mapped. We had adequate maps of VestSpitzbergen in 1972!

    Apologoies for my spelling of Norwegian names - done from memory, so may be faulty!
    Last edited by AntarcticPilot; 15-08-19 at 09:50.

  9. #99
    Join Date
    Sep 2008
    Posts
    2,462

    Default Re: Call yourself a navigator?'

    Quote Originally Posted by AntarcticPilot View Post
    Just to expand on my brief earlier answer. In remote regions, it is most unlikely that terrestrial topographic mapping would be done by ground parties; it simply isn't cost-effective. What happens (and this was our procedure in the Antarctic) is that once an area has been identified as requiring mapping, the first part would be to obtain a number of ground control points (GCPs) - these days, by sending a field party out with a survey-grade GPS; in past times (pre 1980s - Transit was used before GPS; we used Transit in 1983!) this would be a trigonometric survey tied either to a pre-existing survey network or to astronomical fixes. In parallel, there would be an airborne photographic survey acquiring photographs with sufficient overlap for photogrammetry (at least 50%; usually more). The map would then be made using photogrammetric techniques to measure elevation and plan position - these days (since 2000) it would be done using a suitably equipped PC; in days of old by using a specialized photogrammetric plotter. The number of ground control points required isn't all that high; the main criterion is that they be on points readily identified on aerial photos. The point is that GCPs need not be on points such as peaks that are identifiable at great distances horizontally as in conventional survey, so the GCPs for aerial photography can be acquired without heroic efforts to scale inaccessible peaks etc.

    To the best of my knowledge most of the rocky islands of Svalbard have been mapped using these techniques; NordAustlandet and Kvitoya are the exceptions because photogrammetry doesn't work on uniform snow-covered surfaces such as the icecaps of those two islands. These days satellite techniques are used, which don't work so well on the steeper terrain of the other islands.

    Using this technique means that large areas can be mapped without excessive investment in field parties - a few hours flying time can map hundreds of square kilometres of ground, and most of the work takes place in a nice warm office! And the ground party can usually do it's work in a few days of workable weather, rather than months.

    Hydrographic survey is most unlikely to happen at all in such areas except on an opportunistic basis by expeditions such as Parry's. There simply isn't any impetus for routine surveying of remote areas; commercial or naval vesssels don't go there, and people such as Tilman are presumed to go at their own risk! However, Tilman should have had access to perfectly adequate topographic maps of everywhere except NordAustlandet, and HinlopenStretet was also pretty well mapped - it was the parts of NordAustlandet further east that were not well mapped. We had adequate maps of VestSpitzbergen in 1972!

    Apologoies for my spelling of Norwegian names - done from memory, so may be faulty!
    Thanks for taking the trouble to post this, really interesting.

Page 10 of 10 FirstFirst ... 5678910

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Latest YBW News

Find Boats For Sale

to
to