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  1. #21
    Join Date
    Nov 2007
    Location
    Kingdom of Fife
    Posts
    6,079

    Default Re: Electromagnetic log transducer.

    We used to have EM logs on submarines sticking out on metre long fins to get out of the boundary layer and once calibrated they gave good performance. Calibration involved many runs over the measured mile, dived and surfaced, not the most popular activity. I would prefer to see a small boat doppler log, NASA did have one right back when they started up but had problems so it was dropped. With modern software control I would have though it could work quite well, also having the benefit of bottom lock in shallower water giving true speed over the ground, and water lock in deeper water
    Peter

  2. #22
    Join Date
    Jun 2013
    Location
    Hopefully somewhere warm
    Posts
    9,484

    Default Re: Electromagnetic log transducer.

    So has anyone tried the new nasa log yet?

    Very tempted

  3. #23
    Join Date
    Feb 2010
    Posts
    2,563

    Default Re: Electromagnetic log transducer.

    It's a gimmick ...... A lead weighted wooden board and a bit of string on a bobbin were good enough in the past. I saw Dan Snow testing the latest version recently. I think they used their GPS to check they had the right speed

  4. #24
    Join Date
    Sep 2010
    Location
    West Sussex / Hants
    Posts
    28,658

    Default Re: Electromagnetic log transducer.

    Quote Originally Posted by Ladybirdgaffcutter View Post
    You need to know your distance run *through the water* for a few things, so I venture to differ on the last bit.
    So how is the distance run with a paddlewheel log accurate enough for navigation, when it can't get the speed accurate even when not clogged by weed or wee beasties ?

    The Smiths unit on my Carter certainly wasn't, then it hardly ever worked at all due to aforementioned beasties or weed.

    Long before electronic navigation ( apart from ' are you game for a laugh ' RDF ) I used a trail log - calibrated / checked over a measured mile years ago - and still do as backup when cruising any distance, nowadays of course with GPS as primary aid.

    Trail logs can pick up weed too but it's immediately obvious, even at night; a quick flick of the line gets rid of the weed before it can affect the distance run reading - and they don't rely on ships' or any other batteries.
    Anderson 22 Owners Association - For info please ask here or PM me.

  5. #25
    Join Date
    Nov 2007
    Location
    Kingdom of Fife
    Posts
    6,079

    Default Re: Electromagnetic log transducer.

    Quote Originally Posted by Seajet View Post
    So how is the distance run with a paddlewheel log accurate enough for navigation, when it can't get the speed accurate even when not clogged by weed or wee beasties ?

    The Smiths unit on my Carter certainly wasn't, then it hardly ever worked at all due to aforementioned beasties or weed.

    Long before electronic navigation ( apart from ' are you game for a laugh ' RDF ) I used a trail log - calibrated / checked over a measured mile years ago - and still do as backup when cruising any distance, nowadays of course with GPS as primary aid.

    Trail logs can pick up weed too but it's immediately obvious, even at night; a quick flick of the line gets rid of the weed before it can affect the distance run reading - and they don't rely on ships' or any other batteries.
    To be honest up till the advent of GPS most mariners found themselves some what uncertain to their position from time to time certainly enough to bow down to the great god RDF. I can remember spending a whole watch out in the North Western Approaches trying to get a workable fix out of either RDF and we had a good HF/DF set or Consol. My relief took over the task but to little avail until we came back into DECCA range and at least the QM10 didn't pack it in till we got back into Derry
    Peter

  6. #26
    Join Date
    Jun 2016
    Location
    North West
    Posts
    552

    Default Re: Electromagnetic log transducer.

    Quote Originally Posted by Ladybirdgaffcutter View Post
    You need to know your distance run *through the water* for a few things, so I venture to differ on the last bit.
    Go, on, lets have the list.

    I've just forked out 50 quid to replace the paddle wheel that appears to have been destroyed by my own pre-purchase survey, so some justification for it would be good.

  7. #27
    Join Date
    Sep 2010
    Location
    West Sussex / Hants
    Posts
    28,658

    Default Re: Electromagnetic log transducer.

    To be pedantic the yottie version of Decca was the great miracle people like me had been praying for, then Satnav, then GPS.

    To think we used to salivate over the latest RDF kit with a digital frequency selector; then a yotttie friend who worked closely with the RN for Ferranti took one apart and found the frequency knob just turned up the display, the actual selector was only vaguely linked - hence the continued requirement for furious twiddling to get the vague anyway signal - ' and if you tell that to young people today...'
    Anderson 22 Owners Association - For info please ask here or PM me.

  8. #28
    Join Date
    Sep 2010
    Location
    West Sussex / Hants
    Posts
    28,658

    Default Re: Electromagnetic log transducer.

    Quote Originally Posted by JBJag27 View Post
    Go, on, lets have the list.

    I've just forked out 50 quid to replace the paddle wheel that appears to have been destroyed by my own pre-purchase survey, so some justification for it would be good.
    I'd love to hear that one myself, I'd have spent the £50 towards removing the useless thing and glassing over the hole.

    If they put the slings over the paddlewheel when lifting her for the survey, I don't know if you have legal redress but you could at least moan at the previous owner for not marking position and /or removing the transducer and for not briefing you and the hoist team - I doubt you'll get more than a moan in but maybe worth it just for that, a decent owner tries to give every bit of info when selling on his pride and joy...
    Anderson 22 Owners Association - For info please ask here or PM me.

  9. #29
    Join Date
    Jun 2016
    Location
    North West
    Posts
    552

    Default Re: Electromagnetic log transducer.

    Quote Originally Posted by Seajet View Post
    I'd love to hear that one myself, I'd have spent the £50 towards removing the useless thing and glassing over the hole.

    If they put the slings over the paddlewheel when lifting her for the survey, I don't know if you have legal redress but you could at least moan at the previous owner for not marking position and /or removing the transducer and for not briefing you and the hoist team - I doubt you'll get more than a moan in but maybe worth it just for that, a decent owner tries to give every bit of info when selling on his pride and joy...
    No, no, no. Everyone acted in god faith, it's just one of those things. It could have been a different time and place as well of course, I'm just inferring.
    Also, my survey so technically I broke it, if it did happen then.

    The real shocker is 50 quid for a paddle wheel.

  10. #30
    Join Date
    Sep 2010
    Location
    West Sussex / Hants
    Posts
    28,658

    Default Re: Electromagnetic log transducer.

    I'm surprised you got away with £50 !

    Anyway either mark the position for the next lift, or better to fit the blanking cap before glassing over, take away the paddlewheel thing in entirety and shoot it.
    Anderson 22 Owners Association - For info please ask here or PM me.

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