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  1. #1
    Join Date
    Jan 2003
    Location
    Nazare Portugal
    Posts
    14,294

    Default H T electric cable clearance

    How close would you sail.

    Air Draft 17.5m thinking of going to Aveiro but HT cables shown as 22m in Reeds.

    Would you pass 4.5m from cables?

    Assume 22m is HAT!

  2. #2
    Join Date
    Jun 2004
    Location
    Fareham
    Posts
    6,405

    Default Re: H T electric cable clearance

    Surely that should be safe height in the worst conditions so MHWS or HAT with maximum cable sag and maximum arcing distance.
    ۞

  3. #3
    Join Date
    Nov 2015
    Posts
    157

    Default Re: H T electric cable clearance

    I haven't a copy of Reed's with me at the moment, but I'm pretty sure the clearances are at HAT. There is a diagram in the front somewhere (even in the Channel copy, let alone the full one) showing clearances and rises of tide etc.

    I think I would sail with a 4.5m clearance from the cables myself, though I'm sure it would make me terribly jumpy in the same way that going under most bridges does—it never looks like you'll miss it on approach. Usual disclaimer applies, of course, but a routinely accepted breakdown field strength for dry air is about 3MV/m (i.e. 4.5m would breakdown around 13.5 million volts). Caveat is that this changes somewhat with humidity, but you'd be unlucky if they were even 800kV lines, so giving a field strength of about 180kV/m, which I would imagine is OK (though no electrical engineer). Of course, your mast is presumably terminated with a sharp-tipped conductor (aka VHF aerial), so this will worsen things a bit...

    If you have the depth to aim off to one side, you'll probably find more height (depending on the suspension arrangements) and obviously less rise of tide will also give a clearance boost.

  4. #4
    Join Date
    Jun 2013
    Location
    Hopefully somewhere warm
    Posts
    8,240

    Default Re: H T electric cable clearance

    Looks like some pretty tall masts on google streetview...

    https://www.google.co.uk/maps/@40.64...7i13312!8i6656

  5. #5
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    42,146

    Default Re: H T electric cable clearance

    Quote Originally Posted by Sailfree View Post
    How close would you sail.

    Air Draft 17.5m thinking of going to Aveiro but HT cables shown as 22m in Reeds.

    Would you pass 4.5m from cables?

    Assume 22m is HAT!
    If you consult the Admiralty Symbols and Abbreviations , Chart 5011, you will find the meanings of the clearance figure printed on the charts are explained

    ITYWF that it is safe clearance above HAT ( highest astronomical tide) if printed in magenta but, like bridges, the actual clearance if printed in black.

    You will have to look in Reeds for an explanation of the figures they quote and treat with extreme caution
    Last edited by VicS; 12-10-18 at 10:32.

  6. #6
    Join Date
    Apr 2018
    Location
    Mooring, Faro
    Posts
    503

    Default Re: H T electric cable clearance

    Based in Nazare, you should be able to find people with local knowledge. If not, go at LW springs which will give another 2-3m clearance.

  7. #7
    Join Date
    Jun 2004
    Location
    Fareham
    Posts
    6,405

    Default Re: H T electric cable clearance

    Found and old copy of Reeds. They say that the Admiralty symbol - printed in Magenta with zig-zags either side of the number - means "Safe overhead clearance as defined by the responsible authority."

    Put your rubber boots on - you'll be fine!
    Last edited by DJE; 12-10-18 at 10:53.
    ۞

  8. #8
    Join Date
    Aug 2013
    Location
    SW Scotland
    Posts
    17,684

    Default Re: H T electric cable clearance

    Quote Originally Posted by Sailfree View Post
    How close would you sail.

    Air Draft 17.5m thinking of going to Aveiro but HT cables shown as 22m in Reeds.

    Would you pass 4.5m from cables?

    Assume 22m is HAT!
    I'm pretty sure that even 132kV insulators are a lot less than 4.5m long ...
    "Seamen are always wanting to do things the proper way; and I like to do them my way."

  9. #9
    Join Date
    Oct 2013
    Location
    Shropshire - Sundance, Bristol Channel
    Posts
    809

    Default Re: H T electric cable clearance

    https://www.google.com/url?sa=t&rct=...QLav7iSGPsCTA7

    The minimum extent of these zones varies according to the voltage of the line, as follows:
    low-voltage line 1 m;
    11 kV and 33 kV lines 3 m;
    132 kV line 6 m;
    275 kV and 400 kV lines 7 m;

    There's a pylon in our club Pill, 2 boats have gone under it and arced (sp) it's a total no go area, ram and grab onto another boat if needs be.

    I work on a 10m clearance for any power lines.
    Last edited by Yellow Ballad; 12-10-18 at 16:33.
    Tom, Sundance
    2wheels1keel.com

  10. #10
    Join Date
    Mar 2015
    Location
    Isle of Eigg
    Posts
    6,195

    Default Re: H T electric cable clearance

    Quote Originally Posted by GHA View Post
    Looks like some pretty tall masts on google streetview...

    https://www.google.co.uk/maps/@40.64...7i13312!8i6656
    Annd... if you pan to the right you can see one of the pylons in question (I guess)

    https://www.google.co.uk/maps/@40.64...7i13312!8i6656

    If that is the ones then that is a very very very long span across a navigable basin, if theres 22m at the middle then theres going to be a bucket load more at the edges.
    Just call me Dougal, Sir Dougal to you.

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