H T electric cable clearance

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Sailfree

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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!
 
Surely that should be safe height in the worst conditions so MHWS or HAT with maximum cable sag and maximum arcing distance.
 
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.
 
Sailfree said:
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!
Click to expand...

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
 
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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! :o
 
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https://www.google.com/url?sa=t&rct...ubns/gs6.pdf&usg=AOvVaw2sW8bQC_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.
 
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GHA said:
Looks like some pretty tall masts on google streetview...

https://www.google.co.uk/maps/@40.6...4!1sPZAny5dszUbJLPS47jL3UA!2e0!7i13312!8i6656
Click to expand...

Annd... if you pan to the right you can see one of the pylons in question (I guess)

https://www.google.co.uk/maps/@40.6...4!1sPZAny5dszUbJLPS47jL3UA!2e0!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.
 
This is the cable that is in our pill, navionics put it at 4.3m but it's actually higher even on big springs I've seen (infact to get 4.3m I would have thought the clubhouse would have been underwater) It's taken two boats out over the years and I believe both were arcs rather then touching the cable. It may be scare tactics but there was talk about anchor chain fusing together and damage to engines electronics.

Local knowledge is king though, ask if you can.

I have an airdraft of 12.4 plus antenna 1m and anything lower them 20m HAT gets my full attention.

20604648_10159291144305492_5875126651847769733_n.jpg
 
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