Air draught of Sigma 362 - Cables over the Tamar

shmoo

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I want to go up the Tamar in the summer. Will I fit under the cables at HW with a masthead 362? My guess is our air draught is about 12m plus 1m for the VHF so I should have 3m.

Does this sound right?
The cables don't droop over time do they?
Cornish metres are the same as everyone elses?

I really don't want 11000 V coming down the mast - the admiral would really tell me off!
 

john_morris_uk

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Never mind the 'we heel over' joker.

We have a masthead clearance height of 17 metres or so and we go under the cables on the Tamar quite comfortably.

Mind you I do tend to find myself wondering away from the lowest point of the catenary when its close to high water, but I think that this is psychological...

Just to cheer you up, I think its a bit more than 11000 volts on those lines.
 

Birdseye

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If you can guess your air draft, I'm sure someone will come along and guess that you are OK. /forums/images/graemlins/grin.gif

The charts should tell you the clearance - check to see whether this is at MHWS or HAT. Your boats manual will give you the true air draft but dont forget to add any masthead gear and make an allowance for a flash over distance (the voltage will jump over a short distance particularly in wet weather). Then wear your rubber wellies. /forums/images/graemlins/grin.gif

Dont know where the wires are, but we regularly used to toddle up the Tamar to Weir Quay and beyond in a 33 ft cat. Never thought about the power cables tbh - never knew they were there which says a lot for my navigation.

Finally, dont forget the extra toilet roll. /forums/images/graemlins/laugh.gif
 

shmoo

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Heel over phooy, we let the tires down!

Thanks for advice and link.

Seriously, its taller than I thought. The website says 50 feet from deck, or about 15.3m in real money, and the deck must be about 1m above the waterline and 1m for the vhf brings is up to 17m which will clear the first set with 2m, but snag the second set.

John, did you mean you clear just the first (19m) set or both? and does your 17m allow for the VHF anntenna?

Sorry to bleat - wouldn't mind so much if it were just a bridge...
 

john_morris_uk

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The 17 metres allows for our VHF and little if any 'clearance'. I would need to allow several metres if I thought I was actually getting anywhere near a high voltage cable as one wouldn't want to risk the thing arcing across and down through our expensive electonics (and more importantly us).

I physically measured the mast, and height from waterline to mast-step when we first bought the boat, so I have high confidence in the accuracy of our air draught measurement.

Where are you getting your '50 foot' clearance from? I haven't got the chart in front of me, but I seem to remember its a lot more than 50 foot. Are we talking about the cables just South of Cargreen and then at Wier Quay and again North of Hole's Hole or whatever its called?
 

shmoo

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50 ft is the mast height quoted from the link kindly given by an earlier poster. The charted clearance for the cables (from CA almanac) are 19m for the seaward set and 16m for the next set up.
 

john_morris_uk

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The second cable's catenary makes the lowest point well away from the main channel from memory. When its anywhere near high water, we stick to the Eastern side near the bank where there is considerably more clearance.

No-one I know has any sort of problems going up and down that bit of river. A friend of ours has his swinging mooring amost directly under the cables at Wier Quay.
 
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