How high is that wire... REALLY?

[Capn Jimbo]

Method #1

Measure height of pylons ( with vertical sextant angle )
Measure distance between pylons ( horizontal sextant angle )
Calculate catenary.... must be a formula for that.
Allow for tide, apply suitable fudge factor, etc.

A DIY clinometer can work:
https://www.billbogaiv.com/posts/cal...ght-of-objects

Method 3: Have you called "the authorities", poster of the sign, owner of the wires?

[Dr. Sea]

There are phone apps for calculating height of buildings, bridges, etc. Does anyone know how accurate they are? If so, which app is most accurate?

[Fence Man]

Originally Posted by Wotname

Not so bone head IMO, actually quite a good move (I think).

Providing an object is not earthed and doesn't touch adjoining wires, there is no danger in getting close to the wires. Birds do it, helicopters do it, why not a drone?

I think my first concern measuring power line clearance would be the electromagnetic field screwing with the altimeter reading. I'm sure that I've used the wrong scientific terms here, so I'm ready for my beating from the electricians, engineers, and pilots.

We had a rent pasture years ago that had high voltage transmission lines crossing over the fence. We built a two strand fence on insulators, and never did have to put a fence charger on it. Sucker would nail you hard on a humid day. High lines have scared me ever since.

[AKA-None]

Remember don’t be a Darwin Award candidate

[macman4190]

Originally Posted by Jim Cate

Alan Lucas (a somewhat elderly edition) and one produced by the locals, utilizing official NSW Maritime charts. Lucas says that the wire clearance at HAT is 19.8 m. The local guide and its official chart shows 21 m. Our air draft is 21 m, so we thought that by easing over near the shore, somewhat up on the catenary of the cables we would be OK, especially if we were at less than HAT.



So today we moved on up the river, and as we passed the end of Elizabeth Island and the wires came into sight there was a big ass sign saying maximum height of vessel was 17 meters. Yikes!



Jim

High tension wires might require more clearance than a bridge - so there is no arcing. So a mast taller than 17m might clear the wires, but ... The wires might indeed be 21m above the water.

[Wotname]

Originally Posted by Fence Man

I think my first concern measuring power line clearance would be the electromagnetic field screwing with the altimeter reading. I'm sure that I've used the wrong scientific terms here, so I'm ready for my beating from the electricians, engineers, and pilots.

We had a rent pasture years ago that had high voltage transmission lines crossing over the fence. We built a two strand fence on insulators, and never did have to put a fence charger on it. Sucker would nail you hard on a humid day. High lines have scared me ever since.

No beating here

In the unlikely event of the EMI field upsetting the drones altimeter, you might loose the drone but they are way cheaper than Jim's boat.

If drones haven't already replaced helicopters for transmission line inspections, I'm sure they soon will.

[Dsanduril]

This is from the Energy Networks Association - Technical Specification 43-8:



Presumably () the arc distance is less than this. Note that elsewhere in the specification they require much greater clearances anywhere that a person might be (such as the top of the mast). This has more to do with people doing silly things like reaching out and touching things than arc length.

If a person can stand on the object or any temporary object adjacent to it, then the normal clearance shall include an 'application factor' of 2.2 m to allow for the person to move their arm whilst holding a short metallic object. Should it be necessary for a person to move their arm whilst holding a longer object, then this normal clearance may have to be increased by a distance of up to the length of the object.

[Fence Man]

Originally Posted by Wotname

No beating here

In the unlikely event of the EMI field upsetting the drones altimeter, you might loose the drone but they are way cheaper than Jim's boat.

If drones haven't already replaced helicopters for transmission line inspections, I'm sure they soon will.

Funny that you mention the inspection with helicopters...…
The transmission lines that pass over the back corner of our place are still inspected with a helicopter, which led me to assume that a drone would be unacceptable for the application. I'm sure the technology will catch up to that job in no time, if it hasn't already. I bought a Mavic Pro a couple weeks ago, and I can't get over the video quality, not to mention how easy it is to fly. I've been checking cows with it every evening just to get some flight time in and build some confidence.
My concern about electromagnetic interference and skewing the altimeter, would not be losing the drone, but basing the decision to attempt going under with a false reading.

[Jim Cate]

So, being ignorant about the state of development of hobby drones, how would you use one to determine the height off the water of a suspended wire... to sub-foot accuracy?

Jim

[Kita]

Originally Posted by Jim Cate

So, being ignorant about the state of development of hobby drones, how would you use one to determine the height off the water of a suspended wire... to sub-foot accuracy?

Jim

Bottom line,I doubt that you can...the drone might have a decent altimeter but the problem I see when you get down to that accurate of a measurement is the alternator is not designed to be one foot plus or minus I don't believe and on top of that your depth perception is a major factor here..

[Wotname]

Originally Posted by Jim Cate

So, being ignorant about the state of development of hobby drones, how would you use one to determine the height off the water of a suspended wire... to sub-foot accuracy?

Jim

I dunno, I'm just thinking aloud here...
10' is a common increment in modern air data equipment but maybe with $$ you can get better. Some hand held precision pressure air data is good to 1'.

However I think the advantage of a drone is the video feed. It is basically a moving eye; in particular, an ungrounded moving eye so it can approach the wire safely. You sit in the cockpit looking at your lap-device of choice but your eye is dancing around in the air wherever you want it. Presumably you would be looking mainly at the wire and the mast head, approach slowly .

[bushytales]

Originally Posted by Jim Cate

Well, DANG! Looks like we are barred from further up river. I thought about the sextant angle measurement but don't trust my skills to determine height with sub-meter accuracy. Determining the distance off accurately enough is problematic, and besides, I'd have to unpack the shed to get down to my sextant. Don't get it out very often these days!

They appear to be building a new bridge there in Grafton as well as at Harwood. Lots of tax dollars wafting away!

Jim

This might sound silly but it worked for me a few years ago...got a slngshot Good rubbers needed),
Put a series of coloured bits of wool on a long length of string.
Shot the string into the air, over the wire, and down the other side. Used binoculars to check which colour was at the top....pulled it down and measured it...sounds stupid but it worked for us....
Cheers

[sarita]

Hi,

Disclaimer - I am the creator of the SeaNav app.

Our SeaNav app for iOS now has an Air Draught feature in the augmented reality view. You set your boats air draught and a POI on the bridge or cable you want to see if you can pass under and it shows the height of your boat at that point relative to the bridge. It should only be used as a rough guide but it might help. I use it to pass under low bridges on the way out to the channel from up river.



More about it here:-

https://pocketmariner.com/seanav-aug...goes-vertical/

[Fence Man]

Originally Posted by Jim Cate

So, being ignorant about the state of development of hobby drones, how would you use one to determine the height off the water of a suspended wire... to sub-foot accuracy?

Jim

I really can't speak to the accuracy, but the drone I have(DJI Mavic Pro), has an altimeter with 1' increments. It does appear to be accurate, but I sure wouldn't bet my life on it.

[a64pilot]

Originally Posted by Jim Cate

So, being ignorant about the state of development of hobby drones, how would you use one to determine the height off the water of a suspended wire... to sub-foot accuracy?

Jim

If you really wanted to there is this
http://www.aglasers.com
I helped him get it aircraft certified a few years ago, it’s accurate actually to well within 1 inch, it’s an IR Laser if your drone was big enough you could put it on a drone and look at the display with the drones camera.
Me, I’ll just stay away, power lines give me the willies.