Discussion: The Physics of Portaging

The Physics of Portaging ... under a Transmission Line!

While portaging the longer ATV trail section option from Wolf to Nine Mile Lake there is a section below a high voltage transmission line one must walk under After walking under it for about 100m I got a series of shocks (some quite large). Carrying the canoe low with two people holding the wooden handles produced no shocks unless the kevlar canoe brushed against you. The shocks were so painful i considered dropping my expensive kevlar canoe on the bedrock.

GHOSLO and I are interested in figuring out the voltage of the shocks.Transmission line is 1MV and is about 20m above ground. Canoe is 16 ft long and 33.5” at widest. Canoe and gunnels are kevlar fusion. I’m 1.75 m tall. portaging on granite bedrock.

Wow, that's interesting!

I was carrying my carbon fibre canoe behind Hammer. I use a tump line strapped from the yoke to front seat. I was holding the leather tump and not the gunnels with no problem, I soon realized that I shouldn't touch the gunnels because as my hand came close, I got a tingling shock and hair raised on my hand. Had to keep walking because I couldn't put the canoe down. After leaving the power line, I got a shock when I lowered the canoe.
There are high electric fields below the lines. To the extent that the canoe is a conductor, I was somewhat shielded in a partial Faraday cage. I gather the corona (non-virus type) charged the canoe.

I remember one solo Storm race where I had compass trouble under hydro lines, but never thought of a conductive carbon boat as a shock hazard.

We could also lift the canoe up with the stern still on the ground to get underneath It to carry, and as long as the boat was still touching the ground at one end we would get no shocks. As soon as both ends were off then I got shocked touching the gunnels.

That's pretty impressive. And reminds me of why I'd prefer not to live in close proximity to high voltage transmission lines if possible.

Agreed! I wonder if we need to be even more careful about getting caught in lightning with the new canoe materials.

Maybe drag a thin chain behind the boat on portage?

We were thinking of draging a wet rope.

I added the portage (running) heart rate data to my log that shows my heart rate spikes from the two large shocks and then the small one a little later on.

I think that I may understand what happened . I'll try an explanation without the nitty-gritty details. Please correct this.
The overhead wires are at a high AC voltage and the rock below us is approximately at 0 voltage. So everywhere in between there is a voltage ( an approximately 1/r field). Even at heights of a only a few metres, this voltage is considerable.
This is usually not a problem.
Your head will be at a higher voltage than your feet. Your shoes may insulate you somewhat from the rock. Therefore there will be a small AC current running through you. No problem.
However you shouldn't stick a metal rod high in the air above your head!
So we were carrying canoes (open side down) on our head, Head inside canoe. Hammer was holding the edge of the canoe (gunnel), I was not. The canoe is higher than the person and therefore at higher voltage than say the middle of a person.
The canoe may be thought of as a large capacitor that can store charge. (AG got a shock from it even after we were away from the wires and the canoe was on the ground).
Now things are complicated because of the various resistive properties of the materials. (ie. some materials allow current to flow better than others). I think that the fancy carbon kevlar gunnels may be decent conductors). The body of the boat is kevlar which is an insulator (I think).
So as Hammer was walking he was connected to the capacitor (canoe). A considerably larger AC current would flow through him than would be the case without the canoe. When he let go of the gunnel, sparks jumped the gap between the gunnel and his hand. (a very disconserting situation in the best of times but made worse by the fact that he was trying to balance an expensive boat on his head).
I need more data so I propose that we send him back (alone) to try this again, He could try different canoes, different weather, different shes etc. OK?

I like the way you think, GHOSLO! Such dedication to science. And for Hammer to volunteer for your experiment shows selfless dedication too.

Fascinating. I’m going to crawl past the next high voltage line I encounter.

Whoa. Crazy!