Insomniac Question...

[Lazy-Ferret]

OK, I have now over thought this to the point that applied physics no longer work...

Taking a hypothetical situation...

I have a nice long tow rope, which has a loop at each end, and is rated at 1 ton. I also have a Shackle which is rated at 1 ton..

I want to tow a car that weighs 1.5 ton.

So, I take my tow rope, pass it through the cars towing eye, and round my pin hitch, then join the looped ends of the rope with the shackle, making it, so that there are now 2 pieces of rope between the two of us.

Have I actually doubled my ropes capacity?

[briggie]

in my opinion ...... no .... because its only as strong as its weakest component

[Lazy-Ferret]

in my opinion ...... no .... because its only as strong as its weakest component
Buuutttt... surely, if it is all rated at 1 ton, and then doubled up, it is now rated at 2 ton?

[briggie]

but ....... its only as strong as its weakest part

[Peasgood1]

It will most likely pull the car quite safely without doubling it.
I can push a 1 ton car along a road all on my own and I'm not Superman.
I wouldn't lift a 1.5 ton car with it but that is different.

[macabethiel]

I reckon you have a tow rope with a 2 Ton breaking strain provided it is equally tensioned either side of the towing eye.

The shackle though being 1 Ton is the weakest link so if anything were to give it would be the shackle pin as its the weakest link!

[John B]

My mate tried to tow a car with a tow rope which had the alloy hooks on each end, One of the hooks snaped under strain at came flying through the rear window :doh

[spiderpig37]

I would say no as although you have doubled one end the other end is still intheory a single one tonne strap and your accesories are rated at one tonne
If it was being used as a lifting strap doubled in a choke hitch it would be times two less 20% if i remember right from my lifting and slinging course many years ago

[Lazy-Ferret]

You see, the more you think about it, the more it conflicts with your logic. I think the same as Briggie, but other than the weakest link bit, I can't justify it.

[rustic]

...
Have I actually doubled my ropes capacity?

To answer that question, you haven't doubled the ropes capacity, but what you have in effect is two ropes of 1 tonne capacity so capable of carrying one tonne each so 2 tonnes in total, provided that there is no friction around the pin.
Better if it was a pulley.
The shackle of one tonne capacity, if it is lifting gear, will have a breaking strain of a minimum 5 times rated.

Shock loads are what breaks things.
Also ropes and cables have to go around a minimum diameter pin so many times bigger than the rope or cable diameter, otherwise you will put a strain on the rope and lower the capacity. The shackle could reduce the capacity of the rope.

Knots and splices can also affect the ropes capacity. Granny knots will considerably weaken it.:doh

In answer to the title of the thread... I won't be loosing any sleep over this one...:lol:lol:lol

[larson]

still only 1 ton

you have 2 lengths of rope but its only 1 rope thicknes going through your towing eye.
that part is weaker that the 2 lengths together and your shackle is still 1 ton

thats 2 parts under more strain than the rateing. i would tow it but carry a spare as i would expect something to fail

[makeitfit]

I disagree
Assuming you have two lengths joined together by a knot or a shackle .
Each line is still 1 ton rated BUT the load is halved.
As Rustic said , there is a small loss at the turn point but really not to worry about.
Regardless of safe working loads etc this set up will for all intense and purposes hold 2 tons

[solarman216]

OK, I have now over thought this to the point that applied physics no longer work...

Taking a hypothetical situation...

I have a nice long tow rope, which has a loop at each end, and is rated at 1 ton. I also have a Shackle which is rated at 1 ton..

I want to tow a car that weighs 1.5 ton.

So, I take my tow rope, pass it through the cars towing eye, and round my pin hitch, then join the looped ends of the rope with the shackle, making it, so that there are now 2 pieces of rope between the two of us.

Have I actually doubled my ropes capacity?

short answer is yes, if it was not then when I run a rope through a block I would not double my pull, which of course it does, Rick

[larson]

I disagree
Assuming you have two lengths joined together by a knot or a shackle .
Each line is still 1 ton rated BUT the load is halved.
As Rustic said , there is a small loss at the turn point but really not to worry about.
Regardless of safe working loads etc this set up will for all intense and purposes hold 2 tons

i understand that that bit but were it passes through the eye it takes all the load and only 1 rope thickness. would this not be the week point and still 1 ton?

i will ask at work in the morning..

[makeitfit]

A weaker point yes but the rope is spread over the fulcrum ( I think it is) so at one infinite point it's one bit.
real world though it's two bits magically attached round the back :D
Look here for more blurb https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&ved=0CEEQFjAC&url=http%3A%2F%2Fwww.ropebook.com%2Finformation%2F pulley-systems&ei=X_ygUsvLO6Wi0QWHw4HYCA&usg=AFQjCNG4_MRApPfvbca3nwprR9AIWBIeRQ&sig2=xv2e0y_kliHPxJS02hgmnQ&bvm=bv.57155469,d.d2k

[larson]

i arnt clicking the link:lol

ill take your word for it that its what you said you know more than me for sure

[micktheshed]

The ropes need to be attached as if they were two separate ropes acting independently, & then the possible load would only be 1T each if they were both carrying the same tension eg. towing in a straight line.

Imagine a bar with the 2 ropes 1 at each end & the bar pivoting in it's middle where it is attached to the car. Each rope has 1T load but the centre pivot ie. total load, has 2T.

Hooking the rope around a tow hitch or a pulley would still leave one portion of the rope taking all the strain & therefore only 1T total capacity.

Having said that it is the initial pull-away from a standing start that would be the problem, once under-way the load would be much less until '1' a hill or '2' a corner when the load would '1' be higher but shared, or '2' more biased towards one 1 rope than the other.

Been there & done that, as the saying goes.

If it wasn't illegal then a motorway would be the ideal place LOL.