Tirfor style winch as a zip wire for logs

[cornish wood burner]

6mm galvanised (7 by 19 with a steel core) (ie not fibre) when new has a SWL of c. 500kg and a MBL of 2.5 tonnes; for stainless it is a little less than this. This gives a FoS against the quoted 30kg of significantly more than the 5 which is required by the various regs (ie LOLER and, in some cases, PUWER)

 

The 6mm is more than man enough for the job in hand. The only downside over using this instead of (say) 10mm is that whilst it will sit higher when not under load, it will stretch more when loaded. In this instance this should not pose a problem.

 

I think you are getting confused between the weight and the tension in the wire. The wire tension generates an upward vector to lift the 30kg. It also exerts a pull between the two anchors. The combination of these two is the wire tension which is what we should be concerned with. The OP didnt want to anchor 30 ft up a tree so typically we are talking around the 400kg of tension to generate an upward force of 30kg with a reasonable sag. If we add in the extra stresses due to movement etc then your cable is probably between its SWL and MBL. Not a good idea for a new cable let alone a secondhand one.

[scbk]

It's all gobbledygook to me!

 

The reason I was thinking using the trifor cable is it would be very quick to set up and take down at the end of a day, and you could have the zip wire an infinite length you wanted between 0 and 50m

 

 

Does it make much difference to use a single or a double pulley?

[cornish wood burner]

It's all gobbledygook to me!

 

The reason I was thinking using the trifor cable is it would be very quick to set up and take down at the end of a day, and you could have the zip wire an infinite length you wanted between 0 and 50m

 

 

Does it make much difference to use a single or a double pulley?

 

Do you mean a double line? It would double up on the strength but you need to pull evenly on each. Bit fiddly to set up I would think

Your basic idea is OK I guess but you need to make sure you have no wear problem and your pulley needs to run smoothly. Any snatch or jam would increase the strain dramatically.

Also consider what your tirfor will pull. Presumably you have no means to monitor this so I would suggest sizing your cable or rope SWL so it could take the full full from the winch.

My concern with a small cable with a SWL of 500kg is that there are a few other factors that could increase the stress on the cable so if you need 4 or 500kgf of tension to support your load go higher on the SWL to allow a safety margin. When I was young I witnessed a steel cable breaking and believe me you don't want to risk that.

[treequip]

Do you mean a double line? .

 

Probably tandem pulley

[teepeeat]

What type of powered winch do you have in mind?

 

Sorry I was rambling and this would be a bit of a hijack of the thread so will take this elsewhere sometime - apologies to the op

[cornish wood burner]

Probably tandem pulley

 

Of course, thanks treequip.

It obviously won't reduce the setup tension/sag but by running smoother it will reduce the potential high stresses caused by jerks and bounces.

[cornish wood burner]

Hi scbk

I was wondering if you have you a cunning plan to retrieve your nice new tandem pulley up the slope or just rely on pulling it with your retrieval rope by hand.

[Breezeblock]

for braking and retrieval what about a simple bollard at the top then just pull it back up you could probably get away with 1/4 recoil starter rope

[muldonach]

I think you are getting confused between the weight and the tension in the wire. The wire tension generates an upward vector to lift the 30kg. It also exerts a pull between the two anchors. The combination of these two is the wire tension which is what we should be concerned with. The OP didnt want to anchor 30 ft up a tree so typically we are talking around the 400kg of tension to generate an upward force of 30kg with a reasonable sag. If we add in the extra stresses due to movement etc then your cable is probably between its SWL and MBL. Not a good idea for a new cable let alone a secondhand one.

 

I am similarly intruiged by the figures - a 1:25 sag indicates a pretty high cable tension to me - if anything CWB figures are low so would be interested to see the figures you have for a 50Kg weight suspended halfway across a 50m span with total 1m sag?

 

Even if the figures are acceptable a 6mm wire will not last long at all in this application.

 

It is an interesting discussion since I have a similar problem involving soft rather than steep ground.

 

Without wishing to raise difficulties one issue that will arise is the effort of lifting the timber high enough to get it on to the travelling block while having the cableway high enough to ensure the load does not bottom out partway down.

 

Cheers

mac

[tree-fancier123]

I am similarly intruiged by the figures - a 1:25 sag indicates a pretty high cable tension to me - if anything CWB figures are low so would be interested to see the figures you have for a 50Kg weight suspended halfway across a 50m span with total 1m sag?

 

Even if the figures are acceptable a 6mm wire will not last long at all in this application.

 

It is an interesting discussion since I have a similar problem involving soft rather than steep ground.

 

Without wishing to raise difficulties one issue that will arise is the effort of lifting the timber high enough to get it on to the travelling block while having the cableway high enough to ensure the load does not bottom out partway down.

 

Cheers

mac

 

Agreed, the 10mm better

 

If you fit a maillon quick link to the trolley pulley and then connect a progress capture pulley underneath the tandem trolley pulley via the maillon, it may be possible to have the top cable quite high in the tree, and haul the logs up, either by hand, or possibly through a redirect pulley bottom of uphill tree and onto a vehicle or petrol winch, the Petzl traxion is the type of progress capture pulley, can't think beyond having to send the logs with 'haul up line' trailing behind