Thread: portable electric winches

Originally Posted by Stuart02

Yeah there's cradles you can buy, but I thought fixed winches were more in the 45-50 kg? I'll check out the TJM, thanks

Warn state the weight of an XD9000 as 35kg including wire. I weighed the wire from mine and its about 8kg, and the equivalent synthetic rope is about 2kg.

Their portable XD9000i complete with cradle and wire is 47kg:
Warn Industries - Jeep, Truck & SUV Winches: XD9000i Portable

Steve

Originally Posted by Tank

..........
FYI to gain a Mechanical Advantage (MA) using a single sheave block you have to first be pulling to "Advantage", i.e. pulling in the same direction that the load is moving.
.........

Frank's comment here agrees with the diagrams I posted earlier. You need two snatch blocks;one connected to your car and one to the stationary point (tree, etc). An alternative scenario to what Frank described earlier about sitting on the ground - you have a single snatch block connected to the roof frame of your garage. A rope runs up and through it. Your mate weighs 100kgs (exerts a force of approx 1kN) and you weigh 60kg ( a force of approx 0.6kN). He's connected to one end and you to the other. Can you pull him up to the roof? Short answer is NO!.It's the same principle as the old see-saw where the heaviest person could sit on the ground and keep you up in the air until you decided to bail.

Originally Posted by steveG

I'm not arguing with the theory Frank, just that I believe you have applied it incorrectly in this case.
I've read a number of rigging references, but failed to find one that shows the line anchor point on the winch. I emailed you earlier for a copy of the rigging guide but haven't received it yet.
I don't have your experience or knowledge, but that doesn't mean you're correct all of the time.

Firstly, you're giving conflicting information. You say that there is no mechanical advantage to using a single pulley with a winch, but you give a scenario with the 10kg bucket that shows a 10kg line pull over a single pulley results in a 20kg beam loading. That transposes horizontally to the winch situation and gives a pulley anchor point loading of double the line pull - which goes against your no MA statement.

To test for myself, I've just been out on my sloping driveway with a spring balance, some rope, a snatch block, my garage creeper and my fat ass.
With a direct pull on the rope, it takes about 13kg to get/keep me moving up the driveway, but if I tie the rope around my waist and pass it through the snatch block and pull on the free end it only takes about 8kg. Plenty of variables there, but if you were correct the line pull through the snatch block would be the same or slightly higher then a direct pull as there is some additional pulley friction. The reality is that its closer to half the load.

Since this is the recovery section, I can't sit back and let something go if I feel its wrong as I consider it my responsibility to point it out (as I know you would ).
If someone were to take your advice that there is no mechanical advantage, and uses a double line pull with an 8000lb winch, proceeds to anchor the block with something rated to 8000lb its likely that the anchor would break. I'm not comfortable with that.

Steve

Steve, Quote: "You say that there is no mechanical advantage to using a single pulley with a winch", I don't say anything of the sort, the text books say it, along with TAFE teachers and the laws of physics, this is why I am loathe to explain things of this nature, it falls back on me to justify what is a known fact.
Steve I havent recieved an email from you, send me your email address and I will send you a copy and you can dispute the facts with the authors of the Riggers Guide, Regards frank.

Originally Posted by Tank

Steve, Quote: "You say that there is no mechanical advantage to using a single pulley with a winch", I don't say anything of the sort, the text books say it, along with TAFE teachers and the laws of physics, this is why I am loathe to explain things of this nature, it falls back on me to justify what is a known fact.
Steve I havent recieved an email from you, send me your email address and I will send you a copy and you can dispute the facts with the authors of the Riggers Guide, Regards frank.

Not sure what happened to the email I sent yesterday but I've just PM'd you my email address for a copy.

Steve

Originally Posted by Didge

Frank's comment here agrees with the diagrams I posted earlier. You need two snatch blocks;one connected to your car and one to the stationary point (tree, etc). An alternative scenario to what Frank described earlier about sitting on the ground - you have a single snatch block connected to the roof frame of your garage. A rope runs up and through it. Your mate weighs 100kgs (exerts a force of approx 1kN) and you weigh 60kg ( a force of approx 0.6kN). He's connected to one end and you to the other. Can you pull him up to the roof? Short answer is NO!.It's the same principle as the old see-saw where the heaviest person could sit on the ground and keep you up in the air until you decided to bail.

Didge, hook up a snatch block in your shed with a rope through it.....
Tie a big loop in one, then stand/sit in it. grab the other end and try and pull yourself up and get a feel for the force required.
Repeat the test with just the rope tied to a beam in the roof and try to pull yourself up.
Report back what you observe in regard to how heavy each scenario feels.

Steve

Originally Posted by weakestlink

Runner (rope through a single moving block)- MA 1.82

“Admiralty Manual of Seamanship Volume 1”

A single snatch block and winch is a probebly a "Runner". It doubling the cable and halves the pull lenght and halves the velocity or speed over a single straight pull. it may then have a MA of 1.82. It is not double the capacity but it is an improvement of .82.

I wonder if the Winch itself could be considered a block giving a "double whip"? If so the MA would be reduced to 1.67. I will ask some crusty old salty people for us. Bet that discussion will be heated unless I can take it to a pub near Garden Island

Edit do not ask winch manufactures- Looked at two and both claimed a single santch block doubles your MA. http://www.gowarn.com/warn-winches/winch-tips.aspx

this link below also mucked up MA but at least points out that as line comes onto the drum the pulling power is reduced for each layer added

http://www.innovation-engineering.co.uk/theory.htm "As a guide for each layer of wire rope on the drum deduct 10% off the rated line pull. e.g. A winch with a line pull of say 6,000 lbs.. will have a line pull of 5,400lbs.. on the second layer, 4,860 lbs.. on the third layer and 4,374 lbs.. on the fourth layer, etc."

That is a issue well worth considering as is the roughly 10% reduction caused by friction on the snatch block.

Originally Posted by weakestlink

A single snatch block and winch is a probebly a "Runner". It doubling the cable and halves the pull lenght and halves the velocity or speed over a single straight pull. it may then have a MA of 1.82. It is not double the capacity but it is an improvement of .82.

<snip>

That's my view also.

Steve

Mechanical Advantage is the force applied to the load, divided by the force applied to the apparatus.
In a simple lever, pulley or geared system, it is the inverse of the:
Velocity Ratio (VR) is the distance the load moves divided by the distance the effort moves.

(The majority of pulley diagrams I have found don't show the free end of the rope anchored back to the effort (winch) as in a double line pull, perhaps because it seems counter-intuitive to be pulling a rope back towards itself. Thankfully the rope doesn't care which direction the tension comes from it will still exert equal force upon its ends, ie pulling towards its centre.)



An easy way to calculate mechanical advantage is to count the number of parallel ropes in tension between the load and the effort. For my diagram above, the ropes to count are red. Count through where the MA and VR are listed.



Weakestlink's figures do account for friction in the system whereas my physics based diagram is a 'perfect' friction free environment.