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#31
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#32
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And then, as in the original pull by using 3 blocks and 4 lines, all blocks static (not traveling, single sheave), what is the rated gross available pull? Additionally, if you would like to speak with an engineer at The Crosby Group, who I interface with, with their's and other HD industrial products and applications, the contact person and point is here below (a super knowlegeable guy, I might add): Brad Beall Product Engineer bradbeall@thecrosbygroup.com phone: 918-834-4611 x322 fax: 918-834-9447 And, sadly, I am correct, of you will check and listen to Brad very carefully. I have invited him to post here and verify. I've also added more information at Behold, here, if this is of interest to you and others: http://behold-the-rage.com/jeep_page22.html
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Robert A.M. Stephens 26 Jeeps-40 years of Jeepin and countin' http://behold-the-rage.com robert@behold-the-rage.com 406-755-9765 _______________________________ Have Jeep, Have Heart, Will Travel |
#33
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Robert A.M. Stephens 26 Jeeps-40 years of Jeepin and countin' http://behold-the-rage.com robert@behold-the-rage.com 406-755-9765 _______________________________ Have Jeep, Have Heart, Will Travel |
#34
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As long as its all straight line stuff, a real easy way to figure it out and just draw a line normal to the direction of force (winch line) and however many times the line crosses the winch cable is the # you multiply by to get total pulling capacity
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95 YJ - held together by magic "When in doubt, gas 'er out" |
#35
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If the blocks are moving, you get all sorts of math involved and some or all of the math you listed applies. If you're talking about fixing the snatch blocks to the pulling vehicle and the vehicle being pulled, the total avalable force with 3 snatch blocks (2 on the pulled vehicle, 1 on the pulling vehicle) is 48,000 pounds gross pull (assuming you're on the inner most layer of cable). That's assuming the blocks get the line as close to parallel as possible.
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1977 Cherokee: 360/TH400/QT/D44/D44 - Beavis 1984 CJ7: 401/SM465/Atlas/D44/9" - In progress 2004 Pontiac GTO: LS1/T56/M80 - My Free Gear Ratio Calculator (In Metric Too) |
#36
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Thanks Jeff & Robert.
I don't recall where I was when I snaped those pics. The oiler was the USNS Walter S. Diehl (T-AO 197). I believe I was on the USS John S. McCain (DDG-56), two days prior to Gulf War-II. Perhaps I was somewhere in the Northern Arabian/Persian Gulf. When you're out at sea for 6 months at a whack - you tend to forget sometimes where certain pics were taken because there's no land to judge things by - just LOTS of open ocean. |
#37
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Also, please call Brad at The Crosby Group, since they are one of the world's authority on heavy lift and pulling devices as well as applications. It would be really helpful for you and mudpup as a new learning curve for you. I've been doing this stuff a very long time, in the 'real', not only in Jeep stuff but logging, heavy equipment, and so on, and I really do know what I am talking about. In no way bragging or boasting however. I am correct. Just a thought, as best I can offer. BTW- on the 'pull strap' subject, you stated you were an engineer. What type if I may inquire. Thanks.
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Robert A.M. Stephens 26 Jeeps-40 years of Jeepin and countin' http://behold-the-rage.com robert@behold-the-rage.com 406-755-9765 _______________________________ Have Jeep, Have Heart, Will Travel |
#38
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Interesting read.
Robert, who copied whom without giving credit? http://www.dodgepowerwagon.com/glovebox/snatch.html
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Back in the saddle. |
#39
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I included the link on the reference links at the bottom of page 22, since I no longer had the copy other than the Crosby catalog-tech data. Does that help?
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Robert A.M. Stephens 26 Jeeps-40 years of Jeepin and countin' http://behold-the-rage.com robert@behold-the-rage.com 406-755-9765 _______________________________ Have Jeep, Have Heart, Will Travel |
#40
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However, every resource I can find that talks about multiple pulleys in the block-and-tackle arrangement, including the Encarta reference I posted earlier, shows that using multiple pulleys only adds 1x the force on the line for each wrap around a pulley. The fact that using a single pulley happens to double the force doesn't mean that using additional pulleys in a block and tackle arrangment will keep doubling the force. It just doesn't work that way. Who am I going to believe? The writers of text books and encyclopedias or some guy on the internet? Again, no offense intended. But here it is again: Work = force * distance. If I have a 12,000 pound winch that pulls 40 feet worth of cable, I have done 480,000 pound-feet of work. Work = 12,000 * 40 = 480,000 Running the cable through 3 snatch blocks as you have shown, I will have moved the truck 10 feet because that 40 feet worth of cable is removed equally from all lengths. Each length shortens by 10 feet, meaning the truck moves 10 feet. So, with 480,000 pound-feet of work and 10 feet of distance, what's the force on the truck? 480,000 = force * 10 Apply basic algebra 480,000 / 10 = force 48,000 = force Who's right?
__________________
1977 Cherokee: 360/TH400/QT/D44/D44 - Beavis 1984 CJ7: 401/SM465/Atlas/D44/9" - In progress 2004 Pontiac GTO: LS1/T56/M80 - My Free Gear Ratio Calculator (In Metric Too) |
#41
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This forum is generating great quotes for signatures today!
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Steve "Trackbar axle bolt - need FORK LIKE THINGY " |
#42
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#43
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By definition the mechanical advantage will be determined by the length of the line recovered divided by the distance traveled for a straight line pull. So 4 lines, or 3 pulleys, would equal 4 x 12000 = 48,000 lbf assuming an initial pull of 12000lbf. This also assumes the pulleys are ideal and the forces are in the exact same plane. However, since three pulleys were used the efficiency of the system would be somewhere between 80% to 85%, so with losses the actual pull would be closer to 38.4k to 40.8k. Ken
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03' TJ just starting to get broken in... |
#44
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with your theory on acheiving 96,000 lbs from the setup in the picture you somehow made you winch capable of pulling 24k lbs. It is simple physics. Each of the four attached lines to the vehicle is carrying an equal load....96k divided by 4 equals 24k lbs.
__________________
95 YJ - held together by magic "When in doubt, gas 'er out" |
#45
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__________________
1977 Cherokee: 360/TH400/QT/D44/D44 - Beavis 1984 CJ7: 401/SM465/Atlas/D44/9" - In progress 2004 Pontiac GTO: LS1/T56/M80 - My Free Gear Ratio Calculator (In Metric Too) |
#46
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If you ever want to talk to a nice and extremely knowledgeable gentleman in the recovery and rigging business, Mr. Brad Beall is phenomenal.
He cleared up many areas of myth and confusion for me. First off, snatch blocks and winching. It matters only how many lines are in the rigging that are parallel. 1 = x1 2= x2 3= x3 4=x4 It's that simple. Wire rope is dangerous when it breaks.
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I am Savvy. |
#47
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The gross pull rating (i.e. without the above losses factored in) would be 48,000 pounds. And we're talking about theoretical pulling capacities.
__________________
1977 Cherokee: 360/TH400/QT/D44/D44 - Beavis 1984 CJ7: 401/SM465/Atlas/D44/9" - In progress 2004 Pontiac GTO: LS1/T56/M80 - My Free Gear Ratio Calculator (In Metric Too) |
#48
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look at the picture I posted, it shows exactly how the forces work in that setup. There is no need to bother calling people up about a simple physics problem, besides this knowledge is a 1000 yrs old, everyone knows me and derf are correct
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95 YJ - held together by magic "When in doubt, gas 'er out" |
#49
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I'm not going to read this entire thread right now, but R.A.M. Stephens, where are you getting that extra 48,000 lbs of pulling power from? Just curious because it should be 48,000 total, not 98,000lbs, as you have drawn out. Draw a simple FBD and you will see. High school physics stuff here.
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ZJ on 35s |
#50
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btw- He did relate to me that he and Mr. Stephens have arrived at a consensus and the drawings on Behold are being modified as we speak.
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I am Savvy. |
#51
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One snatch block and two lines will typically be interpreted as doubling the power of the winch. Unfortunately the doubling is a function of two lines and not one snatch block. That's where the error came in. If you figure that a snatch block doubles each time one is used and it doubles the total before it, you wind up with Robert's calculations. The correct way is to ignore the blocks and count the lines.
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I am Savvy. |
#52
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__________________
1977 Cherokee: 360/TH400/QT/D44/D44 - Beavis 1984 CJ7: 401/SM465/Atlas/D44/9" - In progress 2004 Pontiac GTO: LS1/T56/M80 - My Free Gear Ratio Calculator (In Metric Too) |
#53
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#54
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It's kinda like tossing leaves under the rear of a TJ, it looks good on paper.
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I am Savvy. |
#55
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As much as I'd like to continue this conversation, I hear the desert calling. Ya'll behave while we're gone.
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I am Savvy. |
#56
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heh, I was just poking some fun, taking a line from his website, just good nature ribbing.
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95 YJ - held together by magic "When in doubt, gas 'er out" |
#57
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Please bear with me and I should have those up at the site shortly. Thank you for your input.
__________________
Robert A.M. Stephens 26 Jeeps-40 years of Jeepin and countin' http://behold-the-rage.com robert@behold-the-rage.com 406-755-9765 _______________________________ Have Jeep, Have Heart, Will Travel |
#58
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In light of that, with all these good posts, I am continuing and in the diagrams for both loads, you will learn something knew I hope, as it is intended. The two issues are static line pull, in which Mr. "Derf" and "mudpup" are correct, and a traveling line load, for which how the concrete truck was originally pulled out (not the re-pull), and I am correct. Watch the page 22 for updates here shortly an I think it will help. Thank you.
__________________
Robert A.M. Stephens 26 Jeeps-40 years of Jeepin and countin' http://behold-the-rage.com robert@behold-the-rage.com 406-755-9765 _______________________________ Have Jeep, Have Heart, Will Travel |
#59
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If possible, please go to the page 22 again for the diagram of traveling verses static block usage. Might help.
Thanks. http://www.behold-the-rage.com/jeep_page22.html
__________________
Robert A.M. Stephens 26 Jeeps-40 years of Jeepin and countin' http://behold-the-rage.com robert@behold-the-rage.com 406-755-9765 _______________________________ Have Jeep, Have Heart, Will Travel |
#60
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So if we look at your dynamic pully block diagram, there are two limits for the distance traveled. One limit occurs where the traveling block is fixed at the load, and we see the mechanical advantage will be 3 for an increase to 48,000lbf. The other limit is when traveling block is fixed at the winch, in which case the mechanical advantage will be 2 for an increase in to 24,000 lbf. So, this system will operate somewhere between 24,000 lbf and 48,000 lbf depending on where the pully is located. Without a reduction in distance traveled by a factor of 4, there is no way to get to 96,000 lbf. Ken
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03' TJ just starting to get broken in... |
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