Calculating pulley load requirement for winch - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Garage - Tools
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 05-18-2009, 10:32 AM
cboy's Avatar
Member
 

Last journal entry: Finished
Last photo:
Join Date: Jan 2004
Location: Atwater, CA
Age: 69
Posts: 3,915
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Calculating pulley load requirement for winch

When running a winch cable through a pulley (or two) to increase the winches pulling capacity, how do you calculate the load requirements for each pulley.

For example, if you use just one pulley (doubling the pulling force and halving the speed of the pull) should the pulley be rated for the full weight of the load being moved or half the rate?

And when using two pulleys, should the load rating for each pulley be rated for the total load being moved or 1/3 of the load?

    Advertisement
__________________
Always learning...and sharing what I've learned. The Scratch-Built Hot Rod.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 05-18-2009, 11:13 AM
Registered User
 

Last journal entry: More painting pics
Last photo:
Join Date: Feb 2007
Location: Ohio
Posts: 371
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Good info here
http://en.wikipedia.org/wiki/Block_and_tackle

When searching try - block and tackle, mechanical advantage.

You probably know this but top block should always be rated for at least weight of total load but preferably more for some safety factor, and if only two blocks are used then both blocks should be rated total load regardless of mechanical advantage as they will be carrying full weight.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 05-18-2009, 11:40 AM
Registered User
 

Last journal entry: More painting pics
Last photo:
Join Date: Feb 2007
Location: Ohio
Posts: 371
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
To explain more. A pulley is rated at it's weakest point, usually the part that is attached to the hoist/ceiling/girder etc. or the part that is attached to the load.

This shackle, eye or fitting will always carry full load regardless of mechanical advantage if only one block is used as an attachment point at either end. It is only when two blocks are used at two different points e.g. two hooks on each side of an engine that you can reduce the rating of the block by half.

Hope that explains it better.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 05-18-2009, 11:40 AM
cboy's Avatar
Member
 

Last journal entry: Finished
Last photo:
Join Date: Jan 2004
Location: Atwater, CA
Age: 69
Posts: 3,915
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Quote:
Originally Posted by scrimshaw
You probably know this but top block should always be rated for at least weight of total load but preferably more for some safety factor, and if only two blocks are used then both blocks should be rated total load regardless of mechanical advantage as they will be carrying full weight.
That's what had seemed logical to me but I DIDN"T know for sure...so I'm glad I asked. So I'm assuming that if you had two separate pulleys on two separate axles on one end of the pull, that the load for each pulley would then be half the weight being moved.
__________________
Always learning...and sharing what I've learned. The Scratch-Built Hot Rod.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 05-18-2009, 12:12 PM
cboy's Avatar
Member
 

Last journal entry: Finished
Last photo:
Join Date: Jan 2004
Location: Atwater, CA
Age: 69
Posts: 3,915
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
The other factor at work here is that this is a trailer winch application not a hoist application. So I'm not dealing with a "dead weight" load. Rather, I'm pulling that weight across flat ground and then up the ramps of the trailer. But to be one the safe side I was trying to get my winch and pulley set up at, or close to, a "dead weight" situation...then I would know I was well within a decent safety factor in terms of a trailer winch pull.

Turns out, I'm not going to meet my "dead weight" load goal. I'm estimating the present weight of the car at 1200 lbs (no motor or trans). The pulley at the "car" end of the winch setup is rated at 800 lbs. The pulley at the winch end is rated at 650 lbs but it is separate from the winch itself so my understanding is this would actually be safe for up to 1300 lbs. The winch itself is rated for 2000 lbs total and is rated to pull 1500 lbs with the two pulley setup I am using.

Given the fact that I'm pulling sideways and up the ramps, I think I'm within the ballpark with the pulleys I have.
__________________
Always learning...and sharing what I've learned. The Scratch-Built Hot Rod.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 05-18-2009, 01:34 PM
schnitz's Avatar
Member
 
Last wiki edit: Building a new shop
Last journal entry: Christmas 2008 came early!!!
Last photo:
Join Date: Jan 2004
Location: Wausau, Wisconsin, in a house...
Age: 39
Posts: 1,163
Wiki Edits: 54

Thanks: 8
Thanked 1 Time in 1 Post
Dewey, two other things (just for safety). When winching, stand off to the side, not in the direct "line of fire" of the cable. Also, after you connect the winch, drape an old blanket over the top of the cable. That way, should the unthinkable happen, you will ease some of the inertia of a snapped cable. It's not good when it happens, but it can and does. Anything you can do to slow the cable's momentum is a good thing.


In a while, Chet.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 05-18-2009, 04:15 PM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,900
Wiki Edits: 0

Thanks: 0
Thanked 72 Times in 60 Posts
When designing a winch pulley system every pivot has to be rated for the dead weight load plus safety factor. The load pulls on each pivot with the dead weight load.

Its not split!
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 05-18-2009, 08:00 PM
Registered User
 

Last journal entry: More painting pics
Last photo:
Join Date: Feb 2007
Location: Ohio
Posts: 371
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by cboy
That's what had seemed logical to me but I DIDN"T know for sure...so I'm glad I asked. So I'm assuming that if you had two separate pulleys on two separate axles on one end of the pull, that the load for each pulley would then be half the weight being moved.
Yes this is correct although we are assuming the load is shared equally between the two pulleys. If the load becomes unbalanced one of the pulleys will be taking more than half the weight being moved and the other one less.

edit: After reading this again I realise that even if the blocks are used side by side at the same attachment point they will still share the load as long as a connection method is used that will allow this. The attachment point on the load however will see the full weight.

Last edited by scrimshaw; 05-19-2009 at 05:15 AM.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 06-07-2009, 10:09 AM
S10 Racer's Avatar
http://www.warsprints.com
 

Last journal entry: W.A.R. (Wingless Auto Racing) Sprint Car Racing
Last photo:
Join Date: Nov 2007
Location: At The Dirt Tracks
Age: 55
Posts: 1,860
Wiki Edits: 0

Thanks: 3
Thanked 57 Times in 52 Posts
I think the industry safety factor standard is 3x.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 06-07-2009, 10:51 AM
grouch's Avatar
Registered User
 
Last wiki edit: How to document your project
Last journal entry: 1949 Olds -- Rotisserie, pt. 9
Last photo:
Join Date: Jul 2004
Location: KY
Posts: 1,143
Wiki Edits: 2

Thanks: 0
Thanked 0 Times in 0 Posts
You should consider the pull that is required to get that dead load to start to move. That can be a lot more than the weight, even if the load has wheels (consider bogged in the mud).

One movable pulley, at the load end, halves the strain on each line but that pulley, its hook or clevis and its axle still have to carry the full load. Same goes for that movable pulley and a fixed pulley at the puller end -- the strain on the line is 1/[the number of lines] but the strain on the block (pulley, axle, side plates, hook, etc.) is 1/[number of shared attachment points]. This all assumes a straight line pull. Sharpen up your trigonometry if you're pulling from some direction that doesn't coincide with the load's direction of travel -- for example, having the end of the line attached to a tree off to one side, a movable pulley on the load, and the puller hooked to a tree off to the other side.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 06-29-2009, 04:41 PM
Registered User
 
Last photo:
Join Date: Nov 2008
Location: in the garage
Posts: 240
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
4Jaw is right! Supposing you have 8000# winch and are going to use it to pull at full capacity and use a 'sheave' snatch block or whatever you want to call it... from the winch to that and then something else. I do believe the first piece is to be 16000#, not 8000#. If you look for "sheaves, snatch blocks, rigging" you will find many items and some associated configurations and load rating info. Good equipment is not cheap, and for good reason. Same with wire rope, chain etc Grade 40 is not 70 is not 100. Another important thing to look at is the radius your wire rope will be subject to along with the correct width 'pulley' for you wire rope. ALWAYS remember safety when doing anything using this type equipment. I can get a pic of what happens when a hitch receiver comes apart. My buddy's head was mere inches from where a guys receiver welds ripped off his truck send the big hunk smashing into his. Most important is to not overload whatever equipment you are using, this can prove deadly.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 06-29-2009, 06:45 PM
Registered User
 

Last journal entry: More painting pics
Last photo:
Join Date: Feb 2007
Location: Ohio
Posts: 371
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
You are talking about a vertical pull, and YOU CAN reduce the load by doubling the block. I suggest you read this--
http://en.wikipedia.org/wiki/Block_and_tackle

Last edited by scrimshaw; 06-29-2009 at 07:10 PM.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 07-03-2009, 09:48 AM
SuthnCustoms's Avatar
Crazy Ole Ironhead
 
Last photo:
Join Date: Jun 2006
Location: Georgia
Age: 53
Posts: 235
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Every response seems to be a good one here,I deal with this type of work daily Being an International Ironworker,one of our main objectives is safe rigging daily.

The one thing i didnt seem to see is the fact of a Fall and Snatch..which is if a load happens to get slack and fall and then it "snatches" the rigging.

A perfect example is a general rule and OSHA requirements is when tying off a safety lanyard to a safety harness,,the rigging AND tie off point must be able to handle a 5000# load capacity with an average weight of a 200# man to be within safe load limits.
The reason being is that even a small jerk of 200# can lead up to an equal weight of over 4000# if the load is "jerked" from slack,this wasnt a "calculated" or "theory" on paper,they actualy used a load cell and dropped 200# 8 foot and the load cell read over 4000#.
When we rig heavy loads,general rule of thumb is we rig for a minimum of 3 times the weight,even more depending on circumstances,like if its windy out,if the crane has to move the load in a tight area where the load may get hung up on something and then drop suddenly..etc etc.
The same thing could apply to a car getting hung up on the ramps because the ramps are putting extra load stress on the rigging because it is on an angle,and if the car happens to get hung up on something and the winch is still pulling and then suddenly pops loose from where it is hung up the load will snatch and jerk.

I would go at least double the weight capacity on rigging at a minimum on ALL the rigging...snatch bocks,cables and winch and hooks.

Also always remember..the heavier the load is,the more stress on a snatch,it is alot harder to stop 1000# on a snatch than it is on 100#,the load stress starts getting ALOT higher on the snatch factor as the weight increases.
Reply With Quote Quick reply to this message

Recent Garage - Tools posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Deep 2 groove short W/P pulley or serpentine? fastrehotrods Engine 19 01-27-2009 01:50 PM
90s SBC Power Steering Pump pulley Removal Help Mustangsaly Engine 12 10-08-2006 06:00 PM
Alternator Pulley Machining leejoy Engine 1 08-29-2006 06:13 PM
Strange pulley issue... Classix_Lover Engine 10 02-12-2006 07:12 PM
Squeeling Fan Belt - Out of true Pulley Billy Boy Engine 3 02-15-2005 06:51 PM


All times are GMT -6. The time now is 09:44 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.