So I was talking to a retired climber who still works in wireless, (someone still passionate about the industry) and he was telling me stories about all the ropes that broke throughout the years. You know what he didn’t mention, any steel cables that broke. He did mention how it has been determined that ropes broke due to wear, poor tagging, and knots. Remember that a knot will weaken the rope. My point here is to make sure you know what the job is and that you’re prepared.
No argument that rope is way cheaper, but think about the purpose before you do the job. We know that each one has a slightly different purpose, rope and steel cable. What are you pulling? What is the combined weight of what you’re pulling up? How high? Is it a serious load that will strain the rope? What shape is your rope in? Do you need a steel rope/cable for the load?
To be honest, when you are using the small Capstan hoist you would only use rope, but aren’t you envious when you see the big drum hoists being used by other crews? Do you have hoist envy? Be honest!
So when pulling up the load remember that the weight is only part of the equation. If the load weight is heavy you need to account for the rope and maybe the drag, Remember that the block will not only have to hold the weight of what you are lifting but also the weight being pulled by the hoist. So it would be lifting 300lbs and the hoist would be pulling 300lbs, so double the weight and add the hardware and rope. I am just saying that when the rating of the rope or cable is close to the load, make sure you think of everything. But, I digress.
OK, OK, I know, there is an application for both nylon and steel ropes. So let’s focus on the winch use. When using a hoist, a full winch, not a small capstan that most crews use on the back of their truck hitches. Let’s talk a drum hoist that is used to haul up heavy loads. Will a rope work for this? Maybe, but think about what you will be pulling up. Make a plan ahead of time. I know that the broadcast guys and larger tower builders already know what to do and have the setup with the steel cables already. They know what they need to do the work. If you are just beginning to get into the heavy loads with the big boy hoists, then make sure you know what you are getting into. You may know rigging, but don’t overlook the tools you will need to do the work properly.
I have seen ropes break usually due to getting snagged or hung up so it’s something to consider when rigging. Make sure you have a plan for the tag line, if you have steel cable you could have serious problems if you get hung up on a guy or another antenna on the way up.
I am told that some people often use ropes for heavy loads. If you have the money for a serious hoist, you should have the money to get a seriously strong and long steel cable, whatever length you need. Rope is very strong, don’t get me wrong, make sure you know your load rating. Steel rope is strong and you need to know its rating. Anytime you work with any load, hoist or no hoist you need to know the rating of your working rope or cable. It is your job as defined by OSHA. You also need to know everything about the winch. It matters when you are going to determine how much to take up at a time or how you plan to use it.
What if the load is a human load? What if the load is a crew mate? What if the load is a buddy that says, “Take me up with the load!”? Would you trust a rope then? This is something you should seriously think about when hauling people up and down using a winch, with a rope. Ropes wear much faster, ropes knot up, ropes get weak from many different things. Pay attention to the rope! Pay close attention to your tools being used at the site before, during, and after the job. Someone’s life may depend on it.
I know that rope is the most common tool used in the industry. I can’t think of many installations where you didn’t use rope. Even when you had a hoist with steel cable chances are you used the rope for the safety line and for the tag line. You can’t be in this business without rope.
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When using the rope for the load line, you may have issues when lifting heavy loads not because of the load rating, but because of the way you knotted the rope or maybe the rope gets a knot in it somewhere up high on the tower. If the rope gets knotted up, get the knot out before handling a load. It takes time. What would you do if you saw a knot in the load rope? Would you and your crew mates just say, “don’t worry about it”? Is that the smart and safe thing to do, of course not! You may think that it’s no big deal, but now you know better. You know the load and how knots weaken the rope. So being lazy in not an option. That is what gets people killed! Yet so many of you will ignore a knot is a load rope because of the schedule. Steel cables rarely get a knot in them, because steel has different properties and if it gets bound, it may break before it would knot up. I never saw anything like that happen, but it’s possible.You should know by now that a knot weakens a rope by 50% or more. Don’t believe me? I have information below that shows you the rope weakness. Then look at these, http://www.bethandevans.com/pdf/8_strength.pdf and http://www.netknots.com/rope_knots/ and http://en.wikibooks.org/wiki/Knots/Properties_of_knots and https://www.physicsforums.com/threads/tying-knots-in-rope-s-tension-weakened-strength.344191/. I mean you should know that from your safety training.
The pros of using rope, it’s cheaper and easy to use. The cons are it knots easy, weakens easy, and wears out quickly!
The pros of steel cable is that it’s very strong, easy to spot damage (if you’re looking), and lasts a very long time because it wears slowly. The cons are its very expensive and heavy and harder to work with.
Be smart, be safe, and pay attention. Plan for what you will be doing!
To learn more about rope testing there is a great Facebook page, https://www.facebook.com/groups/RopeTestLab/ that shows information on rope stress as well as testing gear.
If you go to http://davidschmidtwriting.com/busted.htm you will see it has a good list of how different knots weaken the rope. David Schmidt has in his blog the following. (He has a great reference!) He is writes for SAIL Magazine Information below is taken from David’s article. This is a good reference. I know most of you use Kevlar or nylon kernmantle ropes so this is mostly for a reference.
1/2-inch double-braid nylon is a dynamic rope (it elongates under load) and is commonly used as docking line or for towing a dinghy. Its rated Broke at is 10,800 lbs.
Bowline: Broke at: 5,983lbs, strength lost: 44.6%
Clove hitch with two half hitches: Broke at: 7,021 lbs, strength lost: 35%
Round turn and two half hitches: Broke at: 5,148 lbs, knot rolled open in all three tests before the rope snapped, knot slipped: 52.33%
Figure 8: Broke at: 6,227 lbs, strength lost: 42.33%
Double fisherman’s knot: Broke at: 5,820 lbs, strength lost: 46.1%
Double-braid splice: Broke at: 8,384 lbs, strength lost: 22.37%
Sta-Set (double-braid polyester) is a static rope that is commonly used for sheets and halyards and as general-purpose cord; 1/2-inch Sta-Set’s rated Broke at is 10,200 lbs.
Bowline: Broke at: 5,617 lbs, strength lost: 44.9%
Clove hitch with two half hitches: Broke at: 6,471 lbs, strength lost: 36.6%
Round turn and two half hitches: Broke at: 6,492 lbs, knot rolled open in all three tests before the rope snapped, knot slipped: 36.37%
Figure 8: Broke at: 5,352 lbs, strength lost: 47.5%
Double fisherman’s knot: Broke at: 5,250 lbs, strength lost: 48.5%
Double-braid splice: Broke at: 8,934 lbs, strength lost: 12.4%
Endura braid (rope with a 100-percent Spectra core and a polyester cover) is a static rope used for sheets and halyards; 1/2-inch Endura Braid’s rated Broke at is 19,300 lbs.
Bowline: Broke at: 7,855 lbs, strength lost: 59.33%
Clove hitch with two half hitches: Broke at: 7,448 lbs, strength lost: 61.44%
Round turn and two half hitches: Broke at: 6,166 lbs, knot rolled open in all three tests before the rope snapped, knot slipped: 68%
Figure 8: Broke at: 7,713 lbs, strength lost: 60%
Double fisherman’s knot: Broke at: 6,268 lbs, strength lost: 67.5%
Core-to-core splice: Broke at: 20,594 lbs, strength lost: 0%
Steel Rope/Cable Information
Steel rope is hard to rate in one table because there are so many different types. Just like rope there are strands that are wrapped around each other and they bound in some way. Normally there is galvanized steel and stainless steel, both very strong.
A good overview is at http://www.wcwr.com/catalog/webcat.pdf to learn more on steel rope and cable. It goes over the types of cable that are out there and what the advantages are.
I got this table from http://www.engineeringtoolbox.com/wire-rope-strength-d_1518.html where they list the standard rating of wire rope, 6 strand by 19 wire.
|Rope Diameter||Minimum Breaking Strength||Safe Load|
Another great steel rope reference is at https://www.wiscolift.com/pages/Wire-Rope-and-Cable.html that shows the rating of cables and the styles which I have listed below.
Another resource is http://www.rigging.net/wire.html where they had this table.
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