What is D/d Ratio & Why is this Critical for Lifting Slings?

What effect does D/d Ratio have on lifting slings and their sling capacities?

You may wonder what D/d ratio is and what purpose it serves when lifting loads with different types of slings. After all, it can be confusing as there are multiple factors you have to take under consideration such as knowing the weight of the load, the sling’s working load limit (WLL), and the load’s center of gravity.

Identifying the D/d ratio when using any type of sling for a lift is critical, because if the lifting sling tightly bends over too much during the lift – the sling will get damaged. This could then lead to unsafe rigging practices. To have a safe lifting operation, continue reading more about D/d Ratio, and the types of slings we carry at US Cargo Control to identify which is right for your lift.

What is D/d Ratio?

The term D/d ratio works as a simple mathematical equation where you’re learning the diameter or distance of the load you’re picking up. It is the ratio of the diameter (D) around the object which the sling might be bent, which could be a sheave or another object, then divided by the overall diameter (d) of the sling being used.

The Formula for D/d Ratio:

The diameter of the load divided by the diameter of the sling = D/d Ratio

Unirope's definition of D/d ratio
Photo Courtesy of Unirope

For example, you’re picking up an object that’s 12 inches in diameter and you use a 3/8″ chain to pick it up. This is 12″ divided by 3/8″ = 32, which 32 is the D/d Ratio. If the diameter is 10″ and the diameter of the rope is 1/2, the D/d Ratio is 20.

Why is D/d Ratio Important?

The D/d Ratio has a tremendous impact on sling capacity when using slings like wire rope, chain, polyester round slings, and nylon slings. It can determine the sling’s efficiency or capacity reduction, and allow you to make corrections before continuing the lift. If you see a tight bending of the sling, this means there’s a smaller than recommended D/d Ratio.

Using a smaller D/d Ratio that’s not recommended for your lift can aggravate the bending motion. This can result in fatigue, irregular wear, and increased deterioration. Once this occurs, you’d have to perform frequent inspections and go through costly wire rope replacements.

Each sling type has different strength efficiencies, which is why we included a table below that describes the efficiency of various sling constructions with standard D/d Ratios:

Mechanically spliced, single-part slings25 times rope diameter
Hand-Spliced, single-part slings15 times rope diameter
Braided multi-part slings of 6 parts25 times component rope diameter
Braided multi-part slings of 8 parts25 times component rope diameter
Helically laid multi-part slings25 times component rope diameter
Hand-tucked grommets and mechanically joined grommet5 times sling body diameter
Union Rope’s Rated Capacity, Design Factors, and D/d Ratios

What Will Sling Damage Look Like?

wire rope damage

When a sling is tightly bending around another object, there is a loss of sling capacity. As D/d Ratio decreases, this capacity loss becomes greater and the sling will become less efficient. There is a direct correlation between D/d Ratio and the efficiency of the sling (or rated capacity).

Not only is it important to understand the D/d Ratio of the lifting sling, but it’s also equally important that fittings and rigging hardware used in connection points are adequately strong and spatially correct. For instance, if smaller, alloy shackles are used, the webbing edges can get damaged and sling efficiency is lowered due to the bunching of the webbing.

When not used correctly, this could result in bunching, and being crammed into a space will reduce sling efficiency and capacity. Basically, putting too many slings in an undersized shackle or another fitting can result in lost strength.

To understand what slings or fittings should you use for your job, give our team a call at 800-404-7068, and we’ll be glad to assist you.

Different Type of Slings

Now that you have an idea of what D/d Ratio means, continue reading on what lifting slings you should use that’s worth the investment for your lifting situations.

nylon lifting slings

Nylon Slings

Known as synthetic web slings or nylon web slings, our nylon lifting straps perform well for lifting breakable, delicate objects. Its heavy-duty synthetic material has great stretch and flexibility that help the slings mold to the shape of the load. Not only that, the nylon lifting sling’s material is treated to improve abrasion resistance and reduce wear, even in the most rigorous lifting applications.

Chain Slings

If you’re depending on a sling that requires extra strength and durability, the chain sling is your best choice. The chain lifting sling is the strongest and most durable type of sling and is highly popular to use for heavy lifting operations. They will perform better than polyester round slings or nylon slings because they’re more durable, tolerant to hot temperatures, and cut-resistant.

chain lifting sling
Polyester round sling

Polyester Slings

Manufactured in the USA from a continuous loop of polyester yarn that creates exceptional strength, the round slings are versatile, pliable, convenient, and cost-effective. Because of their many benefits, you can use these in vertical, choker, or basket hitches, making them effective to lift a wide variety of cargo!

Wire Rope Slings

Known as steel cable or wire sling, these are more durable than synthetic slings and more cost-effective than chain slings. Wire rope slings are an excellent choice not only for lifting, but also for hoisting, towing, or anchoring loads. Its fabrication offers abrasion-resistance and heat-resistance, as they are made by weaving individual strands or wire around a core.

Wire rope sling

To understand what lifting slings you should use for any lifting operation, read 3 Factors to Consider When Choosing Lifting Slings.

Tackle the Toughest Lifting Jobs with High-Quality Rigging Hardware

We know the importance of quality when it comes to rigging supplies. We carry a variety of rigging hardware, as well as lifting beams and spreader bars that can lift heavy loads safely and efficiently.

Need a custom lifting sling? We can do that! We can customize a lifting sling to meet your specific needs.

Contact our sales team today at 866-444-9990. Our team of product experts is here to answer any questions about rigging hardware, lifting slings, and more.

New Products: Nylon Bridle Slings

bridle-sling-300x162-redOur nylon lifting slings category continues to expand with the most recent addition of 600+ new Nylon Bridle Slings.

A nylon bridle sling offer s both incredible strength and ease of use due to its light weight and ability to collapse for easy storage.

Other benefits include:

  • Four configurations available (single leg, double leg, triple leg, or quad leg) to meet a variety of applications.
  • The synthetic nylon is more flexible than chain or wire rope.
  • Quality hardware from Pewag ensures quality. Oblong links are manufactured in Grade 100 alloy steel; hooks are all in a Grade 80 alloy steel.
  • Each bridle sling leg stretches approximately 3% at rated capacity, helping to absorb shock during a lift.
  • Nylon fabric will not conduct electricity like a chain sling or wire rope sling.
  • Multiple leg design in the 2-, 3-, and 4-leg styles allow the bearing points to be rotated, which extends the sling’s working life.
  • Available in two different ply thickness.
  • The 2-, 3-, and 4-leg styles can be used in different hitches, offering excellent versatility.

We offer three end fittings online- oblong, hook, and sewn eye. Each sling also has a master oblong link. Two widths (1″ and 2″) and two ply options (1-ply and 2-ply) are also available for order online.

Other recent additions to the nylon sling category include Drum Slings and Drum Lifters, as well as a request quote form for Custom Boat Slings.

Like all of our nylon slings, our nylon web bridle slings are made in the USA.

If you don’t see the sling you need, give us a call. We’re always happy to customize a bridle web sling assembly to your specs. You can reach our lifting slings product team at 800-660-3585.

Click over to our website to see all of our Lifting Slings & Rigging Slings, or click the buttons below to go directly to each category of nylon bridle slings.

single

double3

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Employee Recommendation: Nylon Lifting Slings

slingNylon lifting slings are extremely versatile products and some of our best-sellers. Sales Specialist Jon tells why in this video.

Click over to shop these specific categories of slings, and keep in mind that all of our slings are completely customizable. You can call Jon or reach any of our sales team members at 800-660-3585 to discuss options.

 

Expansion of Nylon Lifting Slings Selection Includes New Bridle Slings

Tim Guenther, CEO
Tim Guenther, CEO

A big goal we’ve initiated for 2013 is taking a good close look at all of our product categories. We want to be sure we are offering the products our customers need, at the best prices possible.

Our most recent overhaul was the updating of our nylon lifting slings. While we were already offering a wide selection of the most common lifting straps like eye & eye slings and endless slings, one area we were not covering was bridle slings.

An entire category of nylon bridle slings is now available, including single-leg, double-leg, triple-leg, and quad-leg options in a tough, durable nylon webbing.

A bridle nylon lifting slings offer some advantages over other types of lift slings because the leg design on the double, triple, and quad styles allow bearing points to be rotated with each use, extending the sling’s life. It also offers benefits in comparison to a similar lifting slings in wire rope or chain, since the fabric body offers more flexibility and is generally easier to handle. Nylon also stretches (each leg of the sling will stretch approximately 3% at rated capacity), which allows the sling to absorb shock and create a load distribution that’s more even.

Our bridle nylon lifting  slings are made in the USA and custom-made to your specifications so we ask that call our lifting sling sales team at 800-660-3585 to place an order.

Another new change to the nylon lifting slings page is the addition of a simple online form where you can request a price quote for a boat sling.

image of boat lifting slings order form

Find quote form here: Boat lift straps

Options such as keel pads, edge guard, and chine sleeves can be indicated, as well as sling length and weight requirements. Once submitted, a sales team member will contact you with a quote. Keep in mind that no boat is too big or too small, so feel free to call us whether need a single ply lift strap for a small boat like a kayak, or a thick 4-ply web sling for a travel lift or mobile boat hoist.

Our product lines are constantly evolving and we’re always interested in knowing what products our customers need. Leave us a comment below, email us at customerservice@uscargocontrol.com or give us a call toll free at 866-444-9990 and let us know what you’d like to see available on US Cargo Control.

-Tim