When you’re hauling cargo on a flatbed (or any open deck trailer), your tiedown work is out in the open for everyone to see, including DOT roadside inspectors. How you secure your cargo when transporting it from one place to another is important, because if you're not aware of how you're strapping down your load, you could create risk or damage to the cargo, others around you, and even yourself.
Knowing the difference between direct and indirect tiedowns, as well as understanding the rules of aggregate working load limit (WLL), is critical to safe cargo securement. Read which cargo securement method is right for your job, and how to calculate aggregate working load limit.
What’s the Difference between Direct and Indirect?
Direct tiedown is a tiedown that’s intended to provide direct resistance to potential shift of an item. Basically, one end of a direct tiedown is attached to the cargo itself.
Photo Courtesy of TruckingTruth.com
An indirect tiedown is a tiedown whose tension is increasing the pressure on the cargo on the deck of the vehicle. You’re using chain or straps that’s going from, over, or through the cargo, and then back to the trailer.
Photo Courtesy of TruckingTruth.com
How are Tiedowns Attached in Direct or Indirect Securement?
As we mentioned, direct securement is where the tiedown goes from the trailer to the load. This means going straight from one side of the trailer to the same side of the load. Direct securement reduces the working load limit by half as it doesn’t spread the force of the tiedown to the entire tiedown.
Indirect securement goes from, through, or over the cargo and then back to the trailer. In other words, it’s using both sides of the trailer for securement where you find the anchor point, and you use chains or straps to put it over or around the cargo to the trailer point. This allows the entire working load limit to be used on the tiedown point it’s tied to, over, or through, as long as it goes from one side of the trailer to the other.
The method you use will depend on your setup and your cargo. You need to make sure it’s sufficient to hold your cargo in place. To ensure you’re compliant, read FMSCA’s cargo securement rules.
We also recommend reading the dos and don’ts on cargo securement to learn more about cargo securement.
FMSCA’s Working Load Limit Rules
Now that you read the difference between direct and indirect tiedowns, you need to know the rules of working load limit (WLL), especially aggregate working load limit.
Working load limits determine how much weight or force tiedowns and other securing devices can secure without breaking. The aggregate working load limit is the sum of the working load limits for each device you use to secure your load. When knowing how many ratchet straps you need, FMSCA states:
“The aggregate working load limit of any securement system used to secure an article or group of articles against movement must be at least one-half the weight of the article or group of articles.”
To determine the number of ratchet straps for your job, read how many tiedowns straps do I need to secure my cargo?
How To Calculate Aggregate Working Load Limit
To calculate Aggregate Working Load limit, add together:
- 50% of the working load limit of each tiedown that is attached to an anchor point on your vehicle, and
- 50% of the working load limit of each tiedown that is attached to your vehicle and goes over, around or through your cargo.
Keep in mind that the aggregate working load limit of any securement system must be at least 50% of the weight of the cargo being secured.
Tie Down Straps from US Cargo Control
To ensure safe transport for both your cargo and your staff, all of our ratchet straps have been extensively tested for safe use, and have labels with working load limit (WLL) information. Most also meet requirements / guidelines from several key authorities:
- Commercial Vehicle Safety Alliance (CVSA)
- Department of Transportation (DOT)
- Web Sling & Tie Down Association (WSTDA)
- North American Cargo Securement
If you don’t see what you’re looking for, we can create custom ratchet straps for you. Whether you need one simple assembly or multiple intricate configurations, we can use any combination of strap size and fittings to create the perfect tie down solution. Just fill out our form or call one of our product experts at 800-969-654 to learn more!
More Trucking Equipment from US Cargo Control
If you need additional trucking equipment, we have everything you need to outfit your truck. From heavy-duty tarps, corner protectors, and transport chain and binders, we'll make sure to get you what you want, when you need it. Start by shopping by trailer type.
Other reads on Cargo Securement and Tiedowns: