Marine Crane SWL: The Ultimate FAQ Guide

The SWL is a crucial safety consideration in marine crane operation as it ensures that the crane is not overloaded and operates within its capacity.

Being aware of the SWL of a crane and operating the equipment according to its specified SWL can prevent lifting accidents and prevent damage to the crane.

What is the safe working load of a marine crane?

Safe Working Load (SWL) is the maximum weight that a crane can lift with rated load or other lifting accessories (rope, sling, or chain) can bear while lifting, hanging or lowering in safe range.

This value is prominently displayed on the lifting equipment, typically on the crane’s boom or jib, to indicate its maximum working capacity. It may also be referred to as the “load rating” or “workload limit.”

Since telescopic boom cranes have multiple lifting points, we will identify multiple SWLs for them.

How to determine the safe working load of a marine crane?

OUCO ensures that the lifting equipment’s rated load is accurately and reliably determined by conducting load testing before the crane leaves the factory.

During load testing, the identified safe working load may be exceeded for testing purposes to determine the maximum load-bearing capacity.

If you purchase cranes from other brands, it is important to refer to the manufacturer’s instructions and specifications.

Load Test in OUCO Factory

What is the lifting equipment?

All machines used to lift, lower, or move loads and materials is defined as lifting equipment, for example:

  • Cranes, winches, hoists, lifters and spreaders, etc.
  • Overhead monorail systems
  • Mobile or aerial work lifting platforms
  • Vehicle inspection lifts
  • Pallet Jacks
  • Forklifts and Material Handler, etc.
  • Vertical Conveyor Belts
  • Jackups

In addition, some small things you may not have noticed are also in the category of lifting equipment, such as:

  • Ropes, chains, slings, shackles etc.
  • Unloader, eyebolt
  • Electric Hoist
  • Construction worker’s safety belt
  • Hydraulic Jacks
  • Manual chain blocks, pull lifts, etc.

How to improve the Safe Working Load of a crane?

One way to increase the SWL of a crane is to optimize the section thickness and use high-density and lightweight materials, such as high-strength steel plates Q355, Q690, and BS650.

Another way is to improve the section shape of the crane boom by using multiple steel plates welded to replace the quadrilateral/triangular boom with a polygonal boom.

Upgrading crane components, such as using tougher and stronger wire rope, hooks, pulleys, or winches, can also improve the SWL.

Increase the stability, outriggers or pads can be used to ensure the machine is on a stable footing, reducing the risk of tipping over and allowing for a slight increase in the maximum load.

Finally, remember to seek the advice of qualified crane designers and test your crane after making any modifications.

What factors should be considered in the design of crane booms?

  • Geometry of the boom cross section
  • The material of the steel plate used for the boom
  • The angle of the boom cross-section and the length of the sides
  • In the case of telescopic boom cranes, the mass, length and center of gravity of each section of the boom must also be considered
Marine Crane Base
Marine Crane Base

What is the difference between the SWL of marine cranes and offshore cranes?

The safe working loads for marine and offshore cranes can differ due to unique operating conditions and environmental factors.

Marine crane SWL: The weight lifted by the crane through the hook, excluding the weight of gears, blocks, hooks, and wire ropes while ensuring safety.

Offshore crane SWL: The rated static load that each complete set of cranes can safely lift on the cargo hook, including the weight of gears, blocks, hooks, and wire ropes.

And offshore cranes are designed with higher load capacity and advanced safety features to ensure safe and efficient operation in challenging offshore environments.

Does the safe working load of the crane change?

In a crane or lifting device designed with a pre-set safety factor as the standard, its safe load may change over time.

With use, the lifting equipment may experience wear and tear which can impact the pre-set SWL until it can no longer safely handle the workload for which it was designed.

Therefore, in order to ensure the accuracy and suitability of the pre-set SWL, components that are prone to wear or failure need to be regularly inspected, repaired, or replaced.

Quarterly checks and tests are necessary to maintain the safety and reliability of the lifting equipment or device.

How to calculate the safe working load of a crane?

To determine the SWL of a crane, you first need to identify the crane type, boom length, boom luffing angle, and weight and distribution of the load. Then, the SWL is calculated based on the weight of the load, the angle and the radius of the boom.

It is essential to note that measurements should be taken on flat ground, in a normal position and environment by a qualified operator. All relevant factors should be considered before operation, and consulting with a professional is recommended.

Moreover, the SWL should never be exceeded during operation to avoid accidents or structural failure.

Two methods can be used to calculate the load capacity of a crane: geometry and load chart.

Geometry Method:

To calculate the load capacity accurately, you need to measure the jib, cables, and ground to form a triangle. Measuring the dimensions of this triangle will allow you to make approximate crane load calculations.

The standard formula for calculating the maximum lifting capacity of a crane:  (radius between the ground and load) x (lifting height x lifting capacity)/100.

However, it is important to take into account the base of the crane to shorten the actual radius slightly.

Load Chart Method:

All crane manufacturers provide capacity charts for their cranes, which can be used by operators to estimate the load capacity before and after each job without complex calculations.

Simply determine the required boom length to lift a given load for any distance or height, as identified on the load chart.

Crane Capacity


The information provided above outlines the concept of safe working load by OUCO.

If you still have questions about SWL measurement and specifications, please do not hesitate to reach out to our team of professionals at OUCO for assistance.


Recommend Reading:

Why Are Most Cranes Yellow?

What is the Boom of a Marine Crane? 8 Things You Need to Know

Everything You Need To Know About Marine Crane Structure

Scroll to Top