Crane Boom Recoil from Sudden Loss of Load

Catastrophic crane boom backwards collapse caused by crane boom recoil from sudden loss of load can be avoided, even if crane boom stops are ineffective, or not fitted.  The video below explains the simple calculations needed.  These calculations should form part of a Naval Architectural Analysis for a mobile crane mounted on a barge.

Boom Backwards Recoil Collapse in Marine Salvage

Some of the sections from the video are shown below, beginning with an amateur video of a crawler crane boom backwards collapse on a barge during a salvage operation in 2018.

The next clip illustrates the crane boom recoil issue with a 1/12th scale model.  In the first part a heavy load is dropped when the model boom stops are not connected.  in the second part, the boom stops (which have springs in the model) are connected.

The Excel analysis finds both a closed form analytical solution to the maximum boom recoil angle and also provides a time domain integration of the boom pendant wire sudden tension reduction from the lost load.

The next clip shows the close comparison of the boom pendant wire tension change in the first 0.5 seconds after the load is dropped.  Both Excel and OrcaFlex predict that the tension becomes zero after 0.22 seconds.  During this time the pendant tension is accelerating the boom’s angular velocity.

The time domain motion of the boom angle is compared in the next clip, then the Excel closed form solutions for a range of dropped load sizes and initial boom angles is shown, for two different pendant wire sizes.

Floating Service Load Chart

A Floating Service Load Chart is required by US Army Corps of Engineers (USACE) Manual EM-385-1-1, Safety and Health Requirements, November 2014, for all mobile cranes mounted on barges, pontoons, etc.  This can be provided by the Load Handling Equipment (LHE) manufacturer.

Naval Architectural Analysis

If a manufacturer’s Floating Load Service Chart is not available, a floating service load chart may be developed and provided by a qualified registered engineer or naval architect, competent in the field of floating cranes.  STA provides the NAA Service.

Additional Codes and Standards

In developing a Floating Service Load Chart and de-rating any floating crane, the following codes and standards must be considered:

The relevant FRs do not mention crane boom recoil or boom stops.  ASME 30.5 specifies that boom stops shall be provided on mobile cranes to resist the boom falling backwards.  No design guidelines are given.  ASME 30.8 has similar wording.  P-307 requires boom stops to be checked, but does not mention precautions to be taken if the crane does not have boom stops. Similarly, EM-385 notes that a crane should have boom stops.  NAVCRANECEN Instruction 11450.2 gives a specific analysis to be performed to check if crane boom recoil will result in contact with the boom stops.  The load to be used in the analysis is stated with reference to the Floating Service Load Chart.

An example of a Floating Service Load Chart is shown below, with the crane boom recoil limitation on maximum hook loads also included.

An example of a safe lift at a high (77º) boom angle, on a barge mounted mobile crawler crane without boom stops is shown below.

A detailed structural dynamic analysis of the boom and the boom stops can be performed using OrcaFlex, as shown in the next example clip.


  • Calculation of maximum crane boom recoil angle from closed-form analysis equations in Excel
  • Calculation of maximum safe loads at high boom angles
  • Prevent backwards crane boom recoil accidents
  • Time domain “instant” solutions in Excel
  • Detailed time domain simulations relatively quick with OrcaFlex
  • Structural checks using non-linear dynamic analysis of boom stops and booms performed in OrcaFlex
  • Low cost, high value, advanced structural engineering calculations save lives and save money.

Cruise Ship Collision Barrier

A new type of Cruise Ship collision control barrier is under design and development.  The design brings a very large cruise ship (or any other vessel) gradually to a stop, converting the vessel’s initial kinetic energy to potential energy, which is stored in two structures on either side of the barrier.

Cruise Ship Collision

Cruise Ship Collision Barrier – Simulation with OrcaFlex

Hydrodynamic analysis with OrcaFlex is used to confirm and improve upon closed form analytical solutions developed by STA.

Designs have been developed for cruise ships up to 333m length with gross tonnage 150,000 and a starting collision velocity  of 6 knots.

Efforts on the project were interrupted in September 2017, by Hurricanes Harvey, which effected our Houston office, and Irma, which effected our Caribbean interests.

Marine Salvage Dynamics – Sewol Salvage

Sewol Side Lift Partly Emerged 1

Sewol Salvage: Stewart Technology Associates worked as Technical Advisors to Shanghai Salvage Company using STA software and were responsible for all dynamic analysis of the complex lifts in the open ocean environment.  All lifts are dynamically sensitive and involved cutting edge marine salvage dynamics. Analyses were performed with waves in the time domain using FEA (OrcaFlex).

Marine Salvage Dynamics of Sewol Salvage raised with ZPMC 12,000 ton floating crane and 1,200 ton lifting frame.

32 HMPE upper slings, 8 balance slings, 34 pairs of steel lower slings.

Fully coupled 6 DOF time-domain dynamic analyses in OrcaFlex with diffraction forces on the Sewol and ZPMC crane barge.  All individual sling tensions computed during all stages of the Sewol Salvage.

Sewol and Floating Dry Dock 1

Sewol wreck transfered to semi-submerged floating dry dock in open ocean.  OrcaFlex time domain dynamic analysis of three main vessels, lifting frame and all slings.

The following video describes how STA has examined the issues of unusually low freeboard and trapped water on the pontoon deck.

The video provides a description of how OrcaFlex is used to cope with time domain calculations of the wave motions of the floating dry dock when the deck becomes submerged and the buoyancy of the wing tanks is of critical importance.

More details of the accident can be found at:



The  portfolio item below provides a short OrcaFlex Tutorial with a Mooring Analysis example.

SPM Squall Analysis

CALM Buoy modeled in OrcaFlex

CALM Buoy modeled in OrcaFlex used in Wind Shift, or Squall Analysis of Suezmax Tanker

CALM Wireline1

Wireline view of SPM CALM Buoy modeled in OrcaFlex.

A Suezmax tanker is moored via a hawser.  View list of STA software.

SUEZMAX Perspective1

Suezmax tanker seen in shaded perspective view in OrcaFlex, moored to SPM CALM buoy during squall analysis.

The portfolio item below provides a short OrcaFlex Tutorial with a Mooring Analysis example.

6 Ways Riser Analysis Can Improve Riser Design

Published by Stewart Technology Associates on July 18, 2016

Dynamically positioned drill ship in storm conditions.
Riser tensioners seen actively tensioning riser until 7:50 on the timer.
Riser emergency disconnected, EDS activated at the BOP at 7:50 and the top end raised about 3 meters.
Moonpool with hung-off riser shown after EDS activated.

The portfolio item below provides a short OrcaFlex Tutorial example of Mooring Analysis.

View list of STA software.

In the offshore oil and gas industry, risers connect drilling and production platforms to the sea floor. They transport oil and gas from the well to the platform or inject fluids into the well to facilitate drilling or production. Risers are critical to the operation of the platform, and any failure could mean a loss of production capabilities and a serious loss of profit.

Risers enable the platform to move up and down, or side to side during production and drilling operations. They also must efficiently transfer fluids to and from the sea floor. The impact of wave action, tidal action, high pressures, low temperatures, and corrosion must not affect the platform’s movement. In order to do the job properly, with minimal maintenance and downtime, an extremely efficient and reliable riser design is required.

In the past, the main way to evaluate a riser design was through building prototypes, testing them extensively in real-world conditions and redesigning the riser until it met all the requirements and specifications necessary. This could be a tedious and expensive process, and it could still yield sub-standard designs, in some cases.

Today, riser analysis takes out some of the guesswork. Using special software packages and talented engineers, riser analysis can model the forces at work on a potential riser design. It looks at waves, tides, temperature, pressure, vortex forces and vibration to determine the strong and weak points of a design, and improves them to avoid structural fatigue, leaks, inefficient fluid transfer and other common problems. This can reduce design and prototyping costs, and lead to a final product that is efficient, durable, safe and low-maintenance.

Riser analysis is now a critical tool for improving the performance of drilling and production operations, and here are a few of the ways it can help to improve riser design:

1) Determining the Right Type of Riser for the Job

The type of riser used for a particular application will depend on the type of platform, the depth of the seafloor, the depth of the well and the sub-sea conditions. Riser analysis can be used to determine the best type of riser for the application, and help perfect the design and adapt it to particular equipment. The most common types of risers include:

  • Top-tensioned riser: A rigid riser that is held in place vertically through tension, and allows both lateral and vertical movement through a flexible connection between the riser and the platform.
  • Steel centenary riser: A curved riser used to connect two platforms, or to connect the platform to the sea floor, it can withstand some motion and is used on spars, tension-leg platforms and floating production storage and offloading platforms.
  • Flexible riser: Made from flexible pipe, these risers can withstand horizontal and vertical motion.
  • Pull-tube riser: A hollow tube attached to the center of the platform, it houses a pipeline or flowline that is pulled from the seafloor with a cable, and is used primarily on fixed platforms.
  • Attached riser: Used on fixed platforms, compliant towers, and concrete gravity structures, these risers clamp to the side of the platform and are connected to the sea floor with an export pipeline or a flowline.
  • Riser tower: A combination of a steel tower and riser that is used for deepwater drilling, a buoyancy tank is used near the surface to keep it in place through tension and flexible lines connect it to the platform
  • Drilling riser: Transfers drilling mud and other fluids to the seafloor during drilling operations and is only a temporary connection.

With riser analysis, you can choose the best riser for the situation, adapt an existing design for use with your equipment, or create an entirely new or hybrid design, then test and improve the riser before it goes into production.

2) Improving Riser Structure

The overall structure of the riser must be able to withstand the waves, the tides, the high pressures and the low temperatures present below the ocean surface. Riser analysis can be used to model these forces at work on your riser design, determining how they affect individual areas and structures of the riser and how they affect maintenance requirements and the longevity of the system. Using the resulting data, the design can be improved to make the riser stronger, more stable and safer.

3) Determining Insulation Efficacy

In deep water, the temperature can drop significantly, reducing the viscosity of oil and drilling fluid and slowing down production and drilling operations. To combat this, many risers incorporate insulation to keep the fluids at a more desirable temperature so that they can flow properly. Riser analysis can be used to design and test the insulation, and find problems that may reduce the temperature and fluid flow within the riser. By improving the design of the insulation, riser analysis can help to increase production efficiency, leading to higher profits.

4) Designing and Testing Valves

Valves in the riser help control the flow of oil, hydraulic fluid, and other substances through the system, and they must operate in cold, high-pressure conditions without frequent failures or maintenance. Riser analysis can be used to model the flow of fluids through the valves and to find failure points and other problems that can reduce their life cycle or cause leaks. With the data, the valve can be reengineered to promote longevity and efficient fluid flow.

5) Designing Buoyancy Tanks

Buoyancy tanks are critical to keeping a riser stable and accessible in sub-surface conditions, and if they malfunction, oil spills or other problems could occur. Riser analysis can help to design and test the buoyancy tanks, improving their design so that they are safer and more stable, regardless of the sub-surface conditions.

6) Improving Riser Flow

Production risers must carry fuel to the surface efficiently to meet production goals and maintain the platform’s earnings. Riser analysis can be used to model how oil and drilling fluids flow through the riser, determining points of turbulence or restriction. By improving the design of the riser and eliminating these problems, production rates, and profits can be increased.

Riser analysis is a powerful tool that can make an oil platform safer, more efficient, and more productive by improving every aspect of riser design, from the seals to the valves and the overall structure.


3 Projects That Can Benefit From Hydrodynamic Analysis

Published by Stewart Technology Associates on June 20, 2016

View list of STA software.

The portfolio item below provides a short OrcaFlex Tutorial example of Mooring Analysis.

3 Projects That Can Benefit From Hydrodynamic Analysis

Water can behave in many different ways, depending on the circumstances, and any structure or equipment that is in a marine environment or to be used near the water, must be thoroughly prepared for the forces that will operate on it. These forces are constantly changing and include tidal forces, wave action, undersea currents, high pressures, corrosion and chemical reactions. If a structure or piece of equipment is not designed properly for a marine setting, it could have a significantly reduced lifespan, require increased maintenance and pose a threat to nearby personnel.

Industry personnel can use hydrodynamic analysis to improve marine equipment and structure designs. By modeling the behavior of the water and the structure or equipment exposed to it, design problems and structural deficiencies can be discovered, and the design can be improved before the equipment or structure is put into production. This process can save large amounts of time and money, and can improve the safety of marine structures and equipment.

Here are a few examples of projects that can benefit from thorough hydrodynamic analysis:

#1 Oil Rig Design

Large, off-shore oil rigs are often limited-production designs, with only a few examples actually being built. This means it is difficult to test the designs thoroughly before production, and any mistakes in the design can be difficult and expensive to repair later. By using hydrodynamic analysis, the manufacturer can thoroughly test the design before it is put into production, and improve it to minimize any problems.

The hydrodynamic analysis will model the effects of the marine environment on every part of the oil rig, from the anchors that tie it to the seafloor, to the platform legs, risers and superstructure. It can pinpoint structural deficiencies, where forces like wave action slowly wear away at sensitive components, such as moving joints, and eventually cause dangerous structural failures or prolonged maintenance problems. This allows the designers and engineers to redesign these components to better withstand the forces at work in the marine environment, reducing maintenance costs, increasing the design life and protecting the safety of the personnel.

#2 Pump Design

Pumps are critical in a marine environment. Bilge pumps remove excess water from a ship’s hull to prevent an over-accumulation that could cause the ship to sink. Fresh water pumps circulate drinking water through the plumbing for ship personnel, and other pumps may be used for fire protection. Oil pumps are used to keep the moving parts of a ship lubricated, or to transfer oil from production wells to tankers. Fuel pumps provide ships and generators with the fuel they need to run.

Pumps used in a marine environment must be able to withstand corrosion and electrochemical reactions caused by saltwater exposure, and they must be able to transfer fluids quickly and efficiently without overheating and failing. Hydrodynamic analysis can be used to model both the behavior of water on the exterior of the pump and the behavior of liquids as they travel through the pump.

The models can be used to design pumps which are better suited to the forces at work in a marine environment, making them stronger and more resistant to the effects of pressure and corrosion that cause maintenance problems. They can also be used to increase the efficiency of the pump, by showing how the fluids travel through the body and the impellers. By using the results to eliminate unnecessary cavitation and friction, the pump design can be made much more efficient, saving energy, reducing maintenance requirements, and extending the pump’s lifespan.

#3 Accident Reconstruction

Working in a marine environment can be especially dangerous for personnel and equipment. Bad weather, rogue waves, fire, equipment failures and other common problems can quickly lead to dangerous situations in the contained environment of a ship, drilling rig or other marine platforms. Accidents can and do happen, including collisions, fires, oil spills, sunken vessels and other catastrophes. Determining the cause of an accident and the results are often the key to improving marine designs and preventing similar accidents in the future.

Hydrodynamic analysis is one of the most powerful tools for determining the cause of a marine accident. The process can be used to model the behavior of the water and any structures, vessels, or equipment that are in the water. It can help determine why two ships collided using accurate modeling, which part of a structure failed, why fire protections systems malfunctioned during an emergency, or how an oil leak was caused and where the oil will be traveling.

With accurate modeling, hydrodynamic analysis in conjunction with other tools can reconstruct every variable at play during an accident, and determine the cause and effect of each action taken. The results can be used to improve the designs of marine equipment and structures to prevent similar accidents in the future, to institute new safety procedures that minimize casualties, and to take further action to protect the safety of ship personnel and minimize liability issues.

Other Applications

These are just a few of the ways that hydrodynamic analysis can be employed in real-world applications. It can also be used to improve the designs of sea-faring vessels, mooring systems, sub-sea pipelines, floating pipelines, drilling risers, anchors, mooring lines, liquid-storage systems, buoys, marine weapon systems, off-shore wind turbines and wave power generators. Furthermore, it can be used to help during oil spill cleanup or containment operations, for forensic analysis, marine training simulations, risk assessments, financial assessments, emergency preparedness and accident prevention. Hydrodynamic analysis is a versatile tool, and it has many critical applications across multiple industries, including oil and gas production, energy production, shipping services, defense, maritime entertainment and oceanography.

With so many applications, hydrodynamic analysis is very important to any marine based-operation, and through its accurate modeling, it can help improve the design and operation of many marine-based structures, tools and equipment. It can help cut design costs and minimize production delays, and improve the safety of marine-based personnel.


4 Ways Engineer Consultants Can Help Your Business

Published by Stewart Technology Associates on May 20, 2016

Maleo Producer - Mat-Supported Jack-Up on Dry Tow

Maleo Producer, a mat-supported Jack-Up rig converted to a gas production platform (MOPU) owned by Global Production Systems, with structural design and foundation dynamic analysis by Stewart Technology Associates.  The platform is shown during a dry tow to the site in Indonesia on board the heavy lift vessel Black Marlin.

Side view of mat-supported jack-up Maleo Producer showing deployment stages for Roson.

Side view of mat-supported jack-up Maleo Producer showing deployment stages for Roson.

4 Ways Engineer Consultants Can Help Your Business

There are many challenges in the off-shore oil and gas industry, from operating in an unforgiving marine environment safely, to offloading oil and gas efficiently and designing drilling rigs, risers, moorings and other equipment that can withstand the punishing environmental forces at play. No matter how well-rounded and diverse your team is, eventually, you will run into an engineering problem or situation beyond your knowledge and expertise, or something that requires a different discipline or skill set.

While expanding your team is one option, finding someone with the necessary skills can be difficult, time-consuming, and potentially costly, and it may not be worth the effort if you need only temporary or intermittent assistance. In these situations, the most convenient, cost-effective option is to use outside engineer consultants who can work closely with your team to achieve the desired results, while bringing a unique set of skills and fresh viewpoints to the task at hand.

Here are a few of the ways that engineer consultants, like the team at Stewart Technology Associates, can help your off-shore exploration or production operation:

#1 Structural Design and Analysis

Designing equipment and structures that can stand up to the rigors of a marine environment, including forces such as rain, snow, wind, wave action, tidal forces, deep sea pressures, corrosion and chemical reactions, can be a difficult process. It can include thousands of hours of design, simulation, prototyping, testing and analysis work. Even with a highly-qualified team and large budget, it can be a grueling process fraught with pitfalls and mistakes. By working with experienced engineer consultants, you can eliminate guess work and get the project finished and into production in a timely manner. Some of the structural projects that engineer consultants can help you with include:

  • Fixed platforms
  • Tension-leg platforms
  • Jack-ups
  • Liftboats
  • Semi-submersible platforms
  • Drillships
  • Barges
  • Bouys
  • Moorings
  • Single-point moorings
  • Pipelines
  • Risers
  • Anchors
  • Foundations

Engineer consultants can help throughout the design process; from the initial planning of the structure, to creating the final design and selecting the appropriate materials and construction methods. Using software such as ORCAFLEX, ASAS or ABAQUS can employ finite element analysis and model how your structure will behave in real-world conditions by simulating the effects of vibration, heat, fluid movements and other variables. This will determine where likely failure points are, allowing design to be improved before production. The software can also be used to improve existing designs and model previous failures to avoid future incidents.

By working with engineering consultants during the design process, you can avoid common problems that lead to structural failure, safety problems and increased maintenance, and you can develop a reliable, long-lasting structure that will serve your needs more thoroughly.

#2 Hydrodynamic Analysis

Anything in a marine environment is bombarded by waves, tidal forces, inclement weather, high pressures, corrosion and electrochemical processes. These forces cause wear and stress on marine structures and equipment, leading to increased maintenance requirements, higher operational costs and structural failures or safety issues. Engineer consultants use hydrodynamic analysis tools, like OrcaFlex, to model the hydrodynamic forces at work on your structure, allowing you to improve the design, increasing durability and reducing maintenance costs. Hydrodynamic analysis improves the performance of equipment and marine structures, including:

  • Drilling rigs
  • Production platforms
  • Mooring systems
  • Anchors
  • Anchor points
  • Mooring lines
  • Anchoring hardware
  • Underwater pipelines
  • Floating pipelines
  • Risers
  • Tankers

Engineer consultants can help your marine equipment and structures perform as expected, and keep workers safe.

#3 Fluid Dynamics Analysis

Systems designed to store and transport fluids like oil must be designed to avoid leaks, eliminate bottlenecks that reduce transfer efficiency and move fuel safely. Engineer consultants use software like OrcaFlex to model the behavior of liquids in equipment like risers, pipelines, pumps, swivels and tanker ships, leading to improved designs.

For pipelines, risers, and swivels, the software determines where there are impediments to flow, allowing you to create a design with higher flow rates. It also shows the forces at work on the seals, allowing you to design seals that are more resistant to leaks and other failures.

An analysis of fluid dynamics can also be used on pumps to increase flow rates and to make them operate more efficiently, reducing energy usage and costs. In tankers, it can help design holds that minimize the movement of oil and prevent sloshing, leading to greater ship stability during transit, increased safety and reduced fuel costs.

#4 Other Areas

In addition to these basics, there are other ways engineer consultants can improve your oil and gas operations:

  • Risk Assessment: Engineer consultants can examine your overall operations and suggest improvements to increase safety, efficiency and financial health. They can also report to insurance agencies to evaluate your operation and so that a project can move forward.
  • Emergency Preparedness: Engineer consultants can design safety systems, equipment and strategies that keep employees protected and minimize liability during emergency events, like inclement weather or fire.
  • Marine Simulation and Training: Engineering consultants can design training programs, software and equipment that helps employees learn to use marine equipment safely, effectively and efficiently, including systems like jack-ups or liftboats.
  • Forensic Analysis: Engineer consultants use tools like hydrodynamic and finite element analysis to determine the cause of an accident, and how to prevent it in the future.
  • Oil Cleanup: Engineer consultants can develop effective oil cleanup procedures and equipment that minimize costs and environmental damage in the event of a leak or a spill.

Engineer consultants offer a wide range of valuable knowledge and skills that help your oil and gas operation design better structures and equipment, improve operations, enhance safety and increase profits.




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