How to better understand your heave compensation needs

As a heave compensation specialist, at TENSA, we receive a lot of client’s enquiries on the right product to choose for different lifting applications in offshore operations.

The following table outlines the key criteria you can use to decide on the right heave compensation product for your project:

Choosing the right system

Dynamic load reducer (DLR) is used with offshore cranes to reduce the dynamic loads associated with lifts from moving vessels.

Passive heave compensation (PHC) is generally used to support a stationary load or to reduce motion when the lifting system is moving, for example, when lowering subsea equipment to the seabed. It is also used to minimise loads in the splash zone.

Active heave compensation (AHC) is designed to hold a load stationary relative to earth and is particularly useful for lowering a boat supported load to the seabed or connecting load to a fixed structure.

Common misconceptions

Misconception #1: To reduce crane dynamic loads, a long stroke is needed

The optimum cylinder stroke is between 1m and 1.5m as the shock absorption is most effectively handled over a stroke of 0.5m. The extra stroke allows the system to handle a wide load range without adjusting the setup as the cylinder force increases as the rod is extended.

Misconception #2: Active heave compensation is a good technique to reduce dynamic loads in the splash zone

In the splash zone, you must use passive heave compensation as AHC  will hold a load stationary to the seabed, whereas the load needs to stay stationary relative to the water surface to minimise loading.

Misconception #3: Active heave compensation is suitable for supporting loads connected to the seabed from a moving vessel

AHC is never perfectly accurate and can fail. Hence any rigid connection between a vessel and the seabed could be overstressed. A passive heave compensation device should be included in the connecting string.

Improving port operations with telescopic gangways and motion monitoring

In the past year we’ve seen a growing interest from port operators to use gangways to increase safety and improve operations both in the port and for offshore transfers near the port. For example, Port Botany recently installed a gangway tower at their bulk liquid terminal to improve berth efficiency. There is also the plan by Kimberley Ports to acquire and install gangway to give 24/7 all-tide access to cruise ships in Broome where tidal fluctuations is common.

At TENSA, two ways which we can help port operators improve are through the use of telescopic gangways to improve access at the port and the application of motion monitoring system to increase safety and reduce risks for port assets.

Improving access at the port with telescopic gangways

TENSA offers passive heave compensated, active heave compensated and uncompensated gangways ranging from 8m to 23m long. In an offshore environment, these gangways are used to allow safe offshore crew transfer such as the one used recently by Technip to transfer personnel between tug vessels and barges during the Prelude Project.

TENSA’s aluminium telescopic gangways are lightweight and easy to install, thus imposing lighter loading on the host vessel. For port operators, this means the gangways can be located either on the wharf or on a movable base.

When combined with the Active Heave Compensated Pedestal (AHCP) we developed, the gangway base can be raised or lowered. The pedestal has been designed so that it can also be active heave compensated, allowing the gangway height to be adjusted by up to 5 metres, if, for instance, a vessel needs to be accessed at a high level to accommodate transfers to a wharf in a highly tidal region. The pedestal can be set to automatically adjust height as the tide rises or falls.

Possible applications of the gangways and pedestal system in port operations include:

  • Transfer of personnel from a vessel to the wharf in locations with large tidal variations such as Broome, Darwin, etc.
  • Transferring tourists from cruise vessels to ferry vessels in locations such as Exmouth, Broome Great Barrier Reef, etc.
  • Transferring tourists from ferry vessels to wharves where there is a limited berthing facility
  • Transferring crews or personnel from tug vessels to barges in offshore operations

With the ability to be installed and removed very quickly (less than an hour), gangways need only to be on the vessel when required.

Motion monitoring to increase safety and reduce risks for port assets

TENSA’s motion monitoring system, Dynamic Motion System (DMS) which provides vessel motion and position information system can support operations at the port by providing:

  • Vessel motions (heave, heave velocity, heave acceleration, unfiltered accelerations, angular rates)
  • Attitude (heading, pitch and roll)
  • Position and GPS data (lat, long, northings, eastings, elevation, velocity)

The DMS has very powerful logging capabilities and can log from remote wireless units and local units at the same time. The DMS is available for sale or on a rental basis.

Potential applications of DMS for port operations include:

  • Measuring vessel motions both in the port and at sea
  • Determining if conditions are suitable for personnel transfer between vessels (either with or without a gangway)
  • Determining if conditions are suitable for specific marine operations – e.g. ROV launching, seabed coring , lifting operations from a vessel
  • Increasing the operating seastate windows for offshore crane operations,
  • Monitoring the performance of existing heave compensation systems.
  • Logging the position and motions of a number of vessels simultaneously

If you have upcoming port projects in need of a telescopic gangway or a motion monitoring system, contact us for a consultation.

TENSA, gangway, AHC pedestal, personnel transfer

Can high speed boats replace helicopters and carry out routine resupply?

TENSA, gangway, AHC pedestal, personnel transfer

Example concept for 40m high speed vessel fitted with TENSA AHC Pedestal and gangway providing personnel access and resupply to offshore facilities

Having to land helicopters in high winds and on heaving and rolling vessels not only poses operational but safety challenges for helicopter transfer. Helicopters are also expensive to operate and maintain, requiring a significant amount of support both on the onshore and offshore facilities.

High speed vessels offer a viable alternative to helicopters and can provide increased safety as well as significant additional functionality at a lower cost. To make this work, TENSA has developed a safe and reliable lightweight personnel transfer system suitable for installation on high speed vessels.

This complete personnel transfer solution mounts a lightweight aluminium telescopic gangway on a heave compensated platform. On the FPSO, there is a simple adjustable height landing platform. A motion monitoring system gives clear guidance on the relative vessel motions and confirmation that conditions are suitable for gangway transfer.

This is a total system that ensures that the operation can be undertaken safely.

A key feature of the gangway is active telescoping. This was developed in conjunction with Uptime in Norway and allows the gangway to be landed on a small flat landing. The end of the gangway remains in the same position by automatically telescoping in or out even if the boats move apart or together.

Vertical motion is handled by active heave compensation of the gangway support platform. The system can also be extended to compensate for relative motions between two moving vessels by using a second wireless motion reference unit on the receiving vessel. The TENSA Dynamic Motion System (DMS) already has this proven wireless connection and differential motion functionality.

With this system, the availability in a location offshore Northwest Australia would be above 90% so that all transfers could be undertaken by boat with appropriate management.

By having the ability to transport up to two 20ft containers, the system can handle virtually all of the routine and urgent supply requirements for offshore production facilities.

The whole gangway system can be secured to the vessel deck with twistlocks so that it can be easily installed and removed in under an hour. This also allows the vessel to be fully utilised for deck cargo if required.

The benefit of this system, according to Derick Markwell, TENSA’s managing director, is that “instead of having regular vessels fortnightly or monthly from the support base and one service a week with helicopter, you can have personnel transfer and up to two sea containers of cargo by boat daily”.

A single vessel could easily service three or four offshore facilities.

TENSA is looking at a system weight of under 12 tonnes, compared to a conventional active compensated gangway system that would weigh around 35 tonnes. The system costs less than 30% of the traditional systems.

“High speed vessels are most applicable at places like Exmouth where the fields are close to shore. There is also an opportunity at the limit of helicopter reach such as the northern Timor Sea. We see it is a compelling solution for the offshore oil and gas industry as it really offers benefits in all areas”.

Photo credits: Southerly and Strategic Marine

TENSA Dynamic Motion System (DMS) aboard Dampier Spirit for helicopter monitoring

Dampier Spirit, motion monitoring, helideck monitoring

Photo Credit: Teekay

TENSA recently provided our DMS Mini motion monitoring system for use on the FSO Dampier Spirit located approximately 40 km off the coast from Karratha.

Teekay Shipping (Australia), the operator of Dampier Spirit will use the DMS for general motion monitoring and as a backup for their Helideck Motion System (HMS). Having TENSA’s DMS Mini allows Teekay to continue to maintain safe helicopter operations to the facility without any interruption. Teekay initially rented the DMS but were so impressed with the ease of use and functionality  that within a few days they decided to buy the unit.

Find out more about the DMS »

TENSA DLR adopted by Paragon Offshore for its jackup drilling rig fleet

In January this year, the US-headquartered Paragon Offshore completed its purchase of a TENSA Dynamic Load Reducer (DLR) 60L for its offshore operations in India.

Instead of renting the DLR on a project basis, Paragon Offshore saw an immediate and long term need to purchase the DLR. The DLR will be used to reduce the crane dynamic loads for its heavy lifts and to ensure uninterrupted crane operations during heavy weather due to the monsoon season in the area.

Find out more about the DLR

Oil Search reduces number of helilifts for its drilling modules by 30% with TENSA helilight mud tanks

Late last year, we concluded a major project with Oil Search Limited to design and deliver 14 lightweight mud system modules for its drilling operations in the highlands of Papua New Guinea.

TENSA’s pitch was to reduce the weight of the modules so that they could be lifted by a chinook helicopter without requiring them to be disassembled and lifted in 2 sections as was required in the past. Great attention was given to the module design by using lightweight materials and weight saving in the details and equipment. In addition, the use of thin stainless components and fibreglass will reduce the ongoing maintenance costs.

TENSA worked with our Chinese partner GN Solids to deliver a system that was fully compliant with Australian and international standards at a very reasonable cost and in a very short time frame. The entire project was completed in less than 6 months and the system has already been used successfully on its first gas exploration well.

Find out more about the Drilling Modules

TENSA DMS proves vital for Cooper Energy’s Bass Strait operation

Convinced by a demonstration of the TENSA Dynamic Motion System (DMS) motion monitoring sensor and software at the AOG 2018, Cooper Energy decided to hire a TENSA DMS Mini complete with its full monitoring software application for their offshore operations on the Ocean Monarch rig.

TENSA DMS is especially useful to monitor heave velocity, pitch and roll for Cooper Energy’s operations in Bass Strait renowned for its consistent long period swells coming from the Southern Ocean. Data was easily logged, reviewed and emailed to allow critical decisions to be made when the rig motions approached workability limits.

Find out more about the DMS

5 applications for TENSA DMS motion monitoring system

TENSA motion monitoring system

In offshore operations, moving heavy equipment from and to vessels in a seastate can be a tricky business. The movement of the vessels can cause large dynamic loads to be applied to a crane when the load is lifted from the deck.

These loads, however, are not easily predicted with the current technology of ‘guesstimating’ the dynamic load by using the significant wave height (Hsig). Instead, TENSA’s off the shelf vessels motion monitoring system, the Dynamic Motion System (DMS), measures the load velocity directly which then allows the dynamics to be accurately calculated.

Here we list 5 potential applications for TENSA DMS motion monitoring system in the offshore operations to improve safety and efficiency:

Crane operations

TENSA DMS measures the vertical velocity of the load so that the appropriate crane chart for the lift can be selected directly.  There is a direct correlation between the measured velocity and the correct crane chart (charts are typically defined by seastate) that should be used. The DMS also offers crane operators powerful visualisation by displaying real time vessels motion, which allows the operators to time the lift on a rising wave and reduce the difficulties of estimating vertical motion of vessels at night or when looking down.

Helicopter operations

TENSA DMS motion monitoring information can also help measure safe operating conditions for offshore helicopter operations. While DMS doesn’t comply with the current onerous CAP437 requirements, DMS system can be developed to incorporate the Significant Heave Rates and Motion Severity Index data displays required by CAP437 at a fraction of the cost.

Monitoring of towed barges and cargoes

The TENSA DMS can be utilised as an inexpensive tool for fleet owners to assess and reduce their operational risk during towing operations. In particular cargo on towed barges experiences damage due to excessive motions. The DMS can send the barge motions wirelessly to the tow vessel and can log the data.

Offshore construction

TENSA DMS can be used to monitor vessel motions and locations during offshore construction phases such as floatovers and in FPSO connecting operations, using its wireless linked GPS and motion sensors. The TENSA DMS motion monitoring system delivers real time heave, pitch, roll, heading speed, course, position, accelerations at the sensor as well as at offset positions which could be the bow, stern roller, crane boom tip or an overboarding sheave on an A frame. Decisions as to whether conditions are suitable for work or whether weather downtime applies can be quantified and the logged data is available for reference. The DMS buoy can additionally be used for measuring wave heights and seastate as well as the other DMS functionality.

Personnel transfer

The TENSA DMS can measure vessel motions when personnel transfers are being contemplated. The DMS motion monitoring allows clear definitions of maximum tolerable conditions for safe transfer, hence significantly reducing the risk to personnel.

Visit our booth J1 at AOG 2018 to see a demonstration of the TENSA Dynamic Motion System (DMS). The DMS is available in different versions: DMS Max with wireless connectivity and inbuilt 24 hour  battery, the entry-level DMS Mini and the DMS Buoy, which is a DMS inside a portable buoy for delivering real time wave data.

3 Reasons Why You Should Visit TENSA at AOG 2018

TENSA Equipment will be exhibiting at the Australasian Oil and Gas Exhibition and Conference (AOG) 2018 from Wednesday 14 to Friday 16 March at the Perth Exhibition and Conference Centre (PECC).

Join us at Booth J1. To help you make the most of your visit, we give you 3 reasons why you should join us:

Reason #1: Learn how TENSA products can solve your problems

TENSA products are designed to provide high value efficiency, safety and reliability of our clients’ offshore operations.

If you are curious about what we are doing, visit our booth and we will share with you how our products can:

Reason #2: Meet TENSA engineers and discuss your challenges one-on-one

Do you have specific questions or require customised solutions for your offshore operations? Our motion monitoring and heave compensation experts will discuss with you one-on-one about your options.

This will be the perfect opportunity to learn more about how our products can be tailored to your specific operational challenges and get your burning questions answered by our engineers.

Reason #3: Experience DMS demonstration and watch videos of TENSA innovative products

Get a chance to learn first hand how to use TENSA motion monitoring unit, the Dynamic Motion System (DMS) at our booth.

You will also have the opportunity to watch demonstration videos of TENSA gangways in operations and our upcoming new product, Roborigger.

Get invited to connect with our network!

TENSA is organising a networking drinks function for a gathering of industry specialists and practitioners in the oil and gas industry.

Request your invite and get in the know of our latest innovation projects, meet with the who’s who in our TENSA network and simply get a chance to review the AOG 2018 over light bites and drinks with friends!

TENSA Awarded NERA Grant for ROBORIGGER and Active Heave Compensated Pedestal

TENSA is delighted to announce we have been awarded two innovation vouchers from National Energy Resources Australia (NERA).

The NERA innovation vouchers were awarded for our Active Heave Compensated (AHC) Pedestal and soon to be launched Roborigger, two products which deliver innovative solutions to technical challenges faced by various companies in the oil and gas and construction industries.

Our AHC Pedestal provides an alternative to using helicopters for transferring personnel from one vessel to another at offshore oil and gas facilities. The Pedestal reduces relative motion between vessels enabling a lightweight gangway on a small high speed vessel to match the motion of a larger vessel. If helicopters are replaced by vessels, transferring personnel becomes less costly and safer, improving health and safety as well as financial outcomes.

The Roborigger is a battery powered wireless device which uses gyroscopic and inertial forces to accurately rotate and orient loads. Moving and orientating heavy equipment can be a workplace health and safety challenge, the Roborigger will eliminate the need for personnel to land and unhook heavy loads. It has other applications including the ability to hold wind turbine blades stationery when they are being attached to the hub of a wind turbine and can also assist with pipelaying vessels as pipes are moved across from one vessel to another.

We are extremely proud of our innovative products and thank NERA for their recognition of our work.

Click here to see our full product range and please contact us if you would like further information: dmarkwell@tensaequipment.com.au