A smart solution for Active Heave Compensation
Smart Tools for Design, Testing and Support Make Value-adding AHC Technology Available for an Increasing Number of Vessels
Active heave compensation (AHC) technology adds significant value to the offshore vessel by increasing its operational uptime. Scantrol – a Norwegian control system provider – enables more crane and winch manufacturers to deliver AHC equipment by focusing on providing cost-effective standardized AHC control solutions and smart tools for design, testing, operations and support. This makes both the end-users and equipment manufacturers confident that AHC adds value to their product without causing extra uncertainty.
Active heave compensation is a technology used on lifting equipment in order to filter away the heave movement influencing a vessel during offshore operations. The principle is to keep the load motionless with regards to the seabed, a fixed installation or another vessel. AHC requires a control system that in real time precisely and actively controls the equipment to work against the wave-caused movements.
AHC technology is used in various applications. Offshore cranes, launch and recovery systems (LARS) for remote operated vehicles (ROVs), wellhead intervention winches, oceanographic winches and ship-to-fixed installation gangways are all candidates for AHC technology. What they have in common is the need for isolating the load from the vessel`s heave motion. The user benefit of AHC is increased operational uptime of the vessel. The lifting equipment can be used for subsea operations even if the weather is not ideal. This user benefit is critical for many offshore projects, which means that AHC is becoming a more common criteria for vessels offering a tender for a job. AHC is gradually becoming an industry standard for deck equipment – not only for the main crane.
Scantrol is a Norwegian provider of AHC control systems for of winches and cranes. The company was established in 1988, is located in Bergen and employs 18 highly skilled engineers focusing on R&D, marketing, sales and service/support. The company has a long track record delivering control systems for trawlers, and has also so far delivered more than 60 AHC systems to vessels in the offshore industry.
Challenge: High Cost and Complicated Drive and Control Technology are Limiting Factors
By providing standardized systems customized for each application instead of developing a new control solution for each project, Scantrol and its customers exploit economies of scale. At the same time the Scantrol AHC has been proven to work, since each project it built on the common AHC software and communication platform. AHC Toolbox is a set of supportive tools used during the design, testing, operation and for remote support. The toolbox ensures adequate AHC winch capacity, large time-savings in testing, intuitive monitoring of operations and rapid, cost effective support independent of where the vessel is located. As the AHC technology is becoming more common on more types of vessels, drives companies are gaining experience with how their drives solutions – hydraulic or electric – works in an AHC setting. As this functionality is seen as an important and profitable technology in the time to come, many of the drives providers improves their parts and solutions so that their AHC performance improves. This is a solution that control system companies, winch manufacturers and vessel owners should be very satisfied with.
Challenge: Winch Design - Cost vs Capacity
AHC often requires that the winch utilization (speed and torque) to some extent must be increased compared to a winch without AHC functionality. This is also true for the power consumption capacity. As an independent control system developer, Scantrol is not interested in increasing the size of the end-users winches more than required for a given AHC performance, as this increases the end-user's costs. In order to have good AHC, the correct winch dimension must be found – not the largest possible. Together with resource people from the Norwegian University of Technology and Science (NTNU) Scantrol has built a motion simulator that is connected to the database of Global Wave Statistics (1986)[1] giving Scantrol, the crane/winch manufacturer and the end-user insight into what heave
requirements are expected with 80% and 95 % confidence interval in different oceans and for different points on a standard offshore vessel. These heave results are used as input in an AHC analyzer software designed to calculate winch speed, torque and power consumption required for AHC operations. Some of the other inputs needed in order to make these calculations are load, wire weight, wire diameter, drum diameter, number of motors, gear ratio and operation depth. The result of the simulations Scantrol use as basis for advices to any end-user or manufacturer of winches and cranes, who is considering adding AHC functionality to their lifting application.
Challenge: Complex and Time Consuming Commissioning and Testing
It is in the nature of an AHC system that is has to be responsive and precise. If the heave compensation responds too late, the system will compensate in another phase or frequency than the heave itself, which inevitably leads to much poorer result. Often poorer than not having AHC activated at all. In order to avoid such damaging and embarrassing results, many of today`s AHC solutions require time consuming and complex testing and fine-tuning after the lifting equipment has been installed on board the vessel. In order to avoid another task during the already busy sea trial, Scantrol`s AHC solution is completely tested on the winch or crane on the factory`s testbed. So when one of the control system provider`s commissioning engineers attends a sea trial, it is ideally just to show the ship owner that everything works perfectly. On the factory test bed, there is more time to sort out issues and a more controlled environment compared to on board a crowded vessel during sea trials. Not only does Scantrol and its crane and winch manufacturing customers complete the test before installation on board the vessel. The test is done remotely with a so called Dynatest tool, a tool that simulates the scenario of being in rough seas. The system then starts compensating for what the system perceives as signals from the motion reference unit (MRU) – an AHC system`s main sensor measuring heave, pitch and roll. In reality the whole process is a simulation set up to register and fine tune the control system and winch response to the heave. The software engineers can supervise the manufacturer during test from the company offices in Bergen. By doing so the end-user, the winch manufacturer and Scantrol save time and costs. Long term relationships and training courses are keystones to succeeding with this, since the remote testing tends to run smoother the more experience the winch manufacturer gets.
Challenge: Operator Skills
Starting to use AHC technology can require that operators have to adapt to a reality that they are unfamiliar with. Therefore Scantrol focuses on the user-friendliness and simplicity when the human machine interface (HMI) is developed. Based on its experience with sophisticated trawl control systems, the simplicity philosophy has been implemented also in the AHC products. Remote assistance also for training helps the operators and ship owners overcome the threshold caused by introducing AHC on board a vessel. When a vessel installs more than one AHC system from the same brand, this is not only reducing the costs since some central AHC resources can be shared between the applications. It is also convenient for the operators, as they can use their knowledge across applications on board the vessel. If the winch or crane manufacturer got a good control systems, but do not intend to invest in developing their own AHC controller, that is something that easily can be outsourced to companies like Scantrol, since the AHC controller easily can be connected to other control systems by using a simple Modbus connection or similar. The crane or winch operator can then continue using the control system interface that they are used to and prefer, and still get AHC.
Challenge: Existing Ships Need AHC
In order to get the very limited number of new contracts for offshore work, vessels are often required to have AHC equipment installed on board. For those vessels not having this, the consequence can be that the vessel is excluded from the bidding process. By using AHC Analyzer, another of Scantrol`s AHC Toolbox tools, it is easy to calculate the AHC capacity of existing lifting equipment, where the winch specifications are given. If more capacity is required, hydraulics experts, many of which Scantrol has partnered up with, can retrofit the equipment to perform much higher speed and torque than initially. Both original winch manufacturer and other companies with the right skills and knowledge do these upgrades. Upgrades comes at a cost that tends to be much lower than building a new winch or crane, and it will increase the operational uptime of a vessel dramatically.
By upgrading existing equipment smaller vessels can also start competing with large offshore vessels, which reduces the costs for the end users, who want to get jobs done efficiently in line with today`s low conjuncture.
An important aspect that easily can be forgotten is that there are different tolerance for heave depending on what operation the ship is doing. An offshore crane installing a heavy component on the seabed is typically more heave critical than a tether management system (TMS) for a ROV, where some heave can be tolerated as neither of the involved objects are fixed. For the latter case, upgrading or building a new AHC winch for filtering away most – but not all – heave could be a very cost effective way of increasing the operation`s weather window.
Future developments
The AHC technology is becoming more common, and the variation of application using AHC will continue to develop. This development is driven by customer needs, control system developers` ideas and the general technological development, making these kinds of advanced control solutions cheaper and more convenient.
Scantrol has experienced that a growing number of wind farm projects and other renewable energy projects require the service vessels involved to be equipped with AHC cranes and winches for construction and service. Also heave-compensated gangways are about to becoming a standard for larger vessels serving the wind-farms.
Albeit the significant value adding nature of AHC, Scantrol focuses on reducing costs when offering their controllers. By connecting more than one AHC application to the same system, by using standardized off the shelf solutions and by always trying to improve the AHC tools for design, testing, operations and support, the costs - and the prices - have been falling and will continue to fall.