Using Taut Wire Systems to deliver critical data for effective Dynamic Positioning. By Christian Blinkenberg
Safe operations in the shipping and marine industry are reliant on the availability of accurate, current data. Protecting people, the environment, vessels andother assets is key for all businesses and Dynamic Positioning (DP) is one tool that enables planning of work and manoeuvres effectively.
Data needs to be continuously updated – change needs to be recorded and highlighted in real time however, when it comes to the use of DP reference sensors, a number of circumstances can affect their ability to produce data which is fully accurate.
External factors including, but not limited to: the acoustic signal; visibility; severe weather; and limited battery life of transponders can impact on the sensors’ performance and lead to loss of crucial information. Ultimately, this introduces the risk of misinformed and potential costly manoeuvres being made.
This potential for error has been taken into consideration in the design of the latest taut wire systems (TWS). Such systems can be deckmounted to assist in situations where other DP reference sensors may not achieve full reliable data sets. As a self-contained system that can easily be deployed, TWS offers reliable continuous data coverage during operations.
To achieve this, the TWS deploys relativepositioning DP reference sensors that measure the angles and distance to a deployed weight on the seabed. This data outputs to a ship’s DP control system and measures across ship’s angle (X), along ship’s angle (Y) and wire length (Z).
By computing the X, Y, Z into a position, the DP system then determines the vessel’s movement relative to the weight. From here, the ship deploys the weight to the seabed when the vessel is in the required position and once in mooring mode, the TWS maintains a constant tension upon the wire so that it’s ‘taut’.
As the vessel moves relative to the depressor weight, the angle between the gimbal head and depressor weight changes. However, the DP system utilises the outputs to maintain position.
Through being installed on a vessel, such a system provides the operator with a complementary positioning system that works with the vessel’s relative-positioning DP reference sensors. The TWS determines the vessel’s threedimension movement relative to the deployed weight of the taut wire with this data being output to a ship’s DP control system.
Systems can be designed to be an independent DP peripheral sensor that will operate in water depths up to 400m and to integrate into a range of DP consoles. Once deployed, the system provides continuous, uninterrupted data. It can be used in close proximity to an installation and also in open water locations.
The TWS allows users to operate their vessels in conditions where other sensors may not be able to give a reliable continuous data positioning service and thus a very high degree of accuracy either autonomously or in an area with installations or other vessels.
This enables a contractor or operator to reduce the risk of not having an accurate data-set and is therefore suited to multi-purpose work vessels, DSVs, construction and intervention vessels operating up to 400m water depths.
Feedback from clients suggests the desired DP system features a Bridge Remote Control Panel where the TWS can be easily viewed by system operators and bridge crew. This would include alarms, inputs and outputs that can be monitored in real time.
Systems can vary but a typical deck unit and control station would feature a double A-frame boom for rigidity and accuracy along with a pneumatic cylinder for assisting constant tension mode and shock absorption. The boom is deployed and recovered using hydraulics and includes the gimbal head at end of the boom to measure wire angles. An electrically-driven winch unit and depressor weight complete the instruments required for an effective deck unit.
An instrument cabinet is sited in a sheltered area of the vessel with flexible outputs to suit client or vessel specific requirements for ethernet, digital or analogue. Consideration should also be given to housing spare parts.
Since first supplying its TWS just under a decade ago, Forum’s customer base has included DP system integrators and vessel owners globally while more than 25 systems are in operation worldwide.
Forum Energy Technologies’ Subsea Rentals business recently launched its updated D-POS system which is SIL2 certified with all external sensors made of stainless steel for prolonged operation in harsh environments. The system is fitted with a SIEMENS motor which is ‘tropicalised’ and can be used in any climate.
In addition, the breaking resistor is sized accordingly for continuous use of mooring mode for an unlimited time. There are no time constraints of this unit being in mooring mode. For the operation, the TWS unit doesn’t require any air supply which makes it less dependent on external auxiliary units.
The D-POS also comprises a deck-mount Taut Wire unit with 500m of 4.9mm anti-spin wire and 460KG depressor weight, an external local control cabinet, an instrument cabinet, a bridge remote control panel, and a set of system manuals and basic field spares kit.
Forum’s forward-thinking development of the TWS, for which the company holds Quality ISO 9001:2015 accreditation as well as ISO 14001 (environmental) and the OHSAS 18001 (Health and Safety) accreditations, reflects the ongoing topical industry debate about which transmission methods of collating data are most reliable, efficient and effective.
While all DP reference sensors have strengths and weaknesses, key to reliable DP operations is having the redundancy and ability to utilise as many sensors as possible to ensure good quality, continuous and acceptable coverage to allow the ship to operate despite harsh conditions.
With an ever-increasing focus on costs and efficiencies during offshore operations, any means of optimising vessel time through preparation and verification of procedures, personnel, health and safety aspects as well as equipment becomes a critical component to factor into the project plan.
Christian Blinkenberg is Eastern Hemisphere business development director for subsea at Forum Energy Technologies. The company is a global oilfield products company, serving the subsea, drilling, completion, production and infrastructure sectors of the oil and natural gas industry. The company’s products include highly engineered capital equipment as well as products that are consumed in the drilling, well construction, production and transportation of oil and natural gas.