It’s Fun Fact Friday again and we’re talking about dynamic positioning. If you’re ever wondered how a vessel stays in place on the ocean while the wind is blowing and the waves are crashing, this is the article for you! A computer on board the vessel takes readings from displacing effects – wind, current, and waves – and then controls thrusters and propellers to stay in place. A mathematical model of the vessel, along with sensor information from the ship, satellites, and even the sea floor, gives the computer information to adjust each thruster and keep the vessel steady. According to Wikipedia, some vessels that use this technology might be “ships and semi-submersible mobile offshore drilling units (MODU), oceanographic research vessels, cable layer ships and cruise ships.”
Image Credit: Kongsberg
Why would a vessel need dynamic positioning?
Sometimes vessels don’t have the option of mooring or anchoring due to pipelines, issues with the seabed, or just deep water. In these situations a vessel may need to drill for oil and gas, make extractions, make repairs, complete research, or wait. For any of these reasons, a vessel may need to stay where it is without the use of physical restraints. A dynamic positioning system provides a method for a vessel to stay in a designated area, with multiple levels of control.
Kongsberg classifies DP control in three levels: high precision, relaxed, and Green DP® control.
High Precision is highly accurate, precision control, but uses more power and creates more wear and tear on the systems.
Relaxed control is a smoother operation but may not keep the vessel still enough for some applications; this type of control is usually used in calmer weather conditions.
Green DP® control is a Kongsberg specific DP control system. “This new approach is based on forecasting the vessel's motion, rather than acting on present conditions, using a method called 'nonlinear model predictive control', which optimises the predicted vessel offset against the use of thrusters. By doing so, small and short-term disturbances that do not force the vessel out of its operational boundary are 'filtered out'.” Instead of a reactionary approach, this new control system predicts what will happen, even ignoring some small movements, saving energy and wear.
Sometimes, dynamic position and mooring are both needed. According to RigZone, “Sometimes mooring and dynamic positioning are used together to keep the vessel on position. Additionally, with a dynamic positioning system, these vessels many times can stop operations and move out of the way of threatening storms, such as hurricanes and cyclones, further strengthening the safety of the offshore development.”
Image Credit: Marine Insight
What other benefits are there to DP systems?
Vessels with dynamic positioning can complete objectives quickly without disturbing the seabed or using another form of physical restraint. These systems can also be programmed to follow a moving target such as a diver, who may be working underwater. The system can lock on and follow within a target zone, keeping the diver safe as they move around underwater structures and platforms.
What’s the downside?
According to Marine Insight, “they require a higher capital investment and functioning expenditure. This is due to more consumption of fuel, costly equipment / systems and requirement of trained manpower to handle the systems.” In other words: a more sophisticated positioning system costs more money and more manpower.
Image Credit: ResearchGate
What about oil rigs?
Some smaller DP2 and large DP3 oil vessels use dynamic positioning while drilling for oil and gas. This can ensure they stay in place over the well without the need to be moored to the sea floor. These DP systems are larger than others, with more generators and more thrusters, but they function just the same.
Check out this short video from Tangaroa on how dynamic positioning systems work:
A quick plug to our awesome readers: OneStep Power tests DP2 and DP3 vessels to run in Closed Bus, increasing fuel efficiency by 8-16% and reducing emissions. Traditional closed bus tests can shorten equipment life, require disconnection of safety equipment for testing, and only test a small part of the system. To fix these problems, we developed our own safer, non-destructive testing. OneStep Power’s proprietary tests do not reduce equipment life and keep all of your safeguards in place throughout the process, while taking less time than traditional tests. Give us a call or shoot us a message to start a conversation about saving money and reducing emissions safely with our testing.
Happy Friday!
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