What is the difference between DP1, DP2, and DP3 vessels?

“Dynamic positioning may be the most important shipboard navigation system since the compass.” - Professional Mariner, Journal of the Maritime Industry.

It’s Fun Fact Friday and today we’ll take a look at the differences between different types of dynamically positioned vessels. First, what is dynamic positioning and why is it important? Dynamic positioning provides the ability for a vessel to stay on station, that is, stay in one spot while coping with waves, wind, and currents. There are so many inputs from sensors and so many adjustments needed that a computer is required to keep a vessel steady in adverse conditions. According to Professional Mariner, “Inputs to the system come from wind sensors, gyrocompasses and special devices such as vertical reference units.” With a DP system, computers read all of these sensors and control azimuth thrusters underneath a vessel that have the ability to turn 360 degrees and provide the exact amount of force needed to keep the vessel on location.

Azimuth thrusters on the back of a vessel.

“Global Azimuth Thrusters Market 2017 - Rolls-Royce, SCHOTTEL”. Image from OpenPR.

Why would a large vessel in the middle of the ocean need such precise station keeping?

The technology was first used for drilling into the Earth’s second layer for samples in the 1960s. When oil companies took an interest in dynamic positioning, that’s when it really took off. DP systems provided a way for offshore oil rigs to stay in precise location over a well and drill in the middle of the ocean with little worry of the forces around it. As satellites became more ubiquitous and computers more powerful, DP systems became more common, eventually being required for smaller vessels to ensure ships like offshore support vessels don’t crash into anything. Even a small bump into a drilling rig could be disastrous, which brings us to the different levels of DP systems.

What are the different levels of dynamic positioning?

According to IMO guidelines, DP systems are rated DP1, DP2, or DP3. The levels build on each other, with each succeeding level having the abilities of the previous level. DP1 systems are the most basic, with the ability to keep their position in automatic mode. DP2 fulfills DP1 requirements but can also keep station with the failure of an active component. The redundant system must provide the ability to keep station until work can be safely stopped, and the transfer of operations must be automatic. DP3 takes DP2 one step further with the ability to continue operation with the failure of an active or static component, even with the total loss of the equipment in a compartment to fire or flood. Systems may also be required to be watertight depending on the vessel and damage to one system must not affect the backup. Systems also must be physically separated for DP3. Side note here: DP1 vessels are not very common, with DP2 and DP3 becoming more common due to the additional level of safety they provide.

OSV testing its azimuth thrusters. Image from MarineLog.

So what’s the short version?

DP1 is the most basic standard, with the ability for a ship to automatically hold station. DP2 has redundancy, but DP3 has segregated redundancy that would allow for a more serious failure. If human lives are on the line, DP2 or DP3 is required. Divers, construction workers, wind installers, and drillers need to stay safe and on location. You wouldn’t want to be underwater or working on a turbine when your vessel started to float off course.

What types of ships are fitted with DP systems?

As technology improves, many new vessels are equipped with dynamic positioning systems. Just a few of the most common types of ships are offshore support vessels, offshore construction vessels, oil rigs, pipe and cable laying vessels, diving support vessels, and cruise ships. Check out our article on 22 types of dynamically positioned vessels for the full list. Not only are newbuilds fitted with these systems, they can be retrofitted as well. Installing azimuthing thrusters and the needed computer systems can open up a lot of jobs that may not have been previously available to vessel owners. Dynamic positioned vessels can also utilize other technologies like laser range finding for precision navigation next to floating rigs or turbines.

WTIV with laser range finding floating toward a wind turbine.

SceneScan laser positioning from Wärtsilä. Image from Wärtsilä.

How do we ensure these systems are safe?

That’s where OneStep Power comes in. We have developed unique testing methods that are safer and more comprehensive to provide assurance for fault ride through for DP2 and DP3 vessels. All that means is we test redundant DP systems to prove if there is an issue, the vessel will survive the fault and continue station keeping. We also test that when running in closed bus for additional efficiency, fuel savings, and reduced maintenance, a fault won’t take all of the generators offline. Having a backup system is only good if it works and we have found many vessels may not operate as expected during a fault. Safety is our top priority, and you can learn more about our proprietary testing methods like the GVRT and ZeroDIP on our Services page.

That’s it for dynamic positioning systems! They provide the ability for a vessel to stay on station, have varying levels of redundancy from none to complete, and are becoming more and more common. If you have any other questions about DP systems or testing them for fault ride through and safety, please reach out to us on social media or give us a call.

Happy Friday!

PS - for an older, but still excellent video on dynamic positioning, check out Dynamic Positioning Systems, Principles, Design and Applications from Marine Online: