• David Armes

22 Types of dynamically positioned vessels

We’ve collected a list of all the types of dynamically positioned vessels we could find. Some of the categories overlap and some ships may even fit into 3 or 4 categories, but they all have one thing in common: computer controlled stationkeeping. Dynamic positioning systems are complex, but their function is simple: take inputs from gyrocompasses, wind, motion, and wave sensors, and use all of that information to keep the vessel exactly where it is. DP systems are needed for safety of workers, stationkeeping in deep water, and maneuverability. Dynamic positioning systems come with three ratings: DP1, DP2, and DP3. DP1 is a simple dynamic positioning system with no redundancies. DP2 has redundancy in case part of the system fails. DP3 has the greatest redundancy and is built to survive a fire or flood in a compartment. In high-reliability situations like diving and drilling, DP3 is usually used.


Dynamic positioning forces

Dynamic positioning forces. Image from Kongsberg


You may be wondering why we amassed so much information on dynamic positioning. OneStep Power has developed safer, more efficient methods of testing high-reliability power systems on dynamically positioned vessels. Traditional short circuit tests can damage systems and only test a single pathway. We knew there had to be a better way, so we developed a test that is safe, non-damaging, and tests the entire system from the generators to the lightbulbs. We continue to innovate with new technologies like the GVRT, ZeroDIP, DCShortCUT, and ACShortCUT; we are always working on new ways to keep people and equipment safe. Now, let’s get to the vessels!


Offshore Support Vessels - these are vessels that operate on the ocean, specialized for different purposes. They include several vessels listed below: Platform Supply Vessels; Seismic Survey Ships; Anchor Handling Tug Supply Vessels (AHTS); Diving Support Vessel (DSV); Inspection, Maintenance, and Repair Vessels; and Construction Support Vessels. Most supply, support, and construction vessels have stationkeeping for loading, unloading, working, and keeping people safe. There is more detailed information in our article specifically about offshore support vessels.


Wartsila offshore support vessel on the ocean

Offshore support vessel. Image from Wärtsilä.


-Platform Supply Vessels - One of the most common types of offshore support vessels is the Offshore Supply Vessel, usually called a platform supply vessel. They transport people and supplies from land to offshore rigs They usually have a large open deck where lots of cargo can be stored. They actually spend less than half their time travelling, with most time spent loading and unloading.


-Seismic Survey Ship - Seismic vessels shoot sound waves into the ocean and measure the return to map the seafloor and explore for oil and gas. They also study underwater structures like trenches and underwater mountains, using dynamic positioning to stay on track while mapping large areas of the ocean floor. They are strange looking ships that have the appearance of a ship cut in half.


Seismic vessel Ramform Atlas

Ramform Atlas Seismic Survey Ship. Image Credit: PGS


-Anchor Handling Tug Supply Vessel (AHTS) - Anchor handling tug supply vessels assist large vessels like drilling rigs with anchors, mooring, and can tow rigs if needed. They have a high bollard pull and are extremely stable in the water.


-Diving Support Vessel (DSV) - these vessels are specialized for underwater maintenance and inspections. They contain one or more moonpools through which a diver or remote operated vehicle can be lowered into the water. Most of these vessels require a DP3 dynamic positioning system because divers are directly at risk if the system goes offline while they are underwater. What happens if those systems fail? Check out our movie review of Last Breath.


Moonpool on a diving vessel. Image from Stanford


-Inspection, Maintenance, and Repair (IMR) Vessel - These vessels are also considered construction support vessels, depending on the specialization. The main difference is that ships specializing in IMR are designed for inspection, repair, and maintenance, but not necessarily for new construction. They are highly technical and can perform some light construction if needed.


-Construction Support Vessels - Construction support vessels are purpose-built for offshore builds. They can stay out for longer than other vessels, many have heavy lift cranes, and support IMR work as seen above. There are many categories of vessels and they frequently cross over in this category, sometimes to multiple categories depending on the vessel.


-ROV Support Vessels - ROV support is commonly done by IMR and construction support vessels. Specialized ROV support ships have additional features to support remotely operated underwater vehicles. They include the ability to transport and launch multiple ROVs, additional computers, thrusters, and extra crew accommodations for ROV support staff.


Cable Lay - Cable lay vessels do just that, lay cable for data transmission like the internet and international phone calls, and power generation from offshore wind farms. They are very specialized and are easy to spot, having one or two huge carousels or baskets that contain thousands of kilometers of cable. They carry so much cable that they frequently spend weeks at port just loading the cable onto the ship. In addition to the unique attributes above water, they also pull a plough that digs a trench and lays the cable as the ship moves. There are many hazards cable lay ships have to avoid, like rocks, reefs, pipelines, and other underwater cables. Their dynamic positioning systems keep them precisely on track during operations to install cable exactly where it needs to go.


Cable lay vessel Van Oord Nexus on the ocean with an empty basket

Cable lay vessel Van Oord Nexus. Image from Offshore-Fleet.


Cable Repair Vessels - Sometimes the data and electrical cables that cable lay vessels install are damaged by anchors, fishing equipment, or even sharks (check out our article on how undersea data cables work for more on sharks and spies!). You can also learn more about how subsea cable is repaired. While cable lay vessels are designed to lay new cable, they also perform cable repair operations, making cable repair vessels rare. However, ships like the newly ordered cable repair vessel for Orange Marine have features normal cable lay vessels don’t; according to Offshore Engineer, “The vessel has three cable tanks to carry fiber optic and power cables, one of which [is] fitted with a carousel. The remotely operated vehicle (ROV) used for cutting, inspecting and burying cables will be stored in a dedicated hangar on board.” The new vessel will be equipped to perform inspections and repair cable more efficiently than a full size cable lay vessel, loading enough cable for repair jobs can take just a few hours compared to weeks.


Pipe Lay Vessels - Pipe lay vessels are purpose-built for installing pipe on the ocean floor. Tug boats can handle pipes that are towed in and sunk, but these vessels handle the larger and more complex jobs. Smaller pipes can be put on a reel, similar to the carousel on a cable lay vessel, and larger pipes have to be stovepipe welded as they are slowly fed down into the water. Some vessels lower the pipes almost horizontally, called S-lay, while some lower the pipes almost vertically, called J-lay. In S-lay, the pipes must be somewhat flexible, because they have to bend twice and are subjected to more stress while being installed. J-lay only bends the pipe at one point and puts less stress on the pipes. Similar to cable laying vessels, pipe lay ships use their DP systems to ensure precise installation and avoid underwater obstacles.


“Audacia; Source: Allseas”. Image from Offshore-energy.biz


Drill Ships - drill ships have a large drill and a moonpool for deepwater offshore drilling, working in water 2,000 to 10,000 feet deep. The biggest difference between these vessels and semi-submersible rigs is the ability to move quickly between locations under their own power. These vessels are less stable than larger rigs and in deep water cannot anchor, relying on dynamic positioning to keep them in place while they are attached to drilling equipment thousands of feet below.


Dredgers - dredging vessels move sediment from the bottom of waterways. The sediment can be deposited over time, reducing the draft for larger ships, be contaminated, or simply removed to make a channel deeper. The dredge removes the material from the bottom or shore and depending on the vessel, stores it on board, drops it on a barge, or shoots it somewhere nearby. Due to the need for precise digging, these ships have DP systems to keep them on track while picking up the sediment.


Dredger spraying sand

Dredger spraying sand. Image from Wärtsilä.


Crane Barge or Crane Vessel - Crane vessels perform lifts on the water, the largest using ballast tanks to lower their center of gravity and keep level. The biggest crane vessel in the world is Heerema’s SSCV Sleipnir. With two large cranes, it has a 20,000 ton lift capacity and is kept on station by a DP system with 8 thrusters. The stationkeeping system ensures safe deepwater heavy lifts when there are no anchor points available. SSCV Sleipnir has set multiple records, including lifting a 15,300 ton module for the Leviathan Natural Gas project.


Construction Vessel - Many of the vessels already covered on this list can be considered construction vessels, such as construction support vessels, pipe lay, cable lay, dredgers, and crane barges. But, some vessels define this category, like the Pioneering Spirit, the world’s largest vessel. After decades of planning, building and even rebuilding, this vessel can do it all: huge lifts, construction, deconstruction, and pipe laying. It has eight diesel generators powering 12 azimuth thrusters to keep it on station during record-breaking lifts like the 44,000 ton Johan Sverdrup topsides installation in 2017.


Rock Dumping Vessels - Rock dumping vessels deliver rock and concrete to secure and protect underwater structures like pipelines, cables, and wind turbine foundations. Fallpipe vessels have an underwater pipe with an ROV at the end to precisely deliver rock in deep water of up to and over 1,000 meters. As more underwater pipelines, data cables, and power cables for wind farms are installed, these vessels are needed to deliver rock to protect them.


Fall pipe ROV covering an underwater pipe with rocks. Image from Offshore-Fleet.


Cruise Ships (Passenger Vessels) - Everyone knows about cruise ships - what you may not know is that these luxury liners use dynamic positioning systems. Cruise ships use dynamic positioning instead of anchoring to minimize disruption to marine ecosystems. DP systems also provide additional safety and supreme maneuverability in tight areas.


Heavy-Lift Vessels - Heavy lift vessels include some crane vessels like the SSCV Sleipnir and construction vessels like the Pioneering Spirit. Heavy lift vessels like these are specifically designed to pick up, install, or decommission very large items like topsides and jackets that other ships could not lift.


Heerema SSCV Sleipnir delivering the Brent Alpha jacket to port

Sleipnir delivering the Brent Alpha jacket. “Photo by Heerema Marine Contractors”. Image from Offshore-energy.biz


Mobile Offshore Drilling Units (MODUs) - These are offshore drilling vessels that typically drill for oil and gas. It includes drillships as mentioned above, but also includes drilling barges, jack-up rigs, submersible rigs, and semi-submersible rigs. Any of these vessels can be dynamically positioned to ensure stationkeeping while drilling - even some jack-ups have DP capabilities for precise movement.


Shuttle Tanker - Shuttle tankers transport oil from offshore wells. They provide an alternative to building pipelines where conditions are harsh, the water is deep, or the location of the well is remote. Tankers also allow oil producers to keep their oil separate, whereas pipelines usually blend oil. Shuttle tankers are safer than conventional oil tankers because they operate in a wider range of conditions and stay on station in adverse weather conditions with DP systems.


Floating Production, Storage and Offloading unit or FPSO Ships - FPSOs are offshore vessels that process and store hydrocarbons. They are usually attached to multiple wells, and in deepwater may need dynamic positioning to stay on location. They have advantages over traditional rigs in that they can be easily moved and are ideal for marginal production wells where a rig wouldn’t be economical.


Floating Production, Storage and Offloading unit on the water

“FPSO Kwame Nkrumah (MODEC)”. Image from Offshore-Fleet.


Naval Vessels - Dynamic positioning systems are becoming increasingly common on Navy vessels. According to Military & Aerospace Electronics, “Vessel types that use DP include naval amphibious assault ships, mine sweepers, and military survey ships, surface and semi-submersible mobile offshore drilling vessels, oceanographic research vessels, and cruise ships.” These systems improve the vessel’s ability to precisely scan and survey.


Whew! That’s a lot of positioning and stationkeeping. Dynamic positioning is an interesting technology designed to keep huge vessels still against the elements. It’s also a system that requires frequent testing and verification as lives depend on it. There are a lot of dynamically positioned vessels out there, and we are excited to test them and make sure they are running safely and efficiently. Check out OneStep Power’s DP testing technologies and our news article on ABS releasing new guidance on testing DP vessels.


Happy Fun Fact Friday!



Sources:

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https://en.wikipedia.org/wiki/Dynamic_positioning

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