SUBSEA SYSTEMS: Mini-sub with arms fills work gap between manned diving, ROV units

Nov. 1, 2001
Free-diving unit surpassing 2,000 ft

Remotely operated vehicles (ROV)s are the workhorses of the deepwater offshore industry. These units can quickly and efficiently perform a wide-range of activities at water depths where manned intervention is either impossible or impractical. Even with all the capabilities of these vehicles, there is no substitute for having a man in the water. This is the thinking behind a new one-man, one atmosphere submarine with manipulation arms called Deepworker 2000, developed by Phil Nuytten. - The new Deepworker 2000 can be launched off of a boat no larger than 130 ft in length.

This manned unit is a hybrid between the ROV and a hard suit diver, both of which have limitations. In many ways, the new unit could be thought of as a manned ROV. The term Deep Marine Technology's President, Paul McKim, uses is direct operated vehicle, or DOV. The DOV, named Deepworker 2000, has been in operation for over four years, but is just now just reaching commercial deployment in the offshore oil and gas industry.

Modern ROV units can do many things, but there also are some broad limitations. Three of an ROV's major drawbacks are:

  • The umbilical and tether limit its range of motion
  • It requires a dynamically positioned dive support vessel
  • It is piloted by remote control from the surface.

The DOV addresses these three limitations by offering a manned unit that is connected to the surface via digital acoustics. McKim said these subs have been operating offshore Alaska and the Pacific Basin on telecommunication projects for the past year and a half. In that time, they have logged more than 1,000 hours of work in depths over 1,500 ft. While this work was going on, McKim said he contacted principal engineers of several operating companies to gauge interest in bringing the Deepworker 2000 into the Gulf of Mexico. The interest has been positive, he maintains, and the unit will move to the Gulf later this year.

Person on site

For close in, detailed work, it is much faster to have a person watching and manipulating the arms of the DOV. An ROV is flown by a pilot who is monitoring it on a television screen. McKim explained that this provides a 2D perspective that makes certain operations difficult. The pilot of the DOV uses his feet to control the Deepworker 2000. This leaves the person's hands free to manipulate the arms. In addition to TV cameras mounted on the sub, the pilot has a 360-degree view out of his cockpit bubble. - This Deepworker 2000 performs underwater intervention down to 2,000 ft water depth.

In the work on telecommunication lines, McKim said, there were a number of instances when having a man in the sub, communicating with the surface, made it possible to accomplish complex tasks in a matter of minutes rather than the hours it might take with an ROV.

Areas such as pipeline surveys and platform inspections lend themselves well to this type system. The pilot can log findings on the sub's computer, so that once the dive is complete, so is the inspection or survey. McKim said there currently are 14 Deepworker 2000 units in operation.

The design comes from Phil Nuytten, who also developed the new-generation of hard suits. While the subs have logged hours for the military and in the telecommunications industries, McKim said the move into the oil industry was strategic, in that he wanted a track record to show traditionally skeptical operators before coming into the Gulf of Mexico.

Safety priority

Generally, the main concern anytime a person is in the water is safety, McKim said. To address this, the Deepworker 2000 has been certified by Lloyds to dive to 2,000 ft water depth. McKim said the unit has been successfully tested to 8,000 ft, but this large safety window is important. In addition, there is full redundancy on the sub's computer system and it has the ability to be retrieved to the surface by remote control.

The Deepworker 2000 carries its own power supply in the form of battery packs. These are good for 72 hours of pilot time. The typical dive will not last more than 4-5 hours. At that time, if an operation is not complete, a second vehicle will relieve the sub.

The "spread" that travels with the Deepworker 2000 includes two subs as well as spare battery packs. This means there is always a second sub charged up and on hand, in case it is needed. The vehicle uses a digital global positioning system to navigate underwater and is in constant communication with the surface.

A destination can be programmed into the vehicle's computer system at the surface and the vehicle can guide itself there and back. The Deepworker 2000 calculates its own optimum descent rate from the mother ship and operates within a cone of communication with the ship.

The deeper the sub travels, the larger the diameter of the cones, and the further it can travel from the ship while still sending and receiving digital acoustics. Currently, the Deepworker 2000 can send digital pictures through the water to the ship. It cannot send real-time video, but if it were to trail a fiber antenna, this would be possible. The surface support vessel follows the DOV on a pipeline survey, for example, but does not have a physical connection with the sub, as it would with an ROV. This makes such operations progress much faster.

On-job time

Much of what an ROV does is handled by the pilot on the DOV. McKim said this cuts down on the maintenance requirements of the vehicle and improves operational time. On the telecommunication jobs, he said the DOV would operate 12 hours a day for 10 days straight with only one, 15-minute period of shutdown time. Most of the problems that would be associated with an umbilical were eliminated from this project, McKim said.

The Deepworker 2000 is small and lightweight with half the surface footprint of a comparable ROV spread, according to McKim. It can be launched off of a 130-ft vessel for about half the price of renting a dynamically positioned vessel to accommodate an ROV.

The sub design is the same across all units, but the hydraulics or photographic package may be modified to fit a specific job. For example, McKim said that several vehicles are being used to film television documentaries. Also, a DOV can be outfitted with tracks to crawl on the seabed, which can be useful in laying fiber optic cables or various types of umbilicals.

Currently, two DOV "spreads" are being introduced to the Gulf of Mexico. Each consists of two subs and the requisite support equipment. McKim said the whole spread fits in two containers.

There may be plans to bring a third spread into the market later and the company is considering manufacturing them in Houston. Future designs may allow the subs to dive deeper, but for the time being, McKim said the goal is to add another option to the submersible market above 2,000 ft water depth.