|
 The Navajo with imaging module. Since its formation in 1997, Sub-Atlantic has produced a number of ROV systems. After two years of development, the Scotland-based company's latest system is in great demand. During the six short years since Sub-Atlantic, UK, was formed, the company has produced an impressive list of robust subsea products, designed in-house by a dedicated team of enthusiastic design engineers. Sub-Atlantic's products include electric ROV systems (Apache, Mohawk, Cherokee and Super-Mohawk - all named after native American Indian tribes), electric pan and tilt systems, hydraulic power units and valve packs, electric thrusters and their top selling hydraulic propulsion thrusters which enjoy the envious position as the global market leader. Now, after two years in the development (and its largest product development budget), production of the Aberdeen-based company's new Navajo ROV is struggling to meet worldwide demand amidst great enthusiasm in the marketplace. So, what is so different about the Navajo? "Well basically, Navajo is easy, capable and affordable," says Scott Jamieson, head of sales at Sub-Atlantic. "I use the word easy because everything about it is easy. It is easy to build, easy to sell, easy to transport, easy to launch, easy to fly, easy to interface tools and accessories and easy to maintain it in good running order. The difficult part was designing it to be that way."
"This system produces 55kg of axial thrust, is rated to 300 metres and is unbeatably priced. Everything about it feels right," says Jamieson. The Navajo is extremely versatile and suitable for wide ranging applications:
The underlying design principle of the Navajo is simplicity. "Our design goal was to make the system as foolproof as possible. This meant looking very closely at our own and our competitor's designs and the experiences of our existing clients. Instead of relying on operating procedures to maintain system operation, we designed out the potential problems instead," says Colin Millum, Sub-Atlantic's director of mechanical engineering. "Take the Navajo thruster. We designed it to run full of water because at some point during it's life, the water will eventually get in there anyway, then bang!" Electric cables were also identified as a risk item, so these were reduced to one only. Thrusters plug directly into the electronics enclosure with a combined structural/electrical, water-blocked connection. This module is known as the propulsion module. "Essentially, when you remove the frame and the fairings from Navajo, you're left with two units, the propulsion module and the imaging module joined by a single cable. It's as simple as that. Most other systems out there are lots of bits attached to a frame with lots of cables and connectors. That's a lot of bits to go wrong," explains Millum.
This is simply a one-atmosphere electronics enclosure with structural mountings for four thrusters and attachment to the Navajo frame. It also incorporates electrical connectors for the imaging module, the umbilical and for external equipment such as sonar, manipulator and tools. The electronics inside the module consist of quick removable boards connected into a mother-board, eliminating complex wiring. Entering the electronics bottle is easy with a bayonet quick connection system.
This is a one-atmosphere clear transparent enclosure incorporating a +/- 90 degree tilting platform on which is mounted a low light mono camera, a Sony colour zoom camera, a 50-watt dimmable halogen lamp and a laser scaling system. Two parallel lasers project their beams onto the viewed object to establish its size. The imaging module also contains two forward facing and individually switchable, high intensity discharge lamps (HID). These provide pure white penetrating beams equivalent to 120 watts of halogen light. A flux gate compass is included in one of the module end domes. Frame The Navajo frame is manufactured entirely from high impact resistant polypropylene, a material that is slightly buoyant in water and maintenance free. Hydro-dynamic fairings lock into the main frame sections, providing protection to the buoyancy modules. Sliding covers give quick, easy access to connectors, sonar and transponders, which are all mounted inside the frame out of harm's way. Lead ballast weights are mounted low down along the underside of the Navajo frame. Standard buoyancy payload is 10kg with an additional 7kg module available as an option. The centre of the payload is located at the front of the Navajo to allow for tools and manipulators.
The surface control unit (SCU) is a 5u high, 19-inch rack mount design. It comes as standard, fitted into a very compact 8u size flight case with retracting 15-inch flat screen monitor. Power input is self-selecting between 80 to 230 Vac (13 amps @ 230 volts). The umbilical connects directly to the rear of the SCU that supplies 300 Vdc to the Navajo. Opening a small front cover reveals Navajo's hand controller, a Sony PS2 games controller, chosen for its robust design, ergonomics and global availability. This is used to control all vehicle functions, including manipulator. Alternatively, tools and manipulators can be controlled from the SCU console or via a computer through the Navajo's communications link. Video overlay is also included and switchable to desired camera. By adding a second monitor, simultaneous video can be obtained from the mono and colour cameras. Finally, a sophisticated line insulation monitoring system (LIM) provides earth fault protection for the system as well as for personnel and divers working with the ROV. Manipulators, Tools and Work Skids Navajo is supplied ready to fit tools and a range of auxiliary items. One, two and three function electric manipulators can be purchased from Sub-Atlantic that mount directly to the Navajo frame. The electrical connector is even provided with the switching functions. "It really is as easy as that," explains Jamieson. "Most other systems required brackets, wiring changes, additional nodes and things to interface the simplest tool. Not with Navajo, it is really plug-and-play." The Navajo has fixing locations for tool skids that can be fitted under the vehicle. These are generally more intricate, neutrally buoyant tools designed to carry out job specific tasks as currently the practice used in the offshore oil industry. The ROV has more than enough thrust to deal with these and, for control, it has a communication/ power connector that supplies serial comms, 24Vdc and 300 Vdc to drive and control motors and hydraulics for complex functions. A surface PC connects to the comms port on the rear panel of the SCU. In addition to manipulators, other tools include CP probes, sampling skid, dead fish removal skid, cleaning brush and hydraulic packages, including torque tools. Sub-Atlantic will be introducing new tools in the future to cater for different applications and can design bespoke packages to suit client requirements. . Details: Sub-Atlantic, Tel: +44(0)1224 723623, E-mail: sales@sub-atlantic.co.uk, Web: www.sub-atlantic.co.uk |
The Navajo can be quickly transported and deployed from a small vehicle. 
The Navajo's one-atmosphere propulsion module 
The imaging module. 
The surface control unit is very compact and easily transportable. The controller is a Sony PS2 games controller, chosen for its robust design, ergonamics and global availability. 
© 2003 Underwater World Publications Ltd.