EoW May 2009

technical article

Wireless systems would seem to be the logical choice, considering the advanced systems found in these ROVs. Unfortunately, wireless systems under water tend to perform very differently from their performance in the open air. Traditional video signals could be transmitted to the controller via radio waves, but radio will not travel far underwater. Sound travels well underwater, but sound waves would be too slow and could not handle the data transfer rate required for the high-resolution video images. That is when the Deep-Sea ROV cable came to fruition as the only logical solution to a communications dilemma. Using a non-traditional method of tethered deployment, the small expendable cable was fed from a spool located inside the vehicle. Conventional tethers would be spooled out from the host ship or command centre. Where standard tethers would limit the mobility of the vehicle, this cable allowed the BOT operator unprecedented freedom to explore. There would be no more entanglement situations as the ROV could simply leave the entangled cable behind and continue exploring. The ROV would simply spool out more cable via its sophisticated mechanical payoff. No more returning in the same path in which you came, this vehicle could be driven into one location and out another. With a completed mission the umbilical would simply be cut and left behind. The initial purpose of the Deep-Sea ROV was to explore ship wreckage. The first official job of the Deep-Sea ROV as an Oceaneering asset was a film documentary of the Titanic, Last Mystery of the Titanic, which aired live on the Discovery Channel on 24 th July 2005 from the site of the wreck. In addition, the Deep-Sea ROV has successfully demonstrated the ability to conduct close-in inspection of subsea equipment, improved search and recovery operations, and security inspections of The Deep-Sea ROV was a box shaped BOT measuring 27" long by 15.5" wide by 17.5" tall. Interestingly enough, these dimensions came from the requirements of its first mission, a trip into the RMS Titanic. The Deep-Sea ROV had to fit through the portholes on the Titanic, measuring 18" wide by 24" high. The outside of the BOT was comprised of syntactic foam made of spheres of glass impregnated into a two-part epoxy-type resin. 3 Deep-Sea ROV 3.1 Purpose vessels and piers. 3.2 Description

This special makeup allowed the BOT to have buoyancy at great depth. Inside the frame were 600metres of the Deep-Sea ROV cable. The ROV housed two video cameras, one being a high-resolution camera for filming segments and the other, a monochrome camera used for navigation purposes. In order to see at these depths, the ROV was equipped with two sets of halogen floodlights and two sets of LED arrays. The halogen flood and spot lights were utilised during filming sequences, while the LED lights were used to navigate due to their low power consumption. The cameras and lights were mounted onto a tiltable bar that allowed up to 210º of travel in the up/down range. The operator controlled the tilt angle from a button located on the operator’s joystick. To position the cameras azimuthally the operator could manipulate the four thrusters via movement of the joystick. The operator had the ability to control the yaw and pitch, which was described as being very similar to flying a small airplane. In addition, the operator had the ability to control the buoyancy of the ROV by releasing small weights from the underbody of the vehicle or syntactic foam blocks from the top of the vehicle. All the sophisticated electronic equipment located on this ROV was powered by a high energy-density battery system, which provided 12–18 hours of operation. Refer to Figure 2 for a schematic of the Deep- Sea ROV.

Both the first and second generation cables had no requirements for buoyancy; they only had to be guaranteed to sink. 2.1.3 Deep-Sea ROV cable This third generation cable differed from the previous two generations of cable by having the following enhanced properties: smaller diameter – this cable was 1 almost half the size of the previous two versions, making for a more compact spool, hence a smaller ROV design or potentially longer cable runs neutrally buoyant – this cable was 2 constructed of a blended polymer jacket, which consisted of two different types of material added together to give the cable neutral buoyancy properties more hockle resistance – this cable had 3 a greater chance of relieving itself from a high stress kink situation than its predecessors. This was due to the fact that the jacket was much more rigid than previous cable jackets 2.2 Invention construction This cable was a 1-fibre construction, meaning it contained only a single optical fibre for data transmission to and from the vehicle. The design was oil-filled buffer tube, approximately 900microns in diameter. The tube contained oil, optical fibre, and strength elements. The oil consisted of a low viscosity mineral oil. The optical fibre was a standard dispersion- unshifted, matched-clad single mode fibre of 255microns in diameter. The strength elements consisted of a multifilament thermoplastic yarn, with good tensile properties and superior abrasion resistance. The buffer tube consisted of a dual polymer blend. See Figure 1 below for a schematic of the cable design.

Figure 2 ▲ ▲

3.3 Advantages The main advantages of the Deep-Sea ROV over traditional ROVs were its small package size, high-energy onboard power supply, and an expendable fibre optic tether (Deep-Sea ROV cable). The ROV was capable of manoeuvring into small cavities within a wreck that would be inaccessible to manned submersibles, divers, or larger ROVs and because it used an onboard power supply, there was no need for a bulky tether; a bulky tether would make filming almost impossible as it would stir up too much sediment for a clear shot of the subject.

Figure 1 ▲ ▲

2.3 Purpose Typical ROVs used a large tether for power and communications. Unlike typical ROVs, power in this case was provided onboard using a high energy density battery system. A revolutionary communications link was needed to feed commands to the ROV as well as send back video imagery.

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EuroWire – May 2009