EoW May 2009

EuroWire – May 2009

technical article

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

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

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

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.

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.

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.

3 Deep-Sea ROV

3.1 Purpose

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

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

vessels and piers.

3.2 Description

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.

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

Figure 2

for a schematic of the Deep-

Sea ROV.

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

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Figure 2

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