ALL IN A DAY’S WORK SEABED SURVEYS ROV SHIFT
Due to short daylight hours in Norway, shifts are 12 hours (6am – 6pm). First port of call is to check in at the ROV shack for a handover. Connected by an umbilical to a winch onboard the ship, the ROV pinpoints its location on a navigation screen. Precise positioning of the vessel is calculated via satellites (within centimetres).
The ROV also provides sonar allowing clarity up to 200m which is as good as a video. Video with date, time and positional information overlaid is constantly recorded on hard drives and is known as the Black Box (similar to aircraft). Upon completion of a project the DVD recording, together with a written log is presented to the client and includes cable laying detail e.g. time/date/depth etc.
THAT SHRINKING FEELING! All of RSIP’s ROVs have the capability of reaching 3000m, ambient pressure increases by one Bar per metre of depth. The phenomenal
A sonar from the vessel to the ROV returns a ping, thus mathematically measuring the angle, the amount of time i.e. speed of sound in water (measured constantly) to pinpoint their exact location subsea. A pipeline/structure may be pinpointed by sonar on the ROV and can therefore be avoided.
FLYING THE ROV
Pilots ‘fly’ the ROV by sitting on a cyber- chair on the vessel, which comprises a joy stick on the arm, feet up in front, and a wall with huge monitors, The vehicles have 360 degrees visibility with cameras built into the arms, on top and below, which tilt up and down.
pressure at such depths is illustrated by installing a polystyrene cup in the ROV. Having reached just 2000m and returning to the surface, the cup had shrunk to the size of a thimble! Quite a thought!
At such depths visibility can be very poor, with the seabed being disturbed by cable laying or even by fish. In fact Neil goes on to say fish create quite a challenge, predominantly bottom-feeders like cod.
Many projects require seabed surveys. Imperative when planning installations subsea, likened to a lunar landscape there are hazards to overcome. Neil goes on to mention that at Ormen Lange, the seabed is very strange. During the ice age a huge chunk of Norway broke off and fell into the sea, known as the Storegga slide, leaving a huge underwater mountainous range – large blips on the sonar with that one!
Other high technology, such as multi- beam echo sonars, assist in surveying the seabed. These in simplistic terms are 60 ‘fingers’ of narrow beams which illustrate/profile the seabed and illustrate the topography. Fibre Optic Gyros (FOGs) are used to calculate the altitude and heading of the ROV.
TAXIS!
ROV’s are configured to be ‘taxis’ to take and operate tools and sensors to the depths.
All the data collected is date and time stamped then transmitted to the surface using Fibre Optics. However, latest developments are to reduce the subsea processing and do all this on the surface – the technology is ever-evolving.
It was a delight to speak to Neil, his modesty, dedication and enthusiasm is infectious!
Fliss Chaffer Interviewer Wind Energy Network
Click to view more info = Click to view video
www.windenergynetwork.co.uk
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