The ROV for Inland Surveys and Inspections:
Shallow Water Surveys

CASE STUDY 1: GRAND UNION CANAL
Culvert Inspection using ROV Technology

Consulting Engineers Evans Grant & Co have been appointed by British Waterways to conduct a condition survey of the culverts which connect the Tringford pump station and it's surrounding reservoirs. This network of inter-connected reservoirs in the Hertfordshire countryside form the basis of the system to maintain the water level in the Grand Union Canal. The original Wilstone Reservoir was constructed in 1802 and quickly followed by construction of the Tringford and Startopsend reservoirs within 25 years, probably due to an under-estimation of required water capacity to maintain the then busy canal traffic. These three water sources, now a tranquil bird sanctuary and recreational area, are still today linked together by a network of brickwork culverts that remains virtually unchanged from the original construction.

In order to perform the inspection of several hundred meters of enclosed culvert consultants Evans Grant used a combination of their specialist diving skills and the newly acquired VideoRay Remotely Operated Vehicle (ROV). This device, used in sections of the culverts inaccessible to divers, consists of a high power videocamera, lights, three axial thrusters and a neutrally buoyant tether all controlled from the surface and 'flown' down the culvert. The colour CCDcamera, which can be panned and focused from the control panel, provides standard video output which is viewed on a monitor and stored on a conventional videotape recorder together with verbal commentary from the engineer.

The VideoRay, supplied in the UK by Ohmex Instruments, is the smallest commercially available ROV which is suitable for industrial applications, weighing just 4Kg it is easily transported to site in its two carry cases and powered from a small generator or local power source. Previous attempts to inspect the culvertsweremadeusing aROVmachinedesignedfor use in the North Sea, apart from being too heavy and large for the job, its powerful thrusters created turbity by agitating sediments, the subsequent poor visibility prevented the capture of any useful video record without waiting long periods for settlement.

The initial observations from the survey show that, with the exception of bottom sediments drawn in over time by the intake flow, the condition of the brickwork culverts remains in remarkably good condition for workmanship which is nearly two hundred years old.

Thanks for permission to use historic and current content to British Waterways and also the cooperation of consulting engineers Evans Grant Ltd. For further information on the VideoRay ROV visit www.ohmex.co.uk

OHMEX Ltd. - 412 SOLENT BUSINESS CENTRE
MILLBROOKROAD - SOUTHAMPTON - SO15 0HW
TEL: 02380 510 903 FAX: 02380 510 733

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CASE STUDY 2: Osiris Projects

Osiris Projects, one of the UK’s leading inshore hydrographic/ geophysical survey contractors, has put a new 8-pound ROV to work on a half-dozen projects and counting. A new tool for underwater surveying, VideoRay ROV is significantly lighter, less expensive, and more maneuverable and compact than other ROVs the company has used, according to Andrew McLeay, a director at Osiris.

McLeay says the ROV is helping Osiris broaden its activities, because it is easily deployed from a small vessel. Further, the VideoRay’s size -just eight pounds and 9in W x 14in L and 8.5 in high - lets it enter pipelines and confined spaces for detailed visual inspections.

Recently, Osiris used VideoRay for surveying long sea outfalls off the north east of Scotland. VideoRay viewed pipes in situ to examine condition, debris, and function. “We were most impressed with the ability the VideoRay gave us to operate from our small (8 metre) trailable survey boat. Normally a larger boat would have been needed to accommodate a conventional ‘small’ ROV,” said McLeay. “The VideoRay unit proved to be extremely useful and we have hours of excellent footage of outfall diffuser blocks in 15 - 20m of water.” Had he used a different ROV, McLeay would have had to use a larger survey boat, which would add 800 pounds to the cost of the project.

For another project, Osiris was contracted to inspect the deteriorating concrete columns and structures of a reservoir enclosed by a roof. The only access in was through a manhole, and health and safety regulations prohibited sending a man in to visually inspect. Osiris raised the water level and dropped VideoRay in to take a look. “One of the main advantages of VideoRay is how easily it gets into inaccessible places,” says McLeay. “In this case, we got into a tight spot and minimized the risk to humans by sending the ROV in to do the job.”

McLeay has used VideoRay in waters with high chlorine levels that S would endanger divers. “We just wash it off afterwards,” he says. He drops VideoRay in the water to handle projects where there is a danger to divers due to moving parts, such as the inspection of lock gates.

McLeay says he saw how the ROV would pay for itself with a single 10-day project. “If we would have had to use a larger survey vessel and another ROV, the 10 days of mobilization costs would have nearly equaled the cost of the VideoRay,” he says. “It is much easier and more convenient than other ROVs, which require a larger generator and more space on the vessel. We just pack the VideoRay in a van or station wagon, show up at the reservoir, and drop it in over the side.”

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Suggested Configurations

For less demanding surveys, we recommend the VideoRay Explorer. For more intensive operations, we recommend the VideoRay Pro III with:

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