What is a ROV?
Remotely operated vehicles ROVs are a safe and widely used type of underwater vehicle serving a range of military, commercial, and scientific needs.
Using a series of propellors, ROVs are unoccupied, highly maneuverable underwater robots operated by a person on the surface. An "umbilical" cable carries power and and control signals to the vehicle and video, status and other sensory data back to the operators.
Most ROVs are equipped with at least one video camera and lights. Additional equipment may include one or more sonars, a stills camera, a manipulator or cutting arm and a wide range of sampling options.
In larger systems used in current a tether management system (TMS) is used that allows the ROV to be deployed to depth using a strong but heavy umbilical cable and then flown out from the TMS using a lighter, more flexible cable.
ROVs provide virtually unlimited bottom time and have high bandwidth for high-resolution video and data transmission. These systems have precise navigational control and tracking which makes them ideal tools for conducting underwater research and surveys.
ROVs can vary in size from small vehicles fitted with one TV camera, which are used for simple observation, to complex systems incorporating dexterous manipulators, video cameras, mechanical tools and other equipment. They are generally free flying, but some are bottom-founded running on tracks or wheels.
ROVs were first used by the military in the 1960s. The United States Navy is credited with advancing the technology to an operational state in its quest to develop robots to recover underwater ordnance lost during at-sea tests. ROVs gained prominence when US Navy CURV (Cable Controlled Underwater Recovery Vehicle) systems recovered an atomic bomb lost off Palomares, Spain, in an aircraft accident in 1966, and then saved the pilots of the sunken submersible Pisces off Cork, Ireland in 1973, with only minutes of air remaining in the submersible.
By the 1980s, ROVs were becoming widely used by the offshore oil and gas industry. Since then, designs have evolved and capabilities increased so that ROVs can operate at greater depths, carry much higher-resolution cameras, more sensitive sonar, and more capable manipulator arms. They can be controlled from the surface using fiber optics communication systems. Depending upon an ROV’s size and capabilities, price tags can range from a few thousand to several million dollars.
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What is the horsepower of the ROV?
The use of a measure of horsepower to describe an ROV’s capability has been used in the offshore hydraulic workclass industry to try to provide a metric to compare one ROV against another. It has never been a very good measure even for systems using like power distribution methods (electo/hydraulic) since the efficiency of thrusters varies so much from one machine to the next. To try to compare ROV’s using brushless DC thrusters to Hydraulic ROV’s using horsepower is even less meaningful.
The problem with using this method to compare is that it assumes similar efficiencies between the two. The fact is, using hydraulics to provide the means of driving thrusters is relatively in efficient. It is generally the preferred choice with work class vehicles (Shilling Robotics Quest ROV system being a notable exception and an example of an extremely efficient ROV) because using hydraulics is a more practical method of conduction energy in the rugged conditions of the offshore work environment.
Efficiency is of a lesser concern with the large workclass vehicles since they are able to carry the necessary Hydraulic Power Units (HPUs) and haul the large diameter umbilicals needed to carry the large amount of power. What they win in ease of use in reconfiguring with different tooling packages more then compensates for their lack of efficiency. With smaller inspection class and light intervention vehicles, the benefit of efficiency becomes more pronounced. By driving the ROV using brushless DC thrusters we are able to achieve energy efficiencies in excess of 100% of hydraulic systems. This means that we are able to use much smaller diameter umbilicals (resulting in the need for less thrust). In addition, by using High Voltage DC transmission rather then AC and using sophisticated DC/DC converters to step down the voltage, we are able to do away with heavy transformers on the ROV. The result of all this is a much smaller ROV volume and mass. Drag on an ROV increases roughly as a cube of its dimensions. i.e. double the Length, Width, Height of the ROV and you cube the drag requiring the larger ROV to have a cube of thrust to achieve the same maneuverability.
So, back to the question of horsepower “How do you compare capability of two drastically different vehicles?”
There is not one answer to this question though comparing thrust to surface area seems to us to be the closest and most informative way of performing a rule of thumb comparison. If you calculate the bollard pull of the ROV in each plane of freedom (vertical, longitudinal and lateral) and divide that area by the surface area of that vehicle, you will come up with a figure that can be roughly used to compare two vehicles.
We have prepared a graph comparing the following vehicles:
Make |
Model |
Link |
Power Transmission |
Comments |
Perry Slingsby |
XLS |
Electro/hydraulic |
one of most powerful workclass ROV’s on the market. |
|
Saab Seaeye |
Tiger |
Brushless DC |
Industry standard offshore inspection class ROV. |
|
Seaeye/SeaView Systems |
Raptor |
Raptor |
Brushless DC |
SeaView in-house developed modification to the highly efficient Seaeye Falcon DR. |
 |
|
| This chart shows that the all three of the vehicles compared have very similar thrust to surface area specifications for both longitudinal and lateral thrust. They vary somewhat in the vertical thrust since they are used for different tasks. The chart shows that the SeaView modified Saab Seaeye Falcon DR, the “Raptor”, develops ample thrust for its size making it a very capable yet cost effective alternative suitable for many tasks traditionally considered the exclusive domain of the workclass ROV. |
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How much does your service cost?
When you first contact SeaView Systems one of our senior people, experienced in underwater robotic inspection and intervention operations will discuss your project in detail. Once we have a good understanding of just what you are trying to achieve we will attempt to suggest a range of options to you. Naturally, the more sophisticated the solution the more expensive it will be. However, we will attempt to provide you with as wide a range of options as possible in order to meet your goals and budget.
Long distance penetrations in excess of 5000ft will incur a Penetration Premium which is a figure calculated by a set formula which varies as a function of penetration distance, minimum pipeline/tunnel access (smaller diameter=more cost), maximum water depth (deeper = more cost), and number of bends of 45 deg or more (more bends = more cost). This charge is in recognition of the difficulty of the task and helps us to fairly charge for the in house development of the specific technologies needed for us to provide this very unique capability.
For return business customers certain discounts may be applicable though these will require the mutual execution of a Contractor Services Agreement between SeaView and the client which will carry with it certain rights and obligations for each party. We invite prime contractors to contact us to discuss this special relationship.
We apply a sliding discount structure applicable to projects involving longer lease periods. Contact us to discuss your specific project.
- back to top -What are the differences in the sonars that you use?
When first discussing profilers with the uninitiated, there is sometimes some confusion as to how they differ from an imaging scanning sonar or a sidescan sonar.
First of all, let’s look at the difference between a scanning sonar and a sidescan sonar. With a scanning sonar, a small transducer emitting thousands of ultra sonic audio pulses per second is rotated about an axis using a small motor to drive it. The transducer rotates around an axis much as a lighthouse lamp rotates. In contrast, a sidescan sonar has a fixed transducer which also emits thousands of pulses per second but its movement is a linear one generated by towing the transducer through the water rather then an angular movement achieved with a motor.
Next we must differentiate between an imaging sonar and a profiling sonar. Imaging sonars are typically used to provide an image of the seabed or water column much as a radar does on land. They provide a multicolored (‘chromatic’) display which shows stronger echo returns as brighter colors than points with weaker echos. E.g. you may get a bright yellow image from a strong return off of the side of a steel shipwreck and dark blue image off of the weak return from a smooth sand bed.
A profiling sonar on the other hand provides a digitized version of the echo returns. The sonar’s processor looks at the return signal for each pulse and decides where along that pulse’s return time lays the strongest return. Rather than providing an analog range of colors for each pulse it provides a single dot or x,y point at the point of strongest return.
Another differentiating factor between imaging and profiling sonars is the shape of the transducers beam pattern. An imaging sonar is typically a fan beam whereas the profiler emits a beam pattern like a spot or pencil beam.
The imaging sonar fan beam (typically around half power +/-15 deg from horizontal) is configured to ensure that all targets above and below horizontal are detected while retaining an angular resolution (about 1.7 deg). The profiler on the other hand is a very specific tool for performing engineering measurements. Its spot or pencil beam (half power about 1.7deg from both horizontal and angular rotation) means that it is able to provide high resolution measurements both in terms of the horizontal plane and of angular displacement around its motor axis.
OK, so what does all this mean to you? When we are inspecting a pipeline, our profiler takes very specific measurements of the internal dimensions of the pipe at that location. Not an average over the fan beam as it would be if we used and imaging sonar. The profiler then provides us with either a series of digitized “dots” 
in a screen shot (as in figure below) or it can save those thousands of digitized points as an ASCII file which can then be imported into CAD software for post processing.
If combined with the recorded penetration depth we now have the necessary x,y,z points required to build a 3D model of the pipe (x & Y from the profiler and z from the umbilical counter). Once input to CAD, such parameters as volume of sedimentation or percentage restriction in pipe can be calculated.
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What are your means of positioning the ROV?
More than once we have been asked why we don’t put a GPS on our ROV’s in order to position them. Were it only that simple! Unfortunately, RF energy at the frequency used in GPS positioning systems only travels a couple of inches through water. Instead, we have to rely on a number of other alternatives available to us. We will briefly discuss them here.
Pipeline Tunnel Positioning: Penetration Distance
This is the simplest means of positioning available to us and provides an accurate means of determining position when performing pipeline and tunnel penetrations where we are only moving significantly in one direction, down the pipe or tunnel. This system works by running the ROV’s umbilical cable through a series of spring loaded idler wheels attached to an optical encoder. The encoder is attached to a computer which keeps track of the number of “counts” coming from the encoder. The count is then scaled for feet or meters as required. We write our control software in-house so we are able to configure the system to meet job-by-job requirements. One feature that we often customize for our clients is the ability to show not only the ROV’s position in a pipeline as a penetration distance but also as a station position. By using a station position the inspection engineer reviewing the recorded video and sonar data is more easily able to correlate the position to their construction drawings. We find that this can save a lot of time and confusion. If you think this service would aid your project, please don’t hesitate to ask us about implementing the option.
Open Water Positioning: Ultra Short Baseline Acoustic Positioning (USBL)
USBL is a means of providing a position of the ROV using acoustic positioning. It works by using a Differential Global Positioning System (DGPS) derived position and an accurate heading, pitch, roll and heave sensor to position a transceiver carried on a vessel on the surface. The transceiver is equipped with a phased transducer array capable of resolving both range and bearing to a transponder or responder carried on the ROV. Since the position and attitude of the transceiver on the vessel is known, the absolute position of the ROV is able to be derived by combining that position with the relative range, depth and bearing from the USBL system. This makes for the most simple and efficient means of providing a position in open water conditions.
What’s the difference between a Transponder and a Responder?
The difference between a transponder and a responder is generally more about the way the USBL device is used on a mobile underwater object (ROV for instance) than the hardware itself. A USBL transponder is a device that receives an acoustic signal from the surface transceiver, waits a predetermined time (milliseconds) and then sends out a reply pulse. The surface transceiver receives this pulse and calculates the range to the transponder by halving the time and using the speed of sound through water (approx 1500m/s). This system has the advantage that it is simple to deploy as it doesn’t require any independent wiring and can often run on internal batteries. The downside is that as the sound path has to travel both from the surface transceiver down to the transponder and then back from the transponder to the transceiver, inaccuracies are introduced to the calculation due to variations in speed of sound in water, thermoclines etc.
The Responder is a similar device except that instead of taking the trigger signal as an acoustic signal from the surface transceiver, it receives the trigger as an electronic pulse sent down the ROV’s umbilical. This pulse then causes the responder to send out an acoustic pulse to surface where it is received by the transceiver. Though this method requires that the ROV be configured by a competent electronic technician to allow the signal to travel from copper on the surface to fiber optics in the umbilical and then back to copper in the ROV, the advantage is that the responder system doesn’t have to travel twice through the water column but rather just once. This results in us providing a significantly tighter position to the client.
When working in deep water we generally place a transponder on our aluminum deployment garage and a responder on the ROV itself. This way, we are able to keep a general track of the deployment cage while achieving a tight position on the ROV itself. An example of this method was demonstrated in our recent NOAA/NURC project. http://oceanexplorer.noaa.gov/explorations/08lophelia/welcome.html
Restricted Access Positioning: Doppler aided Inertial Positioning
Originally designed for navigating nuclear powered submarines and space craft, the IMU is essentially an array of very sensitive accelerometers (based around a fiber optic gyroscope) sensing movement in all 6 degrees of freedom. The device measures the rate of change of velocity in the fwd/rev, up,down, port,stbd planes as well as the corresponding rotational axis of the sensor. These accelerations are then integrated two times (the first integration giving velocity and the second integration giving displacement). This process is done many times a second to give the device the ability to not only dead-reckoning its position in space relative to a known start point but also to know its attitude to a very precise degree with respect to North and vertical.
When fitted to a specially designed skid on the Falcon DR and mated with Doppler sonar (to null out any drift errors when the unit is stationary) and a profiling scanning sonar, the system allows us to geo-reference any solid underwater object. This means we are able to model the interior of a tunnel or pipeline or perform very high resolution hydrographic surveys in locations otherwise inaccessible to conventional navigation devices (USBL)
I won’t go on about it more here but invite you to read the paper written by Colin Crichton and Richard Hallyburton of CDL, the manufacturers of the IMU. Please click on the link to be routed to their website where you can download their paper CDL flooded tunnel system .
It is a very impressive technology. While CDL initially intended it for use in performing tunnel investigations we (SeaView Systems and SeaVison Marine Services) have been pioneering its application for performing other restricted access surveys.
Please do not hesitate to contact us for further information about this technology, how we deploy it, the available deliverables and how they may be used to support your application.
- back to top -What makes SeaView Systems special?
We proudly tell anyone who will listen that our advantage in the ROV industry is our people.
SeaView Systems has industry leading capability, including the ability to perform 10,000ft penetrations through conduits as small as 24", and an ROV operation that can be mobilized into a single 20' shipping container and deployed using a self contained LARS system to depths of 3300ft in sea states in excess of force 5 using our dynamically controlled heave compensation winch. This is not so much a matter of extraordinary equipment, but rather one of extraordinary personnel.
At SeaView Systems, we buy our base equipment “off the shelf” but then use our unique technical skill sets to redesign and modify that equipment where necessary in order to perform the extraordinary. Having the capability to perform our own, in-house engineering we are able to provide services that cannot be purchased “off the shelf” but meet unique needs that we have identified as not being addressed by the mainstream industry but which have great value to our customers.
Not only are we a strong underwater intervention engineering house but we also have the operational experience to make us a very strong field operations team. We don’t claim that things always go perfectly in the field; anyone involved in field operations knows that that is not the real world. But the way that we overcome issues when they do occur is our mark of a truly professional team. Having been part of the design team, each of our key operations team members has a fundamental understanding of the technical aspects of our operations. This leads to efficient fault finding in the field and operational efficiency.
Every ROV company will tell you that they run a team of highly trained professionals. The fact is that few really do. It takes half a lifetime of technical training and field experience to get to where we are. With SeaView Systems you will get a knowledgeable, competent solution provider who will not oversell their capability. Please feel free to contact us to discuss your ideas and we will be happy to provide references from customers that have used us for similar projects.
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