How to buy or rent a Remotely Operated Vehicle
Written by Scott Macknocher, industry professional with 25 years of related technical, operational and management experience.
Read time: 13 minutes
Despite having roughly the same aim, that is to operate remotely underwater, Remotely Operated Vehicles or ROV for short, come in various sizes and with differing capabilities depending on their specification and design. Therefore when undertaking the selection of an ROV for a specific activity, assignment or project, there are some important considerations to take into account before making any commitment either to hire or buy.
This article therefore offers an overview of some of the most important aspects associated with the selection of conventional ROVs available on the market today.
Remotely operated vehicles have evolved significantly from early, relatively basic units developed in the 1960’s for military use, to the highly complex systems used today in support of offshore oil exploration, oceanographic activities and military operations, etc.
ROVs were originally used to replace divers in dangerous situations (usually military-related) and to operate at depths beyond the reach of diving capability. In many respects ROV still fulfils this basic need, but in reality, the advanced capability of ROVs today means that in many cases, divers are no longer required even at depths within diving reach.
In fact, ROVs and more generally, remote underwater intervention, is now considered a fully industrialised technology, to the point that hundreds of these systems will be operational around the world at any time, operating in depths up to 3,000m/10,000fsw (Note: a small number of ROVs, can and do work beyond 3,000m but this is a small percentage of the overall worldwide fleet).
Finally it’s worth mentioning that this article is aimed at those persons not particularly familiar with the design, the operation or the mobilisation of an ROV and therefore tries to provide outline guidance to assist in the selection of an ROV. It is not a comprehensive guide and is not intended as such. In fact we would always recommend that relevant expertise in the subject area should be sought when undertaking activities such as this. To that end, Dockstr does have in-house expertise in this area and is available to assist in the selection, audit and assessment of ROV systems, their component parts and the wider field of underwater intervention tooling.
Therefore if you require help with the sourcing of an ROV or ROV services, our team can be contacted at any time on firstname.lastname@example.org.
How does an ROV Work?
In simple terms, ROVs are controlled remotely, from the surface by an operator. Control is achieved through a physical umbilical link which provides power and control to the ROV. And although small (mini/micro) ROVs can be deployed from shore, most ROVs are operated from a host vessel such as a ship, mobile drilling rig or fixed offshore platform.
Electrical power from the host platform powers the ROV which uses thrusters to manoeuvre itself as required by the operator. Operator controls are achieved through electrical or optical signals that are transmitted through the umbilical together with the power.
The ROV will be equipped with various cameras, sensors, manipulators and intervention tooling depending on its size and the tasks it is required to perform. These tasks can vary widely from simple visual inspection to complex survey activities or heavy intervention using tools and/or fluid intervention.
ROVs have come a long way in terms of reliability and capability since the early military systems such as the RCV225 which was originally designed to inspect torpedo tubes on submarines. Today, a wide range of systems are available for hire or purchase and the main considerations to be made when selecting an ROV are dealt with below.
Types of ROV
There are mainly two types of ROV used in offshore and industrial applications today: observation- or inspection-class (OBSROV) and work-class (WROV).
Such classification does not really include the many smaller mini/micro ROVs appearing on the market as these tend to be (although there may be exceptions) suited for inshore and non-commercial activities.
In terms of distinguishing between an OBSROV and WROV, these tend to be classified by the propulsion system being either electric (OBSROV) or electro-hydraulic (WROV).
That said, there are ROVs that defy such categorisation and there are currently examples of mainstream WROV that are being introduced with electric propulsion although the acceptance and uptake of these remains to be seen; the industry has been here before with the original Schilling Quest ROV in the early 2000’s
WROVs are today almost all hydraulically powered, are more powerful and can perform many more tasks than an OBSROV such as construction, pipelay, drilling and completion. However they tend to be much more expensive.
OBSROVs are usually only suited to visual and very light intervention tasks, and therefore these are typically electrically driven.
- Hydraulically powered
- More power
- Can perform more tasks
- More expensive
- Typically electrically powered
- Visual & light intervention tasks
Typical operations for ROV's
The type and specification of ROV required will be primarily determined by the type of operation(s) intended and the depth of operation required. Typical operations may include:
1. Visual survey & inspection;
2. Geophysical survey requiring the carrying of sensors (e.g. sonar, positioning aids, bathymetry, profiling, metrology, etc);
3. Basic intervention operations such as using manipulators for connecting and disconnecting crane or winch wires;
4. Light tooling such as wire cutting or cleaning of structures;
5. More complex tooling operations such as hydraulic intervention or the carrying of under-slung tooling skids;
6. Specific construction support to operations such as pipelay or cable installation;
7. A combination of the above plus other bespoke tasks relatingmto specific activities.
Once the required scope of work(s) has been accurately set out, the operational and technical requirements must be then be determined before any selection process can begin.
The type of technical considerations to be addressed will be derived from the required scope of work.
- ROV depth rating
- ROV payload requirements
- Type of the propulsion
- Type of manipulators
- ROVs multiplex capability
- Tether Management System or Free-swimming mode
- Lunch and Recovery System (LARS)
- Certification requirements
- Technical support
ROV depth rating: Maybe obvious, but not only the depth rating of the ROV has to be considered. Length of umbilical and suitability of LARS will also be required to meet the operating depth requirements.
ROV payload requirements: Will be determined by what the ROV must carry and will determine the buoyancy needs.
Type of propulsion: Hydraulic or electrical? Hydraulic offers considerably more power but at a cost in terms of ROV size and weight, footprint, input power, LARS, etc…
Type of manipulators: Manipulators are vital to most ROV operations and are therefore very important as even very simple activities like hydraulic intervention will be hard without the right manipulators.
The ROVs multiplex capability: The multiplex capacity of the control system will determine the sensors and tooling that can be carried.
Tether Management System (TMS) or Free-swimming mode: ROVs can operate with or without a TMS. Typically, the deeper the operation and the more complex the operation the more likely the requirement for a TMS to be used.
Launch and Recovery System (LARS): The deployment system or LARS must safely deploy the ROV to its working depth within the operational weather or sea-state parameters (see more on this below).
Certification requirements: There may be contractual requirements around the certification of the spread or parts thereof.
Technical support: If the ROV is second hand, how easily can it be technically supported? Is there adequate spares available and does the original manufacturer still exist and do they offer support?
And there are operational considerations to be taken into account before selecting an ROV for a particular project or undertaking
- Host installation
- Permanent installation or not
- Dimensions and weight
- Mobilisation complexity and cost
- Input power
- Environmental consideratins
Host installation: What type of installation will the ROV operate from? The impact on system requirements can be very different when operating from a mono-hull vessel compared to a fixed installation for example.
Permanent installation or not: Will the ROV be installed permanently on a host vessel or platform or will it be mobile and move regularly.
Dimensions and weight: What space does the ROV spread require? And is the deck of the host installation strong enough to support the weight of the spread and to accept the forces transferred from the LARS to the installation during operations?
Mobilisation complexity and cost: What will the mobilisation cost be? Some ROVs can cost >$100,000USD to mobilise in more complex examples.
Craneage: And linked to mobilisation, does the host installation have sufficient crane capacity to mobilise the ROV spread. If not, does it exist locally?
Input power: How much power does the ROV require? Large work-class ROV’s require >500kVA and therefore does the host installation have enough power available during maximum demand?
Crew: Will the ROV be easy to the crew? You need to be able to source personnel who are trained in the operation of the specific ROV in question.
Environmental considerations: What are the required environmental operating conditions and how do they compare to the contractual operating requirements? An ROV operating in Northern Norway from a mono-hull vessel will experience vastly different environmental conditions to that of one operating in South East Asia from a semi-submersible drilling rig for example.
There are many areas to consider before committing to the right ROV system irrespective of whether you are renting or purchasing outright.
The commitment can be significant (measured in millions of US$) however, if the correct planning is not undertaken and the wrong ROV is sourced, the consequences can be measured in hundreds of millions of US$.
Hiring the correct expertise is therefore essential and failure to do so will almost certainly cost money in the long term. At Dockstr, we have an extensive resource of companies ready to provide the expertise required, from auditing, to engineering and from ROV sales to service provision and these can be accessed here:
Explore more companies on our marketplace
Finally, if some of the issues raised above seem obvious, it is worth recounting an incident some years ago when an ROV was hastily sourced for a short-term project. The ROV was mobilised onto a mono-hull vessel together with other project related equipment and the vessel made its way to the designated work site. Upon deploying the ROV it was found that there was insufficient umbilical to allow the ROV to reach the required operating depth....