Underwater Buoyancy Technology enables more efficient dive operations
Working underwater has always presented challenges including diver safety, site conditions and possible damage of equipment/other assets. When moving objects under water precise real time information on the location, depth, and underwater weight of the object is critical but not always available. Past operations have shown that upon movement of an object underwater using buoyancy, the operation can go out of control leading to uncontrolled ascent/decent leading to injury or damage to equipment. When moving an object with lift bags in the water column, if air is not added or removed, the air in the with bag will wither expend (on ascent) or compress (on decent) resulting in the acceleration of the object in the direction of travel.
The issue of uncontrolled ascent is addressed by procedures outlined for example in the ADCI consensus standards version 6.4. For over 40 years, with the adherence to rigorously applied procedures lift bags have been used by divers to safely move, place and recover objects. Among the myriad of applications routinely accomplished using conventional lift bag technology are salvage of large and small vessels, pipeline and offshore cable construction, de-salination plant construction, confined space utility construction, mooring placement, mine recovery and draft reduction.
Prior Technology Advancements
During the last 20 years or so there have been several new technologies that entered the portfolio of capabilities available to teams performing underwater work. Two notable technologies are advanced underwater communication systems and the development of effective working class ROVs.
The deployment of advanced underwater coms has enabled dive teams underwater to maintain timely communication among the underwater team and with the dive supervisor as well as with topside support. This advancement relative to traditional line of sight communication has significantly improved the use of the time divers have on the bottom and has expanded the conditions in which they can safely operate.
Working class ROVs have enabled remote visualization of the working environment by advanced cameras and sensors and has also enabled the manipulation of certain types of equipment particularly in environments where it is more difficult/expensive for divers to operate.
Advanced Buoyancy Technology Enters the Scene
With the recent advances there are still significant opportunities for improvement not fully addressed with current capabilities. Challenges remain where the rate of ascent or decent can cause risk of injury to divers or damage to property and equipment. Often precise information is not available regarding the depth of objects under control and as such controlling a soft and precise placement from the topside or via divers or remote vehicles can be difficult.
Subsalve USA is now offering the BCS advanced buoyancy control technology for underwater lift bags that has been developed to provide precise information regarding the location of an object under control in the water column, the ability to remotely control the ascent and decent of the object, the management of the rate of ascent and decent of the object under control, as well as the ability, when needed, to initiate a lifting operation at a preprogramed time or by a remote signal.
These systems have been fully developed and have been deployed after rigorous qualification testing by customers including the Royal Australian Navy.
There are many situations where this technology can aid in the successful execution of a project and improve the task efficiency. In pipeline construction and maintenance, it is common to place and sometimes replace pipe sections and valves for example. When doing so careful alignment of the objects is required and the effective mass and momentum (particularly in the Z – water column depth direction) can be challenging for the current underwater actors. With the BCS operators can observe and control the precise depth with fine control of the object buoyancy via lift bags allowing closer and safer placement of the object and minimizing any force required to be applied by the team making connections. This allows for more efficient task management of the underwater team. Power plant maintenance of cooling systems has similar tasks to be carried out as with pipeline maintenance but often with the added complexity of obstructed overhead access making crane work difficult and objects in the work area in close proximity. This combination of constraints makes the ability to have live precise control with a limited team especially important. Advanced instrumentation placement and retrieval is another challenging application. Some instrumentation packages are very expensive, can be quite large, and operate at depths that make placement and retrieval operations difficult. The precise control of the BCS aids in the safe placement of instrumentation in some situations. In addition, instrumentation often needs to be recovered for detailed data offloading and power supply replacement. Here, the reliable remote actuation of the BCS either by a pre-programmed timer or via an acoustic signal can dramatically reduce the time and cost to recover instrumentation. Ordinance removal and placement is a similar application. These objects need to be treated as sensitive and are often treated as if triggers are active for safety redundancy. The remote actuation of the BCS can be beneficial to keep personal in designated safe zones to initiate a lift. In addition, the unique ability to control rate of ascent can be used to avoid the actuation of any pressure switches on the object assumed to be active.
Designed with the Diver in Mind
The BCS systems are designed for simple use and can be applied to most underwater lift bags and their respective air supply. All components are able to be tested and validated prior to deployment, and all underwater interfaces are designed to be operated with a single hand in low visibility.
The systems can be flexibly configured for diverse applications. In the basic deployment, the end-user preprograms the BCS module via a simple tablet interface. If they choose manual control through the simple graphic interface, the tablet remains attached to the BCS by a [certified wet connect] hardwire giving the operator full details of depth, rate of ascent/decent, and volume of air supply. In addition, the operator can control on the tablet the addition or venting of air to change the buoyancy and control the ascent/decent. Alternatively, if the operator chooses autonomous mode, they can select a preprogrammed ascent/decent rate and have the system actuated either by a diver switch or at a preprogrammed time/date. For full remote actuation, the system can also be actuated by sending a secure acoustic code.
The BCS Buoyancy Control Technology offers additional capabilities to the dive team to improve operational safety, prevent equipment damage, and improve overall productivity.