SUBROV, a versatile submarine ROV system, or getting a grip on AUVs Jan Siesjรถ Chief Engineer ROV Systems Saab Underwater Systems 1
Introduction
The capabilities of submarines are enhanced with the possibility to deploy AUVs. To recover them is complex and expensive. The SUBROV is a submarine ROV system that solves this problem and enhances the submarine capabilities. The SUBROV is a new version of an ROV proven in the offshore industry. It has been updated with technology from the ongoing Double Eagle SAROV program and reconfigured in a package that is compliant with the 21-inch torpedo tube. Using its maneuverability and active control system the SUBROV can dock to an AUV with a docking tool. The AUV can then be moved, rotated and reinserted into the submarine torpedo tube. Alternatively, the SUBROV can connect to the AUV to download data and recharge its batteries. The SUBROV can also be used as a general-purpose tool to inspect, deploy antennas or do light intervention. It is a self-contained 21-inch package, handled as a torpedo, not requiring a dedicated tube. This paper presents the SUBROV together with tests and trials. 2
Background
The SUBROV is vehicle based on the well-proven Sea Owl 500 ROV that is extensively used in the offshore industry.
Sea Owl 500 ROV system This ROV has been used for many years in the civilian and offshore industry for inspection, light work, salvage (torpedo recovery) etc. It has a unique control system that based on
artificial stabilisation. This means that it is much more stable than a conventional gravity stabilized ROV. It behaves like a much larger ROV in terms of stability. It is this stability together with an adaptable and robust control system that allows it to dock with a much larger AUV effectively adding stabilization, propulsion and hovering capability. This then allows the AUV to be controlled such that it can be reinserted into a waiting submarine. The Sea Owl 500 is not in its original configuration compatible with a submarine torpedo tube. The SUBROV is derived from the Sea Owl 500 by rearranging the propellers in such a fashion that the thrust and torque is optimized for moving an AUV and that the form factor is compliant with a 21’’ tube. In addition the control system is enhanced to make it adaptable to the changing dynamics when docking it to an AUV. 3
Characteristics/Capabilities of Equipment
The SUBROV system is intended for use from a submarine torpedo tube. The SUBROV has the following capabilities: • Inspection • UW-works • Communication platform • Active docking tool for an AUV
3.1
System Overview
The SUBROV system consists of an operator’s console, a power supply or battery, a winch and an ROV. The ROV can either be configured as a normal cable powered ROV or it can be powered from an onboard battery pack. Battery operation means endurance is limited to 2-5 hours, but a very small fibre only tether can be used that enhances range, submarine safety and reduces system weight. The console is used for controlling the ROV and to display video and sonar images to the operator. The power supply is a converter that can transform the onboard supply to power for the ROV. The winch is a tether management system with functions to maintain tether length and tension in order to keep the tether safe. The ROV is a highly manoeuvrable and versatile vehicle that can be configured for a multitude of tasks.
System Layout 3.2
Characteristics
The system is designed to have the same dimensions and form as a torpedo. This means that installation can easily be performed in the same manner as loading a torpedo. The only interfaces required on the submarine are power and the standard penetrator for the tube hatch. Length Diameter Weight Power Supply
6.5 m 0.533 m 700 kg (max)
ROV length Diameter Weight (ROV) Speed Depth (operation) Tether Length
1.8 m, 2.4 m with battery 0.533 m 120 kg, 180 kg with battery 0 – 3 knots 0 – 500 m 100 m, 2000 m (fibre only and battery)
Wet end
Dry end
5 kW
3.3
Features and Functions
Manoeuvrability The ROV is extremely manoeuvrable. It can be operate with complete stability; 360 degrees in both pitch and roll. It has auto depth, heading, pitch and roll. Making it very easy to operate even for an untrained operator. Inspection The system can be used to inspect both the submarine itself as well as the area surrounding the submarine. The ROV is equipped with both colour and low light cameras. The ROV is also equipped with sonar to help navigation and to relocate objects.
Intervention The ROV can be equipped with tools to perform various tasks such as cutting wires, retrieving or moving objects with a manipulator.
Communication The system can be used to carry an antenna module that can be brought to the surface to establish radio communications. It can also be used to dock and connect to underwater communication nodes.
AUV Docking/Recharge/Recovery The ROV can be equipped with an AUV gripping tool allowing it to be used to dock with an incoming AUV. The ROV can then move the AUV into a torpedo tube for recovery. As an alternative to recovery the SUBROV could establish a connection to the AUV to download data and to recharge the AUV batteries.
3.4
Multiple roles
The SUBROV vehicle is a member of a family of the Saab vehicle packages and components. It can thus be combined with the energy modules of the SAROV package to allow untethered operation. In this capacity it can assist divers with transportation, navigation and power. In addition to being used onboard a submarine it can also be part of a ship based or containerized system. The same vehicle can therefore be shared between several platforms and fulfil a number of functions.
Example of containerized installation The design was from day one targeted on modular design and open architecture with the possibility to replace main system elements.
Double Eagle/SUBROV modularity, Propulsion Packages, SAROV Package and Payload samples This allows upgrades and reconfiguration, enabling use of new technology and changes in naval tactics/strategy as part of an evolutionary strategy. It has also lead to a system where core functionality and core subsystems have been reused in several products and configurations, all to provide system with extreme stability yet still highly manoeuvrable. The SUBROV can thus fill several different functions depending on the configuration. The configuration can be changed at ship or workshop level, the reconfiguration only taking a few hours (change of tools to communication). The SAROV package extends the functionality of the SUBROV into AUV operations. With this package the SUBROV gains the capability of being operated without a tether to carry out short-range survey or transport operations. This eliminates the need for several different vehicle types simplifying operation, maintenance and lowering costs. The same components are used in both the SUBROV and the Double Eagle system. This allows use of common spare parts and maintenance resources. 4 Trials The SUBROV concept has been tested with a real 21’ torpedo shaped AUV (AUV62F from Saab). The objective of the test was to demonstrate the capability of a SUBROV demonstrator to pick up, transport and insert the AUV into a torpedo tube of a drifting or bottom lying submarine. 4.1
Test setup
The trial was performed from a torpedo-firing platform set in Lake Vättern. This platform contains an underwater torpedo firing tube of the same type that is installed on Swedish submarines. A mock submarine outer hull was mounted in front of the tube in order to more exactly simulate a real submarine.
An AUV was placed on the bottom approximately 50 m away from the platform.
The test system with docking tool The test system consists of a slightly modified Sea Owl 500 ROV fitted with a Didson highresolution sonar and a docking tool. The docking tool is a motorized lasso that allows a loop of stiff wire to be deployed under the ROV. This lasso is then used to lift and grip the AUV. The ROV also has two video cameras, one forward looking and the other looking down at the docking tool. 4.2
Recovery phases
The entire docking sequence is illustrated below.
Step 1 Step 2 Step 3 Step 4
The ROV is launched. The ROV docks with the AUV. The ROV swims back to the submarine. The AUV is inserted into the tube.
Step 5 Step 6 Step 7
The ROV releases the AUV and pushes it into the tube. The ROV swims back out. The ROV swims back into its tube.
4.3
Test execution
All of the AUV recovery steps above were successfully performed during the trials. The launch and recovery of the ROV itself into a tube were not tested due to the fact that the test ROV is not in the SUBROV 21’’ configuration.
Approach of the AUV As can be seen in the pictures the AUV is clearly visible both on the video display and on the sonar display. The sonar allows the ROV to fly in to within half a meter of the AUV allowing docking to be done in very poor visibility. With a slightly modified placement of the array it would be possible for an operator to perform docking in zero visibility. The propulsor of the AUV was clearly visible on the sonar allowing an exact docking point to be chosen.
Catching the AUV In the catching phase the ROV pulls the lasso around the AUV. If the AUV is on the bottom the ROV can use the lasso to move and lift the AUV in order to be able to pull it along the AUV body.
Liftoff When the ROV has brought the lasso to the correct position then the lasso is tightened attaching the ROV firmly to the AUV. After that, the ROV simply lifts the AUV and the whole package is piloted as a normal ROV.
The ROV/AUV swimming The Operator the swims the whole package back to the submarine.
Inserting the AUV
When the submarine is reached the AUV is inserted into its tube. The tube is clearly visible on both the video and sonar displays. Tests were performed to insert the AUV based on video/sonar and sonar only information. With a little bit of practice the AUV can be inserted based only on the sonar display. This is due to the fact that the control system allows the AUV to be positioned precisely in depth and heading. The operator can thus align the AUV based on the sonar and then insert it into the tube.
AUV insertion Once the AUV is thru the hatch it is pushed into the tube. The lasso is then released and the ROV swims back and the front is pushed against the AUV to move it all the way into its tube. 5
Conclusion
The trials have shown that an operator with very little practice is able to recover an AUV into a torpedo tube using the demonstrator system. The SUBROV with optimized sonar configuration will be able to do this in zero visibility. This proves that the SUBROV can provide an effective way to add AUV recovery capability to an existing submarine. In addition to this it adds many useful extra functions that allow submarines to be more effective in taking an active role in covert operations.