SUBROV, a versatile submarine ROV system, or getting a grip on AUVs

Jan SiesjöChief Engineer ROV Systems

Saab Underwater Systems

1 Introduction

The capabilities of submarines are enhanced with the possibility to deploy AUVs. To recoverthem is complex and expensive.The SUBROV is a submarine ROV system that solves this problem and enhances thesubmarine capabilities.The SUBROV is a new version of an ROV proven in the offshore industry. It has beenupdated with technology from the ongoing Double Eagle SAROV program and reconfiguredin a package that is compliant with the 21-inch torpedo tube. Using its maneuverability andactive control system the SUBROV can dock to an AUV with a docking tool. The AUV canthen be moved, rotated and reinserted into the submarine torpedo tube. Alternatively, theSUBROV can connect to the AUV to download data and recharge its batteries. The SUBROVcan 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 usedin 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 gravitystabilized ROV. It behaves like a much larger ROV in terms of stability. It is this stabilitytogether with an adaptable and robust control system that allows it to dock with a much largerAUV effectively adding stabilization, propulsion and hovering capability. This then allowsthe 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 torpedotube. The SUBROV is derived from the Sea Owl 500 by rearranging the propellers in such afashion that the thrust and torque is optimized for moving an AUV and that the form factor iscompliant with a 21’’ tube. In addition the control system is enhanced to make it adaptable tothe 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 hasthe 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 winchand an ROV.

The ROV can either be configured as a normal cable powered ROV or it can be powered froman onboard battery pack. Battery operation means endurance is limited to 2-5 hours, but avery small fibre only tether can be used that enhances range, submarine safety and reducessystem weight.

The console is used for controlling the ROV and to display video and sonar images to theoperator. The power supply is a converter that can transform the onboard supply to power forthe ROV. The winch is a tether management system with functions to maintain tether lengthand tension in order to keep the tether safe. The ROV is a highly manoeuvrable and versatilevehicle 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 thatinstallation can easily be performed in the same manner as loading a torpedo. The onlyinterfaces required on the submarine are power and the standard penetrator for the tube hatch.

Length 6.5 mDiameter 0.533 mWeight 700 kgPower Supply (max) 5 kW

ROV length 1.8 m, 2.4 m with batteryDiameter 0.533 mWeight (ROV) 120 kg, 180 kg with batterySpeed 0 – 3 knotsDepth (operation) 0 – 500 mTether Length 100 m, 2000 m (fibre only and battery)

Wet end

Dry end

3.3 Features and Functions

ManoeuvrabilityThe ROV is extremely manoeuvrable. It can be operate with complete stability; 360 degreesin both pitch and roll. It has auto depth, heading, pitch and roll. Making it very easy to operateeven for an untrained operator.

InspectionThe system can be used to inspect both the submarine itself as well as the area surroundingthe submarine. The ROV is equipped with both colour and low light cameras. The ROV isalso equipped with sonar to help navigation and to relocate objects.

InterventionThe ROV can be equipped with tools to perform various tasks such as cutting wires,retrieving or moving objects with a manipulator.

CommunicationThe system can be used to carry an antenna module that can be brought to the surface toestablish radio communications. It can also be used to dock and connect to underwatercommunication nodes.

AUV Docking/Recharge/RecoveryThe ROV can be equipped with an AUV gripping tool allowing it to be used to dock with anincoming AUV. The ROV can then move the AUV into a torpedo tube for recovery. As analternative to recovery the SUBROV could establish a connection to the AUV to downloaddata 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 untetheredoperation. 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 orcontainerized system. The same vehicle can therefore be shared between several platformsand fulfil a number of functions.

Example of containerized installation

The design was from day one targeted on modular design and open architecture with thepossibility to replace main system elements.

Double Eagle/SUBROV modularity, Propulsion Packages, SAROV Package and Payloadsamples

This allows upgrades and reconfiguration, enabling use of new technology and changes innaval tactics/strategy as part of an evolutionary strategy. It has also lead to a system wherecore functionality and core subsystems have been reused in several products andconfigurations, all to provide system with extreme stability yet still highly manoeuvrable.The SUBROV can thus fill several different functions depending on the configuration. Theconfiguration can be changed at ship or workshop level, the reconfiguration only taking a fewhours (change of tools to communication). The SAROV package extends the functionality ofthe SUBROV into AUV operations. With this package the SUBROV gains the capability ofbeing operated without a tether to carry out short-range survey or transport operations. Thiseliminates the need for several different vehicle types simplifying operation, maintenance andlowering costs.The same components are used in both the SUBROV and the Double Eagle system. Thisallows use of common spare parts and maintenance resources.

4 TrialsThe SUBROV concept has been tested with a real 21’ torpedo shaped AUV (AUV62F fromSaab).The objective of the test was to demonstrate the capability of a SUBROV demonstrator topick up, transport and insert the AUV into a torpedo tube of a drifting or bottom lyingsubmarine.

4.1 Test setup

The trial was performed from a torpedo-firing platform set in Lake Vättern. This platformcontains an underwater torpedo firing tube of the same type that is installed on Swedishsubmarines. A mock submarine outer hull was mounted in front of the tube in order to moreexactly 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 high-resolution sonar and a docking tool. The docking tool is a motorized lasso that allows a loopof 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 thedocking tool.

4.2 Recovery phases

The entire docking sequence is illustrated below.

Step 1 The ROV is launched.Step 2 The ROV docks with the AUV.Step 3 The ROV swims back to the submarine.Step 4 The AUV is inserted into the tube.

Step 5 The ROV releases the AUV and pushes it into the tube.Step 6 The ROV swims back out.Step 7 The ROV swims back into its tube.

4.3 Test execution

All of the AUV recovery steps above were successfully performed during the trials. Thelaunch and recovery of the ROV itself into a tube were not tested due to the fact that the testROV 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 thesonar display. The sonar allows the ROV to fly in to within half a meter of the AUV allowingdocking to be done in very poor visibility. With a slightly modified placement of the array itwould be possible for an operator to perform docking in zero visibility. The propulsor of theAUV 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 bottomthe ROV can use the lasso to move and lift the AUV in order to be able to pull it along theAUV body.

Liftoff

When the ROV has brought the lasso to the correct position then the lasso is tightenedattaching the ROV firmly to the AUV. After that, the ROV simply lifts the AUV and thewhole 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 visibleon both the video and sonar displays. Tests were performed to insert the AUV based onvideo/sonar and sonar only information. With a little bit of practice the AUV can be insertedbased only on the sonar display. This is due to the fact that the control system allows the AUVto be positioned precisely in depth and heading. The operator can thus align the AUV basedon 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 theROV 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 intoa torpedo tube using the demonstrator system. The SUBROV with optimized sonarconfiguration will be able to do this in zero visibility.

This proves that the SUBROV can provide an effective way to add AUV recovery capabilityto an existing submarine. In addition to this it adds many useful extra functions that allowsubmarines to be more effective in taking an active role in covert operations.