On 4th June 2003, the European Parliament adopted a legislative resolution on double hulls or equivalent design requirements for oil tankers so that old, unsafe and dangerous oil tankers like the Prestige will no longer be allowed to transport oil in EU waters. In future, heavy grades of oil will be transported by double-hull tankers only.
The introduction of double-hull vessels is widely seen as the response to the need to prevent maritime disasters. However, to be effective, it must be coupled with measures towards more efficient and cost effective inspection procedures. Adequate tools must be provided to the surveyors and ship-owners, as well as to state and port authorities, providing them with the capacity to perform rapid but safe and reliable inspections.
To date, maritime vessel inspections are based on close-up visual inspections and steel plate thickness measurements. Prior to inspection, a ship must be made fully available at the harbour area where all access spaces must be made safe and prepared accordingly, often in dry dock, thus resulting in considerable ship idle time and, consequently, a significant cost. In the case of big double-hull tankers it can easily amount to multiples of
Ship integrity and pollution prevention call for periodic ship inspections with high costs and risks to those involved. The Remotely Operated Tanker Inspection System (ROTIS) has been developed to enter the flooded ballast tanks (even during ship navigation) to perform close-up visual inspection and wall thickness measurements, using tele-operation from remote sites. The advantages are lower costs (e.g. avoiding ship stand-by), lower risks and reliable results.
ROTIS II is the follow-up to the ROTIS project (completed in June 2002).
The objective of the ROTIS II project was to develop a remotely-operated underwater vehicle dedicated to ship inspection and certification, requiring a minimum of human intervention in a difficult and dangerous environment, and without the need of emptying the ballast tanks. Based on the experience of the first prototype, the project aimed at the specification, design and implementation of a new ROTIS II prototype that met all the tolerance requirements, as well as the particular safety and operational specifications.
In particular, the ROTIS II project:
- corrected / met certain technical issues identified on the first ROTIS prototype (in particular its size and shape);
- significantly enhanced all ROTIS functionalities by implementing advanced control techniques to automate certain tasks, through the incorporation of advanced supervisory techniques that will integrate all available sensors.
ROTIS II reduced the time needed for measurements and reporting in the certification phase, in order to meet the requirements of the classification companies.
The system addressed the following operations requested by the classification companies:
- close-up visual inspection
- steel plate thickness measurements
The ROTIS reference application scenario is relevant to operations inside the ballast area, between the inner and outer hulls of double-hull vessels, with the aim of performing remotely all the inspections required during vessel surveys, taking into account safety and other operational constraints, such as operations in potentially explosive atmospheres.
Description of work:
The ROTIS II system is made up of the following elements:
- a small, versatile, remotely operated vehicle (ROV) equipped with ultrasonic sensor equipment for thickness measurements and a camera system for visual inspection;
- an intermediate unit, providing energy for the ROV based on a secure air generator, and high bandwidth wireless communication links to the central unit;
- a transportable control station for the system, providing an easy-to-use human machine interface, the inspection recording equipment and reporting software.
Each component and subsystem of ROTIS II is designed considering subsequent industrialisation. All subsystems are finally integrated in an operationally ready, class-approved ROTIS II prototype, with particular emphasis given to safety and usability issues.
The main research activities were:
- choice of the correct NDT (non-destructive testing) probe: extensive early testing activities involving various manufacturers and technologies in order to perform plate thickness measurement and coating condition assessment;
- communication system: new technological developments in order to obtain a very thin and neutrally buoyant tether for power and communication, and to design a new tether for the management system;
- the human machine interface: re-engineering activity to enable the ROTIS II operator to efficiently and quickly perform the high quality inspections in the flooded ballast spaces, with logging of data for future reporting or use in the CAD interfaces of the classification companies;
- vision system: enhancement of the vision system to support the operator in the most critical tasks, such as the centring and passing through the manholes.
The final deliverable of the ROTIS II project was a complete prototype system, ready for deployment and operation on double-hull vessels by properly qualified operators. The functionality of the system was tested in conditions as close to reality as possible.
- The ROTIS small vehicle (ROV) is introduced within flooded ballast tanks, between the inner and the outer hull, and has therefore access to virtually all cells and structural parts of a double hull vessel through standard man-holes and openings.
- Dexterous 3 joint arm to reach all surfaces, also webs and flanges of the stiffeners.
- The system can operate on a transiting vessel as well as in harbor.
- ATEX compliant system, can be deployed on loaded tankers.
- Weather-independent operation controlled remotely thanks to wireless system architecture.
- Reaches everywhere in the tank without risk of entanglement due to on-board tether drum.
- Components of the ROTIS system are 2-man transportable. The components described above can be carried and commissioned by two persons on board a vessel.
Rotis II is designed with portability and ease of deployment in mind. The system is enclosed in three separate boxes, each portable by 2 men. It is easily shipped by air. It can be quickly deployed once on board of the vessel in the following steps (guideline only):
- Delivering the boxes on board of the vessel
- Flooding of the chosen ballast tank
- CS is installed in the place of convenience, normally within the superstructureSimplified model of the ship's double hull's cells is prepared using the editor provided
- At the same time, the IU can be installed next to the entry hatch of the ballast tank and connected to the appropriate outlet (compressed air or AC power)
- Rotis II ROV is wheeled to the location, slid out of the box and submerged in the tank
- Start-up checklist is followed and the system is powered on
- The UTM probe is calibrated on a provided test piece of metal (if UTM measures are to be conducted)
- ROV is navigated to the place of inspection, passing to the desired cells while its position is tracked on the 3D model for the purpose of pilot's orientation
- Measurements are taken; still pictures of the inspected areas are recorded, etc.
- The ROV is brought back to the hatch, back-tracking the original entry route
- The system is switched off after following end-of-mission checklist
- ROV is removed from the tank and packaged
- IU and CS are disconnected and packaged, the system is shipped to the next destination