Ships and their tanks need constant inspection to ensure the safe transport of goods and people. The EU-funded project 'Remotely operated tanker inspection system II' (ROTIS II) wanted to develop a robot-like system that inspects a ship's ballast tanks, reducing inspection costs and increasing efficiency. The project aimed to develop a system that is ideal for oil tankers, dry and mixed cargo, and floating production, storage and offloading (FPSO) vessels. ROTIS II sought to build and test a prototype under actual conditions. It constructed a small vehicle that fits between the inner and outer hulls of double-hull vessels with versatile three-joint arms and other useful features. The vehicle can monitor hull integrity in harbours or even during transit using wireless operation. In more detail, the developed prototype has three main parts. The first is the remotely operated vehicle (ROV) with six cameras and an ultrasound probe with an automatically extendable wire to power it and transmit data. The second is the intermediate unit which is the power and relay station that controls the system, placed close to the hatch of the ballast tank. Lastly, the control station, connected through wireless technology, operates the ROV and logs inspection data. The cost-efficient system is designed to be carried easily and shipped easily. If the prototype and technology are fully exploited, safety on the high seas will be enhanced in many ways. The new system will have the potential to reduce maintenance costs and repairs considerably.