The paper describes the main results of a wide research activity, still under development, carried out at Laboratory of Drives and Experimental Automation for Marine Systems (DREAMS Lab) of the University of Genoa and specifically oriented to the design and the prototyping of low cost self moving units conceived for inspection of critical and/or dangerous marine enviromnents (holds, tanks, double bottoms,..) or ducts in ships and/or in off-shore plants (ventilation, refrigeration, conditioning,...).Three different units are, in particular, analyzed and discussed:

• electro-pneumatic unit able to move itself on horizontal, inclined or vertical surfaces with vacuum or electro-magnetic devices of connection to the surface. Steps of motion are realized by four orthogonal pneumatic actuators. The unit is fully automated, with control by on board PLC, driving valves and connection devices. Electrical and air compressed supplies can be proposed external or on board;
• 3D cartesian unit able to inspect confined spaces as double bottoms, with the capability to jump stiffeners, girders or other structural elements. The unit has dimensions compatible with manholes and can be driven wireless by joistick;
• autonomous flexible robot emulating the gub motion and able to move itself  inside circular or rectangular ducts having straight portions, curves and elbows.

Each unit can be equipped with vision systems (video-cameras, thermo-cameras,..), sensors or transducers able to detect on field diversified measurements of physical or chemical variables (ultrasonic thickness on walls, humidity, temperautre, surfaces hardness,...) or with small tools able to make local operations (scraping, hammering, sanding,...). The inspection autonomous units are conceived to be a practical support to register's inspectors, technicians and operators during ordinary or extraordinary maintenance interventions or peridical inspections.