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www.sea-technology.com May 2016 / st 31 I n the world of ROVs, AUVs, landers and other vehicles, towed systems are often forgotten or their usefulness underevaluated. Dropcams and towed systems were born long before ROVs and AUVs appeared because they require less electronics and controls. Towed systems are still in use, and for some types of op- erations and scientifc applications they are more cost effcient than other platforms. Application of Towed Systems There are many different applications of towed systems. From simple fat-water surveys for coastal zone management to surveys in trawl nets, towed systems can be used with numerous sensors and instru- ments. Towed systems were invented when underwater robot- ics was science fction and scientists primarily needed to obtain underwater images of large areas. Divers have, even with scooters, a limited range of actions, so it was neces- sary to attach a camera to some kind of towing frame. With the ongoing development in electronics, towed systems have developed into multipurpose, multifunction platforms without propulsion but with some type of ac- tuators. Applications are clearly in science, where large areas can be inspected in short cruises and from relatively small boats and vessels. Thanks to microelectronics, HD cameras, LED lights, fber optics, and a large number of sensors, sniffers and water quality samplers, it is possible to carry out surveys related to coastal zone management, EOD recovery and debris search with high cost effciency; for example, searching for bombs and mines from WWI and WWII in the Baltic and Northern Seas. ROV operations often require big vessels, normally with type two or three dynamic positioning. Due to the necessity to operate in any kind of environment, ROVs need strong thrusters, which mean a lot of energy con- sumption. Depending on the kind of ROV, the additional components like generators, winches, technical staff and others on surface not only increase the ship size but the operational costs. Obviously, there are strong arguments for the use of ROVs when you need to stay on a spot or stop at one site and operate a tool. But when you are searching for something in a high-current environment, for example during salvage operations, a towed system can be the better choice. Ongoing Developments Towed systems for the inspection of trawl nets have been in use for several decades. Mariscope got into the game with the development of the Magnus Tow for the German Bunde- sanstalt für Fischrei in Hamburg in 1995. This system used Magnus rotors instead of propellers to position itself in the trawl net during the trawl. This system was a hybrid since propulsion was used to position the unit at the right place during the operation within the net. The company has developed a new hybrid system with- out rotors: the Observer III. The frst application is a stand- alone system to be attached inside a trawl net during op- eration. Here, the position is fxed, but the system needs to automatically start and stop recording and control the lights and other sensors in order to reduce power consumption. System Details and Software In the stand-alone version, the Observer III receives its power supply through lithium-ion or Li-Po battery packs. The packs are sized according to the sensors, cameras, lights and the duration of the deployment. Since the system operates autonomously in this mode, all functionality can Modern Towed Systems New Developments for Multipurpose Platforms By Christian Haag • Christian Dreyschultze • Raúl A. C. González Side view of the Observer III with HD cameras, laser pointers, LED lights and electric-driven depressors.