The conventional observation techniques from research vessels in the deep sea incur huge expenditures because of operational costs and unavailability of vessels during required times. These uncertainties are limiting the detailed Ocean’s monitoring. Thus, the observation platforms have laid great emphasis on improving the quality and endurance of measurements/observations, leading to the development of unmanned systems such as deep sea and coastal moorings mounted with sensors/instruments for continuous sampling of many ocean properties. Moored buoys are one of the most common and cost-effective means to obtain oceanographic data. But the moorings can provide data only in temporal scale, so, a large network of moorings have to be deployed for spatial scale observations. This limitation was overcome by using mobile platforms such as Remotely Operable and unmanned systems for both surface and sub-surface measurements. The ROV operations for ocean observations are limited to the order of days due to the available ship time for the operation, tether induced drag and require large power supply to propel the ROV; whereas untethered vehicles such as Autonomous Underwater Vehicle (AUV) execute its mission by drifting, cruising, or gliding through the ocean with a speed ranging from 0.5m/s to 2.5m/s. The advantage of AUVs over ROVs is their endurance, where propeller-driven vehicles typically operate in the order of 8- 50 hours.
In the recent times, many bio-inspired underwater vehicles were researched at laboratory scale using, but they could not achieve the efficiencies as anticipated compared to that of the conventional thrusters required for long-range applications. Similarly, underwater Gliders use buoyancy based propulsion where the speed and the vehicle response are limited. But, navigation of gliders in regions of strong current affects the observational capability due to the ineffective vehicle manoeuvrability. Gliders can operate in the order of months in transoceanic ranges creating a large amount of data sampling at the expense of very limited transit speeds ranging from 0.15 m/s to 0.25 m/s. They perform well in a vertical plane, but, the operations in horizontal directions are greatly affected due to the saw-tooth pattern principle, thus leading to operational constraints in a horizontal plane.
Very few hybrid vehicles in line with current research are being developed worldwide as a combination of different propulsion strategies, which are still in nascent stages. Considering the advantages and limitations of different propulsion strategies underwater, the HPURV is conceptualized to improve the vehicle efficiency using different propulsion techniques using the same vehicle and intermittently switching/combining these based on the requirement. This research would help improve current scenario of slow-moving Gliders for horizontal measurements as well improve their overall performance in terms of quick response and achieve better speeds.