Development of Surf-Zone Capable Unmanned Surface Vessels
Dr. Peter Traykovski | Woods Hole Oceanographic Institution
One of the critical areas for underwater munition detection and remediation is very shallow water less than 5 meters (m) deep. The very shallow water emphasis comes from the fact that munitions are most likely to be encountered by the general public in depths that are suitable for wading, swimming and scuba diving, with potential encounters more likely in the shallowest water. In many environments there will be occasional to frequent breaking waves in depths from 0.5 m to 3 m, and there are very few platforms that have been optimized to work in this region. The current most used approaches consist of specialized large amphibious vessels or small personal watercraft (jet-skis) that are not optimized for survey work. The objective of this project is to develop and test a range of modular Unmanned semi-autonomous Surface Vessels (USVs) for use in shallow water and surf zone conditions.
In the past 5 years, the laboratory at Woods Hole Oceanographic Institute (WHOI) has developed two shallow water USVs. The Jetyak is a 3.5 m long, 1 m wide gas powered, 150 kilogram (kg) weight, jet drive vessel capable of carrying payloads of up to 100 kg with moderate hydrodynamic drag, moderate endurance (~ 8 hours [hrs]), moderate speed (~ 4 to 6 meters per second [m/s] maximum), and relatively poor surf zone performance due to the air intake of the gas engine. The small surf vessel (SSV) is a 2 m long, 50 centimeter (cm) wide, 10 kg weight electric motor/battery powered, jet drive vessel capable of carrying low drag payloads of up to 5 kg, with low endurance (~ 2 hrs), high speed (~ 10 m/s) and good surf zone performance due to the semi-submersible hull and drive system and self-righting design. Neither vessel is optimized for munitions response work in the surf zone as the Jetyak cannot handle breaking waves reliably, and the SSV is too small to carry sensors for munition detection. The goal of the proposed work is to develop and test a series of modular USVs with lengths from 3 to 4.5 m and weight less than 150 kg, with semi-submersible and self-righting hulls that can carry acoustic, electromagnetic and optical munitions response sensors in and outside the surf-zone. The modular design would allow swapping of drive systems with different hulls, and sensor packages, to optimize tradeoffs between endurance and performance, e.g. jet drives could be swapped for propeller drives for more efficiency but worse shallow water performance and safety. Based on our previous experience, extensive in-situ testing is required to determine the performance envelope of these vehicles with respect to wave height, breaking frequency, and mean currents and to optimize maneuverability characteristics which are essential for navigation in the surf zone with endurance and speed. The in situ testing will be combined with numerical modelling analysis using commercial off the shelf (COTS) software to optimize performance.
The proposed development effort would have benefits to both munition response work and near-shore research in general. Unmanned semi-autonomous surface vessels that can carry acoustic, electromagnetic and optical munitions detection and bathymetry sensors and can operate in and outside the surf zone in nearshore water depths, offer many cost and performance advantages over the manned systems that are currently used. In addition to allowing more efficient surveys of munitions, the bathymetric survey capability of these systems will improve the ability to understand coastal erosion processes, which will become increasing important in the next century with anticipated rising sea levels.