Semi-portable mount for a direct-reading broadband ADCP on a coastal vessel

The authors have built a semi-portable mount for their direct reading BB-ADCP that allows underway current data to be taken aboard the RN Blue Fin, a coastal research vessel with no seachest and nearly 2 meters of freeboard. The mounting system, which is essentially a 14 foot long by 3 inch diameter stainless steel pipe, is deployed off the side of the vessel, secured to a low-profile deck plate, and steadied using wire stays fore and aft. The ADCP itself is shrouded in a symmetric hydrofoil to reduce shed vortices and the associated strumming vibrations created above a vessel speed of 4 knots. Vertical position of the ADCP is set using a 1/2 inch diameter pin and a series of matching holes in the strut and collar. The transducers can be set at multiple depths between the surface and 1.3 meters; the authors currently operate the ADCP with the transducers at a depth of 1 meter. The entire system-ADCP, strut, and hydrofoil-can be assembled ashore and then lowered into the deck plates using a small crane (hence the qualifier, semi-portable). The system provides sufficient rigidity to obtain good bottom-track and water column current data. Navigation data from a differential GPS and an external fluxgate compass is integrated with the acoustic data using TRANSECT (ver. 2.72) and NAVSOFT (ver. 3.10) data acquisition software. Testing continues under different combinations of speed, sea-state, and ADCP mode settings