The research vessel AHI (Acoustic Habitat Investigator) is a 25′ aluminum-hulled vessel designed for seabed mapping surveys in the U.S. Pacific islands. The AHI can either work in conjunction with a mother ship such as a NOAA research vessel, or can operate independently from a small boat harbor in inhabited islands. The AHI is equipped for high-resolution surveying of the seabed in depths from 10 to 200 meters. The hull and cabin house a 240 kHz RESON 8101 multibeam echosounder, a POS/MV position and orientation sensor (with two GPS antennas and an inertial measurement unit), and a small rack of survey electronics and computers. The boat can carry up to six people but typically operates with two people, including a coxswain and a surveyor. The safety and operations manual (PDF) provides more details about the vessel and its operations.
Design and Construction
The AHI was built by SAFE Boats International in 2003. The boat design is based on the SAFE Boats 25′ full cabin boat with diesel I/O with modifications necessary to accommodate the vessel’s survey mission. The AHI is designed to be very seaworthy for its size. The hull is built of 5/16″ aluminum with three buoyancy tanks integral to the hull. The boat is heavily constructed in order to withstand routine deployment and recovery from a mother ship via boat davits. A rigid foam collar provides redundant floatation and stability in rough waters as well as protecting the boat when coming alongside the mother ship. The enclosed cabin is air-conditioned and is designed to protect both passengers and survey electronics from the environment.
AHI’s survey system is based on a RESON 8101-ER multibeam echosounder and an Applanix POS/MV position and orientation system. The POS/MV acts as the master clock for the survey system. An SAIC ISS-2000 (PDF) data acquisition and survey control computer combines position and attitude (roll, pitch, heave and heading) with the sonar’s range and backscatter data, records it to hard disk and provides a variety of navigation and sonar data displays. A Seabird SBE-19 SEACAT Profiler Conductivity, Temperature, and Pressure Recorder is used to designed to measure conductivity, temperature, and pressure and calculate a sound velocity profile in the survey area. The survey system was designed to be operated by a single operator and had to fit into a very small space. The majority of the equipment fits within two Hardigg 8U shock-mounted racks. More details about the survey system design are available.
The AHI has a planing hull with a deep-V construction and a maximum speed of 21 knots. The boat typically transits at 10 to 16 knots and surveys at 6 to 10 knots. A single fuel tank holds 100 gallons of diesel fuel. Fuel consumption is highly variable depending on boat speed. High speed transits can consume 16 gallons per hour while operations at survey speeds consume 1 to 2 gallons/hour.
The engine is a 230 hp Volvo Penta KAD43 (PDF) with dual propeller (DP-S) inboard/outboard drive. The main engine’s fuel is delivered through two parallel Racor primary filters and a single Volvo secondary filter. A 3.5 kW Kohler marine generator powers the survey electronics and battery charger. The generator’s fuel is delivered through separate primary and secondary filters. The survey electronics and cabin are cooled by an engine-driven air conditioner.
Two 12 V marine, deep-cycle 55 A hr. batteries are charged by the main engine’s 60 A alternator, the generator’s 15 A alternator and a Guest 15 A three-stage battery charger. These batteries are separated to support engine and house loads but a battery combiner automatically charges both batteries. 120 VAC is provided either by the generator or shore power. A 2200 watt uninterruptible power supply conditions power for the survey electronics.
AHI in CNMI-Guam
In 2003, the R/V AHI was deployed from the Sette in Saipan Harbor and worked independently around Saipan, Tinian, Rota, and Guam during the cruise period. The bank tops and shelf environments of Saipan and Tutuila, as well as the offshore banks of Marpi and Tatsumi, were completely characterized in water depths ranging from 20 to 250 meters. Only partial surveys were done at Rota and Guam, due to time limitations and equipment problems. Optical validation surveys during 2003 collected a total of 126 seafloor video segments from underwater camera sled deployments were completed at 27 different islands and banks over the course of 40 days at sea.
In 2007, the R/V AHI returned to Saipan aboard the NOAA Ship Hi’ialakai, which also has two multibeam sonars, an EM3002D and an EM300. During HI0702 (12-22 May, 2007) multibeam surveys were conducted around Santa Rose Reef, Guam, Rota, Aguijan, Tinian & Saipan. The AHI was used to conduct hydrographic surveys to International Hydrographic Organization standards of Saipan (#81076), Tinian (#81067), and Rota harbors in collaboration with personnel from NOAA’s Office of Coast Survey. During HI0703 (25 May – 12 June, 2007) both vessels surveyed around the Northern Mariana Islands, including Anatahan, Sarigan, Guguan, Alamagan, Pagan, Agrihan, Asuncion, Maug, Supply Reef, and Farallon de Pajaros, which are all part of the Izu-Bonin-Mariana island arc system.
Multibeam surveying in approximately 15-1000 m water depths is now complete around all islands except Guam, Rota, and Agrihan, where shallow areas remain that must be surveyed using a small boat. Additional survey data have also been collected by a number of other government andacademic groups, particularly in the northernmost islands. The majority of these data are already available in swath form from the National Geophysical Data Center and are being combined into a set of gridded products in collaboration with the NOAA Vents Program Office.
In 2004, CRED was contracted to continue their investigation of coral reef ecosystem resources within the Garapan Anchorage outside of Saipan Harbor, in support of a possible expansion of usage of the anchorage. A field team of 8 people spent three weeks in Saipan collecting an additional 122 km of seafloor video track in November and December. See the report from that field mission here.