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SABVABAA - Inuit word meaning: "flows swiftly over it"

A hovercraft dedicated to Arctic Ocean research

Sea trials at Southhampton

Vision

To promote geomarine research in the Arctic Ocean by combining modern technology with the advantages of a drifting sea ice cover.

Motivation

Research in areas covered by sea ice is severely constrained by logistics. Only a few western icebreakers are able to penetrate into the central Arctic Ocean during the summer season while Russia has a number of capable vessels. The other option is use of aircraft landing on the ice during a narrow time window determined by return of daylight by mid-March extending through April-early May when persistent fog sets in and the summer melt starts to accelerate. Ship and aircraft operations are expensive and require extensive planning. There is, however a plethora of small, but nevertheless important scientific projects with modest logistic requirements such as deployment of drifting buoys for atmospheric and oceanographic measurements, measurements of sea ice thickness, oceanography of the upper part of the water column and geophysical imaging of the seabed and sub-bottom sediments. An example of this is expressed in the journal Hydro International LowBudgetHydrography.pdf. Present logistic opportunities in areas completely covered by sea ice severely limits what can be achieved while at the same time our recognition of a changing global climate accelerates our need to understand how the system works.

Background

Dr. John K. Hall, a retired marine geophysicist with the Geological Survey of Israel, intends to explore the use of hovercraft as an alternative polar research platform. The concept was earlier laid out in a research proposal to the European Union Marine Science and Technology III program in March 1995 (http://www.geo.uib.no/hjemmesider/yngve/docs/Hovercraft_MAST_proposal.PDF). The project is a tribute to the memory of his parents and grandparents. John’s polar experience dates back to tours of duty over a period of 14 months during 1966-68 on U.S. scientific research station Fletcher’s Ice Island (T-3), an 6 km by 15 km and 25 m thick tabular sheet of glacial ice drifting around in the central Arctic Ocean. John’s PhD thesis (Hall-PhD-thesis.pdf) at Columbia University, New York in 1970 was based upon a wide range of oceanographic and geophysical measurements and geological sampling of the seafloor sediments carried out by Lamont Geological Observatory (http://www.ldeo.columbia.edu), as the island drifted under the influence of winds and currents. T-3 was first occupied during the International Geophysical Year in 1957 and manned until 1974. It exited through the Fram Strait sometime around 1984.

The T-3 camp on a 6 km x 15 km and 25 meter thick ice island in the Arctic Ocean.

T-3 Drift Track.

Hovercraft – an alternative platform for polar research

A hovercraft rides over water and ice on a cushion of air exerting a pressure on the ground that is less than that of a seagull standing on one leg or 1/10 that of a human. Modern, medium sized hovercraft are powered by conventional diesel engines and carry payloads of 1-4 tons. Present use of hovercraft under arctic conditions include craft for coast guard operations over ice in the Gulf of Bothnia by Sweden, Finland and Estonia, service over ice to a drilling platform offshore Alaska, as well as past service to Eskimo communities in Alaska by the U.S. Postal Service.

Hovercraft factory testing October 2007.

A 12 m long and 6 m wide 2000TD Mark III hovercraft with 2200 kg payload has been constructed at Griffon Hovercraft Ltd. (http://www.griffonhovercraft.com) in Southampton, England. Sea trials and initial crew training have been completed. The craft will be exclusively used for over-ice scientific missions and stationed at UNIS, Longyearbyen. The name of this research hovercraft is R/H SABVABAA, which is an Inuit-Inupiaq word meaning 'flows swiftly over it'. R/H SABVABAA is registered in the US state of Delaware (DL 1519 AB).

The hovercraft SABVABAA has been designed as a research platform from the start. The 14 m2 cabin provides scientific work space, kitchen, sanitary facilities and sleeping space for 4 persons. Deck space amounts to 25 m2. The craft is equipped with long range tanks for an additional 1500 liters of fuel, which will give a total endurance of more than 50 hours at an economy cruise speed of 20 knots.

Cabin interior with work bench for computers and instruments (right) and space for seating/sleeping (left). The seats can be converted to beds. A small kitchen section is located on the starbord side behind the passenger seat.

Cabin interior towards rear with work bench for computers and instruments (left) and space for seating/sleeping (right). The room in the rear contains another 2 beds athwart-ship

A probe for continuous measurements of ice thickness (by AWI/Univ of Alberta) can be attached to the front of the hovercraft. An airgun compressor is located in the red square box on starboard deck about midship. On the port side will be an auxiliary power pack for 230 volt AC (6 kW) as well as hydraulic power to drive the sediment coring winch.

Area of operation

The hovercraft will only operate in areas covered by sea ice. Longyearbyen will serve as a base and supply point for missions north into the ice pack. Transit legs across variable distances of open water will be necessary to reach the ice edge.

Driving in pack ice

In general, an ice covered ocean is a fairly safe place. The ice cover is made up of a mosaic of ice floes of many different sizes. Young ice is smooth and even, but pressure ridges form in areas of compression. During a complete annual cycle, the ice surface melts about 0.5 meter on the top and about the same amount of ice freezes to the underside. Multi-year ice often forms an undulating smooth surface.

Camp on sea ice at 85 degrees north in 2004. Note Twin Otter aircraft parked on the ice runway (right, middle). The camp is on 2.5 meter thick ice and the runway on 1 meter thick ice.

Summer melt ponds near the North Pole in 2001.

The most important consideration for driving a hovercraft in pack ice with multiple obstacles, is to proceed cautiously at a speed which properly considers the maneuverability of a craft resting on an air cushion. Crossing open leads presents no problems. We have collected and evaluated the following information relevant to use of hovercraft over sea ice in the Arctic Ocean:

1. continuous video recording taken from a Twin Otter flying at 50 meter altitude over a distance of 250 km;
   
2. pictures of the ice surface taken at 10 minutes interval on an icebreaker cruise from Alaska to Tromsø in 2005 (http://www2.geo.uib.no/Healy-2005/);
   
3. visual observation from scientific icebreaker expeditions to the North Pole in 1991, 1996, 2001, and 2005;
   
4. chartered smaller hovercraft (hover height 0.4 m) for tests north of Svalbard 1992.

Because of obstacles in the form of pressure ridges, we will be unable to maintain a straight course from point A to point B, but rather travel an estimated distance of 1.5-2 times the direct route. For comparison, the distance wheel trailing the dog sled on Wally Herbert's Trans-Arctic Expedition from Alaska to Svalbard in 1966 measured a distance 1.7 times the direct route. It is also worth noting that all diesel driven icebreakers operating in the Arctic Ocean principally follow criss-crossing open or partially open leads. Only rarely is a straight course through unbroken ice floes attempted as fuel comsumption will increase by 50-100%.

Safety

The hovercraft is built to meet the Code of Safety for High Speed Hovercraft under the International Maritime Organization (IMO). It has a double hull and massive reserves of buoyancy. The craft remains floating at full payload with safe freeboard with nine of the twenty-eight compartments flooded. Most importantly, a ruptured bottom does not impair the craft's ability to hover on the air cushion and move over water or ice surfaces. Wave heights of 1 meter can be handled comfortably, but the craft is clearly not a vessel for routine open ocean operations. Emergency equipment includes survival suits for each person on board and a 6 man life raft in deck container to be supplemented by an extra raft if needed. Emergency location is by a Jotron Float Satellite Emergency Radio Beacon (EPIRB) in addition to a full suite of communication equipment (see below). The craft also carries a portable electric winch which can be mounted on the front or rear.

The fact that a hovercraft moves at relatively low speed (less than 20-30 km/hr) and a small distance (0.7 meter) from the ice surface, means that it can traverse ice floes of any thickness, travel unobstructed across open leads and can park on the ice, while providing a heated shelter for its small crew (2-4). All these factors significantly reduce the risk of travel as compared to other means of transportation in the Arctic Ocean. Requiring only one person for operation, it also minimizes the number of personnel in these fragile Arctic environments.

Hovercraft and the environment

The model 2000TD hovercraft is powered by a water-cooled 440 Hp Deutz diesel engine. The craft has a maximum speed over water of 35 knots and an economy speed of about 20 knots. Hover height is 0.7 meter. It consumes about 1.2 liter fuel per kilometer, i.e. less than 0.5% of an icebreaker. At rest, it sits on two skids, 5 cm wide and 10 m long.

Measurements of air- and water-borne noise from a 2000TD hovercraft has been published by Blackwell and Greene, Jr. (2005) (Hover_noise1.pdf) and also measured by a consultant (The English Cogger Partnership) at the request of Griffon Hovercraft Ltd (Cogger_2000TD noise report.pdf). The highest sound levels from a hovercraft are in the frequency band 80-95 Hz. We may compare acoustic noise measurement from operation of a 2000TD like SABVABAA with sound levels of a Bell 206 Jet Ranger helicopter reported by Newman et al. (1985) (http://www.volpe.dot.gov/acoustics/pubs2.html). At a distance of 100 m, the noise levels from the 2000TD hovercraft are substantially lower than that from the Bell 206 Jet Ranger helicopter as shown in the figure below. Note that a difference of 6 dB in sound pressure is equivalent to a reduction of 50% in sound pressure amplitude. For comparison, the current EØS-rules define maximum noise level from a snowscooter to be 85 dB at 15 meter distance.

Underwater noise levels from a Griffon 2000TD are also considerably lower than conventional vessels of comparable size (Hover_noise1.pdf). This aspect is also recognized in an updated impact assessment for offshore Alaska operations (Updated impact.pdf).

The U.S Postal Service commissioned extensive environmental studies in connection with use of an API-88-80 hovercraft to deliver mail to remote villages in Alaska. The API-88 hovercraft has five times the engine power of the 2000TD. In these studies, the impacts of the API-88 on waterfowl and fish were characterized as insignificant (http://volpedb.volpe.dot.gov/outside/owa/work.view_proj?p_proj=PRJ00166). Monitoring of subsistence gill-netting and winter blackfish fishing also showed negligible impact.

Noise measurements for a Griffon 2000TD hovercraft compared to a Bell 206 helicopter

Marine Seismic Capabilities

Echosounders:

• Knudsen (http://www.knudsenengineering.com) 12/200 kHz echo sounders in a tow-body
• Knudsen Model 3200 CHIRP System using 4 transducers in a tow-body

Seismic system:

• Bauer compressor 140 liter/min
• Air-gun 20 in³ (future upgrade to 40 in³).
• Seismic streamer, 50 meter, 6 channels

Seafloor Sampling Capabilities

• Hydraulic winch with 2000 meter Kevlar aramid fibre line.
• Sediment corer, 6 meter, I.D.7 cm with hydrostatically boosted drive-in.

Geophysical/Oceanographic Measurements

• Lacoste and Romberg G-27 damped gravity meter.
• Ice thickness measurements with an EM probe and laser altimeter from AWI.
• CTD and Valeport Monitor SVP for future use with a Kongsberg-Simrad EM710 multibeam sonar system with swaths to 2000 m.

Ice Drill

• Hydraulically powered ice drill for 15 cm diameter hole and max. ice thickness 3 meter.

Electrical Power

• Deutz 440 hp diesel engine – Alternator 24v at 140 amps (3360 watts).
• Battery bank – 4 Freedom Truck 12v 102 Ahr batteries – Series/parallel –12/24v to lab
• Separate Freedom Truck Starter batteries – 2 x 12 v 104 Ahr batteries.
• Backup emergency batteries for aircraft/marine VHF and Iridium Phones.
• Solar panel Kyocera 2 x 130 watts – in series supplying 24v @ 10.8 amps.
• Generator set – 230 v at 50 Hz, 6 KVA – 6 outlets 2 exterior.
• All interior lighting/navlights are low power LEDs.

Navigation

• Furuno 10.4″ M1934C/20 Chart Plotter and Display –C-MAP compatible.
• Furuno 1934C Radar – 4 kw-48 nm.
• Furuno GP-320B GPS –12 channel, 90 sec cold start –8 channel splitter.
• Furuno PG-500 Fluxgate Compass and Heading Sensor.
• FLIR Mariner Forward Looking Infra Red camera, displaying 25 fps on a cockpit laptop.
• NAVMAN Diesel 3200 diesel fuel management system with GPS input.
• Auxiliary mobile GPS units.

Communications

• Thrane/Sailor SC4000 Iridium Satellite phone, base-station and mobile. Provides Voice, Internet, and Data Transmission as well as Iridium transponder interrogation anywhere in the Arctic Ocean.
• Thrane/Sailor SP3300 Marine VHF, base-station and mobile.
• ICOM A110 Aircraft VHF transceiver, base station and mobile.

Other Equipment

• Katadyn Power Survivor 160E Reverse Osmosis water desalinator.
• Two rooftop CCTV camera monitors, continuous or intermittent storage on disk.
• Multiple laptop computers in a gigabit LAN network, with NMEA navigational input.
• Six Man RFD Seasava Plus R Leisure Marine liferaft in deck container.
• Jotron TRON 40S GMDSS Float Satellite Emergency Radio Beacon, EPIRB.
• Four Vetus linear polythene 103 gallon (390 liter) removable long-range fuel tanks.
• Three forward Helle headlights and two fog lights. Two Francis roof-mounted spotlights.
• Revolving yellow light to indicate high-speed craft.
• Portable electrical winch for bow or stern mounting.
• Simrad IS15 Anemometer with digital readout.

References

Blackwell, S. B. and C. R. Greene, Jr., 2005. Underwater and in-air sounds from a small hovercraft.

Newman, J. S., E. J. Rickley, and M. Locke, 1985. ICAO Helicopter Noise Measurement Repeatability

Click to see images