FLIP Diagram
FLIP diagram from Marine Physical Laboratory brochure.


Research Platform FLIP was a 355-foot-long non-propelled manned spar buoy designed as a stable research platform for oceanographic research. 

FLIP Highlights

  • FLIP was towed to its operating area in the horizontal position and through ballast changes is "flipped" to the vertical position, a process that takes less than 30 minutes. This put the stern 300 feet below the surface, a depth required for the original submarine acoustic research.  The platform could either float freely or be moored (anchored) to the ocean floor at depths of up to 5,000 meters.
  • The diameter of the hull was 6.5 meters from the 91- to 49-meter depth, tapering to 4 meters at the 20-meter depth. This change in diameter made FLIP less responsive to wave motion; in 10-meter waves FLIP's total vertical motion had been less than 1 meter. The hull was also designed to resist twisting.
  • Constructed at the Gunderson Brothers Engineering Corporation in Portland, Oregon in 1962, FLIP was made of approximately 700 tons of Tri-Ten steel, a product of U.S. Steel Corporation.
  • Carrying a research team of 11 people and a crew of 5, FLIP could sustain research operations for up to 30 days without resupply. Fresh water was carried in a 1,500-gallon tank, and replenished daily by a 31-gal/hour reverse-osmosis water maker.
  • FLIP had no propulsion power. Three diesel generators supplied 340 KW electrical power for ship and scientific needs. The engines were mounted on trunnions for operation with FLIP in either the horizontal or vertical position.
  • About 3,000 cubic feet of air at a maximum pressure of 250 psi was stored in eight storage flasks located inside the ballast tanks. FLIP had two Ingersoll-Rand Model H25M air compressors to charge the air flasks.
  • Because its design accommodated riders in both horizontal and vertical positions, FLIP’s interior spaces often appeared misleading and even bizarre, with doors mounted on the floor, portholes in the ceiling, objects mounted on swiveling trunions, and sinks and toilets mounted for both configurations.


FLIP was configured to deploy a wide array of scientific equipment and sensors.

The two scientific laboratory spaces on FLIP provided approximately 500 square feet of space. There was significant flexibility in installing equipment on FLIP and most installations could be accommodated. Equipment could be deployed from any of the three deployment booms, attached at any location along the submerged hull and even below the 300 draft by attaching short extensions to the hull. Or they could be placed on the external working decks for easy access. Equipment or sensors could also be deployed by lowering them from the 60-foot-long booms mounted on the upper hull.

FLIP had a variety of booms and winches for deploying equipment. The winches could carry loads up to 1,000 pounds and the booms were capable of carrying loads out to the ends of the booms of up to 800 pounds.

For unique requirements, the MPL Industrial Shop could construct special mountings to assist in the deployment of sensors or for mounting equipment directly on FLIP. An example of unique installations occurred in 2012 when the MPL Industrial Shop constructed an extensive special mounting on FLIP in support of an Office of Naval Research project.

Doppler Sonars

The stability and size of FLIP made it possible to study the physics and energetics of surface and volume processes in both the ocean and the atmosphere near the air-sea surface as well as surface processes just below the interface with Doppler sonar [frequencies from 75 to 200 kHz].

For example, it is possible to study internal wave motion in about a cubic kilometer of the upper ocean in a very unique manner by using Doppler sonars developed by scientists at MPL. When mounted on FLIP, in 20-meter range bins, the movement of the ocean could be measured to an accuracy of 1 cm/sec relative to FLIP in a cubic kilometer of the ocean if FLIP was drifting or a larger volume if FLIP was moored. The 75 kHz sonar was rated at 35 KW and is made up of 1720 elements assembled in trapezoidal modules, that can be mounted individually or all together in a single high-resolution narrow beam array.

Surface wave slopes or surface wavelengths can be measured from 40 meters at the lowest frequency down to 5 meters at the highest frequency with the various Doppler sonar. Measurements have been made of momentum flux, strain, Langmuir cell circulation and wave slope distribution.

Mooring Capabilities

The first FLIP mooring was a single anchor moor in 5500-meter water north of Hawaii in 1969. Subsequently, a multiple anchor capability evolved. It was later possible to place FLIP in a three-anchor mooring in virtually any depth of water. In September 2001, FLIP was moored in a water depth of 4,242 meters, 250 miles southwest of Oahu, Hawaii.

Deep-water moorings took a full day to accomplish, from first light to past dusk, in waters 4,000 to 5,000 meters deep. About 50 tons of gear aboard the tow vessel were required for a deep mooring. Moorings in 4,000-meter water with a mooring scope of 1.5 have had watch circles in the range of 80 to 200 meters, depending on currents. The mooring lines were recovered and reused.

Three point moorings in the deep ocean are routine operations, especially for deployment of acoustic arrays in which flow noise must be minimized and acoustic navigation of array elements is required. The transponder system for doing Array Element Location (AEL) could be surveyed in and tied to the GPS navigation system with the GPS receiver aboard FLIP.