Many thought it would sink. But it never did. Self-upending of the strange baseball bat-shaped Scripps research vessel FLIP at sea was a most unusual experience. Even for its seasoned crew. They had to cope with operating both horizontal and vertical facilities on board. The uniquely stable vessel was designed for precise deep ocean research activities.

Martijn van Wijngaarden, FLIP article
Ir. Martijn van Wijngaarden.

Article researched by ir Martijn van Wijngaarden (pictured on the right), independent marine consultant and SWZ|Maritime guest editor,

R/P FLIP operated successfully in the Pacific from San Diego for more than five decades. Performing far beyond expectations. Eventually got retired and left its home port with flying colours. Leaving behind a legacy of offshore energy producing Spars. And a polar successor.

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One of a kind

The iconic FLoating Instrument Platform (official name FLIP) was originally built to support research campaigns into the fine-scale phase and amplitude fluctuations in undersea sound waves caused by thermal gradients and sloping ocean bottoms. These acoustic research expeditions were conducted in the Pacific for the US Navy. The FLIP vessel was conceived, crewed and maintained by the Scripps Institution of Oceanography. FLIP was outfitted with Doppler sonars, hydrophones, sensors, and two fully-equipped science laboratories to analyse collected data.

General Arrangement for R/P FLIP design (Scripps).
General arrangement for R/P FLIP design (Scripps).

FLIP’s unique design made it the only vessel in the world capable of operating both horizontally and vertically. It was deliberately designed for upending in deep waters. The long, cylindrical end of the FLIP hull had six large ballast tanks. When flooded with seawater, these forced the hull to submerge stern first, while air filled compartments in the forward part made FLIP’s bow to rise.

Its scientific sensors were fitted externally to the hull. They could thus easily be exchanged and tested whilst afloat at the dockside. This versatility contributed to FLIP’s longevity as research facility. Its incredible appearance and interiors earned FLIP its reputation as the strangest, most recognisable ocean research vessel ever built. Only 17 metres of its sky-pointing bow remained visible above the waterline after the crew partially flooded the long FLIP underwater body.

Design and building

FLIP was designed virtually from scratch by two Scripps laboratory scientists in 1960 to create a more stable space than a conventional research ship hull could offer to study how sound waves behave under water. They had some prior experience with buoys and submarines, but wanted a type of hull that could stand vertical and independent of waves in the water. They took the bold step of developing a floater made for safe overturning as a long, slender semi-submersible manned buoy.

Their innovative design R/P (Research Platform) FLIP would become truly unique as the world’s first and only vertical launchable vessel. The Scripps management showed an entrepreneurial and energetic spirit as the unprecedented FLIP novelty was constructed, commissioned and tested within one year. FLIP was made of approximately 700 tonnes of Tri-Ten steel.

FLIP Action Roll.

The ship-shaped bow transited to a long tube-shape tail. The profile of this most unusual hull form cannot be easily described. But to many Americans it resembled a giant baseball bat. Through some 180 tonnes of permanent concrete ballast distributed deep in its keel, it maintained a horizontal afloat condition when it was docked at the Scripps pier of its home port San Diego.

FLIP’s hull was specially designed to reduce torsion. To avoid any potential interference with the acoustic instruments FLIP had no propulsion power. Therefore, it was always towed to location by tugboat.

Towout to research location (photo: US Navy).
Towout to research location (photo: US Navy).

Upending operations

On station, the tug slipped its towing wire and FLIP was on its own, free floating in the ocean. With its onboard water ballast and air tanks it could trim its stern a full ninety degrees down. A carefully controlled operation that took its experienced captain/chief engineer nearly thirty minutes for the full transition. Most of the rotation happened quickly in the last minute, after which it settled gently into its new orientation and reached a stable vertical equilibrium. Gently bobbing from then on during its research deployment.

Bow rising as FLIP is upended for research position (photo: US Navy).
Bow rising as FLIP is upended for research position (photo: US Navy).

The transformation from horizontal to vertical was one of the most impressive sights on the ocean. The platform that lived up to its name was frequently mistaken for a capsized ocean transport ship. But FLIP would always flip back up again to horizontal position. Compressed air stored in its eight flask-type pressure tanks was used to push the seawater out of the ballast tanks. The submerged aft of FLIP rose steadily until FLIP was once again level with the water.

Weird facilities for orthogonal rotation

After flipping at location, researchers lived and worked there for weeks in a row while conducting scientific studies in the open ocean. Onboard facilities had to be provided for both horizontal and vertical operations of FLIP. Overhead lights were fitted on the surfaces that were the ceilings in both the towing (horizontal) and flipped (research station) orientations. And portholes were mounted in bulkheads and ceilings, depending on the actual vessel state.

Most rooms onboard FLIP had two access doors: one to use when horizontal and the other for when FLIP is vertical. Bunk beds, dining tables, toilets and stoves were built on swivels and gimbals, so they turned with the hull. But things that would not rotate so well, like sinks, were built both horizontally and vertically in each room. There were two showers on board, but only one that could be used in the vertical and one that could be used in the horizontal position.

Double sinks that never sank (photo: Scripps).
Double sinks that never sank (photo: Scripps).

Most of its operational equipment was designed to rotate through 90 degrees, from the air compressors to the galley cabinets. The diesel generators were mounted on trunnions and connected to their fuel and exhaust piping using flexible hoses. Laboratory equipment was stacked in strengthened and pre-rotated instrument racks.

Scientific instruments were built sideways into the walls so when FLIP rotated, the instruments would automatically swing into a usable position. The workboat was an exception to this. When FLIP was upended so was this bow-suspended boat. The crew was instructed to tilt it back to horizontal by hoist wires for its horizontal deployment. The same needed to be done with the research instrument booms. These tall bowsprits were standing upright after flipping and had to be winched down to horizontal working position.

Stable motion behaviour

For precise oceanographic measurements the FLIP needed to be minimally affected by prevailing ocean swells. This was achieved by a long slender cylindrical hull with a low centre of weight. That guaranteed floating stability. And favourable motion behaviour, as the majority of the hull volume remained well below the wave influence zone. The tall floater has endured gale force winds and seas on station mid-ocean from Hawaii.

The diameter of the cylindrical hull was tapered to just 4 metres in the waterline region. This small waterplane area made FLIP almost immune to wave induced forces. Typically, the FLIP vertical heave motions would be below one tenth of the ambient wave height. FLIP’s heave, pitch and roll natural periods in the upright position were designed to be well outside any occurring ocean swell conditions. This eliminated any chance of motion resonance with waves.

R/P FLIP main particulars (source: Scripps).
R/P FLIP main particulars (source: Scripps).

During its oceanographic data collection FLIP was used both in moored and free-drifting mode. The hull was naturally weathervaning, orienting such that the keel was into the wind. The working decks were thus in the lee of the hull, protected from wind. Where a constant heading was required during scientific experiments a small hydraulically operated thruster maintained azimuthal direction.

Crew constraints

FLIP was originally designed without living quarters. However, this concept was quickly abandoned due to the hazards of scientists having to board it from small boats, which were – unlike the very stable FLIP platform – not immune to ocean swells. Extraordinary interior amenities were thus created to accommodate people staying on board the whole time: during tow, upending and vertical research position.

As an oceangoing steel hull platform, FLIP provided basic accommodation for eleven researchers and five crew members for up to 35 days. During the flip, everyone had to stand on deck while the deck below gradually became a bulkhead, before stepping onto a deck that was the bulkhead just minutes before. Once the transition was completed, staff had to cope with working five storeys above the ocean, contending with steep stairs, narrow booms and the confined spaces necessary to make FLIP operational.

Engineer moves around on board FLIP.

One crew member described his stand-up home as ‘a treehouse floating in the middle of the ocean’. All the liveable space was vertically stacked, with corridors being replaced by ladders. This made simply going to bed (in a former dry tank below the waterline) or to the toilet (in the tiny quarters well above the waterline) a challenging multistep process. The interior arrangements caused a permanent Escher-like dazzling effect on crew and visitors.

Crew preparing for research position (photo: Scripps).
Crew preparing for research position (photo: Scripps).

Spar prototype and offshore legacy

With its proven favourable motion behaviour, FLIP served as prototype for the much bigger Spar type buoys, which came into use in the offshore oil and gas industry. And perhaps we will see large Spar hulls supporting floating offshore wind turbines in future.

A total of 21 large Spar type oil and gas production platforms are now moored stationary in the deep waters of the US Gulf of Mexico. The largest Spar to date was installed offshore Norway. These Spars are also towed to location and upended. But unlike their venerable predecessor, none of them is self-righting or capable of reversing this.

Aasta Hansteen Spar towout from Norway (photo: Statoil).
Aasta Hansteen Spar towout from Norway (photo: Statoil).

Research achievements

Outfitted with research instruments by scientists from universities around the world, FLIP’s stability and lack of engine noise made it ideal for observing tidal forces, internal waves, and small-scale turbulence. The slender hull and outwardly extended instrument booms allowed undisturbed measurements at sea. Also, the vertical spar hull did not suffer from vortex-induced flow vibrations.

FLIP was imperviable to wave motions, thus allowing researchers to conduct a range of sensitive research activities including meteorology, geophysics, physical oceanography, marine mammal research, acoustics and laser propagation experiments in a stable and silent environment.

Countless research campaigns acquired invaluable field data on wave heights, acoustic signals, water temperature and density, and air-sea interaction. FLIP has also been used to examine ocean circulation, storm wave formation, and how thermal energy is transferred between the ocean and the atmosphere.

Over its illustrious career, FLIP has set a perfect record of 390 successful flips. It has contributed to several discoveries and has served its many research users by being an exceptionally effective facility. This has resulted in a productive harvest of 36 scientific papers and abstracts released for public use.

FLIP 50th anniversary.

This research will continue. FLIP will be succeeded by new unmanned assets and networks of smaller buoys being developed. FLIP’s legacy also lives on in the novel French research vessel Polar POD, whose contemporary design and size is inspired by FLIP.

All good things must come to an end

After having celebrated its 50th anniversary, FLIP gradually moved into well-earned retirement and Emeritus status. FLIP’s distinguished career finished its final chapter when it was towed for the last time from San Diego Bay to a West Coast dismantling and recycling facility in August 2023. Six years after its last research voyage and three years after reviewers determined that the costs to renovate it could not be justified.

This ended the 61-year long life of a truly remarkable self-flipping platform. An extraordinary piece of maritime engineering that served oceanographic research with distinction. Earning admiration from the maritime and oceanographic professions. Leaving its well-wishers from around the world behind in amazement. With a legacy of offshore energy producing Spars and a polar successor to take over the baton.

Farewell to the unique R/P FLIP (photo: Scripps).
Farewell to the unique R/P FLIP (photo: Scripps).

Picture (top): R/P FLIP in upended position at research location (photo: US Navy).

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