Sunday, 5 April 2015

The Flip Ship

Imagine staying inside a room which would tilt itself square as and when needed. You might think such things sound good in fiction and not in real life, but if I tell you that designing such a room or in our case, a ship or platform has it's unique advantages, especially for Oceanographic Research.

Read on. Yes, there exists a platform that can flip itself on its own.

Fig. 1:R/P FLIP
(Courtesy: www.google.co.in)

You and I just wonder of her design, but there were these two MPL scientists, Dr. Fred Fisher and Dr. Fred Spiess who designed FLIP in the 1960's out of a need for a research vessel for studying acoustics of submarine rockets for The US department of Naval Research.

This baseball bat shaped ship of about 700 GT is a remarkable example of engineering technology.

The open ocean platform, R/P FLIP (Floating Instrument Platform) owned by the U.S. Office of the Naval Research (ONR) is  operated by the Marine Physical Laboratory (MPL) of the Scripps Institution of Oceanography. 
Serving her purpose for more than 50 years since 1962 when she was launched by the Gunderson Brothers Engineering Company in Portland, she has given her significant contribution to oceanographic research.


What do you think created a need for designing a vessel that can flip?


As the saying goes ..'Necessity is the mother of invention'.

Carrying out research in open sea is really a tough job. There are interactions of the vessel with the wind, with the current and tides. This makes it difficult for a vessel to maintain its position. For effective collection of oceanographic data, it is important to focus on the design aspects of the vessel. This is where R/P FLIP stands out differently. The vessel in such a mission should be wisely designed such that she has good stability even in rough seas and capable of maintaining its position even in high waves.

There should a considerable difference between the vessel's natural period and wave period so that there is minimum effect of waves on the scientific devices used while measuring oceanographic data.

After conducting a number of experiments and considering several configurations for the desired hull form, aiming for easy accessible working deck space and stability of FLIP in both horizontal and vertical positions, the design was finalized taking into account the arrangement of sensors and other scientific equipment to be placed on board.


Fig. 2:FLIP in vertical position
(Courtesy: www.google.co.in)

In her vertical position, the FLIP has less wetted surface area compared to that in horizontal position, this reduces the frictional resistance acting on her hull. Wave loads acting on it are reduced causing less motions of the vessel.  


Following were some of the requirements for design consideration of the FLIP:


  • The hull of FLIP ship is specially designed to reduce the torsion effect when acted upon by water pressure. 
  • Acoustically quiet for avoiding unwanted acoustic reflections when ballasted.
  • Flexibility in terms of space for mounting and movement  of scientific equipment on board.
  • The location of underwater hydrophones should be easily traced.
  • Shallow draft of 15 feet and 300 feet draft for placing of hydrophones.

Fig. 3:FLIP towed to research site
(Courtesy: en.wikipedia.org)

You must be wondering why a 108 meters long FLIP which partially floods does not have her own propulsion system?

Well, the reason is interference of propulsive devices with her highly sensible acoustic devices on board. For this reason, FLIP needs to be towed to the research site.

A hydraulically operated propeller at the tail end rotates the FLIP about her vertical axis.

What do you think might be the reason for tapering spar design of FLIP? The spar tapers from about 6.5 meters diameter at 91-49 meters depth to around 4 meters diameter at 20 meters depth. Think of it relating to oscillations of the structure.

The varying diameter of the spar shape is useful in giving less response to wave motions. This can be understood when the vessel moves less than a meter in a 10 meter wave height.


Equipment deployment


A wide range of scientific equipment including sensors can be deployed by the FLIP.


Fig. 4:FLIP in operation
(Courtesy: www.google.co.in)

Also, with the help of variety of booms and winches, sensors can be installed at different locations on the submerged hull which has attachments for their placing. This positioning of sensors depends on the weights and types of sensors.

Ambient noise measurement is done using vertical hydrophones that can be placed at different locations and horizontal hydrophone arrays (DIMUS) at bottom of hull.

Wondering how sensors are laid on ocean floor?
This is done using a fair lead attached to the bottom of the hull, which can deploy 3000 meters long array of sensors. Up and down motion of Meteorological instruments on the boom helps to collect data near the water surface.


Fig. 5:Scientific equipments on FLIP
(Courtesy: www.apl.washington.edu)

High resolution, narrow-beam array Doppler sonar employed on board measures wave motions in about a cubic kilometer of surface water and with lowest and highest frequencies wave motions upto 40 meters depth can also be measured. The figure to the left shows variety of scientific equipment on flip.


So how does she work?


Is there any special advanced mechanism for flipping? If so, how it was possible to build it with that advanced technology almost 50 years ago? Many such questions will be arising in your mind. Let me introduce you to her working, I m sure working of such a unique ship has already generated curiosity in you.

         

  video


The FLIP works on the concept of ballasting. Yes, it is this simple concept that gives her uniqueness. The concrete ballast provides buoyancy in horizontal position. It is as simple as when a body is filled with water it submerges. So now it is easy for you to understand its working.
  • The hollow body of FLIP first deploys anchors when towed to a research site.
  • Then with the help of ballast tanks of capacity of 9 tons of water weight located in long thin handle of vessel, ballasting of tanks with sea water is carried out.

Fig. 6:Rotating FLIP
(Courtesy: blog.kineticarchitecture.net)

  • Now, one end of FLIP has more ballast, causing it to sink, while the other end is filled with air. This process lifts the barrel equivalent to 5 storey out of water and the ship slowly becomes vertical. Most of the buoyancy when flipped is provided by water at depths below the influence of surface waves. Diesel engines with a combined output of 340 kilowatts makes this possible just under 30 minutes.
  • When the operation is carried out, setting the ship back to her horizontal position is another difficult task but its just the opposite of what we learnt above. It means de-ballasting the tanks with the help of about 3000 cubic feet of compressed air (stored at 250 psi ) forces water back out and FLIP is again brought to her horizontal position taking half the time needed previously.
All this happens without disturbing the scientific equipment which are stored in cases mounted on walls.
Fig. 7:Ballasting of tanks during flipping
(Courtesy: www.amusingplanet.com)

Designed for operating safely in both shallow water as well as water depths exceeding 2000 meters, the lowest exterior of FLIP is about 15 feet above the waterline when vertical. You will be glad to know that  FLIP is rated to handle even massive 80-foot swells.


Fig. 8:Interior designed for both horizontal and vertical operations
(Courtesy: www.dailymail.co.uk) 

Have you wondered where do the crew stay during flipping? its like an amusement park ride for the crew and riders as they remain on the external decks during the flipping evolution. The wall becoming ceiling after flipping, interiors that are curved or which can flip 90 degrees, heavy equipment like generators mounted on trunnions are some of the specially designed features of the FLIP. 


Operations


Out of a home base at Scripps' Nimitz Marine Facility in San Diego, California, the normal area of FLIP's operation is off the west coast of the United States. 

FLIP also supported research in studying wave heights, water temperature and density, collection of meteorological applications like variations in properties of earth's crust, study of ocean floor using Doppler sonar, energy transfer between atmosphere and ocean, pressure variations and its effects on wave properties, reverberation etc.

FLIP contributed for a set of experiments called High Resolution Air-Sea Interaction project, which measured wind and swell conditions. That data is helping to improve weather models and other ocean-atmosphere databases.LSD

Article bySiddhi Indulkar

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