Sunday, May 2, 2010

Modular, massively scalable, self-propelled oil sweeper/collector

A simpler, smaller  system is possible with construction time down to hours and using (much more common) end-door containers. Small sweepers could be used to coral oil  towards a single location rather than have it spread everywhere. The remainder of this document describes a grand-scale application.

The self-propelling, floating barrier can be many miles wide. The barrier will extend at least 3-4 feet below the waterline and will have no gaps along its length that would allow surface oil to leak through. It is obvious that such a structure moving through the oil-soaked waters must carry the oil before it, allowing the oil to be efficiently skimmed and removed or collected and burned.  

Such a sweeper/barrier could be 0.5 to several miles wide and, moving about 1-3 miles per hour in zero wind, 10 miles of sweeper could clear about 100-200 square miles of ocean per day. In windy conditions the device would move downwind and clear much more of the ocean each day. Ten miles of sweeper/barrier chain would cost between 10 and 40 million dollars to construct.  Fabrication could be relatively straight-forward and several miles per day would be achievable without any special construction facility. 

A prototype of 100 feet sweeping-width would cost about $100,000 and would be sufficient to prove the principal and to determine handling characteristics, speed and manoeuvring capability in various weather conditions. 

Essentials of Design:

1) The proposal involves shipping containers simply because they are readily available, about the right size, and can be disposed of when no longer required. Any other water-tight floating object of similar size would work.  Containers should be made water-tight by applying a sealing material (e.g. fibre-glass + epoxy resin) to all seams. Side-open containers should be chosen so the doors could be orientated skywards and kept closed. These are are commonly 20 feet x8 x8. The seals on the doors should be undamaged to stop rain from entering.

The container's robust flat surface has the following advantages:
  • skimmer pumps and oil separators could be securely fitted to the top surface.
  • a bridge could be assembled for one or more pilots.
  • workers could walk from one region to another when required (for example to re-fuel skimmer pumps).
  • fuel pipes and waste-oil pipes could  be laid along the entire chain.
  • if electric powered outboards are used, then power generators would be required at intervals along the chain. 
  • a helium "blimp" could be secured with CCTV to give the pilot a "birds eye" view.
2) The containers would contain some number of 40gallon drums of ballast water to achieve optimum draft.

3) A method of articulation should allow tolerance of ocean forces and allow some degree of deformity. Some articulations might have greater hinge functionality to allow bigger deformations of the chain-like barrier. One solution is shown in figure 3. A prototype could use an array of inflated tyre inner-tubes (figure 4).

4) Three or four outboard boat motors will be attached to each container. It is likely that electric powered marine motors would be most practical meaning that power generators would be required at intervals along the barrier chain.  Each container should have sufficient motive power to travel just 2-3 knots of speed sideways (along the direction of the container's short axis) in zero wind. The barrier chain does not have to be powered to move upwind in sweeping mode. All up-wind travel can take place with the units moving through their long axis in single file, minimising windage as well as total hull resistance. Tidal currents may not be so important because in general the oil slick would move almost commensurably with the tide and the aim when sweeping is to achieve movement relative to the oil.

Electric powered marine motors with remote-control capability are available with 160 Lbs of thrust.
5)The flat-bottom craft is just 8 foot  wide and side wind or rough seas could tend to tip the craft over. This would be unlikely when the sweeper chain is in concave or parabolic shape while sweeping oil. In forward (straight - line) travel the risk is greater. Therefore some software would need to be written to induce "side-winder" pattern when the sweeper chain is travelling  in forward (straight - line) mode and the conditions are producing risk of capsize. Such a feature would simply increase the effective width of the craft and therefore improve stability.

6) The oil will accumulate against the barrier as the barrier moves forward.  Pumps should be fitted to the top surface allowing an oil/water mixture to be skimmed and hoovered from the surface.  The oil mix could be separated using industrial oil separators sitting on the container chain and the clean water returned to the ocean.

7) A pilot vessel will provide storage for the recovered oil as well as fuel for pumps and generators and extra manpower.

Proposed Development Process;
  • Appropriate motors and generator should be chosen (eg Minn Kota range of electric marine motors).  These should be fitted to one watertight shipping-container.  If necessary, ballast drums should be added (and chained to walls) till draft is satisfactory. The container should then be driven to an oil region for testing. At first all testing should occur in low-wind conditions.
  • If successful, the next test should involve two containers with articulation. At the early stage, the method described below as "prototype articulation" could be used. 
  • If successful, more units should be added and handling characteristics tested. In the early stages, oil/water could be hoovered manually off the surface till some surface-dwelling skimmer device is sourced.
  • The oil sweeper chain could be incremented indefinitely to become a few or many miles long. A chain should have one pilot per quarter mile and chains should be able to be disarticulated (and re-articulated) quickly so that other vessels can readily pass through the chain. They should be well-lighted so they can operate all night and display flags to improve visibility by day.
  • If necessary container transport ships could take partly assembled units to remote areas and a loading ramp with winches developed.  This would allow the chain to be removed more quickly if demanded by weather changes.

Assuming that shipping containers are purchased for $3000 and 3 motors for $3500, and allowing $3500 for articulations and other per-container costs, the incremental cost per container is $10,000. For one mile of sweeper chain, the cost would be $2,500,000 excluding skimmer pumps, oil separators and labour. Ten 10 miles of oil sweeper/collector capacity would cost 25 million using these per-container costs. 

Figure 3

Articulations between containers could involve custom-made inflatable rectangular cuboid 
rubberised PVC structure; one surfaces would be glued to metal plates for attachment to the containers. Two adjacent pvc cuboids would be connected by tight bindings on the oil side. On the other side the bindings would be elastic to allow hinging.  One of these clean-side bindings could be removed to allow the configuration in figure 5.

Figure 4.

Articulation for testing prototype; arrangement of inflated 48 inch tyre tubes. Some curtain-like structure will be required to prevent oil-soaked water leaking through the articulation.

Figure 5. On the sweep

Figure 6. On the move

It is anticipated that the craft will move upwind using the higher speed configuration and then go down-wind for the sweeping function. "SideWinder" pattern not shown here.

this concept has never been tested

Vince Stewart, Auckland, New Zealand


  1. Great concept. I hope the right people are reviewing options such as these.

  2. It appears to be a promising option, however, and perhaps I missed it in your description, how will it handle in the upcoming hurricane season quickly approaching? We have currently been blessed with good weather, but the predictions for the upcoming storm season do not bode well for any of the applications offered. When those storms hit, the great mixing bowl in the Gulf will make small of our efforts.

  3. From author (Vince). Hi, thanks so much for your comment. There are indeed risks in trying anything. But if the idea has value and remains untried, the loss might be immense.
    Any craft that leaves the shores must be able to get to shelter when a hurricane is forecast. The container chain must do that and also be lifted out of the water. The figure 5 configuration must be proven to work before the seamen and the environment are subject to more risk.

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