Revisiting the Ocean Cleanup, a plan to remove plastic from the oceans

UPDATE: The Ocean Cleanup released a feasibility study in June 2014 that attempted to address many of the concerns we had below. You can read our updated technical review here.

Boyan Slat’s plan to clean plastic from the world’s oceans is making the media rounds again. Unfortunately, as covered in a previous post on DSN, this plan has some major issues that are unlikely to make it feasible. While not the first to claim to solve the problem of oceanic plastic, the widespread media coverage of this well-intentioned but misdirected venture even prompted marine debris scientists to create a list of guidelines for  potential inventors of plastic-capture systems.  I am reposting the original article below to explain why we here at DSN don’t think that the Ocean Cleanup Project is a realistic solution for removing plastic from the ocean. While a viable plan does not to my knowledge exist, we can still do our part to stop more plastic from entering the world’s seas starting with these 6 simple tips to reduce plastic consumption.

And because it’s cocktail week, of course I had to find the perfect drink to toast this crazy contraption, the Wet Dream.

1/2 oz amaretto almond liqueur
1/4 oz Blue Curacao liqueur
1/4 oz creme de bananes
1/4 oz sweet and sour mix
1 splash pineapple juice
1/4 oz Chambord® raspberry liqueur

Mix all ingredients except chambord. Chill and strain mixture into a martini glass. Float chambord to the bottom of the glass.

I’m just going to come out and say it, any project that touts itself as the “World’s first realistic Ocean Clean-up Concept” is just asking to be torn apart.

“The Ocean Cleanup” is the brainchild of a 19-year old Boyan Slat. He proposes using the oceans themselves to clean up plastic. By setting up a line of giant sifting booms across the major ocean gyres, ocean currents will push plastic into these giant traps to be collected and reused for profit.  He plans to set up an array of 24 of these sifters and calculates they will clean the ocean in 5 years.

The Ocean Cleanup’s proposed plastic sifting boom.

Before I add my two cents, here’s what Miriam had to say about the idea at the Marine Debris Listserv:

Dear all,

I’ve tried to stop fact-checking to every cleanup scheme, but I guess it’s an addiction at this point. Also, I feel that as a community we cannot move forward with practical solutions to marine debris until we lay some of these common misconceptions to rest. These points respond Boyan Slat’s TEDx talk, but you can also see photos of his proposal here: and

  • Most zooplankton don’t survive being caught in a standard manta net, never mind being spun in a centrifuge. They might still be twitching, but they have lost a lot of their important parts, like antennae and feeding apparatus. When we want to capture live zooplankton, we use special live-collection nets and are very, very careful. For gelatinous zooplankton like salps, the only way to bring them up in good condition is to individually capture them in glass jars on SCUBA. I am highly skeptical that any significant proportion of zooplankton are viable after caught in a net and spun at 50 RPM. (though I realize that he’s not proposing to do this on a large scale.) 
  • Mooring fixed “ships” in the open ocean (avg depth 4000 meters) is highly improbable for a lot of reasons. Just to pick one: I could not find data on the absolute deepest mooring in the world, but this implies that it is approximately 2,000 meters. So these ships would have to be moored at twice the depth of one of the deepest moorings that existed ~2007. 
  • Having seen no data, I can’t really speak to the efficacy of floating booms in removing microplastic. However, Giora Proskurowski & colleagues have shown that microplastic get mixed down below the surface in fairly moderate winds. These booms would be unlikely to function in any significant wind and wave action. And the mixed layer in the open ocean can get quite deep, around 100-150 meters in the winter with storms. 
  • Speaking of wind and wave actions, ships on fixed moorings and thousands of miles of booms (because the scale of this is also improbable) have the potential to create a lot more marine debris, and seem particularly hazardous to entanglement-prone marine life. 
  • This isn’t even getting into issues of scale (the California Current alone is ~300 miles across), maintenance and fouling…

I realize that Mr. Slat is a student, and have no doubt that he, and the inventors of countless other plastic cleanup schemes, have only the best of intentions. I am hoping we can work together as marine debris professionals to channel their energies into more productive directions.


Miriam Goldstein

While I can’t speak to what these booms will and will not pick up, I completely agree with her I am highly skeptical whether the design is even feasible from an ocean engineering standpoint. Here are some of the major unanswered technical questions:

1) How does the sifter work?  To be honest, I am not completely sure. The website and TED talk are completely devoid of technical details. But from what I can gather from the concept art and the talk, I think the booms have large nets underneath them that gather plastic into what I think is a oversized swimming pool leaf trap shaped like a manta ray. UPDATE: I misinterpreted the images on the website. The design as it stands now has no nets, only the initial tests had nets. Now I have to ask, what is that sheet hanging down from the booms?

2) The booms.  The claim is that only 24 sifters are need to clean the ocean and span the gyre radius, which means the booms have to be huge. Possibly 100’s of kilometer wide. Are they rigid or flexible? Are they the manta rays? How will they be kept in formation?

3) Anchoring something that large.  I am going to assume that the booms need to stay relatively taut to retain their shape and the most obvious way to do this will be with multiple anchor lines. The water depths are deep (>3000 m), horizontal surface motions needs to be small and then there is all that water pushing on what is essentially a giant paddle. That means a fairly sophisticated plan for anchoring the array will have to be developed. Having seen how large anchors are for low-tension subsurface moorings (>1000 kg), I can’t even begin to imagine what they are going to use or how that is going to be set up.

4) Biofouling. I forsee two major biofouling issues. The first is biological growth, which can be particularly bad because all the major mechanical parts are near the surface. There is going to be growth on the mesh, on the booms, on everything submerged which can make the booms and nets heavy, dragging them underwater. The second is fishbite. Did you know that fish attack underwater moorings like crazed rabid zombie munchers?  Now I don’t know if fish would actually chew on the mesh, but previous experience indicates they are not picky about what pieces of underwater line they snack on. So what will happen if fish gnaw holes through the collection nets?

5) The assumption of low current speeds. This is a bad assumption. While the array may not be placed in the most energetic current regime, storms and eddies can briefly induce large currents which could place a lot of stress and shear on such a large array.

6) Zero bycatch by net avoidance .  Sorry, I couldn’t resist.

Swim free zooplankton!

The Ocean Cleanup project is still in the planning stage, so all these problems have the potential to be solved. But I think it is highly unlikely that an array of this size and magnitude will ever be feasible.

ADDENDUM: Additional criticisms of the Ocean Cleanup Project


17 Replies to “Revisiting the Ocean Cleanup, a plan to remove plastic from the oceans”

  1. Dear all,
    I investigated a bit the issue. Other colleagues and former colleagues of mine also looked into this and one in particular is trying to make the difference. From what I know, the Foundation running the Clean up project has requested to some scientists to formulate questions and point out potential difficulties/problems/side effects of the whole project. I voiced my concerns, some of which are exactly the same as you listed. This to say that they are aware that there are some major issues and they are trying to work them out properly.
    BUT (and it’s a big but) when I asked for the blueprints of the “object” and its anchoring system, to better evaluate the situation, nothing was given to me. The reasons were that apparently they were not ready and the engineers are still working on them…… umpf…..
    Then I asked if the scietists offering their reports would have been made part of the decision making process, but the answer was that it was supposed to be volunteering work (in fact nobody is going to be paid to do this revieweing) and that most likely no.
    So it seems that the Foundation is willing to be provided with critics and solutions but it will all be done via volunteer work (which per se is quite fine) of people that, despite they good intentions, might not make it to make any difference in the end.
    I hope things will change.

  2. Perhaps this idea could benefit from using existing structures such as oil platforms. While not a solution for every waterway, a plastic catchment structure near the outflow of major rivers could catch a lot of junk before it heads out to sea. Perhaps the multiple oil platforms in the gulf of mexico could mount some sort of plastic catching apparatus to clean up the gulf of mexico, and there have been towers built for other purposes of the coastline of New York and New Jersey and in the North Sea. If this could be done at a reasonable cost I’m sure the oil industry would love to claim that their ugly oil platforms were providing some sort of environmental benefit by capturing a few tons of trash every year.

  3. While I encourage as many people to participate in these types of discussions, what I find disturbing are the constant negative comments. Sure, Boyan Slat many not have thought of “every” technical detail…that is a given with any technical project. However, what would be really encouraging to see (and hear) from people would be more positive feedback. With this problem at hand at least someone is thinking about cleaning up the oceans. Good on Boyan Slat for that.

    His endeavor might not be perfect, but it does push the thinking forward…unless you are one of the negative people who think that simply shooting down this idea is being constructive. Rather than criticizing his approach, why not try to build on what he is trying to do? Why not help contribute to a solution to his technical drawbacks, rather than just point them out? Try explaining the problem, and then offering your thoughts on what you think will need to be done to solve them? Even if the cost is huge it doesn’t matter…the oceans are far more important than money. Once people have a dollar figure they will be able to focus on raising the necessary funds.

    And don’t use that, “what he says is impossible” BS either….ANYTHING is possible if enough minds are working on the one solution…that is what creates solutions. By creating a negative pseudo competition out of this will only serve to stifle progress, or slow it down to a crawl.

    I know this might sound cliché, but if you’re not part of the solution you are definitely a part of the problem.

  4. If you’re solution causes more damage to the ocean that the problem it’s trying to solve, then no, we don’t need to help you improve it. We need to stop you.

    One of BP’s “solutions” to the Deepwater Horizon blowout was to pump toxic dispersant into the wellhead. Should we have praised them for “trying to do something” and made sure they got plenty of positive feedback?

    Not all proposed solutions are good, and when people with significantly more experience point out how destructive your approach is, the appropriate response is to listen and learn. There are real, hard-working professionals working on this problem. Don’t insult their efforts by pretending that they don’t exist.

  5. Explaining to BP that their solution is wrong, and “why” it is wrong, is positive feedback. Telling them to stop making suggestions without explaining to them “why” their solution is not a good idea is just as ignorant as the bad solution.

    Absolutely not all solutions are going to be good ideas…but just telling people that you disagree without a reasonable explanation is not constructive either.

    What is ideal is when people explain “why” the solution is, or is not, a good or viable solution, and then offering alternative solutions or supporting ideas.

    I also most certainly did not attempt to insult anyone’s intelligence. However, when I observe someone being attacked for simply presenting an idea, then my intelligence is insulted.

  6. Then I don’t really see what your issue is with this post? Dr. Martini links to numerous sources, including from ocean plastics researchers, and highlights exactly why these plastic skimmer projects are misguided potentially harmful.

  7. While you may perceive what I posted as unwarranted negative criticisms, they are serious, and frankly quite basic, ocean engineering concerns that need to be addressed and have not been since the original article was posted nearly 6 months ago. I wish I could have given solutions, but as the project is presented now it’s almost completely unclear how the Ocean Cleanup is going to accomplish what they said they are going to do. If the designers are serious about this project, they should be able to answer these questions. And as with all ocean engineering projects of this magnitude, if it fails, you are just adding more trash to the ocean.

    Plastic pollution is a major problem, but throwing money at a solution that could potentially cause more damage than it is touted to remediate is not the answer.

  8. Interesting. I too was hoping that with this post the Foundation would be able to answer some of these questions, but 6 months later it seems are though they are unwilling (or perhaps just unable) to. In their defense, I am not sure I would give you a copy of my blueprints, but a simple Q and A on the project page would have gone a long way.

  9. Dr. Martini:

    I most certainly do not frown upon negative criticism, and I can certainly understand your argument. If the world never heard any negative feedback we would just be moving from one disaster to the next.

    All I’m saying is that criticizing by stating what is wrong with a proposed solution is not providing the necessary feedback that is needed to move forward. It “might” make people stop and rethink their proposals, but it would be far more productive if they too received help with alternative solutions to consider (i.e. what they possibly should have proposed in lieu of their initial idea). I see this happening in politics all the time…it’s easy to criticize one’s opponent’s policies, but quite pointless unless that critic also provides an alternative policy.

    So sure, throwing money at a solution that could potentially cause more damage than what it is touted to remedy is not the answer, but we need to know more from the critics than what could be wrong. I’m just asking that the critics also help by providing alternative solutions (i.e. their ideas) as that is the best path to a resolution. I firmly believe that if everyone worked together on this mess we would clean up the oceans very quickly…even if the costs turn into billions of dollars.

    Of course, we also need to remedy the cause…but that is a topic for another discussion :-).

  10. Hundreds, if not thousands of scientists around the world are considering this problem and anyone who offers up an idea is to be commended. I was really interested but watching the clip of his proposal only made me think of the cartoon of two scientists studying an equation on a blackboard. The only problem seemed to be the process that was labeled “Then a miracle occurs”.

  11. I agree with this comment….find something to add to the plan…as an ordinary concerned citizen, I, too see many problems to overcome but applaud the efforts of anyone trying their best to come up with solutions. Go “Ocean Cleanup”!

  12. Very interesting. You have some great points. I like the concept of oil rig/Boyan Slat’s idea of catching debris Before it gets into the ocean. After all, isn’t that where a lot of the trash comes from? I’m just reading all this just because.
    It could work.. couldn’t it?

  13. I know there is still a lot to be studied, you all have great points. Keep up the process, one day we will come up with a solution.

  14. Dr. Martini, My wife and I are older laypeople greatly concerned about the state of our ocean habitat and the damage humans continue to cause, The “Ocean Clean-up Array” may have its design issues, but we’re heartened that a millennial would have spent so much time on an Earth centered project. Perhaps you should offer young Mr. Slat an internship, or fellowship, so each of you might benefit from the strengths of the other. Often, it’s the serendipitous discovery/product of dreamers, scientists and engineers, working in consort, that are the best.

  15. Hi
    Read the different comments here and even though I understand the issue with this idea and the challenges it brings I believe it should be achievable, that is to clean up the mess we make.
    Having said that it seems to me that the idea in principal has merit but it will need to change direction.
    I have spent all my life at sea on the ocean proper.
    I think two things, that gathering the plastic in these vortexes is most likely the wrong place to do it.
    Rather it needs to undertaken closer inshore and anchoring the mechanism is just asking for trouble.
    It will be necessary to harness the ocean not fight it.

    In principal it needs to be a much smaller mechanism. I would suggest that if we looked in the right place the technology is already out there but it’s everyone’s thinking that has to change. I have watched from a distance since this idea gained some momentum and always understood the problems that they face. It’s not unlike the group of idealists who are trying to introduce cities on the ocean I think seasteading they call themselves. No matter what they have never been on the ocean and cannot conceive the issues they face. Scientist engineers cannot handle this either because they in turn do not have ocean going experience that is necessary to create something like this project.
    There is only a handful of people in the world that have lived and experienced the ocean in its fury because it too hard and everyone avoids like the plague.

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