Speed limits on cargo ships could reduce their pollutants by more than half

Putting a speed limit on cargo ships as they sail near ports and coastlines could cut their emission of air pollutants by up to 70 percent, reducing the impact of marine shipping on Earth's climate and human health, scientists have found. Their evaluation of the impact of vessel speed reduction policies, such as those proposed by the California Air Resources board, appears in ACS' journal Environmental Science & Technology.

David R. Cocker III and colleagues explain that is the most efficient form of transporting goods, with more than 100,000 ships carrying 90 percent of the world's cargo. However, engines on these vessels burn low-grade oil that produce large amounts of air pollution. Because fuel consumption and smokestack emissions increase exponentially with speed, the authors explored how speed limits could reduce pollution.

They found that slowing container ships to about 14 miles per hour (mph) reduced emissions of carbon dioxide by about 60 percent and nitrogen oxides by 55 percent compared to emissions at traditional cruising speeds of 25-29 mph. Soot emissions fell by almost 70 percent. The authors suggest that imposing these speed limits on vessels near ports and coastlines could significantly reduce their pollution and protect the health of people living in those areas.

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More information: Environmental Science & Technology doi: 10.1021/es302371f
Citation: Speed limits on cargo ships could reduce their pollutants by more than half (2012, October 24) retrieved 22 July 2019 from https://phys.org/news/2012-10-limits-cargo-ships-pollutants.html
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Oct 24, 2012
During the heart of the recession the shipping companies themselves actually discovered the logical truth that sailing slower costs less money.

The problem was the demand side for goods and services wanted things done faster, but they had to negotiate this with the ports and other vendors and transport companies.

As I recall, it was discovered that cutting their cruising speed by 10% saved over 20% on fuel, which is by far the most expensive part of cargo transports.

The kinetic energy equation makes this obvious from the V^2 component:

1^2 = 1

0.9^2 = 0.81

Since the kinetic energy ultimately comes from your fuel, this translates to, in this case, a 19% savings in fuel, neglecting friction, etc, but frictions are higher for higher velocity, explaining why they got more savings than the pure kinetic energy formula alone would imply.

Speed = stupid and non-economical for mass transit.

I have proven this for all manner of transportation, except emergencies, of course.

Oct 24, 2012
Note that I've been saying this for years now, and anyone who knows anything about my posting history would know that.

Unfortunately, the way our capitalistic system works, shipping companies compete for the contracts and get paid by the cargo they haul, so they have an apparent short term or individualistic motive for higher speed, but in the long term this is detrimental both to themselves and our civilization, even though they may not actually suffer from it because they may make enough money to be padded individual and not realize it, or the owners may die before the differences matter.

But a rational civilization would plan it's consumption and logistics better, from top to bottom, and therefore produce more fuel efficient processes over the long term.

Because final purchase prices would actually be lower, due to lower transport prices and lower pollutions, "freedoms" would be enhanced by a "socialist" policy, AND the company would actually make more income.

Oct 24, 2012
Had you read the article's conclusion, you would have realized that their primary concern was a recommendation to reduce speed near port cities and coastlines - Thereby reducing local pollution while having very little impact on total transport time by allowing ships to travel at their normal cruising speed through international waters.

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