On a Floating Bridge

A few weeks ago I was contacted by Sophia Campbell about her flightless trip to India from the UK.

With complicated calculations, the distinction from a huge array of vehicles efficiencies in each category, and fine-tuned judgment necessary to even start to calculate accurately your carbon emissions on a complicated journey, its no wonder that you might be in need of some help. I asked a range of people to help me out on my own calculations last year, but, more often than not, the answers I received were a general figure that came nowhere near close to the actual engine model I was riding on. Well, the below calculations have been kindly researched by, again, my dad. He is an electronic engineer, with a background in physics. He often contributes to the oil drum website, and you can read more of what he’s written on other subjects here

Modern ships are a very efficient way of moving cargo. The best of the huge diesel engines they use convert over 50% of the energy in the fuel to propulsive energy fed to the propeller. The best of petrol car engines struggles get 12% to the wheels.

There has been some alarm recently about the emissions from cargo vessels. They total about twice that from aircraft but this is because they shift so much cargo. In 2007 it was something like 51 trillion tonne-kilometres by sea, about 300 times as much as by air. There are improvements that can be made to the emissions from ships but what the world needs to do most is to cut down on international transport, but what long distance cargo transport that is left is best done by sea.

Calculating

The total amount of fuel used to shift those 51 trillion tonne kilometres was about 410 million tonnes. That works out as a global average of 8.0g of fuel per tonne-kilometre of cargo moved. Each gram of heavy fuel oil burnt produces 3.1 grams of carbon dioxide. This gives 25g/tonne.km as the global average for all shipping. However I found a site of a Norwegian shipping company, Wallenius Wilhelmsen, that states that the emissions for their container ships range from 10g/tonne.km for their older ships to 7.5g/tonne.km. for their latest.

If you travel on a container ship you will very slightly increase the amount of fuel used. Taking the figures from the Maersk Regina, which can carry 3000 forty foot long containers, and assuming 150kg for a passenger, his or her luggage, food for the voyage, bedding etc. the ship will sink 0.012mm deeper and have fractionally more resistance to moving through the water. I found a site that said, for a tanker nearly full, an increase in the load of 1% will increase the fuel consumption by about 0.6%.

This means that the 150kg of additional load taken on for the passenger will increase carbon dioxide emissions by between 2.25g/km for the world shipping average to 0.67g/km for one of Wilhelmsen’s best container ships.

In comparing this with flying, it is worth noting that by releasing the emissions at sea level rather than in the stratosphere, the global warming effect is about 2.7 times less. Slightly offsetting this is the fact that older sea vessels emitted more sulphur dioxide and nitrogen oxides.

I believe container ships limit passengers to 9 as international regulations require a ships doctor for more than this.

I hope this helps

Links

Reconciling Past and Future Trends in Ship Work, Energy, Emissions, (University of Delaware)
Wilhelmsen Corporate Social Responsibility PDF
Maersk Line Shipping Container Details
Growth Trends in Air Cargo Details (boeing.com)