The pollution from ships burning really low grade diesel is widely reported. I wondered about CO2 emissions, and found a report that the huge carrier vessels burn about 16 tons of fuel an hour. Since they travel at some 30 mph and carry about 5000 cars, if my arithmetic is correct this works out to about 35 mpg for each car on its voyage. Sound about right ? If correct, it surprises me. For one that is a huge transport cost in money for the manufacturer to pass on to the consumer. It also made me wonder why rail is not used more, e.g by dropping the cars off on the west coast for transport across the country.
I don't know that your math is right, but maybe i'm wrong. here's how i figured it: it's 5,133 miles from tokyo to san francisco. divide that by 30 mph and you get 171.1 hours of time to cross that distance. i then took the 32,000 pounds of fuel per hour and divided that by 7.15 (the weight of a gal. of diesel) and got 4,475. it takes 4,475 gallons per hour x 171.1 hours and that equals 765,762 gal. of diesel for the trip one way so then i took the number of miles traveled divided by the gal. of fuel and got .0067 mpg. I took that times the 5000 cars and got 33.5 mpg I then divided that by two, because the boat has to go back to tokyo to get more and that equals about 16.7 mpg per prius to get 5000 of them here and get the boat home.
Yeah. I assume that the boat doesn't go home empty, so that would negate some of the lower mpg, but still something to consider. and then there's the cost of transporting them once they hit the states to get to the rest of the country, but that is more negligible than the boat.
That seems like a very high consumption of fuel for a ship that only carries 5000 cars. Its likely for a much bigger container ship. Reading from the link on roro, the toyota ships only go 17-19 knots and only 15% of the hull is underwater, meaning low drag which should save fuel. The ships come back empty, this should be at a lower fuel consumption than full. Transportation costs in the prius also include getting parts from parts of asia outside of japan.
I looked up the cost of bunker fuel, the stuff the ships burn. $2/gallon today. So the round trip assuming an empty boat back is ~ $1200 per car to San Francisco. Perhaps double that to the East Coast ? Wow
This page gives 120 tonnes fuel consumption per day for a Panamax ship, about a third of the number used for the calculations above.
I am guessing the fuel consumption numbers are too high on a per hour basis. Not evidence, just hunch. Icarus
I believe those numbers are vastly too high. Ocean transport is efficient. Even small freighters get 500 ton-miles per gallon. Larger ones get around 1000. (By contrast, US freight rail claims 500, and a typical value for big rigs including deadheading is about 100 ton-miles per gallon.) A Prius is 1.5 tons, the distance is about 5000 miles, so that's about 7.5 gallons of fuel to ship one car one way at 1000 ton-miles per gallon. Or 15 at 500 ton-miles per gallon. That makes the fuel penalty for ocean transport seem negligible. But possibly, they can't pack cars densely enough to achieve that level. So the ton-mile data might be correct for grain or coal, but perhaps not for less dense freight? I'm pretty sure that almost all the energy expenditure is overcoming hull friction and displacing the water, so I'm fairly sure that the boat uses (nearly) the same energy with a light or heavy load. In your terms, 15 gallons, for 5000 miles, per car, works out to be about 300 miles per gallon, for moving the Prius on a boat. That seems much more like it. I'd give very short odds that ocean freighter transport is more efficient that car transport. (You want to talk about inefficient transport, talk about driving to the store to pick up 30 lbs of groceries. Fifty miles per gallon, to move 30 lbs, is 0.75 freight ton-miles per gallon. This is why I think that, for the average American, the majority of food transport fuel is what they burn driving to the grocery story, not what is spent shipping the food to the grocery store.) My guess is that you underestimated the load. The article says 15,200 shipping containers. Pretty sure a Prius is smaller than a shipping container. Here's a benchmark: A 21000 ton ship hauls 2000 cars: Video: Nissan unveils the City of St. Petersburg; an eco-friendly Leaf transport ship By contrast: "Here Emma Maersk, and her sisters, at about 170,000 gross tons," Emma Mærsk - Wikipedia, the free encyclopedia If those numbers scaled, then the Maersk ship would be able to carry about 17,000 cars. That doesn't fully reconcile your estimate with mine -- yours would be around 120 MPG -- but it makes them closer. I also strongly suspect that the article quoted fuel consumption when running flat out. For their purposes, why not. For (small) displacement hulls, fuel consumption tends to be highly non-linear in speed. Even for larger hulls, I'm betting that average consumption would be less than the figure cited. Also, no doubt this has been asked and answered on the internet a dozen times already. But I surely could not find a decent internet reference on it.
...the article mentions 7.3 million Barrel/day is ship bunker fuel. So that's about 8% of total daily crude oil production. According the article, regulations now in place to force 90% sulfur removal from ship bunker fuel by 2020. I am thinking we do not make much bunker fuel here in USA as we crack everything down to gaso+diesel. They had good idea in theory to convert ships to nuclear power...not sure about safety/terrorism aspect. I am very receptive to the SMR concept and here is a good use of it.
...then that's another example of why nuclear is incapable of solving CO2 issue, and we are forced to proceed with fossil fuels and hope for best, which I think is where we are.
I thought the ship problem was the sulfur pollution, now we can't even have very efficient transport. You can use that nuclear power to remove sulfur, but everyone would have to agree to ultra low sulfur fuel, otherwise the ships would just fill up in places where they didn't have the rules.
...good calcs. It is unlcear if they mean 16 metric tonnes or 16 tons (Tennessee Ernie Ford/USA units). But they said "tons" so you made the correct assumption. I am thinking ship bunker fuel has a density spec of closer to water let say 0.98 or 8 lbs/gal Here's how Tennessee Ernie Ford does the calcs:
Yes on your take on the fuel consumption. In real round numbers, large Ro/Ro car carrier ships run on the order of 25,000 horsepower, cruise around 20 knots (23 mi/hr) and have a BSFC of about 0.3/lb hp-hr. Heavy marine fuel oil runs about 8 lbs/gallon. 25,000hp x (0.3 lb/hp hr) x (1 gal/8 lb) = 937.5 gal/hr (23mi/hr)/(937.5 gl/hr) = 0.0245 mi/gal 0.0245 mi/gal x 5,000 cars = 122 car mi/gal for the one way trip. Those are obviously very round numbers but 35 mi/gal per car and 500 mi/gal per car both loo0k unrealistic. OTOH, what percentage of the hull is underwater is nearly irrelevant, what counts is the amount of water displaced which is directly proportional to the total weight of the ship. In fact if only 15% of the ship is underwater, that means it has a lot of structure sitting up in the wind adding air resistance compared to a ship with larger percentage of it's structure underwater. That's not a real big hit on fuel consumption though because sea water is about 850 times as dense as air. The 32,000 lb/hr mentioned earlier would support about 100,000 horsepower, car carrier ro/ros run a lot less that that, about 1/4 of that for a large one.
For the precise level of calculations we are doing here , a metric tonne = a standard ton. 2204.6 lbs vs 2000 lbs
Thanks for the additional data, folks. This pdf has an interesting graph: If I am reading the units correctly, about 30 grams of fuel is burned per car*mile. This works out to (very roughly) 100 mpg gasoline for a ship travelling 24 knots/hour. Much better than my OP link suggested, but if the ship is mostly returning empty (likely, since it is outfitted for cars) that is $200 - $400 fuel costs from 100-200 petrol equivalent gallons consumed depending on whether the ship docked on the West or East coast. I calculated using the best fit line; actual ships have quite a large variation in efficiency
Nice graph. If tDW is Tons Dead Weight, that includes cargo, fuel, water, ballast, crew, basically everything except the empty ship. That would mean fuel consumption per ton of useful cargo would be higher than the chart shows. Edit: I read the pdf and it states that the tDW is tons of cargo, not TDW http://www.naos-design.com/it/images/stories/stampa/RoRo2004.pdf
