Getting A Grip On Titanic's Fuel Use

I was dumbfounded by the statistics I saw on Titanic's use of coal, and James McElroy was intrigued. Here is his research on the question.

Marc,

This started as a post to your Blog on the Titanic Exhibition but it just got out of hand. If you want to use it feel free. It's just something I like to do.

Jim McElroy

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Fun with Numbers

The fuel consumption numbers quoted for the Titanic do appear questionable but the way the statistic was presented is even more interesting. 60 lbs every 1.5 sec? WTF! It is the same mind boggling approach seen every day at the supermarket when asked to compare two products that are $1.98 for 24 oz. or $2.29 for 28 oz. The intention is to confuse.

Anyhow, the quoted fuel consumption is obviously 40 lb of coal per second, 72 tons per hour, or 1728 tons per day. Since the trip across the Atlantic required 6 days, the ship's capacity of 6,000 tons would have run out 3 days and 11 hours into the trip. I think that was before they met their iceberg. That would probably have been a "good thing", at least we wouldn't be visiting various Titanic road shows.

Being incurably curious, I looked up the Titanic's fuel consumption posted in the Titanic specifications listed on the website

http://library.thinkquest.org/21583/to/spec.htm

quoted at 825 tons of coal per day. This means that 4950 tons would be consumed on the trip, much more suitable for the 6000 ton capacity.

This leads to thoughts of global warming. Is there some way to graphically show the thermal cost of this trip? Well, yes, in a general way. Coal has a heat content that varies greatly with the source and composition. It is a raw material, not a manufactured product. Coal of the type used for marine propulsion has a heat value ranging from 11,000 BTU/lb to 14,000 BTU/lb (per Marks Mechanical Engineers Handbook) so we'll pick 12,000 BTU/lb because it is an easy number to work with. For those who studied computer science instead of the real world, a BTU (British Thermal Unit) is a standard unit, dating back to the days of James Watt, and is defined as the amount of heat required to raise the temperature of one pound of water from 60 deg F to 61 deg F. From this we can state that the 4950 tons (9.9 million pounds) of coal, would release 118.8 billion Btu's of thermal energy. We could round off to 120 billion Btu's, but what the hell, I have a calculator (score one for Computer Science).

Whee-ooo! That's a lot of Btu's, right? Or not. Is there any way to graphically describe how much heat this is? Well, yes, you knew there would be didn't you. We'll pull out another number from Mark's Handy Handbook and note that it requires 144 Btu's to melt one pound of Ice at 32 deg F. The heat produced by one trip across the Atlantic could melt 825,000,000 pounds or 412500 tons of Ice. To give a more visual perspective we look up another number, the density of Ice at 32 deg F which is 56 lb/cuft. A cube of ice weighing 825,000,000 lbs will occupy 13.22 million cubic feet and will measure 245 feet on each side. An iceberg of this dimension would weigh almost 10 times the gross tonnage of the Titanic and be almost one third of it's length. The top surface of the cube would be 24 feet above water level. This is probably comparable to or larger than the iceberg which did in the Titanic. You think it may have been a preemptive strike? If so it didn't work there either. Icebergs in the northern hemisphere are becoming an endangered species.

What about modern transportation? We can do exactly the same calculation for Air Travel. From the website

http://travel.howstuffworks.com/question192.htm

I acquired a fuel consumption figure of 5 gal/mile for a loaded Boeing 747. The figure was attributed to the Boeing website but I could not confirm. Probably a marketing news release. Anyhow, using 3,500 miles as the distance from New York to London, about the same as the Titanic route, it takes 17,500 gallons of jet fuel(kerosene) to cross the Atlantic once. The density of kerosene is 6.8 lbs/gal and it has a heating value of 19,810 BTU/lb. Jet fuel is a manufactured product and the numbers are pretty precise. Using the same calculation we find that a Boeing 747 flying from New York to London will release 2.36 billion BTU each trip. But wait, a 747 carries only about 500 passengers, while the Titanic carried about 2000. So, it takes four 747's to carry the same passenger load, or 9.44 billion Btu's compared to the Titanic's value of 118.8 billion Btu's to transport the same number of passengers. This is really why you see so few ocean liners on the transatlantic crossing today, not passenger convenience.

From here you get into the details of where combustion products are deposited, at ocean level (next to the world's largest carbon sink) or in the stable stratosphere where they stick around and block heat loss. The same type of calculations can be and are made for these effects, but I'm gonna bail.

Regarding Jim's last paragraph, most climatologists and atmospheric chemists believe that most of the carbon dioxide released by combustion processes remains in the atmosphere. The ocean is nearly supersaturated with CO2, and can only take it up in certain locales, one of which isn't too far away, actually, as Jim mentions - cold, sinking water near Iceland. Another primary sink for CO2, the weathering of rocks on land surfaces, is widely-dispersed, and the numbers are still poorly-understood. That's why CO2 has increased 15% or so, from 315 to 380 ppmv, just in my lifetime - it just accumulates.