Last week I pondered what the environmental impact of my last vacation was. I took a cruise from New York City to Bermuda on the Explorer of the Sea. The technical specifications indicate the boat has six Wärtsilä 12V46C diesel engines which supply 75,600 kwh (75 MWh) of total power. My estimate is that while cruising between the ports, the engines are probably at about 3/4 full power, and at the dock the engines are merely supplying electricity to the boat (20 MWhs). Megawatt Hours or MWhs are the units of energy commonly used in the electricity industry. The estimate of use are just guesses on my part - I really don’t know how RoyalCaribbean operates the Explorer since I missed the Bridge tour. For reference a typical New England Resident consumes 653 kWH or .653 MWh per month (1000 kWs make a MW). Last month according to my electric bill I consumed 303 kWh of power at home. However given that I spend half of my waking time in my air conditioned office, a better estimate of my total energy use is 800 kwH a Month or 26.6 kwH/day.

The other useful comparison is not just looking at overall energy usage, but also looking at the distance traveled. I didn’t just get on a cruise ship and stay there. I got on cruise ship and traveled to Bermuda. Here’s a comparison of the efficiency of the different modes of transportation Traveling by airline is one of the least efficient methods of transportation. The two jets powering a typical Boeing 737 are functionally nearly identical to gas turbines used to produce electricity. Each engine produces the equivalent of 15 MW of power for a total of 30 MW for a 2 hour flight between Boston and Bermuda. However unlike the Explorer of the Sea which transports over 5000 people, a 737 jet only moves 180 passengers or so at the most.

Using the emission rates from here, I can also calculate the total emission impact of the cruise and compare it to what would be my typical usage over that same 5 day period. I used the emission rates from and uncontrolled diesel plant to best represent Explorer of the Seas, and the average emission rate for power generation to represent my typical usage in Boston. In truth most of the power in New England is sourced from gas plants which are somewhat “greener” given the lack of Coal plants in the area. For the flight, I used the emission rates of medium sized gas turbine. The top secion is MWhs of power consumed, and then the corresponding emission from that power.

It comes as no surprise that taking the cruise was not good for the environment. I was personally responsible for producing more than 10 times what I would normally contribute in CO2 compared to staying in Boston. The other emissions (SO2 and NOX) are insignificant given that they are typically produced by coal power plants. If I had been on a coal steam liner than those would’ve been through the roof as well. I was a little surprised to find that cruise ship did not perform better than flying. Traveling by boat should actually be one of the most energy efficient means of traveling. I imagine my assumptions on actual energy use may be on the high side, but the qualitatively the answer doesn’t change. Cruising or any vacation that involves significant traveling is not good for the environment. I’m not here to preach that people shouldn’t go on vacation, but merely reinforce that every action we take does have an impact on the world. What you do with that knowledge is your decision. It certainly won’t stop me from going on my next vacation, but it does make think about what else I could be doing better.