gryffron wrote:88V8 wrote:But I wonder how the comparative carbon footprint would be if all holiday trips were by ship
Here we go. Got the figures from the web.
London to New York. 3500 miles.
Queen Mary 2 - 4 1/2 days @ 430 tons/day = 1950 tons fuel / 2620 passengers = 0.75 tons fuel/passenger
Jumbo jet.. 8 hours @ 11 tons/hour = 88 tons fuel / 366 passengers = 0.25 tons fuel/passenger.
So travel by cruise ship 3x worse than flying. Ballpark.
Gryff
Your ballpark is grossly incorrect I am afraid, as is your terminology.
Queen Mary crossing London-New York 3500 miles in 4.5 days (108 hrs) is doing 32-knots. (Actually Southampton > New York is 3632 nm, so 33.6 kts)
However large shipping economic motoring speeds are typically approximately 12-knots, going up to maximum 20-knots for fast commercial traffic.
If you are doing 33-knots you are at the screaming limit of the "hull limiting speed" for a ship of the size of the Queen Mary. You are literally digging a hole in the water the entire way. That is why the QM2 is so long, simply to be able to do 33 kts.
If you look at typical speed vs fuel efficiency curves for large commercial vessels (
https://www.sciencedirect.com/science/a ... 3315300127) you will see the ordinary curves don't go beyond 20-knots. There is a very good reason for that and the shape of the curves tells you why.
Queen Mary 2 is 80,000 tonnes displacement, 345m length. The commercial car carrier in the research paper I cited is 200m, 32,000 tonnes. I've done the transatlantic crossing a few times in comparable vessels and we generally did about 12-18 kts, and you can quite happily put 2500 passengers on something of 32,000 tonnes in a fair degree of comfort, complete with food/water/etc. Certainly a similar level of comfort to most UK housing stock and most UK lifestyles. Such a vessel would easily have provision for a 3-tier ticketing.
Look at the fuel curves for the 32,000 tonne vessel and you will see that at 15-knots you will burn 35 tons/day, and at 15-knots it will take 10.1 days, so 350 tons. Divide 2500 passengers into that and you get 0.14 tons fuel per passenger per crossing.
QUEEN MARY in LUXURY FAST LINER SERVICE = 0.75 tons @ 4.5-days
LARGE PLANE = 0.25 tons @ 0.5-days
ECONOMIC LINER = 0.14 tons @ 10-days
Overnight cruise ships are generally doing 12-18 knots by the way, not the 34 knots you think the Queen Mary is doing. She is doing the 34 knots in luxury fast liner service, not as a cruise ship. Cruise ships are generally trying to make their overnight passage so as to arrive at an economic speed about dawn, minimum fuel use.
regards, dspp