How much fuel does a ship burn in an hour?

 At economical speed, the engine of a large container ship consumes 1,660 gallons (6,284 liters) of heavy fuel oil an hour. The answer varies enormously depending on the vessel.

A large container ship like the Emma Maersk is powered by a Wartsila Sulzer RTA96-C 14-cylinder diesel engine, the largest single diesel unit in the world, delivering a maximum power of 108,920 hp. The thermal efficiency of the engine is over 50% at maximum economy. Fuel consumption of large marine diesel engines would be more than 100 metric tonnes per day, depending upon the load, speed, and the weather and sea conditions.

Cruise ships operate differently from cargo vessels. A medium-sized cruise ship carrying 1,500 passengers, running on three diesel generators at 18.5 knots, burned 3.75 tonnes of heavy fuel oil per hour, or 38 US gallons of fuel oil per mile. A large container ship burning the low-sulfur diesel equivalent would see usage jump to 1,880 or more gallons per hour, since heavy fuel oil carries significantly more energy per gallon than road diesel.

Warships burn fuel at different rates depending on speed and power plant configuration. The USS Midway burned about 260 gallons per mile at cruising speed, and at maximum speed of 33 knots that figure would quadruple.

A large ocean liner like the Queen Elizabeth II consumed a gallon of diesel fuel for every thirty inches of passage at maximum speed in rough seas. At its maximum speed equivalent of 34 knots, it would have consumed over 82,000 gallons of fuel over the course of one hour, though it generally cruised at 28.5 knots, burning a gallon of fuel to go about 50 feet.

The easy conversion for estimating purposes is horsepower multiplied by 0.055 equals gallons per hour at full throttle, so an 80,000 hp engine consumes roughly 4,400 gallons per hour, not including generators.

How do they manage to squeeze in 242,000 litres (64,000 gallons) of fuel in a Boeing 747's wings?

 Not all fuel in a 747 is stored in its wings - it has fuselage tanks too, and some models even store fuel in the horizontal stabilizer. These tanks typically are comprised of individual rubber bladder tanks that are contained within aluminum framed structural compartments within the wings and fuselage, between certain wing ribs, spars and the wing root area where the main wing center frame is mounted to the fuselage.

In addition to center main wing and body tanks, there are forward fuselage body and rear body tanks. Bottom line is that a 747 has more than a wing tank or two in each wing — there can be a half dozen tanks distributed around the aircraft.

There is no squeezing involved. The fuel is incompressible so it can’t be squeezed at all. They don’t squeeze the fuel in, they pump it into manifolds under the wings and it flows into the tanks. You can get 64,000 gallons of fuel into the tanks because the tanks have a volume of 64,000 gallons. The single largest tank on a 747 is the centre tank in the fuselage between the wings, but a lot of fuel is stored in the wing tanks.

Taking the 747‑400 as an example, the wings have an area of 525 m², about two‑and‑a‑half tennis courts. Converting to metric, 64,000 gallons is about 242,000 litres, requiring a volume of 242 cubic metres. Dividing this by the area of the wings, 525 m², we find that the wings would need to be on average 0.46 metres thick, about 18 inches, to have the required internal volume. Now of course, there’s other stuff in the wings besides fuel tanks, but this shows how the volume is available.

Fuel from each tank gets pumped around other tanks to maintain center of gravity inflight, and there is engine manifold cross‑feed plumbing and manifold tanks that actually feed each engine. Fuel tank monitoring and management during flight “is a thing,” and yet another critical pilot task, even when most of this transfer stuff might be automatic.