… And the Romans had it figured out 1000 years before that.
Yet somewhere some technological wizards have developed an experiment in January to use a big kite to pull a cargo ship across the Pacific Ocean.
Gizmodo – 12/17/21 – Giant Kite Will Pull a Ship Across the Ocean Next Month – The experiment will involve a parafoil kite measuring 5,380 square feet. It will pull a ship that is 505 feet long.
The ship is rated at 21,528 gross tonnage and 5,200 tons summer DWT. Gross tonnage is a measure of the volume of what a ship can carry. Summer DWT, or summer deadweight, is the measure of how much weight the ship can carry with the drafts available in a port in summertime.
For context, the second largest cargo ship in the world, COSCO Shipping Universe, weighs in at 199,000 metric tons deadweight. That puts it at somewhere around 38 times carrying capacity of the diesel powered cargo ship which will become retrofitted as a sailing ship. Oh, the big ship can carry 21,413 TEU, or the equivalent of about 10,700 of those 40 foot containers you see on the freeway.
At Instapundit, Glenn Reynolds comments:
“So if I recall correctly, 100 square feet of sail will generate about 1 horsepower equivalent in a 15 mph breeze. With a kite area of 5,380 square feet, that’s about 53 horsepower, which is what 1960s vintage VW Beetles had. How much acceleration will that impart to a ship 505 feet long? They don’t give its weight, but it’s a lot heavier than the Beetles, which didn’t move very fast . . .”
To address the professors question, Wikipedia reports the four steam engines have a rating of 900 nominal horsepower and are able to produce 3,600 indicated horsepower. That is sufficient to generate a top speed of 11 kn, or 13 mph.
Let’s do some math.
Using merely nominal horsepower of 900 and the estimated power of the planned sail at 53 hp that gives the engines 16.7 times more output than the sail. Phrased differently, the sails will provide approximately 6% of the horsepower the steam engines can produce.
Please consider the picture – a sail provided 53 hp trying to pull a ship carrying 5,000 tons of cargo or about 10 million pounds of stuff.
Even I can figure out it will be zero.
The better question is once the engines get the ship up to cruising speed, how fast would the ship be able to go if the engines were throttled back to 6%? That’s what will happen when the sail is deployed and the engine shut down.
I don’t understand naval engineering, but it’s safe to bet the speed will be a tiny fraction of 11 kn
Even a Viking would’ve laughed at this experiment.
And the Romans? You could defeat an entire Roman armada in a hour or two by showing up with this contraption because every officer would be incapacitated by sustained laughter.