A friend and I have been having an ongoing debate for years. We were at a pub on a wharf, watching shipping container ships and cruise ships come into dock, and he posed the question. With no wind, no waves, perfect conditions, could he move the ship at all?
In: Planetary Science
Generally, people are a bit stronger pulling than pushing. Assuming you had some ultra sturdy blocks to hold you in place, a rope tied to the ship, and pulled with all your might, you might manage a bit over 1,000 Newtons of force.
Applied to a container ship, assuming zero friction and with a mass of 165,000 tons, this would result in an acceleration of around 6 x 10^(-6) m/s^(2). This is an imperceptibly small amount of acceleration…but if you were to manage to continue to apply this 1,000 Newtons of force for a full hour (which would be a significant feat of strength), you’d get the ship moving at about 2 cm/s, which is fast enough to notice while standing still and watching carefully. In fact, the movement would probably be noticeable after about 10-20 minutes of pulling that hard.
Yes. There are these people who pull an 18 wheeler with their teeth on TV. We can use ropes to pull a sailboat or fishing boat a few feet and secure it against a dock. So we CAN use ropes to move boats, period. It’s only a question of “how fast”. Everything we normally use to move container ships– tugboats, motors, pulleys, heavy ropes attached to trains — is a variation on “pull or push”. The question is not “if”; it’s “how fast”.
With zero wind, zero waves (or *only* waves that help), and with good legs: yes, you can.
It will be slow as all fuck, and it would take an incredible amount of effort to get that first movement down, but it would work.
Yes. Assuming the waves are not pushing the boat in any direction, the laws of physics say that any force applied to an object will have an effect, as long as that force outweighs friction.
Yes. If you eliminate the slightest wind, waves, or current you could even pull it 5 miles per day once it’s moving.
For the nerds:
There is no static friction in water. That’s part of why ships have defined trade for millenia. No static friction means 0 force at 0 velocity so we can definitely do *something* to the velocity before drag gets in our way.
https://pubmed.ncbi.nlm.nih.gov/15028193/
This says a male human can pull 400N. Let’s just say we can do this indefinitely. Sleep is for people who don’t pull cargo ships.
http://www.diva-portal.org/smash/get/diva2:1449680/FULLTEXT01.pdf
This paper gives the drag coefficient and wetted surface area of a container ship in section 2.2 and 5.2. The drag coefficient plots don’t go down to 0 velocity and I expect it’s higher at 0 velocity, but this is a terrible approximation for the internet so I’m gonna just say it’s 4.4*10^-3. They give their formula for drag coefficient which is based on the wetted surface area, not cross sectional area like the normal non-naval-engineer drag coefficient. The wetted area is 19556.1m^2.
How fast could we eventually get it to go? At constant speed, the drag force and our pulling force are equal, so we just plug the 400N into the drag coefficient. I picked a middle-ish value from WolframAlpha’s seawater density of 1027kg/m^3 and I got a velocity of 95mm/s. That’s actually pretty good and adds up to just over 5 miles per day!
How long would it take us to get there? The paper says it’s a Capemax ship so from Wikipedia, 170000 tons (deadweight tons, but the actual boat is usually only a small fraction of the cargo.) From standstill, you will start moving it at 2.6e-6 m/s^2 which would have been enough to reach full speed in 10 hours. However, as the drag starts to ramp up your acceleration goes down until you’re barely accelerating. You never actually hit the full speed above because it’s asymptotic. If we assume it follows an exponential decay, you’re probably within 2% of final speed within like 40 hours.
Checking our assumptions, the drag coefficient is probably higher down in the stokes flow region, and the real world will never give you 2 days of no current, no wind, and no waves anywhere you can pull a Capemax ship. However, Capemax is really big so smaller boats will be easier. If you manage to salvage the Edmund Fitzgerald out from the bottom of Lake Superior, it’s less than 1/10 the weight and representative of Seawaymax vessels.
Don’t know about a container ship, but back in the early ‘90s I worked with Sea Shepherds fixing up an icebreaker they had that they’d just gotten back from the Canadian government who had trashed it. This was *long* before all the TV and media nonsense they got into.
It was in dock and we spent the summer working on it. At one point a big storm was slated to hit the area and we needed to tie on extra mooring lines and add extra protection between the ship and the dock.
To move the ship I just stuck a long board string enough to support my weight between the dock and the ship and stood on the end of it. Moved the ship more than enough to slide extra protection where it was needed.
This was in dock in very calm water in an area with mild tides.
If there had been waves or anything like that it would not have worked as the power of even very tiny waves striking the length of the ship would have completely overpowered then small amount of pressure I could put on the ship even using a long lever.
Perfect conditions let you do anything.
Newtons laws hold pretty damn well.
Force = mass x acceleration.
The mass of a containership is quite high, and the force you can apply by hand is pretty small, but it’s not zero. Therefor the acceleration is going to be miniscule, but not zero.
A cargo ship might weigh somewhere in the order of 150,000 tonnes. Metric because conversions are nicer. That’s 150,000,000 kilograms.
A fit person can usually lift their own bodyweight and more in an ideal scenario, so lets say your friend can bench 200lbs, we can convert pounds of force to newtons and get a force of about 900 N.
`F = m*a`
`900 N = 150,000,000 kgs * a`
`a = 0.000006 m/s^2`
`a = 6×10^-6 m/s^2`
We can use one of the kinematic equations to relate acceleration, distance, velocity (initial and final), and time.
For example, how long would it take your friend to move the cargo ship 1 meter?
If we assume the ship starts at rest and the initial velocity is 0, d = 1m, and a = 0.000006 m/s^2, we can use the following formula to calculate time:
`d = vi*t + 1/2*a*t^2`
vi = 0, so we can simplify and rearrange:
`2d/a = t^2`
And solve:
`2(1m /0.000006 = t^2`
`t = 577s`
That means that it would take your friend about 600 seconds or 10 minutes to move the cargo ship by 1m, given there’s no resistance and he can keep up that 900 N of exertion for 10 minutes straight.
Realistically, there’s resistance to movement, and in this case we have friction between the water and the ship (energy required to move along the fluid), and viscous resistance (energy required to move the fluid out of the way). Ketchup might have similar friction to water, but it’d be harder to move out of the way.
If you want the full physics and fluid dynamics lesson, you can find a great document here on the [United States Naval Academy website](https://www.usna.edu/NAOE/_files/documents/Courses/EN400/0207_Chapter_7_Jun20.pdf).
The amount of resistance in a fluid is proportional to the velocity though, and at the abysmally low velocity your friend is able to push at (average speed of about 1/16th of an inch per second), the resistance would also be proportionally low (but not zero).
Without calculating, I’d guestimate that the resistance would double or triple the time required to move the ship 1 meter. And since it’s really hard to exert yourself at full strength for 20-30 minutes straight, probably safe to assume we double the time again.
So within the hour, I expect your friend could move a mid-large size container ship about 1 meter.
water resistance isn’t like ground friction. The water would result in a slower speed than if you were pulling it in vacuum but it wouldn’t prevent the ship from moving until your pulling harder than a certain amount.
So technically you could get it to move and people *have* done this. I’ve seen groups of people pulling a cruise ship by hand as part of a bet.
The problem is that container ships are massive and we’re talking about a single person. Even under ideal circumstances pulling for an hour would get you something like a literal snail’s pace.
In reality though the slightest bit of wind or current would completely overwhelm anything you’re doing.
[If a donkey can do it for 10 miles, you can do it for 10 inches.](https://i.imgur.com/G3cZHWB.jpg)
> With no wind, no waves, perfect conditions, could he move the ship at all?
Assuming a spherical ship and no friction…
Okay, so in reality, with no waves/wind/other external force, than an average person pushing is now the *only* force on the ship. The acceleration will be minute, but extant. Think moving it a couple centimeters after an hour of pushing minute, or even less.
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