7 ms·

Just to put some numbers on this: The MV Dali (IMO#9697428) is a little over 95000 GT, or ballpark-ish probably around 114000 tons loaded (and it seems to have

by xoa 3y ago

Just to put some numbers on this: The MV Dali (IMO#9697428) is a little over 95000 GT, or ballpark-ish probably around 114000 tons loaded (and it seems to have been loaded, which would make sense on departure). If it was going even 5kn (2.6 m/s) that'd be about 300 million newton-seconds, or about 3.3 times the momentum of a large jumbo jet like a 747 shortly at cruising speed (around 560 mph). It'd still have the same momentum as said jet if it was going just 1.5kn. The ship of course is enormously more stoutly built and the force is going to be transmitted far more directly into whatever it hits vs into explosions driving mass elsewhere. I've read that both on water and in space for that matter enormously massive objects moving very slowly messes with human perception and "common sense", it "feels like" something moving along smoothly and slowly should be stoppable or come to a stop. Enormous momentum and forces can be terrifying things.

KineticLensman 3y ago
> enormously massive objects moving very slowly messes with human perception and "common sense" Yes, hence warnings to amateur boat users (e.g. on a canal boat) not to try to stop a collision with the bank using your arms or legs. [Edit] Boats can also do things that are unintuitive if you are used to driving a car. E.g. turning round the centre of gravity when you steer rather than following the front wheels.
- smogcutter 3y ago
  In the black powder era of warfare, soldiers were given similar warnings about “slowly” rolling cannonballs. People would think they could stop them like soccer balls, and lose a foot.
- bmelton 3y ago
  There are similar warnings for sailing vessels, but because the standing rigging of the ship is usually kept in high enough tension that putting your hands on a pilon to stop a collision might leave your hands vulnerable to being cut off by a mainsail's shrouds.
  - KineticLensman 3y ago
    Ouch! That reminded me of seeing someone get a rope burn from a line on a yacht. I always wear gloves when handling lines on a boat nowadays.
litenboll 3y ago
I had a summer job once, filling trains with sugar. They weighed about 15kkg per wagon (usually 5-10 wagons per train IIRC). One time the pulling cart broke down and we had to switch it for another, but when we took it off the rails we forgot about the "shoe" that is supposed to go between the rail and one of the wheels so it can't move downhill (it was like 1degree of slope so barely recognizable as a slope). It started moving extremely slowly, and all of us except one tried to hold back the force of the train, which of course was imossible and dangerous. The one who did not try to push it very quickly found the "shoe" and put in place. Initially it did not seem to help at all, the train just continued moving at the same pace, tearing up asphalt with the shoe. It finally came to a stop after about 3-5m(?) which takes a fair bit of time with such low speed, and felt like forever given the situation. The train tracks headed out into an open road, so it could have been so much worse if it were not for the only person thinking clearly in the situation (he was one of the more experienced in our group).
- master_crab 3y ago
  Also want to highlight this for another reason. At slow speeds rail and boats suffer from far less “moving” friction than road vehicles. So once off there is very little slowing them down vs cars and trucks that suffer from high rolling friction.
  - theluketaylor 3y ago
    Grady Hillhouse of Practical Engineering recently did a great demo of this. He was able to pull his car in neutral and an empty train car on rails with roughly the same force. https://www.youtube.com/watch?v=nGhBHrr5CYQ https://www.youtube.com/watch?v=nGhBHrr5CYQ
    - kamaal 3y ago
      One wonders how braking works on a train.
      - master_crab 3y ago
mannykannot 3y ago
> If it was going even 5kn... I don't know what sort of speed ships travel in harbors (though I know that they are faster than they appear.) In this case, it was an ebb tide (though within an hour of the low) which might have added something to the ship's speed. https://tides.willyweather.com/md/baltimore-city/patapsco-river--francis-scott-key-bridge.html https://tides.willyweather.com/md/baltimore-city/patapsco-ri...
G0dchi1d 3y ago
Thank you, I've been trying to get a ballpark on the weight, appreciated.
acdha 3y ago
According to https://gcaptain.com/ship-lost-control-before-hitting-baltimore-bridge/ https://gcaptain.com/ship-lost-control-before-hitting-baltim... they were going 7.6kn so your figures are “optimistic” by a factor of two. I really don’t know how much an engineer could have done to stop 600M N/s - that’s just an enormous amount of energy.
apaprocki 3y ago
<checks terminal> "current draft is 12.2m with 116851 t DWT" and last reported speed was 6.7kt. Good estimation! :)
- db0255 3y ago
  I saw radar that showed the ship was going 8.7 knots. And 7.6 knots before colliding.
a_e_k 3y ago
Crazy! Going by the higher 7.6 kn figure mentioned elsewhere in this thread, that'd be closer to 450 million N s. For another comparison, Wikipedia gives an estimate of "Apollo 11 launched from Earth to orbit" at 495 million N s [1]. So this is a momentum that's order-of-magnitude comparable to space launches. [1] https://en.wikipedia.org/wiki/Newton-second https://en.wikipedia.org/wiki/Newton-second
1letterunixname 3y ago
Your math appears off by an order of magnitude. KE = ½mv^2. [J] Ship KE = 0.5 * (114000 short tons) * (7.5 knots)^2 = ~7.7e8 J. 747 KE = 0.5 * (510,000 lbs) * (560 mph)^2 = ~7.25e9 J. 747 avg weight = (MTOW + OEW) / 2 = ~510,000 lbs

by xoa 3y ago

KineticLensman 3y ago

> enormously massive objects moving very slowly messes with human perception and "common sense" Yes, hence warnings to amateur boat users (e.g. on a canal boat) not to try to stop a collision with the bank using your arms or legs. [Edit] Boats can also do things that are unintuitive if you are used to driving a car. E.g. turning round the centre of gravity when you steer rather than following the front wheels.

smogcutter 3y ago
In the black powder era of warfare, soldiers were given similar warnings about “slowly” rolling cannonballs. People would think they could stop them like soccer balls, and lose a foot.
bmelton 3y ago
There are similar warnings for sailing vessels, but because the standing rigging of the ship is usually kept in high enough tension that putting your hands on a pilon to stop a collision might leave your hands vulnerable to being cut off by a mainsail's shrouds.
- KineticLensman 3y ago
  Ouch! That reminded me of seeing someone get a rope burn from a line on a yacht. I always wear gloves when handling lines on a boat nowadays.

litenboll 3y ago

I had a summer job once, filling trains with sugar. They weighed about 15kkg per wagon (usually 5-10 wagons per train IIRC). One time the pulling cart broke down and we had to switch it for another, but when we took it off the rails we forgot about the "shoe" that is supposed to go between the rail and one of the wheels so it can't move downhill (it was like 1degree of slope so barely recognizable as a slope). It started moving extremely slowly, and all of us except one tried to hold back the force of the train, which of course was imossible and dangerous. The one who did not try to push it very quickly found the "shoe" and put in place. Initially it did not seem to help at all, the train just continued moving at the same pace, tearing up asphalt with the shoe. It finally came to a stop after about 3-5m(?) which takes a fair bit of time with such low speed, and felt like forever given the situation. The train tracks headed out into an open road, so it could have been so much worse if it were not for the only person thinking clearly in the situation (he was one of the more experienced in our group).

master_crab 3y ago
Also want to highlight this for another reason. At slow speeds rail and boats suffer from far less “moving” friction than road vehicles. So once off there is very little slowing them down vs cars and trucks that suffer from high rolling friction.
- theluketaylor 3y ago
  Grady Hillhouse of Practical Engineering recently did a great demo of this. He was able to pull his car in neutral and an empty train car on rails with roughly the same force. https://www.youtube.com/watch?v=nGhBHrr5CYQ https://www.youtube.com/watch?v=nGhBHrr5CYQ
  - kamaal 3y ago
    One wonders how braking works on a train.
    - master_crab 3y ago

mannykannot 3y ago

> If it was going even 5kn... I don't know what sort of speed ships travel in harbors (though I know that they are faster than they appear.) In this case, it was an ebb tide (though within an hour of the low) which might have added something to the ship's speed. https://tides.willyweather.com/md/baltimore-city/patapsco-river--francis-scott-key-bridge.html https://tides.willyweather.com/md/baltimore-city/patapsco-ri...

G0dchi1d 3y ago

Thank you, I've been trying to get a ballpark on the weight, appreciated.

acdha 3y ago

According to https://gcaptain.com/ship-lost-control-before-hitting-baltimore-bridge/ https://gcaptain.com/ship-lost-control-before-hitting-baltim... they were going 7.6kn so your figures are “optimistic” by a factor of two. I really don’t know how much an engineer could have done to stop 600M N/s - that’s just an enormous amount of energy.

apaprocki 3y ago

<checks terminal> "current draft is 12.2m with 116851 t DWT" and last reported speed was 6.7kt. Good estimation! :)

db0255 3y ago
I saw radar that showed the ship was going 8.7 knots. And 7.6 knots before colliding.

a_e_k 3y ago

Crazy! Going by the higher 7.6 kn figure mentioned elsewhere in this thread, that'd be closer to 450 million N s. For another comparison, Wikipedia gives an estimate of "Apollo 11 launched from Earth to orbit" at 495 million N s [1]. So this is a momentum that's order-of-magnitude comparable to space launches. [1] https://en.wikipedia.org/wiki/Newton-second https://en.wikipedia.org/wiki/Newton-second

1letterunixname 3y ago

Your math appears off by an order of magnitude. KE = ½mv^2. [J] Ship KE = 0.5 * (114000 short tons) * (7.5 knots)^2 = ~7.7e8 J. 747 KE = 0.5 * (510,000 lbs) * (560 mph)^2 = ~7.25e9 J. 747 avg weight = (MTOW + OEW) / 2 = ~510,000 lbs