5 ms·

How strong do those pumps need to be to drain the ballast tanks and raise the ship after she’s got her new cargo on deck? I’m having trouble wrapping my head ar

How strong do those pumps need to be to drain the ballast tanks and raise the ship after she’s got her new cargo on deck? I’m having trouble wrapping my head around how all this would work. Any Merchant Marines out there?

lightedman 7y ago
Not strong at all theoretically speaking. All you have to do is have enough headroom to pump higher than water level for a given diameter of pipe and have an air intake to match which is higher than water level. You could take forever with a strong pond pump and achieve the same effect. I designed full-building hydroponics systems. You get similar issues with things like vacuum pressure in tanks causing your pumps to not work properly.
crgwbr 7y ago
If time is no object, you could do it yourself with a straw. The pumps only needs to be powerful to drain the ballast tanks quickly.
wmoser 7y ago
The pumps are probably pretty large just so it doesn’t take that long. It’s more of a large volume of water problem than a push it forcefully problem if that makes any sense. There’s something called hydraulic head or pump head that determines how high a pump can pump. It’s sort of a trade off between height it can pump and flow rate. The pumps used are more than likely centrifugal pumps rather than positive displacement. As an aside on pumps, on the ship I work on, we have two fire pumps that are run off 11kV motors, they have to pump a large volume of water potentially pretty high for a deluge/sprinkler system. Our normal ballast pumps are 480v and when they come on the lights flicker but we don’t do much ballasting of the same type as the heavy lifts, it’s more for trim and heel. There are also considerations that a partially filled tank can lead to instability (free surface effect) and they have a definite sequence that they must pump out the tanks to prevent excess stress on both the vessels (on ships the bending is called hogging and sagging). Some ships if they are loaded/ballasted in a certain configuration can actually potentially break in half.
- BuffaloBagel 7y ago
  https://en.wikipedia.org/wiki/Hogging_and_sagging https://en.wikipedia.org/wiki/Hogging_and_sagging
oh_sigh 7y ago
Keep in mind that those tanks aren't under vacuum or have any special physics at play - you could have a guy sitting in the tank bailing them out with a wooden bucket.
- usrusr 7y ago
  He would have to run up a lot of stairs though. But with prefect absence of leakage (a precondition for the bucket-weilder's success was well), proper rain protection and good ventilation it might be just as fast for all practical considerations (not fast at all) to just stand back and allow evaporation to do the job. What I find even more impressive than the engineering dimension is that a market for those things exist, and how easily the the basic financial craftsmanship of playing through price/demand curves and ROI apparently scales. Because the business side looks so amazingly calm from the outside, entirely not like some Isambard Kingdom Brunel cable laying adventure or a 21st century version thereof (seriously, make a movie about that guy and get Musk to play him)
dt5702 7y ago
Naval architect here. As other commenters have noted the size of the pumps isn’t really the issue here - you can have as many as you want it really depends on the time you have available. For me, the cool things about this are the size of the installed power and the stability problem in having one submerged object with multiple half empty ballast tanks lift up another object with multiple tanks. The BOKA Vanguard has an installed power of 27000kW, split between two main diesels and two auxiliaries. This is slightly more than a Los Angeles class nuclear submarine, which goes much faster (perhaps 2x according to wiki) underwater - very much a different resistance problem. There are two 35 tonne and 65 tonne generators/engines. These are not small pieces of equipment. That’s what gets me about these ships - they are on another level of huge. The stability problem is a significant challenge. You can see in the video that they did it on a flat day. Being able to coordinate the pumping of multiple ballast tanks to make sure that both ships remain upright is another cool thing here. Look up the “free surface effect” if you want to learn about that particular challenge. Sources; various Wikipedia pages and Wärtsilä technical sheets.
- remarkEon 7y ago
  Interesting! Thanks. The stability problem does seem extreme, which is what I assumed all the tugs are around for. One of the other thoughts I had was ... what possesses someone to build something like this? It obviously has more uses than dealing with disabled cruise ships, but not many more right? What’s the ROI on something like this?
  - mdorazio 7y ago
    These are also often used to reposition or completely move entire oil rigs, which I think is probably their biggest use case.
  - dt5702 7y ago
    Oil and gas.
- killjoywashere 7y ago
  As I recall, the captain of the docking ship (the smaller ship) relinquishes control when the bow crosses the dry dock's threshold. Does that apply for these open ocean vessels as well?

lightedman 7y ago

Not strong at all theoretically speaking. All you have to do is have enough headroom to pump higher than water level for a given diameter of pipe and have an air intake to match which is higher than water level. You could take forever with a strong pond pump and achieve the same effect. I designed full-building hydroponics systems. You get similar issues with things like vacuum pressure in tanks causing your pumps to not work properly.

crgwbr 7y ago

If time is no object, you could do it yourself with a straw. The pumps only needs to be powerful to drain the ballast tanks quickly.

wmoser 7y ago

The pumps are probably pretty large just so it doesn’t take that long. It’s more of a large volume of water problem than a push it forcefully problem if that makes any sense. There’s something called hydraulic head or pump head that determines how high a pump can pump. It’s sort of a trade off between height it can pump and flow rate. The pumps used are more than likely centrifugal pumps rather than positive displacement. As an aside on pumps, on the ship I work on, we have two fire pumps that are run off 11kV motors, they have to pump a large volume of water potentially pretty high for a deluge/sprinkler system. Our normal ballast pumps are 480v and when they come on the lights flicker but we don’t do much ballasting of the same type as the heavy lifts, it’s more for trim and heel. There are also considerations that a partially filled tank can lead to instability (free surface effect) and they have a definite sequence that they must pump out the tanks to prevent excess stress on both the vessels (on ships the bending is called hogging and sagging). Some ships if they are loaded/ballasted in a certain configuration can actually potentially break in half.

BuffaloBagel 7y ago
https://en.wikipedia.org/wiki/Hogging_and_sagging https://en.wikipedia.org/wiki/Hogging_and_sagging

oh_sigh 7y ago

Keep in mind that those tanks aren't under vacuum or have any special physics at play - you could have a guy sitting in the tank bailing them out with a wooden bucket.

usrusr 7y ago
He would have to run up a lot of stairs though. But with prefect absence of leakage (a precondition for the bucket-weilder's success was well), proper rain protection and good ventilation it might be just as fast for all practical considerations (not fast at all) to just stand back and allow evaporation to do the job. What I find even more impressive than the engineering dimension is that a market for those things exist, and how easily the the basic financial craftsmanship of playing through price/demand curves and ROI apparently scales. Because the business side looks so amazingly calm from the outside, entirely not like some Isambard Kingdom Brunel cable laying adventure or a 21st century version thereof (seriously, make a movie about that guy and get Musk to play him)

dt5702 7y ago

Naval architect here. As other commenters have noted the size of the pumps isn’t really the issue here - you can have as many as you want it really depends on the time you have available. For me, the cool things about this are the size of the installed power and the stability problem in having one submerged object with multiple half empty ballast tanks lift up another object with multiple tanks. The BOKA Vanguard has an installed power of 27000kW, split between two main diesels and two auxiliaries. This is slightly more than a Los Angeles class nuclear submarine, which goes much faster (perhaps 2x according to wiki) underwater - very much a different resistance problem. There are two 35 tonne and 65 tonne generators/engines. These are not small pieces of equipment. That’s what gets me about these ships - they are on another level of huge. The stability problem is a significant challenge. You can see in the video that they did it on a flat day. Being able to coordinate the pumping of multiple ballast tanks to make sure that both ships remain upright is another cool thing here. Look up the “free surface effect” if you want to learn about that particular challenge. Sources; various Wikipedia pages and Wärtsilä technical sheets.

remarkEon 7y ago
Interesting! Thanks. The stability problem does seem extreme, which is what I assumed all the tugs are around for. One of the other thoughts I had was ... what possesses someone to build something like this? It obviously has more uses than dealing with disabled cruise ships, but not many more right? What’s the ROI on something like this?
- mdorazio 7y ago
  These are also often used to reposition or completely move entire oil rigs, which I think is probably their biggest use case.
- dt5702 7y ago
  Oil and gas.
killjoywashere 7y ago
As I recall, the captain of the docking ship (the smaller ship) relinquishes control when the bow crosses the dry dock's threshold. Does that apply for these open ocean vessels as well?