Train submarine

Discussion in 'Boat Design' started by mistereddb, Oct 26, 2013.

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  1. Stumble
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    Stumble Senior Member

    Why not just go by a large fuel ship? A fraction of the price, hundreds of times the capacity, and while it may be slightly more easy to detect, can travel three times the speed, thus outrunning many attackers.

    Plus you can use them now to transport.... Well fuel.

    That towable fuel bladder has a capacity of about 737 DWT (deadweight tons). The smallest oil tanker called general purpose tankers START at 10,000DTW. While the largest oil tankers hold 550,000 DWT.

    Since Australie imports about 1,000,000 barrels per day, or 150,000,000kg/day, which converts to 150,000 tonnes per day. So you need roughly 2000 of those fuel bladders a day delivered to the country, or one ULCC every four days. Which do you think would be easier for a foreign power to stop? A caravan of endless fuel bladders being towed slowly thru the water, or one ship, arriving somewhere once a week.
     
  2. mistereddb
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    mistereddb Junior Member

    Stumble
    Thanks for the information all I could find was this
    http://www.bree.gov.au/documents/publications/aps/2013/APS-205-201308.pdf and I was a bit surprised where all our jet fuel came from.

    As far as cost goes surely they would be cheaper than $10b of high tech subs to protect our oil supplies and maybe relying on one ship that can easily be detected with radar and sunk is putting all your eggs in one basket.


    parkland
    You bring up a good point about the railhead needing to be protected but that would be far easier than trying to protect ships over vast distances at sea.

    With a submarine weight is not the problem but buoyancy as it would displace 28,000t and a train only weighs 2,000t.

    I may be wrong but with a small cross sectional area and being below the waves it would be economical as well as fast.
     
  3. kerosene
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    kerosene Senior Member

    No I got that. But naturally the general shape is of a train. And packing fuel on train cars makes zero sense.
     
  4. Stumble
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    Stumble Senior Member

    The external bladder thing is rediculious as a way of moving bulk fuel. The amount of fuel that the tugs alone would use is probably a significant proportion of the fuel in the bladders. It's just a. Silly idea.

    Protecting a fleet of ships underway is actually not that difficult, you move in fleets, and have guard ships protecting them. Sure you loose a couple, but that's the price of poker. Those bladders could be slaughterd in mass by a single inflatable with a .50 machine gun. They are slow, impossible to protect, and where would you get that many sea going tugs? Since you are going to be hauling 2,000 bladders a day, you need 2000 tugs times the round trip time... So figure 6 weeks round trip, times 2000 tugs is 18,000 ocean capable tugs. At even 2 million each, that comes out to $36,000,000,000 (36 billion dollars). Not including the cost of the fuel bladders which are probably a couple hundred grand each.

    You don't understand the scale of the problem, and your sub thing is a sitting duck. It would be a cake walk to find it and deliver it, balders are just rediculious. The only way to deliver this much fuel is by large tanker or pipeline. That's it.


    And yes you are wrong, sure it has a small cross section, but it has huge wetted surface. Military submarines have massive engines installed powered by nuclear reactors because they are the only thing with enough energy density to power these things along at speed.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    In an alternate universe the train sub might be feasible. Maybe.
     
  6. rwatson
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    rwatson Senior Member

    Yes, it seems you still haven't gotten " head around the wetted surface resistance" yet, despite parklands info.

    Subs are much slower than conventional ships - which is another huge reason why subs don't make economic sense.
     
  7. MikeJohns
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    MikeJohns Senior Member

    You really need to read some books on submarines.

    Why would it be fast ? Submarine power goes by the cube of the velocity. Higher for shallow immersion since there is an adverse wave production as with ships with the addition of a much bigger surface area. Subs are also particularly prone to adverse current resistance.

    A slender sub is a big mistake if you want max speed. The optimum length to diameter ratio is in the 6.5-7.5 region, above and below this resistance increases significantly.

    Submarine fuel tankers have been used extensively and they were always only useful for refueling other vessels when they hid on station. Too expensive too slow and too vulnerable, and too low a capacity when compared with surface ships.

    Subs also need to immerse below significant wave orbitals which means they need to operate deep in rough weather. That is below one half the significant wavelength of the surface waves.

    The train carrying noodle is a structural impossibility. It would buckle so easily you could fold it up with it's own trim tank operation.

    [edit added] Viscous resistance is also dependent on surface roughness, so with a submarine it's imperative that the hull be kept smooth and free of any bio-fouling. Unless you were using drift subs.
     
    Last edited: Nov 8, 2013
  8. mistereddb
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    mistereddb Junior Member

    OK I have spent all day reading about submarines on Google to get a better understanding of them.

    Evidently like a diesel powered ship the faster they go the more power they consume so perhaps nuclear is the way to go but there would be economy of scale by building 100.

    Done a lot of Googling on wetted resistance and it appears that it can be halved with a smoother surface and higher speed to reduce the amount of fouling so I suggest that as wetted resistance is very small compared to cross sectional area it would not be too much of a problem if the trainsub operated at around 30 knots.

    They would be extremely hard to find in a vast ocean and even the small subs Iran is building can sit on the bottom and cannot be detected with sonar from more than a couple of kilometers.

    A number of people here suggest that it could break and may I remind you that it would sit on a prepared bed during loading/ unloading and I am sure model tank tests would be done to ensure that could not happen.

    Sure they would not carry that much fuel but perhaps sufficient for essential services with maybe even a bladder inside them.

    Yep a heap of ships protecting a convoy might be good but who is willing and able to provide them for us as we are flat out keeping our aging population in nursing homes and it appears we don't want a big young Australia.
     
  9. rwatson
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    rwatson Senior Member

    You can reduce fouling on a ship as easily as a submarine, so give us the math as to why the sub hull is more efficient for fuel consumption and better at load carrying.
     
  10. parkland
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    parkland Senior Member

    OK,

    According to my rough earlier "guesstimate"
    1,025,100 (submarine wetted area) / 37752 (emmas wetted area) = 27
    so 1/2 would mean the sub only has 13.5 x more wetted area than a super tanker.
    Even with modest numbers and all the antifouling I can imagine, I'm still not seeing it.
    What numbers did you find?

    There are a lot of other problems too.
    The smaller engines you'll need won't have the same economy as the massive supertanker engines.
    Did you say something about nuclear power? Yeah right, a multi kilometer nuclear submarine would be the most taunting easy military targets ever.

    This will never ever exist as a single 1 piece massive needle shaped submarine, if at all, it would need to be separated into many sections, to avoid stress snapping it in half.
     
  11. parkland
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    parkland Senior Member

    Also your forgetting, in this day and age, it's not getting the fuel to you that would be the issue during time of conflict; it would be whos gonna give it to you?
     
  12. mistereddb
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    mistereddb Junior Member

    rwatson
    If it displaces 28,000t and weighs 8,000t then it should carry at least 15,000t so 100 would carry a lot more but I am not saying it does a better job of fuel transportation in normal circumstances but they would be almost impossible to locate in a vast ocean.

    I do not think it would be any more economical than a conventional ship but I do doubt the significance of the theoretical wetted area resistance otherwise rowing skiffs etc. would not be so long and skinny.

    They would have to do tank tests and the strength and wetted area resistance would be known then.


    parkland
    It seems that nuclear generators are getting smaller and more common but still they would cost heaps more than us Aussies could afford so yes a slower diesel would have to suffice. At least we have a steelworks that may be able to use some of our unemployed. (over here you only have to work one hour a week and you are classified as having a job)

    Yes the smaller motors would not be as efficient as the big ships but sometimes efficiency is the problem we want to import all our fuel because it is more efficient but the NRMA says that we are losing our fuel security doing so.

    That last point is valid but surely we would have at least one friend in the world that would supply us with sufficient for our essential services.
     
  13. Stumble
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    Stumble Senior Member

    You can't tank test your way out of fundamental physics. This thing is too long and skinny to be possible. You need a length to width ration of about 6:1 - 10:1, you a re in the 300:1 range. This thing is too long to be structurally possible. Materials just are not stiff enough to make this possible.

    As for these subs... Let's assume you could build them, and make them work. You would need 100 of them delivering A DAY to equal what Australia needs. Figuring a two week round trip, which assumes a pretty good turn of speed, you still need 1,400 of them. While I doubt your numbers lets assume that they would only cost 10 million each. Even a normal production cargo ship of this size runs more like 50 million, so let's use both numbers...

    So 10,000,000 x 1,400 = 14 billion dollars in construction assuming your numbers are right
    And 50,000,000 x 1,400 = 70 billion more realistically (in reality this number is rediculously low)

    Do you really have even 14 billion to spend on an expensive toy? And let's not even consider the cost of trying to go nuclear. While the fuel costs are obviously lower, the operating costs of sea born nuclear plants are astronomical, which is why the US Navy only uses them on ships that absolutely demand them like super carriers. Even our smaller carriers are running bunker fuel, because the nuclear costs are just to high.
     
  14. mistereddb
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    mistereddb Junior Member

    Well thanks for all the information fellers it appears that we just have to suck up to everybody.

    I do think the world is getting like it was 100 years ago and it is getting ready for another blue just hope we keep our trucks running because I like my food.
     

  15. parkland
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    parkland Senior Member

    Is there something drastic going on down there?
    We have our share of bums and part timers and welfare trash here in canada, but not to the extent that I've thought of building a train submarine.
     
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