Huge Semi-Submersible Ships

Discussion in 'All Things Boats & Boating' started by Leo Lazauskas, Sep 12, 2013.

  1. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    1 person likes this.
  2. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 246, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    All I can say is - awesome!

    I know very little about this kind of ships, and was wondering if they employ some sort of stability-enhancing systems (gyros, for example) because it seems that their metacentric height is extremely low, especially during the loading/unloading phase...?
     
  3. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 139, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    sometimes I guess you are going to need a bigger boat..
     
  4. DCockey
    Joined: Oct 2009
    Posts: 4,622
    Likes: 281, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    From http://129.16.218.54/MSE/Assignment/Heavy Cargo Ships.pdf (Emphasis added)
    A high number of watertight bulkheads and web frames are not only required to provide structural strength but also to increase the number of segregated ballast tanks. An advanced ballast water system with many ballast tanks is required in order to balance the unconventional cargo during loading/offloading operation.

    3.3 VOYAGE CONSIDERATIONS

    Because the cargo transported by heavy lift vessels is nonstandard, the specifications of the cargo, season, and route need to be considered for each voyage. When calculating the stability of the vessel, the buoyancy of the cargo needs to be included. Forces acting on the cargo are inertial forces due to ship motions, forces due to sustained wind load, and gravity forces due to sustained wind heel [15]. The cargo is secured by a sea-fastening arrangement designed according to the extreme design forces. The actual forces will depend on season and route taken. Stormy seas should be avoided.​


    From http://www.automation.com/automatio...tability-of-semi-submersible-transport-vessel
    Emerson supplies a comprehensive ballast control system, which is responsible for helping the Dockwise Vanguard submerge and rise with stability and integrity. It relies on tank gauging systems that provide highly accurate level measurements for load calculations as well as high level and overfill alarms. The Dockwise Vanguard also uses Emerson’s Smart Wireless technology to measure and transmit tank level data to the wheelhouse.​
     
  5. El_Guero

    El_Guero Previous Member

    Where are the waves? All those pictures look like they are in a lake.

    :)
     
  6. TANSL
    Joined: Sep 2011
    Posts: 6,115
    Likes: 268, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    As noted DCockey "season, and route need to be considered for each voyage".
    But having said that, these ships, once loaded and stabilized with ballast, work like any other. They must have a certain minimum freeboard.
    The major problem occurs during loading and unloading as the area of the floating will, in an instant, go from a very high to a very, very, small. So the ballast system and ballasting sequence, to sink / refloat the boat perfectly balanced, is tremendously important.
    It is also necessary to study the positive buoyancy of the load so that it does not deck off too son.
     
  7. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 246, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    In fact, I was referring to that particular situation. The waterplane area of the ship in this position is nearly inexistent:

    [​IMG]

    So the loss of stability has to be compensated in some other way, and it probably has to be done dynamically. A ballast water system (mentioned by DCockey) is one way to go, but I'd think that gyroscopic stabilizers could perhaps be a more compact and effective choice. Fur sure they have examined all of their options, and the fact that water ballast was preferred over gyros is probably an indicator that gyros are not the best solution, even when money is not on top of the list of constraints.
     
  8. TANSL
    Joined: Sep 2011
    Posts: 6,115
    Likes: 268, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Daiquiri, the truth is I do not know exactly how. I do not think at the time that appears in the photo, it touch the ballast in tanks, for fluid movement always creates harmful effects. An active system with stabilizing fins is, in my opinion, much more effective and faster.
    At the time of the photo you may not have serious problems. It may be problems when the load is on deck because then the cog of the whole is much higher.
     
  9. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 246, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Another very interesting reading about the history and operation of heavy-lift semi-submersibles: http://www.argonautics.com/Semi-Submersible Heavy-lift Ships in Operation.pdf

    It is impressive to find out that these giant vessels are sometimes heavily modified and customized structurally for just one single transport. It gives an idea of the money in game and of the economic power of their clients (oil companies, so no wonder there).

    Thanks for this thread Leo, I am learning a lots of new stuff here. :)
     
  10. DCockey
    Joined: Oct 2009
    Posts: 4,622
    Likes: 281, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    My understanding is that semi-submersible ships are only submerged as shown in the photo above when stationary for loading and unloading. Presumably loading and unloading is usually done in good weather in protected waters. At all other times the ships have the entire deck out of the water. Stability considerations when loading and unloading would be in principle very similar to those for a floating dry dock. My guess is the minimum stability during loading and unloading can be considerably less than the stability once the load is fully lifted. Also, several of the descriptions of these vessels which I found emphasized that "When calculating the stability of the vessel, the buoyancy of the cargo needs to be included." I'll also guess that detailed, rigorous analysis is done of the entire loading and unloading process for any large cargos, and the analysis is carefully checked.
     
  11. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 246, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    You can go beyond the guess and bet your house, your car and your cat on that. :)
     
  12. El_Guero

    El_Guero Previous Member

    Why wouldn't they use a catamaran design with the center between bow and stern open?

    It would allow a greater range of ships to be hauled, better CoG, etc, etc.

    Wouldn't it?

    Is it merely the added costs of the second hull?

    wayne
     
  13. TANSL
    Joined: Sep 2011
    Posts: 6,115
    Likes: 268, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    A catamaran has many fewer tons per inch of immersion that a monohull of the same length.
    The catamaran has the advantage of greater stability but a well designed monohull always will have adequate stability.
    Efforts on the deck of a catamaran always be greater than on a monohull.
    A catamaran has much less room for huge ballast tanks needed to load / unload the boat.
    A catamarán is not a good idea.
     
  14. MikeJohns
    Joined: Aug 2004
    Posts: 3,192
    Likes: 206, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Just a self powered floating dock. There have been a few accidents and two of the Mighty Servants sank, one was salvaged.

    The destroyer HMS Nottingham was taken back to the UK from here, for a 40 million dollar crash repair on one of the Mighty Servants. That was after the British Navy personnel aboard forgot how to navigate a ship properly around an island in 2002. Her loading was a pretty standard dry docking except she didn't quite fit.
     

  15. MikeJohns
    Joined: Aug 2004
    Posts: 3,192
    Likes: 206, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member


    You need the displaced volume .
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.