Saturday, June 29, 2013

Zumwalt Tumblehome Hull Tests

ComNavOps stumbled across a Defense News video on YouTube which showed Navy research tests of the Zumwalt, DDG-1000, tumblehome hull undergoing scale seakeeping tests.  After hearing for years that severe tumblehome hull forms have seakeeping issues, it's fascinating to see the scale tests of the hull.  Please check out the video below.  It’s less than two minutes long and well worth the watch because the footage is absolutely fascinating.

The tests showed that hull cuts very cleanly through calm seas when compared to a conventional hull and the video suggested that would offer fuel savings.  However, the tests also showed some possibly serious shortcomings in rougher seas with the hull potentially susceptible to exaggerated pitching, heeling, and snap rolls.  The stern flight deck may be prone to taking water in moderate seas which may be problematic for flight operations.




We’ll have to wait and see how the real ship performs but seakeeping is definitely an issue that needs to be closely monitored.

In case you can't see the video, here is the link:  Zumwalt Tumblehome Video

or

https://www.youtube.com/watch?feature=player_embedded&v=R-s3S3F8Mao


6 comments:

  1. It might be because I'm reading this on an iPad, but I can't see the embedded video. Mind giving me the direct link?

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    1. https://www.youtube.com/watch?feature=player_embedded&v=R-s3S3F8Mao

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  2. Morning again ComNavOps,

    A while ago I was speaking about this design briefly with a chap who knows a thing or two about naval construction and he assured me the design was fully fit even for rough sea states, despite my scepticism.

    Having seen that video, I think I might go back to being a sceptic!

    The speed of that rolling, if genuinely representative of the final product, is something else. Severe sickness, crew injuries from impacts as people get thrown around inside, that thing is going to be a nightmare. Any kind of rough seas is going to massively hamper pretty much all operations.

    On the bright side, it looks like it'll make an excellent river boat, or calm sea vessel. Perhaps a rename to Monitor is on the cards?

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  3. There's an aspect of the DDG-1000 tumblehome hull that's bothered me for a while, but this video is the first thing I've found online that seemed relevant.

    Tumblehome used to be a popular idea in French and French-influenced designs of the late 19th century. It was dropped because it's bad for stability. As a ship with a outward-flared hull rolls, the immersed volume increases, so the buoyancy pushing it back to an upright position increases. The ship gains stability as it rolls.

    With a tumblehome, the righting force decreases as the ship heels: as the angle of roll increases, the ship becomes less stable. To make a tumblehome ship adequately stable it has to be very "stiff", with a very low centre of gravity, which means that its rolls are very short and rapid. The video alludes to this, but doesn't go into details.

    Now, while the ship is intact, that rolling can probably be damped with stabilisers, so it should be possible to avoid the crew suffering too much from the stiffness.

    But warships get damaged in action. At least, they do when fighting real wars, and when fighting lesser operations in confined waters infested with mines. If a DDG-1000 suffers significant flooding, and looses power to its stabilisers, things could turn nasty quite fast.

    You lose buoyancy, so the ship immerses further and lists. The tumblehome means it looses, rather than gains, stability as it lists. You don't have the stabilisers to help correct for this.

    Counter-flooding still works, if you have the reserve of buoyancy to cope with it - but you put all the heavy stuff very low in the ship to get the initial stability, and flooding compartments full of heavy equipment tends to disable that equipment.

    Overall, it doesn't seem to stand up to damage as well as a conventional ship. Is it scheduled for shock testing?

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  4. Look up the following:

    - Borondino class during the Battle of Tsushima
    - French battleship Bouvet

    Both of these were poorly maintained, but given the USN's track record, that's a risk too with the Zumwalt class.

    As John above me describes, the ship unlike a flare hull does not stabilize itself. The risk of capsizing is greatly increased.

    Apart from very rough sees, teh real question is how well the ship can handle damage - worsening this dramatically of course is the reduced manning requirements.

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    1. This is a high risk design, without question. I would have preferred to see the Navy build the Zumwalt as a one-off experimental vessel rather than build three before we know whether it's even stable in blue water environments.

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