Stability during launch

Discussion in 'Stability' started by dougfrolich, May 23, 2014.

  1. dougfrolich
    Joined: Nov 2002
    Posts: 661
    Likes: 21, Points: 28, Legacy Rep: 225
    Location: San Francisco

    dougfrolich Senior Member

  2. mchl
    Joined: Sep 2013
    Posts: 25
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: France

    mchl MCHL Stabilitycalculation

    You can see on the video that the aft watertight door was open at launch. Considering the slope of the slipway, and the yacht trim, you can be sure that the water entered through the open door and flooded the aft compartment, shipping a lot of water and creating an important free surface effect. I think that the second cause of this sinking is due to the fact that the yacht was not supported laterally with side blocks and as the GM was <0 at the time the stern started to lift off the blocks ... (here draft was below the draft at 0 GM). A high VCG may be the third cause, but in this case, only two events were probably enough to lead to this launch accident.
     
  3. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,281
    Likes: 989, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    As has been indicated elsewhere, look at the air bubbling up at the stern on the port side.
     
  4. Emerson White
    Joined: Aug 2012
    Posts: 95
    Likes: 7, Points: 8, Legacy Rep: 61
    Location: Nordland, WA, USA

    Emerson White Junior Member

    Photos released elsewhere showed the door closed before the keel started to get wet.
     
  5. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 254, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    True. Water was apparently entering massively through some opening. The open engine-room door looks like a plausible culprit.
     
  6. Tad
    Joined: Mar 2002
    Posts: 2,308
    Likes: 192, Points: 73, Legacy Rep: 2281
    Location: Flattop Islands

    Tad Boat Designer

    It's the main engine exhaust, which was running while they launched the boat. See pictures 59, 60, and 61 here....

    http://www.smugmug.com/gallery/40857054_ZXJmNh#!i=3259713763&k=nPtDpW9

    Engine room door is shut and engine is running (underwater exhaust).
     
    1 person likes this.
  7. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,281
    Likes: 989, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Photo gallery did not work for me for some reason, but why was the engine running ? To supply power to pumps etc ?
     
  8. TANSL
    Joined: Sep 2011
    Posts: 6,778
    Likes: 494, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    It is possible that the port stabilizer fin touched the bottom of the launch ramp, the boat will heel at a time when the stern was still not sufficient buoyancy and water started entering through some point, but must be closed, was not.
    Maybe the engine was running to, once launched, stop the boat as soon as possible. Anyway, if it was running, the pressure of the exhaust gases would have prevented something, or it would have decreased, the entry of water.
     

  9. Tad
    Joined: Mar 2002
    Posts: 2,308
    Likes: 192, Points: 73, Legacy Rep: 2281
    Location: Flattop Islands

    Tad Boat Designer

    They were launching a really big boat in a very tight space, the engine was running because they needed it to maneuver off the bow dolly and out of that space. There is a marina directly astern and the clearance was tight. The ramp is certainly not intended for such a large vessel. Once she did float, turned sideways, and sank till aground, she blocked vessels entering or exiting a number of marina berths. Which was part of the rush to move her.

    If you look at picture 101 in that sumgmug series you can see the port stabilizer clearly. There is little damage to support the idea that 110 tons of boat pivoted on the tip. It seems to be missing a small amount of paint on the leading edge.
     
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.