Stability during launch

Bad news at Northern Marine. Video shows what happened.

http://www.youtube.com/watch?annota...&feature=iv&src_vid=J2-oDTZHvVM&v=lEBJjsdTyWY

 

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.

 

As has been indicated elsewhere, look at the air bubbling up at the stern on the port side.

 

Photos released elsewhere showed the door closed before the keel started to get wet.

 

True. Water was apparently entering massively through some opening. The open engine-room door looks like a plausible culprit.

 

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).

 

Photo gallery did not work for me for some reason, but why was the engine running ? To supply power to pumps etc ?

 

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.

 

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.