The Rescue Tool.
The golf ball size glob of green gunk enveloping the prop was itself enough to anchor the boat in the depths.
The massive amount of seaweed draped over the hull sealed the deal.
There was only a bit of moisture in the control room after 24 hours submerged.
The engine room did contain less than a teaspoon of water from a known leak.
Shortly after her loss I could place my ear to the pond surface and barely hear the propulsion plant responding to throttle commands. I could also detect the faint thrumming of the dive compressor when that signal was sent. But I could not determine distance or direction. 24 hours later these sounds could not be heard; the lack of any RF reception overnight ensured that the failsafe circuitry kept the blow valve energized until the battery was exhausted.
When the boat was located the next day after a 3 hour search, it was about 25 feet off shore in 8 to 10 feet of water, and 180 degrees from the direction she was last seen traveling. Given the amount of vegetation that came up with her, I can envision no method of failsafe design that would have allowed the hull, or even a marker buoy, to reach the surface once ensnared. After a drying out period, the battery was recharged and all functions were found to be in working order.
George "Crazy Ivan" Protchenko
“There are the assassins, the dealers in death; I am the Avenger!”-Nemo
"I'm disinclined to acquiesce to your request; means No!"-Capt.Barbossa