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Hadal

DSV Plumb

The submersible in this story does not exist. It is named after the plumb line, the weighted cord sailors once lowered to measure depth, and designed the way real full-depth submersibles are.

Side view of DSV Plumb: a long float on top, a crew sphere with three small windows beneath its front, steel ballast weights hanging under its middle, thrusters at the back and on top, lamps on arms at the front, and a frame with skids underneath.
DSV Plumb from the side. An invented design, drawn for this site.

The parts

Thrusters
Electric propellers for steering. The dive itself is gravity: the vessel sinks, then floats.
Float
A block of buoyant foam that carries the vessel back up once the ballast is gone.
Ballast
Steel weights that take it down. Dropping them is the only way home, so they are held by electromagnets that let go if the power fails.
Crew sphere
The only part with air in it. Two people, three small windows, and the full weight of the trench pressing on every side.
Lamps
Below 1,000 metres the only light is what you bring, or what the animals make.

The specification

Invented, like the vessel. Plausible, but not a real design.

Crew
Two: a pilot and a scientist
Rated depth
11,000 m
Crew sphere
Titanium, 1.5 m across inside
Descent
About four hours to the floor of the Challenger Deep
Time on the floor
One hour
Return
Drops its steel ballast and floats up in about four hours
Lamps
Six, aimed ahead and down

The real ones

Only a few crewed submersibles have ever reached the Challenger Deep. These three are where the ideas come from.

  1. Trieste, 1960

    Don Walsh and Jacques Piccard sank for nearly five hours in a steel sphere the size of a refrigerator, hung beneath a huge float that worked like a balloon. They spent 20 minutes on the floor, then dropped ballast to rise.

    Source

  2. Deepsea Challenger, 2012

    James Cameron made the first solo dive to the Challenger Deep in a tall, upright submersible, reaching the bottom after 2 hours and 36 minutes.

    Source

  3. Limiting Factor, 2019

    Built to reach full ocean depth again and again, with a titanium crew hull designed for 1,127 bar. Victor Vescovo piloted it to 10,925 metres in April 2019.

    Source