The ship

Mass by group

Lift is computed at both ends of the operating band and the binding one is used. At sea level the cells are at 85% fill on dense air; at the design altitude they have expanded to fill completely on thin air, which is what pressure height means.

What the arrangement has to obey

• PASSNo enclosed or habitable volume above or adjacent to a gas cell.

  Every habitable space is in the gondola below the hull or in the keel corridor below every cell. Hydrogen that escapes a cell rises away from all of them.

• PASSHabitable spaces are continuously ventilated, never sealed.

  No habitable compartment is sealed. Ventilation is what keeps a slow leak below a quarter of the lower flammability limit.

• PASSConfined runs are narrower than the 150 mm critical passage width, shorter than the run-up distance, or open at both ends.

  1100 mm by 102 m keel corridor. Open at both ends to the free stream, so hydrogen cannot accumulate to a flammable concentration.

• PASSEngine exhaust leaves below and downstream of the entire gas envelope.

  Exhaust exits at station 0.94, aft of the cell block at 0.92, and 12.7 m below the axis. This constraint is what pins the machinery aft, and it costs real trim to obey.

• PASSCentre of gravity at least 2.3 m below the centre of buoyancy.

  2.86 m of pendulum lever, 25 percent of hull radius. This is the entire static stability of the vehicle: there is no other restoring moment in pitch or roll.

• PASSCentre of gravity within 2 percent of length of the centre of buoyancy.

  Centre of gravity at 50.8 m, centre of buoyancy at 50.4 m: 0.36 percent of length aft. Corrected by moving water between keel tanks, which is why the water is distributed rather than in one drum.

• PASSGross lift at the design fill fraction exceeds gross weight.

  29645 kg of lift against 24516 kg of ship: 5129 kg spare.

• PASSLift margin at least 15 percent of gross weight, to absorb preliminary-estimate growth.

  5129 kg of margin on 24516 kg, 20.9 percent. Preliminary mass estimates grow 10 to 20 percent between concept and first flight, every time, and an airship has no way to trade payload for the difference: it either lifts or it does not. A design that closes exactly is a design that will not close.

• WARNEmpty weight per cubic metre of gas at or below the Hindenburg's 0.59 kg/m3.

  0.633 kg/m3 empty, against a historical fleet band of 0.505 to 0.79, all of it duralumin. Compared on EMPTY weight because that is what the fleet table records; consumables and crew are excluded from both sides. This ship also carries a photovoltaic array and a habitat that no ship in that table did, so beating the band is a harder claim than it looks.

• PASSEvery keel bay fits inside the keel corridor envelope, longitudinally and by volume.

  261 m3 of bays inside a 1311 m3 corridor running station 0.015 to 0.9. That corridor is subtracted from the gas volume, so the space you live in is paid for in lift rather than assumed free.

• PASSBallast transfer between the two water tanks can correct the standing trim offset.

  319 kg has to move 32 m to bring the centre of gravity onto the centre of buoyancy, and 1250 kg can. The margin is what absorbs stores burning off over the year, which is a nose-up trend of its own.

• PASSEvery keel bay fits inside the hull section at both of its ends.

  Every bay clears the hull skin over its full length. The hull tapers and the bays do not, so this is a real constraint rather than a formality: it is what stops the corridor running out past the cover near the tail.

• PASSFin area at least 1.3 times the minimum that balances the Munk moment.

  405 m2 of fin against a 284 m2 minimum on a 48.5 m arm: a static margin of 1.43. The Munk moment is certain and the fin effectiveness is not, because the tail sits in a thick hull boundary layer, so the margin is the honest part of this number.

• PASSAt least 19 m3 of habitable volume per person for a mission past the Celentano asymptote.

  141 m3 across 2 crew, 71 m3 each. Tolerable is 5, the performance limit is 10, and 19 is where more volume stops helping. For a year, designing to tolerable is how you get a crew that stops maintaining the ship.

• FAILThe daily superheat lift excursion is smaller than the trim the vehicle rests on water at.

  20 K of superheat moves lift by 2058 kg, which is 2.6 times the 800 kg the vehicle rests on water at. The ship floats off its float in the afternoon and presses 2.1 tonnes onto it before dawn, every day. NO PASSIVE WATER-CONTACT DEVICE CAN BE SIZED FOR A LOAD THAT SWINGS BY THAT FACTOR TWICE A DAY: a relief valve set for the trim is bypassed at the night load and useless at the day load. Either the marine architecture carries an active ballast loop that tracks the superheat, or the vehicle does not rest on the surface at all. This is the largest single unresolved item in the marine case.

• PASSAt least one laterally separated pair with full 90 degree vectoring.

  Differential thrust across the mid pair gives yaw authority at zero airspeed, which is the entire control system during mooring, during a water landing, and any time the fins have no flow over them.

• PASSPropeller discs clear the hull surface.

  Outermost tip is 4.4 m outboard of the hull at maximum radius. The outrigger has to carry that, and its bending moment is what sets the mount mass.