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- Main hull of the craft is a tank filled with gasoline: lighter than water and only a little compressible. It is not a high pressure enclosure. A membrane keep
by sclarisse 3y ago
- Main hull of the craft is a tank filled with gasoline: lighter than water and only a little compressible. It is not a high pressure enclosure. A membrane keeps these two fluids apart mostly, but some maneuvers dump gasoline into the ocean.
- Ballast is held in place with magnets. You actually want to drop ballast as you descend, to make up for the added seawater.
- Sphere on the bottom holds observer and instruments. This is a high pressure part.
- There’s no real propulsion or navigation. You land more or less where you land.
- sjackso 3y agoI recall reading about the craft using gasoline as an incompressible floatation fluid, but I hadn't realized the scale: 100 tons of gasoline, making up 2/3s of the craft's mass.
- bodhi_mind 3y agoBasically the equivalent of a lighter than “air” craft but in a different fluid. I wonder if there’s a word for a craft that controls its buoyancy regardless of medium?
- pvaldes 3y ago> I wonder if there’s a word for a craft that controls its buoyancy regardless of medium sperm whale
- javajosh 3y agoAn Archimedes craft. (I made this up just now).
- gigiggufh 3y agoFluid is a Latin root, so why not "fluidostat" on the model of "aerostat"?
- 4gotunameagain 3y agobecause -stat is a Greek root. merriam-webster borrowed from French aérostat, probably back-formation from aérostatique "of aerostatics," with -stat (after héliostat heliostat) taken as the Greek agentive element -statēs "one who causes to stand" — more at -stat
- deleted 3y ago[deleted]
- moffkalast 3y agoI've never looked at it this way, but it really is literally an underwater blimp lol.
- specialp 3y agoI never knew the scale either. But the book says gasoline has a specific gravity of 0.7. So 100 tons will make roughly 30 tons of buoyancy. The negatively buoyant craft is 50 tons so combined with the air inside that is probably the displacement required to make it positive
- moffkalast 3y ago> The primary 24 volt electrical system of TRIESTE is powered by 56 twelve-volt, 48 ampere-hour, lead-acid batteries located in four aluminium saddle tanks fastened to the top of the float beneath the superstructure. Each of the four battery tanks or boxes is pressure- compensated through the use of transformer oil and, therefore, during submergence the batteries themselves are subjected to full depth pressure.’ Three of the boxes are allotted for powering the craft's five 3-horsepower electrical propulsion motors and for providing power to the lighting systems. > The propulsion system consists of five special General Electric 3-hp de motors. These motors are designed to operate in inert fluid (silicone oil) and are subjected to full ambient pressure during diving operations. > The motors themselves are in five different locations. Two of them provide horizontal motion forward and backward, two provide vertical motion either ascending or descending, and one is installed athwartships for turning. The motors all drive propellers through gear boxes. It actually does have electric thrusters. Interesting that they were able to make the batteries neutrally pressured.
- sclarisse 3y agoAh! I was misled by the general comparison to an unpowered balloon that they make a few times. It’s not much propulsion and they take special care to differentiate it from a submarine that can actually travel the world.
- Zee2 3y ago> athwartships What a phenomenal word!
- HeyLaughingBoy 3y agoIncidentally one of my favorite nautical terms. Just always liked the sound of it :-)
- b215826 3y ago> You actually want to drop ballast as you descend, to make up for the added seawater. The ballast is dropped during the ascension, not the descent. This makes the ascension-step impossible to fail and requires no electricity [1]. Incidentally, I first came to know about the bathyscaphe while reading Peter Watts's Rifters trilogy (which is an amazing hard SF series set in the deep sea). [1] https://en.wikipedia.org/wiki/Bathyscaphe#Mode_of_operation https://en.wikipedia.org/wiki/Bathyscaphe#Mode_of_operation
- elzbardico 3y agoThe document says otherwise. As gasoline is slightly compressible, seawater is admitted in the float during the dive, increasing negative buoyancy, and increasing the rate of descent. So, to control the rate of decent, some ballast is released during diving too.
- Cerium 3y agoBallast is dropped during both descent and assent. The linked document explains how the gasoline used for buoyancy is significantly compressible and becomes denser as the bathyscaphe descends. If no ballast was dropped during descent the rate of descent would continue to increase due to the feedback mechanism of increased pressure, leading to increased compression, leading to increased density.
- a4isms 3y agoFWIW you don’t need a bathyscape to experiment with this. When Scuba diving in temperate locations (like Tobermory, Ontario), people with 7mm wet suits and extra vests or jackets experience this as they descend: The neoprene compresses, and if you don’t add small amounts of buoyancy to your BCD, you’ll start to free-fall.
- jacquesm 3y agoIt's Tobermory. Absolutely beautiful area, so many birds. I went camping there several times. It's also pretty much the end of the world, the only way through is by ferry.
- eutectic 3y agoWhen people say 'carbon fiber is weaker under compressive loads', or 'cylinders distribute compressive forces unevenly', these kinds of issues seem like engineering challenges not fatal flaws. I feel like the problem with the Titan submersible was the lack of respect for safety, not any specific design choice.
- jacquesm 3y agoIt could well be both.
- eutectic 3y agoWell, obviously going with a more conventional construction would make it easier to come up with a safe design. But I feel like people are going to take the wrong lesson from this accident.
- jacquesm 3y agoThe people whose lives depend on this sort of thing will definitely be learning the right lessons and the rest doesn't matter. In fact, plenty of them already had learned those lessons, the CEO of that company was a pretty special case (and not in a good sense).
- eutectic 3y agoThe Boeing 787 is primarily made from carbon fiber, including the wings which experience a mix of tensile and compressive loads thousands of times over their design lives. Of course deep sea submersibles occupy a much smaller market where a comparable degree of rigor may not be justified, but I think it's silly that everyone suddenly seems to be a expert in composite and/or submersible design.
- Aeolun 3y agoAirplanes deal with lesser atmospheric pressure though, not more. Flexibility is probably a good thing.
- cratermoon 3y agoIt says at the link, on page 5, "The compressional loss of buoyancy is of such a magnitude that approximately 1 ton of ballast must be dropped for every 3000 feet of descent to maintain equilibrium."