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Comment by mrguyorama | Hacker News Reader

One thing I've completely missed in all this drama: WHY a carbon fiber hull? Carbon fiber is not known for being easy to work with, or cheap, or strong in compression, or good for water, so WHY would you use it on a submersible as "new" technology?

I must have missed some discussion.

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If the hull were made out of metal it would be much heavier and require a much bigger support ship to launch and recover. This would increase overall system costs.

The lower density of carbon also removed the need for syntactic foam floats.

The CEO had aircraft experience so he liked carbon fiber.

The official reason given by the company is that carbon fiber allowed the submersibles to be positive buoyant. This in turn allowed them to use electromagnets to hold onto ballast, and in the case of a failure the submersibles would loose its weight and go back to the surface. It was also considered cheaper and smaller than using steel in combination with syntactic foam to achieve the same result.

Money.

A heavy sub requires heavy support equipment. Heavy support equipment requires a large boat. Large boats are expensive. It's cheaper to spend a little extra on the sub and save a lot on the support ship.

Also, there’s seemingly little benefit to low weight in this application?

In an interview with Stockton Rush, and sure we should take his insights with a grain of salt, he stated that in deep sea submersibles it's not about weight, but buoyancy. The carbon fiber is significantly more buoyant than titanium, meaning they didn't need very special foam and ways to mount it like is used in Alvin.

The carbon fibre was apparently cheap second hand because it was ex-aviation gear past its service life.

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