Comment by krschultz | Hacker News Reader

Comment by krschultz | Hacker News Reader

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Actually, that idea is employed by every single US Navy (and I assume their foreign counterpart) submarine. The bow & stern planes combined with forward motion do almost all of the up and down depth control after you are under water. The ballast tanks are only really for changing whether you are a surface ship or a submerged ship.

The main disadvantage of not having ballast tanks is that on the surface, you won't float that high (I assume you will be slightly positively buoyant, because requiring power to get back to the surface is crazy, and perfectly neutral buoyancy is nearly impossible to achieve). This doesn't matter for a little thing with a tender, but for anything on its own, I'd rather float a little higher. Also, you have to keep moving to keep lift up. That just doesn't make sense for a boat that you spend a lot of time stalking around with as much stealth as possible.

As for "the most dangerous thing an attack sub can do in combat is launch a torpedo", that's just not true. The majority of the missiles launched against Libya this month came from US subs (SSGN). And there are a lot of capabilities that are secret or borderline secret. Check out "Dark Waters" and "Blind Man's Bluff". Also http://www.globalsecurity.org/military/systems/ship/dds.htm

``Lead On!'', by Rear Admiral Dave Oliver, Jr, 1992, claims otherwise on pages 50-51: ``On the day of interest, while operating at a deep depth, the digital-readout depth gauge on this ship stuck at a few feet shallower than the desired depth. As the submarine was not quite as light as the crew thought, the ship slowly drove itself deeper and deeper. No one recognized that the two other depth gauges were slowly creeping downward, correctly indicating that the ship was going deeper.''

There's a description before this of how 44 psi is 100 feet, and some of the depth gauges showed psi and others feet, and how the standard procedure had been to have the ballast tanks trimmed light, forcing a down angle to maintain depth.

The book continues ``We made several changes in submarines as a result of this incident. For one thing, we don't trim light and run with a down bubble anymore. If the ship takes a down bubble now, except during transitory conditions when the submarine is changing depth, then something is wrong.''

You're wrong on both counts.

The sub design in question has no ballast tanks. It literally "flies" downward and "sinks" to the surface. No navy subs (at least non-classified subs) do this. Not having ballast tanks is a huge design advantage.

Firing missiles from a Sub against a low tech country with no navy to speak of is hardly a combat situation. In naval combat the only thing subs are really afraid of is other subs and aircraft, and the best way to give up your position is to fire a torpedo.

Not having a ballast tank is decidedly NOT a huge design advantage for a military sub, because to stay under the surface you have to keep moving at a certain rate of speed. That is not a desirable trait when your primary goal is to be stealthy.

It IS a great design advantage for non-military subs when your primary goal is to be safe.

The concept is not exactly earth shatteringly new, I've seen concepts of it from navy contractors for decades, the Navy just has no use for one.

For surviving, yes, the only thing can kill a sub is a ship or airplane. How for succesfully completing a mission usually the goal is to remain undetected. That is certainly harder to do.

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