What’s described is a very modest increase in buoyancy, and it would require very modestly larger ballast tanks.
That’s a huge amount of volume overall – even 3 inches. That would be a huge effect on buoyancy.
Our dive officer would attempt to calculate weight onboard to the tens of pounds, roughly speaking. 3 inches of void around the entire hull is probably displacing thousands of pounds of water.
Again,
(1) The buoyancy increase would be the same as an additional void filled with air. Could still be significant, but the difference between air and vaccum is negligible. It is the weight of water displaced that matters, and air is already 1/1000th the density of water.
(2) Larger ballast tanks isn’t the answer. The size of the ballast tanks just dictates the range of buoyancy adjustment that’s required in different phases of maneuver. You’d need static ballast to offset the additional volume of water displaced by the vacuum, and the static ballast could not be the water that fills ballast tanks. It would need to be denser than water.
#2 is right, I stand corrected (and corrected my post).
Doesn’t a Virginia-class SSN, for instance, displace roughly 7,800 tons? “Thousands of pounds” would only equate to a few tons of difference.
It might be tens or hundreds of thousands of pounds – I don’t have the numbers in front of me. But it would be a very large amount, and require a huge amount of static ballast to make up for it.
I really don’t think that’s true. The density of vacuum is zero. The density of steel (which hulls are usually made of) is 8 times that of water. So isn’t a 3" vacuum around the hull offset by making the steel hull just 3/8" thicker?
I’m not advocating the vacuum idea, I just don’t think the buoyancy issue is as great a problem as you suggest. Consider the volume occupied by air in the interior, for which the exact same problem exists. Submarines are cramped, but they are not THAT obsessive about reducing the amount of air space. If they were, they’d be sitting on blocks of solid steel instead of ordinary chairs, etc.
Alright, here’s back-of-the-envelope math: a VA class submarine is about 120 meters long, with a radius of about 6 meters. By my estimates (assuming a submarine is a cylinder), 3 inches of vacuum would add very roughly 500 cubic meters of volume to the submarine. That’s 500 metric tons of water being displaced, so that’s how much solid ballast would be needed to be added to make up for it.
Isn’t my calculation much simpler? Steel is 8 times denser than water, so you need to increase the thickness of a steel hull by the thickness of the added vacuum shell divided by 8.
That might work too – I presume that’s about the same amount of steel in weight.
Well, I HAD just written up some math but by the time I finished double-checking my numbers (I’m only partially foolish) I saw others did the same. So I’m just removing mine to avoid repetitive redundancy.
PS: Totally loving this chat. I’d probably be buying you lot a round at this point.
In addition, it wouldn’t necessarily have to be three inches; one inch would do the work just as well. So it might be only 167 tons being displaced, not 500.
I get that the vacuum hull concept isn’t feasible. But the amount of displacement that 167 tons would represent would be just 2 percent of the Virginia’s overall tonnage.
For an Ohio-class boomer, it would be even less; less than 1 percent.
The numbers would be a lot different for Ohio – they’re a lot bigger than Virginia, and thus the surface area and volume numbers would be a lot more.
*Facepalm * Ah, yes. I forgot that.
The calculation for an additional thickness of steel hull about 1/8 the thickness of the vacuum would still apply.
There is no point in trying to make them quieter until they sort out Atmospheric quality and radiation dangers inherent in living and working for long periods in a closed environment next door to a nuclear power plant.
Given that the Navy has been doing nuke-powered subs for 60+ years now and tens of thousands of submariners have done it (living and working for months next to a nuclear reactor), it should be OK by now - if there were any major health issues, they would have been evident by this point.
If you install enough static ballast for this hypothetical (and, diplomatically, pointless) vacuum bottle to be neutrally buoyant at periscope depth, then you won’t be neutrally buoyant at test depth. The entire hull compresses as you go deeper, affecting buoyancy. This vacuum bottle will compress, too, unless it’s rigidly separated from the inner hull, at which point it’s pretty useless for sound silencing.
(I was, once upon a time, both Sound Silencing Officer and Ship’s Diving Officer)
Your ballast tanks don’t have to accommodate the gross tonnage. They have to accommodate the variable buoyancy of tank levels, stores, weapons, salinity, hull compression, …
The radiation “problems” on submarines have been solved, with shielding and constant radiation monitoring (each crew member wears a radiation dosimeter at all times). There’s no mystery to how much radiation submarine crew members are exposed to.