Perhaps that is true on the newer boats but it is not true on the older SSNs & SSBNs I sailed on.
OK, thanks for the updates. I don’t remember where I got that info from - perhaps scuttlebutt.
Perhaps that is true on the newer boats but it is not true on the older SSNs & SSBNs I sailed on.
Not true for any manned submarine in the USN or other navies. They all have XX% (I can't recall the minimum required) reserve buoyancy with ballast tanks empty (completely blown).
There are several factors which can make achieving that positive buoyancy dicey:
a.) if you're leaking into the people tube (interior of the boat), every ton of seawater taken in = a ton of reserve buoyancy lost;
b.) when you blow ballast tanks at test depth, you're not instantly ridding yourself of all the seawater in the ballast tanks ... you're simply putting a bubble of high-pressure air in the tanks to make a change from the normal submerged neutral buoyancy to a positive buoyancy. As the boat begins to rise the bubble expands, pushing more seawater out of the ballast tanks, giving even more positive buoyancy and so on ... until you finally reach then surface and the ballast tanks are finally empty.
However keep in mind factor 'a' above ... enough water in the people tube and you lose positive buoyancy, and you kiss your ass goodbye. WW II fleet boats were designed with enough positive reserve buoyancy to be able to survive 1 completely flooded compartment, but modern boats have fewer compartments - though I can't speak for RAN Collins class boats, US nukes can't survive a fully flooded compartment. ;
c.) Your rate of rise towards the surface CAN be enhanced by increasing speed and putting 'Rise' on the control planes.
As an aside, the Thresher NEARLY made it to the surface (within a couple hundred feet!) before they lost speed and became negatively buoyant and began back down to 10,000 feet, imploding and breaking up on the way down ... God rest your souls, my brothers of the 'Phins!
- A Cold War submarine vet (SSN-588, SSBN-629B, SSN-669 plank-owner)