fastest sub in the world

[Guest]

Hello,

We have an argument raging here at work about the fastest military sub, and we need somebody to settle it.

I once lived next door to a Royal Navy oceanographer and he, very quietly, told me that the navy was aware of a modified Akula class sub capable of up to 80 knots.

The guy was not the type to shoot his mouth off. He was a serious man in a serious job. So I believed him.

Has anyone ever heard about this? Can anyone confirm it? Or is the Alfa still the record holder?

Thanks for any help you can give.

[davietait]

My mate Bob used to

My mate Bob used to be a 2nd LT on one of the UK SSN's back in the 1970's and they heard an Alpha running deep and very fast from about 1000nm away. Recon it was doing over 40knots and sounded like someone with a metal bucket full of bolts being shaken around !!!

[tom dougherty]

a modified Akula class sub

a modified Akula class sub capable of up to 80 knots

I can't imagine how one could obtain the power necessary to get anywhere remotely close to 80 kts. The Alfa allegedly reached 42 kts at one point, and the Seawolf was also reported to be quite fast on trials.

As speed increases, power needed does NOT go up as a linear function. I found this nifty analysis on the web]If you simply the shape of a submarine to a cylinder with a halfsphere at the front end the hull size would be 360 ft by 33 ft diameter. The frictional resistance coefficient of this shape can be calculated .

Multiplying resistance coefficient times the surface area, and then by 1/2 density X the square of the speed(ft/s) give the resistance of the shape. Multiply this by the speed gives the power needed to move the hull at a given speed.

Assume the efficiency of the propeller to be 75%. Some of the power from the reactor also has to be used for the TGs to generate electrical power for non-propulsive use. Adding this to the curve gives the total power the sub needs to generate.

I worked this out and it gives a curve with the following exponential formula:
Power (mega watts) = 0.0010858492 X (speed in knots ^ 2.8772851590).[/i]
(Note]

if you plot this for a range of speeds you will get an estimate of the power curve of an LA class sub. The FAS website states that the LA class sub has a S6G reactor delivering 35,000 horsepower or 26.0995 Mega watts. Putting this value into the power formula gives a maximum speed of 33.3knots. To do 60knots the LA class would need at least 142 MW of power generated. [/i]

So, notice that there is a exponent function in the formula, which again means that the relationship is non-linear. In the above example, you get 33 kts out of 26 Megawatts, but need roughly 140 Megawatts to get double the speed. Eighty kts would more than double the power needed again, and I know of no submarine reactor that comes even close to 100 Megawatts of power. Outside of some new technology that operates well beyond established hydrodynamics, it is extremely unlikely that a submarine would hit 80 kts.

[Rogue Sub]

80 knots would make the

80 knots would make the boat fall apart, even with laminar fluid injection. When my boat tops out at flank cavitate, it shakes in a circular motion and feels like the world is going to end. I know the seawolfs old top speed before they cut back on its allowable reactor power output due to it causeing the boat to list and disenegrate from the pressure. No way 80 knots. I believe that the alfa is still the record holder. It just goes deeper and and cuts into that denser water(if your familiar with knife curves).

[Antoine]

The official fastest sub is

The official fastest sub is the Papa class with a pretty nice 44.7 kts.
I repeat it is the official ...

But the hydrodynamic laws as Tom explained well have their limits.

The official (again ) fastest objects in the water are the russian rocket torpedoes but they use a particular hypercavitation design to create a vaccum in the water where they can travel at crazy speeds, powered by rocket engines.

Back to subs, the Papa, when she reached the nearly 45 kts used the full power of her two reactors and damaged her hull during the high speed run.

[tom dougherty]

alfa is still the record

alfa is still the record holder. It just goes deeper and and cuts into that denser water

Uhh, no. water DENSITY does NOT appreciably increase with depth, as water is essentially an incompressible fluid (at least under conditions on planet earth). Gases are compressible (hence the problem with diving & the need for decompression). Water PRESSURE increases with density, but that is due to the weight of the column of water. There are local, minor variations in water density due to regional differences in temperature and salinity, and these do have significant effects on sound wave propagation. These minor density variations are not significant in terms of mechanical effects on a moving body (e.g., a submarine hull moving through the water).

Latest data on the Alfa indicates that maximum diving depth estimates during the Cold War were actually overestimated, and the test depth was only about 1300 ft. (400 meters). The titanium was there to permit a thinner hull, which was lighter and yielded more reserve buoyancy for this rather small submarine. The deepest diver (900 meters) was the titanium hulled, one off "Mike" Class Project 685 (Komsomolets), which sank in 1989.