Can submarines go faster, fully submerged? How?

[maxi77]

The single biggest factor affecting dived v surface speed is the complete immersion of the propellor (i.e. the immersion of the top 25-30% of the prop into 'solid' water rather than froth).
The above will give a speed increase in the order of 4:3 (which ties in with the OP's Typhoon figures). The effect is similar (but not the same) for a propulsor as opposed to a propellor.

Benefits from hull submersion are to a large extent offset by the fin and deck appendages (though not completely).

Hard evidence for the above (which is meticulously logged) is easily obtained obtained during trials secured alongside surfaced versus underwater restraint.
The shaft torque meter will not enter the 'red' when surfaced, and water flow is zero when restrained.

Water is compressible - it's particular compressibility at any stage is a matter of great interest when operating a Nuclear reactor.

Steve

Now my experience and what I was taught do not agree with what you say. I was taught that power requirements rose according to speed by a cube rule whereas for surface vessels it was a 7th power rule. Certainly on a frigate we needed 60% of the propulsive power for the last few knots.

Equally the drag effect of a submarines fin was not that much and in terms of trimming required less than a ton of water to compensate even at high speed.

As for compressing water yes it is pressurised in a nuclear reactor but that is achieved with a gas in the pressuriser vessel, a bit like the accumulator in a pressurised water system in a boat.

 

[Tanqueray]

Now my experience and what I was taught do not agree with what you say. I was taught that power requirements rose according to speed by a cube rule whereas for surface vessels it was a 7th power rule. Certainly on a frigate we needed 60% of the propulsive power for the last few knots.

Equally the drag effect of a submarines fin was not that much and in terms of trimming required less than a ton of water to compensate even at high speed.

As for compressing water yes it is pressurised in a nuclear reactor but that is achieved with a gas in the pressuriser vessel, a bit like the accumulator in a pressurised water system in a boat.

Sorry but that is wrong - it's done with a steam bubble, the 'gas in circuit' is there for an entirely different reason. There is no 'gas' in the pressuriser! Steve (EX NCOW & Cat A Nuclear). Ever gone from standstill to max power balancing the ahead throttle against the shaft torque meter (I mean done it, not just been onboard when it occurred)?

Power requirements to get to max speed (as in a car) are not the explanation for the differences in dived/surface speeds.

 

[maxi77]

Sorry but that is wrong - it's done with a steam bubble, the 'gas in circuit' is there for an entirely different reason. There is no 'gas' in the pressuriser! Steve (EX NCOW & Cat A Nuclear). Ever gone from standstill to max power balancing the ahead throttle against the shaft torque meter (I mean done it, not just been onboard when it occurred)?

Power requirements to get to max speed (as in a car) are not the explanation for the differences in dived/surface speeds.

Sorry, steam is a gas, as for playing with throttles I only ever did that on a frigate, rather nice having 20,000 SHP at ones finger tips

 

[Tanqueray]

Sorry, steam is a gas, as for playing with throttles I only ever did that on a frigate, rather nice having 20,000 SHP at ones finger tips

Ever seen a pressuriser? Thought not Next time your frigate is at 300m depth, cock an eye at the shaft torque meter, you'll learn a lot.

 

[maxi77]

Ever seen a pressuriser? Thought not Next time your frigate is at 300m depth, cock an eye at the shaft torque meter, you'll learn a lot.

Don't try and black cat an old hand, I know what a pressuriser is just as I know steam is a gas, whether it is wet steam out of a steam generator on a pwr, or it is dry steam from the superheaters of an oil fired boiler.

 

[st599]

Water is incompressible, so can't get denser.

Water is not incompressible plus its density changes with temperature.

 

[Tanqueray]

Don't try and black cat an old hand, I know what a pressuriser is just as I know steam is a gas, whether it is wet steam out of a steam generator on a pwr, or it is dry steam from the superheaters of an oil fired boiler.

You are not an 'old hand' my dear. You are a typical junior officer who thinks that they know everything but knows nothing.

Disagree? Tell me all about 'mass defect in atoms'. Away you go.

A PWR does not produce "wet steam". I produces.. well you tell me..

I'm sorry Maxi77 , I really don't want a fall out with you as I respect what other departments on a boat do and aknowledge their expertise in their part of ship.
I won't take you on in the CR - That's your POS.

Take me on in mine (Nuclear Chief of the Watch for 22 years )- I'll piss all over you. Your call.

Steve

 

[Greenheart]

You're watching BBC5. Back in a moment with more on nuclear physics

 

[OGITD]

There was NEVER!!!

And I repeat ... NEVER! ... was there a NCOW who looked as good as that on the RP .... EVER ..... but (BIG secret)..... there were a couple who used to wear the gear .....

Edit .... "Tell me all about 'mass defect in atoms" .... can I 'phone a friend'??? a-n-other NCOW?

 

[Greenheart]

Britt could wear any gear. Anything. Including nothing...

 

[PeterWright]

Yes and no to the wave making, submarines do still create surface waves, but they are much smaller and their shape is at it's most efficient dived.

I agree that a submerged sub will make a small surface wave, but if she is fully submerged, it is insignificant compared to the wave made when she is on the surface, and she will not be left trying to climb up it as she approaches hull speed (Re=approx. 3000). As she dives deeper the surface wave will get even smaller, and absorb nearly no energy, so I chose to ignore it Perhaps I should have said that when submerged, the surface wave absorbs an insignificant amount of energy, allowing the vessel to travel faster for the same power consumption than when on the surface.

Again, I agree that a subs hull is optimised for submerged operations, but even if it were not, the simple lack of a major absorption of energy in the surface wave would still render the above statement true. Basic fluid dynamics.

 

[PeterWright]

You clearly do not understand the concept of diesel electric, the diesels generate electric power which is then used in the electric motors which could absorb all the power generated by the diesels.

I do understand the diesel electric concept and it has gone through many evolutions in submarines as they have developed over the past century or more.

In more recent subs, the electric motors were indeed capable of absorbing all that the diesels could produce and were the only motors capable of driving the vessel. But in plenty of earlier sub designs the shaft could be driven directly by the diesel when on the surface or, from the innovation of the schnorkel, at periscope depth. However when dived deeper, a diesel electric sub is reliant entirely on battery power, and it was this feature, up to about 1945, that left them slower dived than on the surface despite requiring more power for a given speed when surfaced.

You're quite right about the steam bubble being used to control pressure in a PWR, steam under these conditions is not a gas but a vapour. It would only be a gas if it exceeded its critical temperature, in which case it would not work in the pressuriser as the crtical temp is defined as the minimum at which it cannot be liquified by pressure alone.

Mass defect - simply the amount by which the mass of the fission products plus neutrons produced is less than the mass of the nucleus which was split + the incident neutron (which caused the split). The energy released by the fission (e) is this lost mass x speed of light squared (mc(squared)) everyone knows Albert's equation.

My PWR's knocked out around 5,000 MW thermal!

Thanks for the trip down memory lane. A lot of years since I worked as a Reactor Physicist.

 

[maxi77]

I do understand the diesel electric concept and it has gone through many evolutions in submarines as they have developed over the past century or more.

In more recent subs, the electric motors were indeed capable of absorbing all that the diesels could produce and were the only motors capable of driving the vessel. But in plenty of earlier sub designs the shaft could be driven directly by the diesel when on the surface or, from the innovation of the schnorkel, at periscope depth. However when dived deeper, a diesel electric sub is reliant entirely on battery power, and it was this feature, up to about 1945, that left them slower dived than on the surface despite requiring more power for a given speed when surfaced.

You're quite right about the steam bubble being used to control pressure in a PWR, steam under these conditions is not a gas but a vapour. It would only be a gas if it exceeded its critical temperature, in which case it would not work in the pressuriser as the crtical temp is defined as the minimum at which it cannot be liquified by pressure alone.

Mass defect - simply the amount by which the mass of the fission products plus neutrons produced is less than the mass of the nucleus which was split + the incident neutron (which caused the split). The energy released by the fission (e) is this lost mass x speed of light squared (mc(squared)) everyone knows Albert's equation.

My PWR's knocked out around 5,000 MW thermal!

Thanks for the trip down memory lane. A lot of years since I worked as a Reactor Physicist.

But boats that had direct drive were not diesel electric and even if they had a clutch between the generator and the motor it was rarely used. One of the reasons WW2 and earlier boats were fastest under direct diesel drive was that transit was on the surface and high surface speeds were important, after the snort system was invented (by the Dutch in fact) and dived transit became feasible higher underwater speeds became important and designs changed to make that practical

This would suggest that a vapour is merely a subset of the gas phase, in this case steam is a gas but in it's vapour phase. "A vapour is a substance in the gas phase at a temperature lower than its critical point.[1] This means that the vapour can be condensed to a liquid or to a solid by increasing its pressure without reducing the temperature."

As it is over 40 years since I did nuclear physics I had lost sight of the term mass defect though I remember helping two gentlemen named Woodward and Fry do those sums for their homework as we were all on the same course.