Can submarines go faster, fully submerged? How?

Greenheart

Greenheart

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This may be a typo, or my misinterpretation. Or it may be some hydrodynamic principle in action, which I don't understand...

The Soviet Typhoon class submarine, described here...

http://en.wikipedia.org/wiki/Typhoon_class_submarine

...can apparently run at 22 knots surfaced, and 27 knots submerged (this info is in the right-hand margin panel).

Is that in line with what is to be expected? Doesn't skin friction increase massively with full submersion?

Maybe just a typo on this page?
 
Modern subs are designed for optimum underwater speed. When surfaced, there are all sorts of additional forces acting on them which result in a slower max speed.
 
I think you will find that as the water gets denser the propellor slip decreases so that in effect it reallly starts to act as a screw, Need a lot of power, hence the speed goes up.

I stand to be corrected on this.

Gordy
 
Nothing to do with denser water, it's because of the wave making on the surface and the fact that the hull shape is designed for lowest resistance underwater. If you look at a ww2 submarine you'll see it's designed for surface running, modern submarines are designed for underwater running.
 
The reference is correct. A submerged sub offers less resistance when submerged, principally because there is no energy dissipated in generating big waves on the surface, Therefore, if it's using the same propulsion system submerged as on the surface, it can go faster submertged. That applies to nukes.

The electric motors on conventional diesel-electric subs were much less powerful than their diesel engines. For this reason, they generally had lower speed submerged than on the surface.
 
pampas said:
I think you will find that as the water gets denser the propellor slip decreases so that in effect it reallly starts to act as a screw, Need a lot of power, hence the speed goes up.

I stand to be corrected on this.

Gordy
Click to expand...

Water is incompressible, so can't get denser.
 
PeterWright said:
The reference is correct. A submerged sub offers less resistance when submerged, principally because there is no energy dissipated in generating big waves on the surface, Therefore, if it's using the same propulsion system submerged as on the surface, it can go faster submertged. That applies to nukes.

The electric motors on conventional diesel-electric subs were much less powerful than their diesel engines. For this reason, they generally had lower speed submerged than on the surface.
Click to expand...

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.

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. There was no direct connection between the diesel and the prop, other than some electric cable. Speed is controlled by the power arrangement selected. In the old O boats we had 4 power levels, shafts in series, group down, group up and batteries in series, the latter being the fastest . Using the diesels as generators was done in all but batteries in series with excess power over that required for propulsion going to charge the batteries. Even the O boats with their semi surface shape were faster dived than on the surface though there was not much in it.
 
pampas said:
I think you will find that as the water gets denser the propellor slip decreases so that in effect it reallly starts to act as a screw, Need a lot of power, hence the speed goes up.

Gordy
Click to expand...

Not water density, but water pressure increases as depth increases, reducing the tendancy to cavitate. Unless they can vary their pitch, props can run faster the deeper they are.
 
savageseadog said:
Water is incompressible, so can't get denser.
Click to expand...

At 200bar the density of water at 0C is almost 1010 kg/m³ !

water-density-temperature-pressure_2.png
 
dancrane said:
This may be a typo, or my misinterpretation. Or it may be some hydrodynamic principle in action, which I don't understand...

The Soviet Typhoon class submarine, described here...

http://en.wikipedia.org/wiki/Typhoon_class_submarine

...can apparently run at 22 knots surfaced, and 27 knots submerged (this info is in the right-hand margin panel).

Is that in line with what is to be expected? Doesn't skin friction increase massively with full submersion?

Maybe just a typo on this page?
Click to expand...

All to do with wave and wake resistance.


http://askville.amazon.com/sumarine...ged-surface/AnswerViewer.do?requestId=2461571

Schroll down for an answer from a man who knows.
 
My understanding is that a submarine when submerged is mainly free of the effects of wave-making - which aren't as simple as just moving water up and down. As I understand it, basically what happens is that the ship is attempting to "climb" the bow wave - the higher the bow wave, the greater the force required to "climb" it (purists, please note the quotation marks). As speed increases, this retarding force increases non-linearly with speed, resulting in the "hull-speed" limitations we all know.

Submerged, there are no wave-making effects that have the same retarding influence except in the case of internal layers in the water, when waves at the interface between water of one density and water of another density can have a similar effect.

Of course, a modern submarine is designed hydrodynamically for better efficiency submerged than surfaced, and that also has an effect.

I doubt very much if pressure/density effects on propeller efficiency have much to do with it - submarine propellers are designed to be as quiet as possible, so cavitation will be eliminated by design. A prop that is cavitating is a noisy propeller.

I remember getting a very glassy eyed look from a submarine officer when I mentioned the potential for detecting submerged submarines using synthetic aperture radar to see internal waves! Everyone involved in that kind of remote sensing research knew the potential for it - but I guess the poor chap hadn't realized it was common knowledge in the academic community! One day the military will realize that you can't classify scientific knowledge.
 
AntarcticPilot said:
I remember getting a very glassy eyed look from a submarine officer when I mentioned the potential for detecting submerged submarines using synthetic aperture radar to see internal waves!
Click to expand...


And you'd get a very 'sideways' look from quite a few others. I've met some very, very sharp senior submariners ( and also a fair few 'pedestrians' ) who constantly surprised with their breadth of arcane knowledge. I certainly wouldn't put money on some in that sneaky, stealthy community being unaware of promising new physical research concepts.

'Don't make waves'. Think about counter-measures..... :cool:
 
bit of fred drift

"I remember getting a very glassy eyed look from a submarine officer when I mentioned the potential for detecting submerged submarines using synthetic aperture radar to see internal waves! Everyone involved in that kind of remote sensing research knew the potential for it - but I guess the poor chap hadn't realized it was common knowledge in the academic community! One day the military will realize that you can't classify scientific knowledge."

Climbed into a shiny new RAF fighter at a static display in Winchester some many years ago. The FLT Lt. pilot was proud to show me some controls but when I inquired about the radar and if it was a

Over the Horizon Type

there was a silence and then lots of questions

Although only 17 but with an interest in physics I'd read about this in journals.

With a father employed by the govt. in secret communications I thought it better to lose the officer and he though it better to follow me.

I knew the area, he didn't.
 
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