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  #1  
Old 07-01-2004, 08:18 PM
Pentax Pentax is offline
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Why can Submarines go faster submerged than surfaced?

I was watching a sub movie, and the sub was in trouble, and needed to return to port, so it submerged, and the captain told the observer that the sub could go faster submerged.

This doesn't make any sense. When the sub is submerged, shouldn't it go slower because it is displacing more water. The engine strength would be constant, so shouldn't the sub go faster when it is pushing against less water (IE surfaced)?
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  #2  
Old 07-01-2004, 08:22 PM
Pentax Pentax is offline
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A couple details

It was a new sub, the show was NCIS (the one with the sarin canister on the sub) (I called the person observer b/c I didn't remember the character's name)

I know that the WWII u-boats ran faster surfaced
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  #3  
Old 07-01-2004, 08:22 PM
Brutus Brutus is offline
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The 'tear-drop' designs of modern submarines are optimized for underwater sailing, whereas the WW2 designs were generally optimized for sailing on the surface. What era was the movie? After all, it may have been wrong
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  #4  
Old 07-01-2004, 08:22 PM
butler1850 butler1850 is offline
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WAG alert...

I'd imagine that when on the surface, due to the turbulance, a slower speed would need to be maintained.

In addition as depth increases, the pressure around the propeller increases, and decreases the effects of cavitation (small bubbles formed by the pressure of the prop blades), providing more thrust for a given RPM.

I'm sure that our naval engineers will be along soon enough to give more details, but that should give you a start.

-Butler
(military technolgy nut)
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  #5  
Old 07-01-2004, 08:22 PM
Telemark Telemark is offline
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I think the answer is hydro and aerodynamics. Either way the majority of the sub is in water, but the layer break between air and water probably would cause all sorts of turbulence, robbing the sub of speed.

Subs are very carefully designed to travel very fast while submerged. Sticking the conning tower and part of the hull above water is not the configuration for optimal speed. They've been designed to have very low drag under water.

For the record, this is simply a WAG, I have no facts to back it up.
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  #6  
Old 07-01-2004, 08:23 PM
astro astro is online now
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Re: surface speed vs. submerged speed

Quote:
Late in the war, Germany reversed that concept, designing boats with streamlined hulls for greater efficiency under water. The type XXI u-boats are generally thought of as the first production submarines designed to be faster submerged than on the surface. A second factor in this was adding a lot of cells to the batteries, as battery capacity was a limiting factor in both speed and range. Run at full speed, a submerged fleet sub would run her batteries flat in about an hour.

The design of the screws is also important, but in that case depth is even more important. Cavitation--the swirling stream of bubbles you see in movies--robs efficiency, but as you reach a critical depth the water pressure becomes great enough that cavitation ceases and the screw gets about as close as possible to 100% efficiency. This happens rather abruptly, with the motor/turbine suddenly speeding up without any increase in power setting as cavitation-caused drag ceases.

The same pressure factor also makes the hull more efficient at depth, with the energy that was formerly wasted in creating a wake--which you get, even if you can't see it, to a considerable depth--now available for speed as the water pressure suppresses the wake and forces the water to flow smoothly around the hull. (By now tear-drop or cylindrical in shape.)

The periscope has little to do with speed, as no submarine intentionally travels very fast at periscope depth in order to avoid throwing up a lot of visible spray and possibly giving away her position. In the old boats, the exposed periscope shears certainly created turbulence and robbed speed, of course. In modern boats, everything that sticks up above the fairwater can be fully retracted.
.
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  #7  
Old 07-01-2004, 08:33 PM
SPOOFE SPOOFE is offline
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Aren't sub hulls designed to deliberately compress while submerged? Wouldn't this lower the overall surface area of the sub, thus lowering friction? Or would that be too infinitessimal to have any real impact?
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  #8  
Old 07-01-2004, 08:40 PM
Pentax Pentax is offline
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Quote:
Originally Posted by SPOOFE
Aren't sub hulls designed to deliberately compress while submerged? Wouldn't this lower the overall surface area of the sub, thus lowering friction? Or would that be too infinitessimal to have any real impact?
Would that be something like the crumple zones on a car? I would see why they would want that to happen in an emergency (but if a sub got low enough to use its "crumple zone", I would think that it would be so damaged that nothing would save it I guess I don't see), but when you bend steel/metal, it gets weak and breaks, why would you want the hull of a sub compressing (as I read it bending all over) as part of normal operation?
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  #9  
Old 07-01-2004, 09:17 PM
RickJay RickJay is offline
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Quote:
Originally Posted by Brutus
The 'tear-drop' designs of modern submarines are optimized for underwater sailing, whereas the WW2 designs were generally optimized for sailing on the surface. What era was the movie? After all, it may have been wrong
Except for later designs, the dramatic difference in speed between surfaced and submerged submarines was mainly because they had to use batteries underwater, not because of the shape of the boat. They just didn't have the same power when using the juice. Today's diesel-electrics have much more efficient electrical power systems.
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  #10  
Old 07-01-2004, 09:22 PM
SPOOFE SPOOFE is offline
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Quote:
Would that be something like the crumple zones on a car?
Well, no, think more like the ribbed surface of the SR-71, which is designed to function best at ultra-high speeds... when the air friction warms up the surface of the plane and causes the material to expand. Or how skyscrapers are designed to sway, quite considerably, under wind or earthquake sress.

As I understand it, they design submarines to "contract" as pressure increases, working with the hardship of deep ocean rather than trying to resist it.

I just wonder if this compression is enough to significantly reduce the sub's friction.
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  #11  
Old 07-01-2004, 09:30 PM
flight flight is offline
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The comnpression should not be enough to significantly affect drag unless the surface was designed to be hydrodyunamic at depth and therefore had open seams at lower pressures that would increase skin friction drag.

I understand that subs will be faster at depth where you lose cavitation and force laminar flow, but what about at a small depth, say 50 feet or so. Would it still be faster than at the surface?
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  #12  
Old 07-01-2004, 09:56 PM
The Flying Dutchman The Flying Dutchman is offline
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A major concern when designing displacement (non planing) hull shapes is minimizing the influence of the bow wave. In fact every displacement hull has a "hull speed" where the minimal energy is wasted and the most effective use of fuel is accomplished because the hull traverses one complete wave length at a certain speed. The formula for hull speed is a function of waterline length.

You can imagine the energy wasted when a hull constantly raises a volume of water in front of it. In fact many ship employ the bulbous bow to help keep the bow wave down.

Submarines generally employ very simple designs to minimize friction drag with little or no consideration for bow waves I suspect.
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  #13  
Old 07-01-2004, 10:12 PM
Tuckerfan Tuckerfan is offline
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Quote:
Originally Posted by RickJay
Today's diesel-electrics have much more efficient electrical power systems.
Maybe in your Navy, but the US, Russia, UK, France, and others use nuclear powered subs.
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  #14  
Old 07-01-2004, 10:49 PM
muldoonthief muldoonthief is offline
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Quote:
Originally Posted by Tuckerfan
Maybe in your Navy, but the US, Russia, UK, France, and others use nuclear powered subs.
Actually the Soviets were still building diesel subs into the 90's - the Kilo was produced from 1982 to at least 1990.

The British Upholder class was a diesel that first entered service in 1990, though they were all pulled out of service by 1994.

Diesels have two big advantages over nukes - they're cheaper to build and operate, and they're much quieter when running on battery, which they do most of the time. For coastal defence, they're ideal. US Naval strategy is to keep enemy vessels as far away from the coast as possible, so we've never gone in for a coastal defence submarine class.
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  #15  
Old 07-01-2004, 11:36 PM
ElvisL1ves ElvisL1ves is offline
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Quote:
Originally Posted by SPOOFE
Aren't sub hulls designed to deliberately compress while submerged?
It isn't that they're designed to do it, but that it can't be avoided. Any metal has a positive bulk modulus, and will shrink under uniform pressure. All the stuff mounted inside the hull has to be able to take hull compression. You might have seen the scene in Das Boot (I think) where a veteran sailor stretches a taut string across the torpedo room, and watches the rookie's face as he sees it go slack during a dive.

Subs have circular cross-sections so that the pressure differential across the hull will be balanced, keeping structural loads in compression only and not in bending, where the imposed stresses would be much higher - that's the same reason airplane fuselages are circular, even though the higher pressure is internal for them.

Quote:
Wouldn't this lower the overall surface area of the sub, thus lowering friction? Or would that be too infinitessimal to have any real impact?
Only by a few percent at most, and no, it wouldn't much matter.

This engineer thinks butler has it - propeller cavitation. Drag is actually lower on the surface because of reduced displacement (you don't have to push as much water out of the way) and reduced wetted area (friction). Heavy waves could push the sub off level or off course, and power would be needed to restore them, though.
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  #16  
Old 07-01-2004, 11:56 PM
David Simmons David Simmons is offline
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I think Brutus and Rick Jay have the answer as to why older submarines were slow under water while newer ones are faster under water.

WWII subs, for example were surface ships that could go under water for short periods of times However, their propulsion for underwater travel was limited in endurance, and power.

Modern, nuclear subs are designed to be underwater at all times and their surface performance is not all that good. Their propulsion systems provides all the power needed via a nuclear reactor that drives closed-cycle steam turbines that drive the propellors.

Nuclear subs spend very little time on the surface. On fishing trips to San Diego we occasionally would see one departing. Pretty impressive. They are the size of WWII light crisers, move fast and generate a large bow wave when on the surface. They went out off shore not very far, submerged and weren't seen again for several months until they resurfaced just outside San Diego and returned to harbor.
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  #17  
Old 07-02-2004, 01:30 AM
Hail Ants Hail Ants is offline
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Soooo...

Does anybody think they can definitively answer 'yes', they do go faster underwater. Because I'm still not convinced. They most certainly can manuever faster submerged in that they essential 'fly' like an aircraft (pitch & bank).

But I still find it hard to believe that, in a straight line, the surface turbulence is even going to come close to matching the reduced drag of a significant portion of the hull not having to push water out of its way.

I speaking about a modern day nuclear sub.
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  #18  
Old 07-02-2004, 02:00 AM
Rick Rick is offline
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Modern subs are faster underwater than they are on the surface. On the surface energy has to be wasted pushing the bow wave out of the way. Look at the opening scenes of Crimsion Tide as the boat is leaving the harbor. The bow wave is massive. The second limiting factor is the cavation of the prop.
Once the boat is underwater the flow is smooth over the hull, no bow wave like on the surface, and the prop doesn't cavitate (unless the skipper screws up)
ON WWII subs they were very slow underwater do to the design of the hull (a surface design) so the drag underwater was higher then it was surfaced.In addition the deck gun(s), conning tower, periscope shears, and all the junk topside acted as brakes, and slowed the boat down.
On this page you can see the difference between a WWII sail/deck and a later design. Compare that to the clear deck on a Los Angeles Class boat In this pic you can also see the amount of water displaced when running on the surface.
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  #19  
Old 07-02-2004, 11:32 AM
av8rmike av8rmike is offline
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Quote:
Originally Posted by Hail Ants
Does anybody think they can definitively answer 'yes', they do go faster underwater.
Yes.

Quote:
A streamlined body moving in a straight line at a constant speed, deeply immersed [...] presents the simplest case of resistance. Since there is no free surface, there is no wave formation and therefore no wave-making resistance.
[...]
A ship moving on the surface of the sea experiences frictional resistance and eddy-making, separation, and viscous pressure drag in the same way as the submerged body. However, the presence of the free surface adds a further component. The movement of the hull through the water creates [...] areas of increased pressure at bow and stern and of decreased pressure over the middle part of the length.
[...]
There is greater pressure acting over the bow, as indicated by the usually prominent bow wave build-up, and the pressure increase at the stern, in and just below the free surface, is always less than around a submerged body. The resulting added resistance corresponds to the drain of energy into the wave system, which spreads out astern of the ship and has to be continually recreated.
The above taken from Sections 1.4 and 1.5, Chapter 5 of Principles of Naval Architecture, SNAME Publications. Basically, what the excerpt is saying is that surface ships have a added drag component not present in submerged bodies. What Hail Ants is referring to is the effect on reducing so-called "wetted area" in form and frictional drag.

Unfortunately, I can't give a definitive answer because there are too many variables, like submerged depth, ship's velocity, and sea condition. Generally though, wave-making drag constitutes a larger percentage of total resistance at higher speeds than form and friction, which can be easily minimized.
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  #20  
Old 07-02-2004, 03:22 PM
David Simmons David Simmons is offline
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Quote:
Originally Posted by av8rmike
Yes.


The above taken from Sections 1.4 and 1.5, Chapter 5 of Principles of Naval Architecture, SNAME Publications. Basically, what the excerpt is saying is that surface ships have a added drag component not present in submerged bodies. What Hail Ants is referring to is the effect on reducing so-called "wetted area" in form and frictional drag.

Unfortunately, I can't give a definitive answer because there are too many variables, like submerged depth, ship's velocity, and sea condition. Generally though, wave-making drag constitutes a larger percentage of total resistance at higher speeds than form and friction, which can be easily minimized.
Based on observation of how much of a nuclear sub sticks out of the water when one is on the surface and knowing the size of the whole vessel, it is doubtfull that the increased frictional drag because of the increased wetted surface when submerged is anywhere near the losses that your cites speak to when on the surface.
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  #21  
Old 07-02-2004, 03:25 PM
David Simmons David Simmons is offline
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And, as I said before, the whole design is optimized and losses minimized for travel submerged because that is where the sub spends its time. Any choices made between surface and submerged design are made to favor the submerged case.
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  #22  
Old 07-02-2004, 03:57 PM
David Simmons David Simmons is offline
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And, last but not least, there is this site. Scroll down to #14 on the list.

I searched Yahoo! Search for "nuclear submarines+surface speed" without the quotes and got lots of info all which added up to what has been said here. The submarine is optimised for submerged travel and there is a lot of loss in making waves and wakes when on the surface.
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Old 07-02-2004, 05:18 PM
Billdo Billdo is offline
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As someone who has sailed a boat relatively close astern of a nuclear sub travelling on the surface at speed, I can tell you that they throw a HELL of a huge wake. Much larger than a normal surface ship of similar size.

They're also rather difficult to discern. For several miles I thought I was converging with a large, black fishing trawler with a smaller one following close behind. It was only when I drew closer that I realized that I was looking at the conning tower and tail of a nuke. It had only a few feet of hull surrounding the conning tower out of the water.

It also made me chuckle that I could see this major warship change course to avoid my little sailboat, which technically had right of way. (When I realized what it was, I made a major correction to avoid it -- no way in hell I was getting near that thing -- but that was after it had made a small but noticable turn away from me.)

In any event, it was an impressive machine.
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  #24  
Old 07-02-2004, 05:48 PM
av8rmike av8rmike is offline
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Quote:
Originally Posted by David Simmons
And, last but not least, there is this site. Scroll down to #14 on the list.

I searched Yahoo! Search for "nuclear submarines+surface speed" without the quotes and got lots of info all which added up to what has been said here. The submarine is optimised for submerged travel and there is a lot of loss in making waves and wakes when on the surface.
Rrrrrrright.... Sounds to me like we're both asserting the same thing. However, I was also qualifying my statement, because it isn't always true that a submerged vessel will have less drag than a surface vessel, which is what the quoted part seems to suggest. There are too many other factors at play for a catch-all answer.
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  #25  
Old 07-02-2004, 07:37 PM
robby robby is offline
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I don't have much to add here, other than to state unequivocally that a given power output, modern nuclear submarines with a teardrop-shaped hull travel much faster submerged than when surfaced.

Surfaced submarines produce massive bow waves that rob energy, as does the cavitation of the screw (propeller) on the surface.

In fact, in practice, maximum allowable power is limited while on the surface, as increasing power beyond the limit results in a negligible increase in surface speed while needlessly wasting the nuclear fuel.

-robby (former U.S. submarine officer)
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  #26  
Old 07-02-2004, 08:50 PM
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It´s quite simple to see, look at the second picture on Rick´s post, all that troubled water was stirred by the sub, the energy to do so came from it´s powerplant, so that energy goes to splash a heck of a lot of water instead of propelling the boat faster. Once the ship is underwater the waving and splashing stops, so it doesn´t rob the sub from its energy.

Besides, I think that in surface cruising the propeller must be really close to the surface, not just cavitation there, it may actually suck some air too. Correct?
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  #27  
Old 07-03-2004, 12:23 AM
David Simmons David Simmons is offline
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Quote:
Originally Posted by av8rmike
Rrrrrrright.... Sounds to me like we're both asserting the same thing. However, I was also qualifying my statement, because it isn't always true that a submerged vessel will have less drag than a surface vessel, which is what the quoted part seems to suggest. There are too many other factors at play for a catch-all answer.
Oh sure. I thought from previous post that it was clear that the WWII type of hull was not optimised for submerged operation and might very well have been slower there than on the surface given the same power capability in both cases.
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  #28  
Old 07-03-2004, 01:20 AM
Ellis Dee Ellis Dee is offline
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Quote:
Originally Posted by robby
-robby (former U.S. submarine officer)
Robby, I have a quick question for you. How is the term "submariner" pronounced? subMARiner, or SUBmaRINer? Or is it not used at all?
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  #29  
Old 07-03-2004, 06:38 AM
Napier Napier is offline
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First of all, whether they are optimized for underwater travel does not determine whether they are faster underwater than on the surface. By way of obvious analogy, trucks are optimized for carrying heavy loads but they still can go faster when they are empty. Optimizing them for underwater travel makes them go faster underwater than they otherwise would have, perhaps at the expense of surface speed That's not the same thing as making the submerged speed greater than the surface speed.

So, I can see a sensible argument that says if it makes surface waves when running on the surface, it must be having an easier time of it - the air wouldn't yield to the water if it weren't easier for the air to yield, right? This seems to confirm the less drag argument, sort of - we don't know if it's friction per se, or other things like inertial forces. Trouble is, I'm not sure this argument is valid. I think a similar argument could be made that if a car displaces sand while driving on the beach, then beaches must be easier to drive on than pavement.

Maybe the sites covered it all properly. All the same it's a pleasant curiosity.
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  #30  
Old 07-03-2004, 09:20 AM
LSLGuy LSLGuy is offline
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I think robby answered it pretty unequivocally. When in doubt, ask the guys who do it / did it for a living.
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  #31  
Old 07-03-2004, 10:12 AM
David Simmons David Simmons is offline
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Quote:
Originally Posted by Napier
First of all, whether they are optimized for underwater travel does not determine whether they are faster underwater than on the surface. By way of obvious analogy, trucks are optimized for carrying heavy loads but they still can go faster when they are empty. Optimizing them for underwater travel makes them go faster underwater than they otherwise would have, perhaps at the expense of surface speed That's not the same thing as making the submerged speed greater than the surface speed.

So, I can see a sensible argument that says if it makes surface waves when running on the surface, it must be having an easier time of it - the air wouldn't yield to the water if it weren't easier for the air to yield, right? This seems to confirm the less drag argument, sort of - we don't know if it's friction per se, or other things like inertial forces. Trouble is, I'm not sure this argument is valid. I think a similar argument could be made that if a car displaces sand while driving on the beach, then beaches must be easier to drive on than pavement.

Maybe the sites covered it all properly. All the same it's a pleasant curiosity.
Yes. Optimising for the submerged case doesn't guarantee that the sub will be faster underwater than on the surface. However, it turns out that the one optimization that counts is the shape of the hull. The blunt nose greatly increases the drag when on the surface because of the large wave while the drag when submerged is small. If the available power is the same the smaller drag case will have a higher speed. Doesn't that make sense? And if, as Robby says, there is a restriction on the surface power settings permitted, that difference in speed is further accentuated.

The shape of the hull for best surface use has been refined over a period of centuries of study and thousands of hours of testing in model tanks. The hull has to have room for cargo, machinery and living space; be stable so that the ship won't capsize; be strong enough to stand up to the stresses; have a shape that offers as little resistance as possible to motion through the water while on the surface. The first three also apply to a submarine, with the cargo being stores and weapons, and the shape was optimised for submerged travel which resulted in a poor shape for surface use.
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  #32  
Old 07-03-2004, 11:35 AM
JimMacMillan JimMacMillan is offline
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A Scuba Divers Input

The OP is something I have always questioned.

I have been a scuba diver (*PADI) for many years. I have been signed off on virtually every skill level available. I have dived with probably a few hundred people over that time. Most of my dives involved large groups of people. After a dive we would head back to the boat or to land, whatever the case may be. Not to brag but I am a good breather and would always have plenty of air left in my tank. So on the way back I would drop down about 3 to 5 feet and swim back with the group while taking in a view of the bottom. I would consistently be back to the target before all the people on the surface. A friend that I frequently dive with noticed this. We experimented, he under the surface and I on the top and it seemed that the underwater diver was always a bit faster. So one day at the docks in Santa Barbara California we found a PADI instructor and posed the surface verses underwater question. The instructor thought about it and suggested that maybe it was the waters “surface tension” that held the surface diver back.

It does seem strange though. After all, a diver wears a buoyancy compensation device, air tank, regulator, and a face mask. All these items for the most part are out of the water while swimming on the surface. But under water they don’t appear have any appreciable effect, just the opposite.

Jim

* PADI = Professional Association Of Dive Instructors
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  #33  
Old 07-03-2004, 12:24 PM
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Remember though, you are using flippers, and I imagine they are breaking the water's surface and therefore not producing nearly as much thrust as when they remain entirely submerged. Even if they come very close to the surface without breaking it, they will still lose some power.
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  #34  
Old 07-03-2004, 01:42 PM
1010011010 1010011010 is offline
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robby's already given the answer. An oddly unsatisfying answer, since it doesn't really tell why increasing power/RPMs doesn't increase the boat's speed.

Is the main factor in operationally limiting power because of screw cavitation, as others have mentioned, or something to do with the physics of traveling at the water/air boundary? If it's cavitation, what would happen if you put a different screw on optimized for surface pressure operation?
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  #35  
Old 07-03-2004, 08:01 PM
David Simmons David Simmons is offline
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It isn't at all uncommon for drag characteristics to increase abruptly at some critical velocity. If drag coefficient is plotted vs. velocity things will be going along smoothly as velocity increases and then suddenly the coefficient will jump in magnitude. Such curves are usually plotted vs. Reynold's number which is a parameter that includes velocity and the viscosity of the fluid.

Turbulence is another characteristic that can appear abruptly. Up to some critical Reynolds number the flow is laminar and then the flow will suddenly become turbulent with just a small increase in velocity.

So it isn't too unusual for increased power to result in a smooth increase in velocity for a while and then a critical point is reached at which time the drag increases rapidly and adding more power merely puts the added power into disturbing the flow with very little increase in velocity.
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  #36  
Old 07-03-2004, 10:11 PM
Gary Kumquat Gary Kumquat is online now
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Hope this help

According to the US miliatry

Quote:
Why can a submarine go faster underwater than on the surface?
A submarine's "tear drop" hull design allows it to slice cleanly through the ocean when there is water on all sides. When a "tear drop" hull submarine is on the surface, a great deal of energy is used to generate the bow wave and wake. That energy is then unavailable for propulsion. The hulls of older submarines, like the World War II vessels and the first nuclear-powered submarine, USS Nautilus, were designed with narrow bows to move faster on the surface than they did underwater.
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  #37  
Old 07-03-2004, 11:14 PM
Rick Rick is offline
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Quote:
Originally Posted by Napier
First of all, whether they are optimized for underwater travel does not determine whether they are faster underwater than on the surface. By way of obvious analogy, trucks are optimized for carrying heavy loads but they still can go faster when they are empty. Optimizing them for underwater travel makes them go faster underwater than they otherwise would have, perhaps at the expense of surface speed That's not the same thing as making the submerged speed greater than the surface speed.
Sorry but you are comparing apples and Kitchen sinks. How much load a truck can carry is not what we are discussing, we are discussing if a change of the medium in which the sub operates changes the amount of drag/ and top speed.
What you are comparing is will the sub go faster with all of its torpedos loaded, or will it go faster empty. Not a valid comparision.
Here is a chart of Older subs and the speeds they can atain
Quote:
Gato Class (Test Depth = 300 ft) Surface flank speed 21.0 (calm seas)
Maximum Submerged = 8.8 knots
As I mentioned before, the hulls on these boats were basicaly a surface ship that could go underwater, look at the pictures on this page and you will see what I mean.
As far as speed goes from here
Quote:
Optimized for speed underwater, her exact top speed remains classified. How much deeper than 800 feet (240 m) she can go is also classified.
Or http://www.naval-technology.com/projects/la/specs.html
Quote:
Speed in excess of 30 knots dived
You will note that they do not list a surface speed. This is because 688 class subs are NOT designed to cruise on the surface.
and from here
Quote:
1953
The U. S. Navy began operation of a fast-submarine test bed, the 203-foot "Albacore." The hull form was similar to that of an airship; the boat went through five experimental configurations; in the first, she demonstrated underwater speeds of 26 knots.
you will note that this is over 3X the speed available to a Gato class WWI sub (listed above) And
Quote:
The first nuclear-powered submarine went to sea: the 323-foot, 3,674-ton "Nautilus." Surface speed 18 knots, 23 knots submerged. On her shakedown cruise, she steamed 1,381 miles from New London to San Juan, Puerto Rico ? submerged all the way at an average speed of 15 knots. She was so fast that, on her first exercise with an ASW force, she outran the homing torpedoes.
Even though she was not optomized for underwater performance, the Nautilus was faster underwater then on the surface.
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  #38  
Old 07-05-2004, 02:27 AM
robby robby is offline
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Quote:
Originally Posted by Ellis Dee
Robby, I have a quick question for you. How is the term "submariner" pronounced? subMARiner, or SUBmaRINer? Or is it not used at all?
Both pronunciations are common.

I did, however, once hear a submarine force flag officer (an Admiral) make a big point at a briefing that the only proper pronunciation was SUBmaRINer, and that no self-respecting submariner would ever use the pronunciation subMARiner, as it implied that submariners were literally sub-mariners, or somehow inferior to other mariners.
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  #39  
Old 07-05-2004, 02:30 AM
robby robby is offline
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Quote:
Originally Posted by 1010011010
robby's already given the answer. An oddly unsatisfying answer, since it doesn't really tell why increasing power/RPMs doesn't increase the boat's speed...
I didn't say that surfaced speed does not increase with increased power on the surface; I said that beyond a certain power output, the further increase in speed is negligible and a waste of power. Above a certain power output, it is possible to increase the power output by as much as 100% (doubling the power output) and gain less than a 10% speed increase.

Quote:
Originally Posted by 1010011010
...Is the main factor in operationally limiting power because of screw cavitation, as others have mentioned, or something to do with the physics of traveling at the water/air boundary? If it's cavitation, what would happen if you put a different screw on optimized for surface pressure operation?
The largest issue is the large surface bow wave created, which would be unaffected by changing the screw. Also, why would you want to substitute a screw optimized for surface operations when a modern nuclear submarine spends more than 95% of its time at sea submerged?
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