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Old 02-14-2020, 07:58 AM   #1
PurpleCow
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Default Do modern subs ever come to rest on the sea floor?

As subs try to remain stealthy and quiet do they ever just settle and wait on the sea floor?
  1. Can modern subs come to reset on the bottom of sea floor?
  2. If they do, is it noisier because of contact with the sub and sea bottom?
  3. If a sub is not resting on the sea floor how do they maintain a steady position with currents and such? Do they use maneuvering thrusters of some type?
  4. Would maneuvering thrusters make a lot of noise detectable by the enemy?

Thanks!
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Old 02-15-2020, 02:42 AM   #2
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Can modern subs come to reset on the bottom of sea floor?
some nuclear boats will have water intakes on the bottom so sitting on the bottom would clog them up.
That and they don't truly know whats down there below the keel, it may be muddy or rocky either way you don't want to sit a $1bn worth of kit on that.

On the rocks it would rip an already stressed and compressed hull apart, and on mud it would act like a suction cup holding the boat on the bottom.

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If they do, is it noisier because of contact with the sub and sea bottom?
even in Sub rescue exercises the boats don't tend to bottom, the only boat that im aware of that used to drive along the bottom would have been NR1, the Russians have probably got something similar.
If a boat was on the bottom you would likely hear the metallic scraping of metal against rock (worrying) or the disturbance caused by a large stationary object against a current flow.

However this is one for the sonar bouys here (see what i did there) they will be able to clear that up ET3R is a good chap and good source for that its his field.

Quote:
If a sub is not resting on the sea floor how do they maintain a steady
position with currents and such? Do they use maneuvering thrusters of some type?
I believe the Ohio and Vanguard classes of SSBN are capable of hovering at depth in order to fire missiles, so id assume theres a system there.

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Would maneuvering thrusters make a lot of noise detectable by the enemy?
low horse power low speed, but high speed screw smaller prop possibly but we know the project 705 has electric creep motors similar to thrusters on each end of the aft diving planes, at speed they were noisy but at slow speed not so.
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Old 02-16-2020, 08:59 PM   #3
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Can modern subs come to reset on the bottom of sea floor?
As mentioned for nuclear subs this would be a big no-no. The Main Seawater and Aux Seawater systems would suck up the mud and other debris from the sea floor damaging the pumps and creating a lot of noise in the process. You could shut these systems down, but it wouldn't be feasible as they're needed for the reactor. Also any hull projections would become dammaged.



Quote:
If they do, is it noisier because of contact with the sub and sea bottom?
Thousands of tons of steel making an impact with the sea floor makes a lot of noise. Also take into account that the electrical bus is still going to make noise (60Hz USA, 50Hz Europe).



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If a sub is not resting on the sea floor how do they maintain a steady position with currents and such? Do they use maneuvering thrusters of some type?
I don't recall which ones now, but some of the fast attacks had trainable Secondary Propulsion Motors that could be deployed. Hovering, to my knowledge, is available on fast attacks as well but is regarded with disdain in it's use. It's seen as a boomers system and there's a little rivalry between the two boat types. Hovering on a boomer is used to maintain depth for missile launch and to assist with depth control at PD. It's not perfect though. We got sucked up to the surface during a Battle Stations Missile drill early in a patrol that resulted in the loss of a radio buoy by beeing smashed against the hull.



Quote:
Would maneuvering thrusters make a lot of noise detectable by the enemy?
Almost certainly unless used at a slow speed. The propellers wouldn't be optimized for stealth the same way the main propeller is, so cavitation would be a problem.



Quote:
However this is one for the sonar bouys here (see what i did there) they will be able to clear that up ET3R is a good chap and good source for that its his field.
I've dabbled in Sonar a little before I became a Radioman. Started working on my Passive Broadband quals and went to a LOFARgram analysis class but that was about it. JiveTurkery is the REAL ping jockey, his sonar knowledge far exceeds mine. I know just enough to know what he's talking about. Radio, ESM, helms/planesman, and lookout were my at-sea watch stations.
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Old 02-18-2020, 12:37 PM   #4
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Originally Posted by ETR3(SS) View Post



I don't recall which ones now, but some of the fast attacks had trainable Secondary Propulsion Motors that could be deployed. Hovering, to my knowledge, is available on fast attacks as well but is regarded with disdain in it's use.
I know the 594 (Tresher/Permit) class had SPMs and I'm pretty sure the 637's had them. 688's definitely have an SPM but its very rare when they get used, to the point that most times they just don't work.
In almost every case, there is tug support to bring the boat to the pier or, worst case the Skipper and Manuv. Watch OOD have enough experience to drive to the pier without the SPM. The only time an SPM is useful is if you're trying to dock in a harbor that has strong currents.

As far as hovering, the 637's were really good at it and most 688's either have some type of negative tank that could be used to hover or else it was added later. If you look at a picture of a COW at work in control and there's something that looks like a joy stick on the side of the BCP desk, that's the control for hovering.
My last Chief had a knack for hovering 688's. All 688 COWs have to know how to do it, but some are better than others.
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Old 02-18-2020, 03:13 PM   #5
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yes they can and do ...veeeerrrry carefully as rocks, muck and ocean bottom detritus are hard on hulls tearing up its vents, stealth cover, or steering.. The USS Seawolf (not to be confused with seawolf class subs) the second nuclear submarine ever built, had this capability. She was eventually fitted with a number of unique intelligence-gathering equipment and devices that would make it very different from other submarines in the U.S. Navy fleet. Along with extra thrusters and a saturation diver dock, she was fitted with retractable sea legs so that she would be able to rest on the bottom for longer periods of time without getting damaged or stuck. <in particular was specialized for missions to enable bottom rests..so bottomline: in answer to the OP as asked: yup they can and do. So while any submarine can bottom for evasion and espionage purposes, they really can't stay for long. Those that are designed to hang out at the bottom aren't likely to see the light of day anytime soon. now about hitting the bottom ie uncharted seamounts at speed....that's a different bottom issue altogether
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Old 02-19-2020, 12:10 AM   #6
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Yes Seawolf (SSN 575) could, but that's a one off class and not representative of all. Halibut (SSGN 587) could as well, along with Parche (SSN 683), NR-1, and possibly Jimmy Carter (SSN-23). But these were all purpose built with the exception of Parche. MSW and ASW intakes on these boats would have to be on the upper portion of the hull to avoid sucking in unwanted material.
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