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Kurushio
Joined: 25 Mar 2006
Posts: 14
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 Posted: Tue Apr 11, 2006 9:48 am Post subject: Cavitation |
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Second question of the day (I'm full of 'em at the moment) 
Cavitation is driving me mad and I can't find any good answer through search. So to dispell the myth once and for all....does cavitation depend on acceleration or speed? |
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Oberon
Joined: 07 Jul 2002
Posts: 1796
Location: Suffolk, UK
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| Posted: Tue Apr 11, 2006 9:52 am Post subject: |
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I think it's mainly based on speed, although obviously at some point during an acceleration to say...20 knots at 50 feet, you're going to get cavitation, it varies more on depth and speed I'd say...however this is mainly guesswork and what I've learnt from SC as opposed to RL experience, someone who's actually done the Silent Service would know more, I'll hand over to them.  |
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Konovalov
Joined: 14 Sep 2002
Posts: 2438
Location: High Wycombe, United Kingdom.
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| Posted: Tue Apr 11, 2006 10:19 am Post subject: |
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| Oberon wrote: | | however this is mainly guesswork and what I've learnt from SC as opposed to RL experience, someone who's actually done the Silent Service would know more, I'll hand over to them. |
Yeah, I remember someone created a cavitation chart for SC. From my experience with SC the shallower you were the more prone you were to cavitating at a higher speed. Go deeper and you can go faster without cavitating. You could creat your own table for DW by simple trial and error. Test at what speed your sub starts to cavitate whilst on the surface. I suspect 7-9 knots. Test also at periscope depth and so on.
Oberon, I much prefer your little Type II boat sig than the spam one. |
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GunnersMate
Joined: 17 Feb 2006
Posts: 225
Location: Boston, MA
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| Posted: Tue Apr 11, 2006 11:04 am Post subject: |
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Cavitation is a product of propellor speed and depth. That's why so much is spent on developing propellors.
Note - I used propellor instead of screw to avoid the inevitable jokes  |
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Nexus7
Joined: 21 Jun 2004
Posts: 275
Location: Switzerland
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| Posted: Tue Apr 11, 2006 12:10 pm Post subject: |
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| Since we're on the matter, I know that cavitation seriously damages the very expensive blades. Maybe it wouldn't be to bad to have a repercussion on the maximal speed of the sub after cavitating, but..... in all honesty, I have no clue in what mass this phenomena could inflict damage... |
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Nexus7
Joined: 21 Jun 2004
Posts: 275
Location: Switzerland
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| Posted: Tue Apr 11, 2006 12:16 pm Post subject: |
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In game it's a matter of depth and speed (and maybe some secundary factor like water current). The deeper you go, the faster you're allowed to go avoiding cavitation.
Maybe someone is able to post a link to a cavitation chart :hmm: |
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OneShot
Joined: 24 Mar 2005
Posts: 704
Location: Germany
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Yskonyn
Joined: 18 Mar 2005
Posts: 43
Location: Netherlands
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| Posted: Tue Apr 11, 2006 3:06 pm Post subject: |
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Again similar to aviation, I guess the problem of aircraft propellers going through the soundbarrier causing massive drag could be seen as a similar case.
Although the 'tactical scenario' for the huge amounts of research into both propellers is quite different; real tactical issues for naval and financial issues for aviation.
In a nutshell really, not looking for a discussion here 
:hmm: |
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Bubblehead Nuke
Joined: 01 Feb 2006
Posts: 41
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| Posted: Tue Apr 11, 2006 9:29 pm Post subject: |
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| Nexus7 wrote: | | Since we're on the matter, I know that cavitation seriously damages the very expensive blades. Maybe it wouldn't be to bad to have a repercussion on the maximal speed of the sub after cavitating, but..... in all honesty, I have no clue in what mass this phenomena could inflict damage... |
Cavitation is the formation and subsequent collapse of bubbles. As the screw (the CORRECT term TYVM) rotates it creats a low pressure area in front of the face of a blade. This basically makes, well, steam, as the water starts to flow over the face fo the blade.. As this bubble passes by the blade it does back to normal sea pressure and this is what collapses this bubble thus making noise.
This collapse releases energy in the form of shock waves. It is like taking a VERY small hammer and just continually beating on the face of the blade. What happens is that VERY small pits are formed and that ruins the smooth laminar flow of water over the face of the blade and makes it noiser. Will it effect speed? Yes, after a LONG LONG LONG time. What the real repercussions are is that the screw may sing, whistle, or cavitate even easier as the damage progresses. It will be replaced LONG before this damage could affect ships speed. |
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nattydread
Joined: 09 Jan 2004
Posts: 667
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| Posted: Wed Apr 12, 2006 6:12 am Post subject: |
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whatever happened to the plans of building ionized water propulsion for subs?
I thought they talked about using the reactor to produce electricity to created a magnetic pulse chamber through the hull of the sub(like the huge cigar shaped inlet/outlet of early jets, MiG 15, F86 Saber, etc) and they could squirt water out the back like a squid. I thought they felt it could allow for high speeds with no cavitation, and no concerns about approaching or exceeding the speed of sound under water on any surfaces...no cavitation. |
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Kapitan
Joined: 10 Mar 2005
Posts: 5385
Location: essex england also st petersburg russia
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| Posted: Wed Apr 12, 2006 7:01 am Post subject: |
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| Speed at depth = cavitation but there is charts on subguru.com that can help you solve this issue. |
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Oberon
Joined: 07 Jul 2002
Posts: 1796
Location: Suffolk, UK
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| Posted: Wed Apr 12, 2006 7:33 am Post subject: |
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| Konovalov wrote: |
Oberon, I much prefer your little Type II boat sig than the spam one. |
How about this one? |
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GunnersMate
Joined: 17 Feb 2006
Posts: 225
Location: Boston, MA
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| Posted: Wed Apr 12, 2006 8:09 am Post subject: |
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| nattydread wrote: | whatever happened to the plans of building ionized water propulsion for subs?
I thought they talked about using the reactor to produce electricity to created a magnetic pulse chamber through the hull of the sub(like the huge cigar shaped inlet/outlet of early jets, MiG 15, F86 Saber, etc) and they could squirt water out the back like a squid. I thought they felt it could allow for high speeds with no cavitation, and no concerns about approaching or exceeding the speed of sound under water on any surfaces...no cavitation. |
Read "Hunt for Red October"  |
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Wim Libaers
Joined: 21 Sep 2001
Posts: 396
Location: Flanders
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| Posted: Wed Apr 12, 2006 1:38 pm Post subject: |
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| nattydread wrote: | whatever happened to the plans of building ionized water propulsion for subs?
I thought they talked about using the reactor to produce electricity to created a magnetic pulse chamber through the hull of the sub(like the huge cigar shaped inlet/outlet of early jets, MiG 15, F86 Saber, etc) and they could squirt water out the back like a squid. I thought they felt it could allow for high speeds with no cavitation, and no concerns about approaching or exceeding the speed of sound under water on any surfaces...no cavitation. |
Magnetohydrodynamic? It works. However, it requires lots of power, may attract magnetic stuff to the sub, and is not completely silent (big generators for the power, and with high currents electrolysis may become a problem). |
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MaHuJa
Joined: 10 Jan 2002
Posts: 447
Location: 59.96156N 11.02255E
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| Posted: Fri Apr 14, 2006 3:48 am Post subject: |
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| Wim Libaers wrote: | | Magnetohydrodynamic? It works. However, it requires lots of power, may attract magnetic stuff to the sub, and is not completely silent (big generators for the power, and with high currents electrolysis may become a problem). |
So, you'd get one hell of a big MAD signature (probably on the order of several miles?) and a giant bubble trail...
How about smaller scale? UUV, torpedo, etc? I guess it would pretty much ruin any chance of magnetic detonation... |
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