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Virtual Earth Exposes Nuclear Sub's Secret
NewsCloud alerts us to a story a few months old that has been getting a lot of play recently. A Seattle blogger, Dan Twohig, was browsing in Microsoft's Virtual Earth when he accidentally came across a photo of a nuclear sub in dry-dock. Its propeller is clearly visible — this was a major no-no on the part of someone at the Bangor Sub Base. The designs of such stealth propellers have been secret for decades. Twohig blogged about the find and linked to the Virtual Earth photo on July 2. The debate about security vs. Net-accessible aerial photography has been building ever since. The story was picked up on military.china.com on Aug. 17 — poetic justice for the Chinese sub photo that had embarrassed them a month before. On Aug. 20 the Navy Times published the article that most mainstream media have picked up in their more recent coverage. Twohig's blog is the best source to follow the ongoing debate. No one has asked Microsoft, Google, or anyone else to blur the photo in question. Kind of late now.
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Tell the truth and you won't have so much to remember.
Is this really so secret nowdays?
I think I remeber that the thechnology to make these kind of silent propellers where sold by a norweigan company to a KGB front in the early 1980:s. As I recall, it was a major scandal when the news brooke.
As I have understod it, most soviet nuclear subs had these improved propellers since late 80's and that most of the eastern block started to get access to the same technology.
Most western submarines has had these kind of silent props for years and I belive that most submarine nowdays have one.
You could try to track the Swedish HMS Gotland with passive hydrophone and see how far that takes you, for instance... she insn't even a NATO sub but she is more silent than even the american SSN subs.
Why three?
I am not a fluid dynamicist. But: To increase thrust at a certain RPM, it seems that you can either (1) increase the diameter of the propeller, or (2) increase the number of blades. The problem with increasing the diameter is that the velocity at the tips increases, which leads to effects like cavitation (which, besides being very noisy, damages propellers). So what you do is increase the number of blades.
Prop-driven airplanes produced near the end of WWII had many-blade propellers for this reason as well: They wanted a lot of thrust, but, if they made the blades any longer, then the tips would have been supersonic. (I think I got this factoid from the History Channel.)
My guess is that a quiet high-thrust propeller would spin slowly and have many, very wide and heavily-curved blades. Let's see if somebody who knows more agrees.
Coordinates are +47 43' 39.58", -122 42' 55.83" for the base (this can be plugged into Google Earth.)
The location of the snapshot is of the dry-dock at 4744'36.08"N, 12243'48.51"W.
This link may or may not work: http://maps.live.com/default.aspx?v=2&cp=ryqjnb4s5 7d5&style=o&lvl=2&tilt=-90&dir=0&alt=-1000&scene=1 0352732&encType=1
There's no propeller visible in the Google Earth imagery. All you can see is that there's what might be a sub; it's quite blurry. The Windows Live imagery shows a blurry whirly instrument of death; looks like a bunch of boomerangs.
Honestly, it's stupid. Half the shit that's classified, is just classified to impress. For example, the top speed of various US air craft carriers. Like that can't be figured out by a foreign government...? Like our *propeller technology* is that much more advanced, and other nation's subs haven't figured out what it sounds like? C'mon.
Please help metamoderate.
I served for a long time.
And I was exposed to all branches for long periods of time. You will not find a less gay friendly place than the Navy. Even the Marines are more tolerant. It's because of the hollywood archetyping of the navy as gay that the navy has had such a buildup of anger about it. The 1993 DADT policy greatly increased the problem, and violence against gays has increased by about an exponent from 1993-1999 (no idea of the exact recent statistic, but it has increased greatly up to today)
Gays int he military are usually quite good. dedicated to serve in spite of additional hassle. The Brits have been open for a while, and they are, man for man, extremely effective. I'm not implying that there is some kind of problem with gayness in the military.
But this is typical trash propaganda. Sounds ludicrously paranoid, but the fact is that there is an effort to portray soldiers as feminine weakling children or sociopathic monsters. You'll find most gays in the Army. You'll find the fewest in the Navy.
The secret bit of these propellors is what materials they are made of, how precisely they curve, and to what tolerance they are engineered. The big problem with propellors is that they tend to suffer from cavitation at high speed, where the sudden change in pressure causes bubbles to form and collapse. Apart from being rather noisy, referred to as "singing" (which is a bad thing for a stealthy submarine trying to make a fast getaway) it also causees damage to the blades (much like desert sand on engine turbine blades).
The purpose of having an odd number of blades is no secret - it is to reduce vibration. As the submarine travels through the water it leaves a wake behind it. Above the submarine there is less water pressure than below - so having two blades above and below at the same time is a bad thing. The more blades, the less vibration, but propellors are more efficient with fewer blades. You will see speedboat propellors with three or four blades, and fishing boats can have propellors with only two blades.
There is also the problem that having different metals in close proximity in a salt water environment, can lead to an electrolysis effect where the metals and water act as a kind of battery. Lots of technical papers on Propellor design
"The most frequent cure for a singing propeller is the popular "anti-singing edge". This is a chamfer applied to the trailing-edge to promote separation of the vortices."
Vintage computer adverts: http://www.vintageadbrowser.com/computers-and-software-ads
Source
Also read about the low amount of use China's submarine fleet gets, and the inexperience they have: Source
This basically amounts to China having never actually used their submarines as a nuclear deterrent, and since they have no ICBMs that can reach the US they have no nuclear deterrent against the US and a comparatively very limited navy. (Report)
The media loves to hype up China's military spending, but if you think China's grounded 1980's built subs, or the speculated five new Jin-class (Type 094) subs, are going to make the US Navy "ineffective", or if you think aircraft carriers (the most expensive ships of all) are just for intimidating small nations, then you're a few warheads short of a nuclear power.
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That's actually an excellent answer. There is an article about precisely that subject here: http://www.aerospaceweb.org/question/propulsion/q0 039.shtml
One thing the article doesn't point out is that increasing the solidity of the propeller disc can have it's own consequences, and there is generally an optimum solidity (depending on various other factors) which results in the highest efficiency.
A deep unwavering belief is a sure sign you're missing something...
"Ducted propulsion" on a navy demonstrator vehicle...
...is this a secret?
We apologise for the fault in this post. Those responsible have been sacked. -- Signed RICHARD M. NIXON
I know Derek (from online, for years, but not in real life), and he's been there and done that.
The general shape is not news; it's the same general shape as on a bunch of US attack sub prop pictures which have been public for 10+ years.
The photo reveals the blade advance ratio for that particular prop design, though, which is useful to adversaries, and is different than the attack sub props.
As far as I know, and I have a naval architecture degree and have followed sub and naval ship design reasonably well for 30+ years, enough details to determine blade advance ratio on Ohio SSBN props have never been public. It was widely known that they were skew / scythe props. But "It's of that general type" and "Oh, look, that's what speed it's designed for" are two different things. A smart hydrodynamicist or naval architect can use that and tell roughly how fast an Ohio can reasonably be expected to go at top end speed, and things about how much cavitation noise it will make accellerating in a sprint. Also, it can help map propellor RPM to speed.
It's important, and the blade advance angle there is very different than the previously widely known ones on attack sub props, and that will tell bad guys something.