U-boot Class 212A: false propellers? - Need propeller experts!

[gerwalk]

I was looking at this photo from the launching of a 212A in Germany. The propeller looks fishy. Seems like the blades are covered by paper or cardboard. The new Revell 212 model has the same squarish blades. IMHO it's fake and the real blades are curved after analizing photos of the Italian 212 with it's prop covered.

What do you think?

[tom dougherty]

Those are edge guards. The

Those are edge guards. The edges of new propellers are usually pretty fine (thin), and they are covered to keep small nicks and other damage from occuring during installation. Keeps them factory fresh, and reduces nicks that cause the blades to "sing". The blades themselves resemble the older J series propellers on the Permit, Sturgeon and Polaris SSBNs. The J series did not have quite the same "sharp corners" at the tips, but they were overall very similar.
See the two prop photos of the J series about halfway down the page on the Casimir Pulsaki SSBN]http://www.usscasimirpulaski.com/anatomy2refit.htm[/url]

Why would one go to the trouble of putting fake propellers on a sub? Why not just shroud them from prying eyes?

[gerwalk]

Hi Tom,
Indeed, the italians launched

Hi Tom,
Indeed, the italians launched theirs 212 with the props covered.
"Why would one go to the trouble of putting fake propellers on a sub?" To confuse? (at least Revell AG was confused by this!! )
Why using edge guards with a fake bronze/brass color (they look like that) when the dunce cap is covered by a dark grey cover?
The Russians showed their Lada prop in all it's glory except for the dunce cap which was covered by a nice golden cloth cap that is rather deceiving.

As for the blades "resembling the older J series propellers": I would say that a good guess would be that they resemble the ones of the Dolphin class (with a fine tip) though a little bit longer.
So far this is what I have:

[anonymous]

I concur. They are edge

[color=#000000]I concur. They are edge guards. When the image of this 212 stern appeared many months ago, based on the blade chord separation at the base around the prop hub of the 212, for a minute or so I thought 'could these blades be variable pitch?'. I always wondered if this boat's AIP propulsion system combined with a computer controlled variable pitch for optimum underwater cruise endurance be possible, or even needed? I am inclined now, unless new evidence comes my way, these propellers are not variable pitch. It does seem to have less blade area compared to the Dolphin seven blade. However, the aspect ratio of the 212 blades is longer, (like a glider wing) for the most efficient lift to drag ratios vs. torsional strength. A blade on a propeller is basically a rotating foil shape creating lift sideways. This appears to be the latest wrinkle between when Dolphin's prop was developed, likely in the early 90's, and the 212, in the late 90's to early 2000's. Why the dunce cap is covered? The shape of the bell concave shape inside could be measured photographically, enhanced to 3D, then the optimal combination of speed vs. vortex attenuation could be theorized IE]



Edited By Dolphin on 1126839816

[gerwalk]

Thanks Steve! Good analysis.

I had

Thanks Steve! Good analysis.

I had that photo for a long time but never noticed the edge guards or whatever they are since a couple of weeks ago when I started to gather all the info on the 212 I got in preparation of the upcoming Revell 212.

What do you think about those straight (sp?) corners? are part of the edge guards, are the blades curved on that spot?

[anonymous]

Follow the plan form in

Follow the plan form in the image. No cardboard trickery here. Das U-31 ist ein schönes Boot!

Thank you Johann for your help on my Dolphin which too is proceeding. Your new 212 is magnificent.

Steve Reichmuth



Edited By Dolphin on 1126839309

[gerwalk]

Thanks Tom and Steve for

Thanks Tom and Steve for clariying this, it's a strange blade shape but very nice.

[chips]

for a minute or so

[/quote] for a minute or so I thought 'could these blades be variable pitch?'.[quote] Those are variable pitch props. the pitch angle at the tip is different than the pitch angle at the hub.
I believe you meant to say "changable pitch props". On changable pitch props (CPP) the pitch can be changed while thr prop is turning. On a CPP system the prop always rotates the same direction; changing the pitch changes the boat speed or direction.

[anonymous]

You are correct Chips. I

You are correct Chips. I thought using the aviation term 'Variable pitch' vs. CPP would be better understood or relate better. Do you think the 212 prop is a CPP prop?

Steve R



Edited By Dolphin on 1127067749

[chips]

I don't think that the

I don't think that the 212 prop is CPP. Looking at the pictures Gerwalk posted, I can't see the blade hub on the prop hub. CPP blades have an attached head or hub; they are bolted to the main prop hub by the blade hub.

The last two USCG Cutters I served on had CPP, 4 blades per prop. We had a pneumatic-hydraulic system to change the prop pitch. On the first cutter we used a vegetable based hydraulic oil in the CPP system; and a certain amount of oil leaking out was acceptable. Four years later, I'm assigned to a another cutter in the same class, and we used a petroleum based hydraulic oil in the CPP system. A change in the CPP seals meant we didn't have to let oil trickle out of the system. We did lose a pneumatic component on the bridge during one patrol. The CPP failsafe system put that prop at full astern. That type of failsafe is not a good thing for a silent sub.

[gerwalk]

This topic is getting better

This topic is getting better every day!
Thanks Chips!

Is there any sub with CPP?

[Antoine]

yes of course.
The french "Naïade"

yes of course.
The french "Naïade" of the beginning of the 20th century had CPP prop.

[gerwalk]

Nice sub! 1904? It was

Nice sub! 1904? It was one of those steam subs?

What about modern subs with CPP?

[anonymous]

I do not know of

I do not know of any CPP blades on submarines yet. The pitch of some props can be changed on the yard then refixed, or set.

All gas turbine propelled ships all use CPP. The gas turbines turn at a high rpm, exotic gear reduction to reverse such would be a waste, it is easier to change the pitch of the blades (reverse). This way these prop shafts always turn in the same direction.





A. Burke class DDG prop seen in Drydock shown blowing air & water out it's blades to reduce propeller reververations.



The first all gas turbine propulsion warships were the very beautiful Kashin class Soviet DDG's in the mid 1960's. Followed soon after by the USGC Hamilton class cutters. Then came the Spruances DD's....and after gas turbines & their CPP's were here to stay. But for submarines? The hubs of these props with CPP's notice are large with complex gearing pitch mechanizums inside. Could such be made tapered and small for a sub prop? Sub props have to be so specialized to operate silently in a wide range of paramaters...water depth, cavitation.

Steve Reichmuth



Edited By Dolphin on 1127197089

[gerwalk]

Very interesting Steve. The only

Very interesting Steve. The only sub props that I remember with a big hub are the russians but I don't think they are CPP (maybe CCCP )

BTW: check the photo I posted on the topic about flood ports:
http://www.subcommittee.com/cgi-bin....ry20974

I wonder what is the use of those louvers in the oval hole at the stern of the Kilo. Could it be a stearing device?