Can anyone explain their unique shape? I know they are variable pitch, but what's with the secondaries?

I was expecting pasties.

N for the answer.  I've never seen propellers like those.

Second ones don't look like they turn.  I am betting they are to prevent cavitation or minimize it so the water flowing behind the ship is smoother and reduces vibration on the hull.

ETA:

Or maybe they do:


Cunard ordered two five bladed and adjustable propellers, which each would have a diameter 5.8 meters. Attached to the propellers would be two Grimm-wheels (I don’t know if that’s also the name in English but that’s what it’s called in Dutch). These Grimm-wheels are 15% to 20% larger in diameter then the propellers and are attached behind the propellers. These Grimm-wheels rotate separately from the propellers and use the slip streams created by the propellers to gain 3,5% of propulsion energy which else would be lost.


The propellers were designed to function with Grimm Wheels. The seven-bladed vane wheels were fitted behind the propellers and freely rotate on the same shaft. These wheels are in use on other ships to reclaim part of the energy normally lost in the slip stream of the propeller and convert it into additional thrust. They were predicted to do the same on the Queen Elizabeth 2 and to save 2 to 4 percent in fuel costs. Unfortunately, some of the vanes were lost during trials, so the remainder of the blades on both shafts were removed and not replaced.

This.  And I don't see any way those second ones turn, it wouldn't produce much thrust and take a ton of power.  



 

Thanks Phatmax.

From Wikipedia



https://en.wikipedia.org/wiki/Queen_Elizabeth_2

Interdasting.  http://www.roblightbody.com/qe2-1987-rebirth.html





 

Looks like they're just along for the ride (freely spin),  and through the magic of hydrodynamics contribute to some efficiency increase.  Probably has something to do with turbulence reduction.

Not one Hunt For Red October joke. I am disappoint.

At first I thought they might be post-swirl stator blades - in short, a fixed set of propeller blades that extract the "lost" energy produced by the propeller in creating swirl in flow downstream of the prop.  A quick Google search shows that they are Grim Vane Wheels, which probably work on the same principle, but apparently didn't work on the QE2.

 

Not even a single ping.

Careful, lad, shome thingsh in here don't react well to bulletsh.

The props in the photo do not look like variable pitch.

The secondarys look like they are to minimize cavitation.  And/or increase efficiency.

That's the VTEC.

The driven propellers are variable. The engines are unidirectional.

It appears, from the above responses, that the secondaries capture the primary propeller thrust and extend the span, adding thrust.

Here's the Russians adding things to reduce cavitation and wake.

Wouldn't adding pistol grips create even more thrusts per squeeze?

Just like a cross cut paper shredder.  Can't have an overboard passenger just shredded lengthwise.  The bits fit into the long handled pool debris strainer much better.

They don't really "freely spin".  They are driven by the prop wash from the unit in front of them, on the inner part of the vanes.  This allows the outer part to generate some thrust.  It lets the combination act like a larger diameter propeller than can be physically installed at the location of the first propeller, which can increase thrust efficiency.