QE2's Variable Pitch Propellers

[highlander0108]

Here is another Ashley Allan 2003 drydock photo.  What I find interesting is the fins located just in front of the prop. I have never seen these before nor do I recall seeing them in any of the various ship models.  I will have to look at my photos of the builders model in the Transport Museum in Glasgow.  Were these added when the ship was repowered and repropped in 1987?  Does anyone know their function?  I suspect is it to direct the waterflow into the propellers and perhaps to increase efficiency or reduce vibration.

[skilly56]

Hullo Ken,

I've just found your query on the fins fitted to the aft end of the stern tube shown. Your assumption is correct. The purpose is to 'straighten' the water flow into the blades, enabling greater thrust, and also reducing cavitation. The improvements are measurable, so the fins do work. If they were not fitted, the water flow into the blades would be angled in toward the rudder due to the forward motion of the ship, and so the boundary layer at the leading edge of the blades would not be square to the direction of travel. If you look carefully at the one fin that is perpendicular to the camera, you can see the bend in the fin that straightens the water flow. I cannot see this device being to beneficial on slower ships, but it must have worked on the QE2.
Cheers
Skilly

[highlander0108]

With the diesel conversion, the ship was fitted with variable pitch propellers, which eliminated all reverse gearing, reduction gearing , or transmissions.  As was documented in other posts, nevertheless, there was equipment associated with this feature, but that took up far less space than reduction gears/transmissions  The pitch of the propeller was adjusted to give variable forward speed to neutral and reverse, while the shaft operated at the constant 144 rpms.  This design was well suited for the diesel-electric powerplant and would allow the diesels to be run at their peak effeciency.  It has always facinated me that with the shaft still spinning, that the propeller blades could be adjusted so that they would essentially spin effortlessly and not propel the ship in either direction.
https://www.theqe2story.com/forum/index.php?action=dlattach;topic=872.0;attach=1961;image
While not the QE2's propellers, this video shows similar units being tested while in drydock.

[Imonlygoingforone]

QE2 only operated at 144RPM whilst in 'Free Sailing' mode, meaning that the vessel was underway on passage, and not manouevring. In 'Combinator' mode, the props were operating at 72RPM as this gave a better range of control for handling the ship in ports or in confined waters.

Incidentally there were 4 modes which were used for the vessels engines. They were :

Harbour mode, where obviously propellors weren't turning, and power was being generated by usually 1 Diesel Generator (DG) for the hotel load of the ship

Ready to sail (AKA 'RTS'), where DG's were run up and put on the board - to achieve RTS there must be 2 DG's on line in each engine room to allow for failures / fires etc.

Combinator, where the power was transferred to the prop motors and therefore allow the ship to depart. As mentioned before, the props were turning at 72RPM - at this point thrusters were also put online.

Free Sailing, where the vessel was deemed to be clear of a port and on passage, generally after the pilot has gone, and 'normal' ships would ring 'Full Away On Passage' (FAOP). The props would reduce in pitch and the revs would increase as the telegraphs were pushed up from 4 to 6 (5 being the position referred to as 'going up through the gate'). They could then be increased to the required pitch/speed for the passage.

 

[Bob C.]

It has always facinated me that with the shaft still spinning, that the propeller blades could be adjusted so that they would essentially spin effortlessly and not propel the ship in either direction.

Were QE2's props counter-rotating (spin in opposite directions) or did both rotate in the same direction?  If counter-rotating and using both props at equal RPM's then there would be no movement of the ship.  But there is a phenomenon called "side force" that occurs when one prop is spinning or both are spinning in the same direction. Side force will swing the ship's stern in the direction of the propeller rotation even when there is no fore or aft thrust.

Anyone know if the 6-bladed fixed pitch props with the old steam plant counter-rotated or spun in the same direction?   

[Peter Mugridge]

Not quite; counter rotation will generate thrust as long as both props have the appropriate ( but opposite! ) blade angle selected.  This would avoid the side force.

[Rob Lightbody]

They were both outward turning always I believe.

[Peter Mugridge]

To clarify that, Rob, do you mean the starboard propellor rotated clockwise and the port one anticlockwise as seen from astern of the ship?  Or is it as seen from inside the ship looking astern?

[Bob C.]

Note:  if images link of QE2 in Dry Dock not active

From this photo, obtained from it appears that the propellers are counter-rotating with the port prop turning conter clockwise and the starboard prop turning clockwise when viewed from the stern.

Also, the British Pathe newsreel in the first post here (https://www.theqe2story.com/forum/index.php/topic,2344.0.html) shows the old props which are clearly counter-rotating and conform to her later variable pitch prop rotation direction (i.e. port turns CCW and starboard turns CW)

There is a view of the STBD prop at 1:06, a better one at 1:17.  The port prop is at 3:38 and there is a distant but vague view of the stern taken with a zoom lens from the mouth of the Cart.

 

[highlander0108]

From this pic, which I posted the underwater window thread awhile back, it is clear that the props are counter rotational and that they are configured in the typical arrangement of outward rotating, with the starboard righthanded and the port being opposite,that is left handed.
http://www.rmsqueenelizabeth2.com/image/Ashley%20Allan%20061.jpg

[Bob C.]

I remembered this pic after I "googled" and found the above one.  In anycase, great topic.

[highlander0108]

A follow-up question for our resident ship's engineers would be how fast would it take to reverse the pitch of the propellers specifically.  For instance, while manouvering at the pier, how quickly would the captain be able to say throw the port in forward and starboard in reverse to aid in pivoting the ship?

[Imonlygoingforone]

A follow-up question for our resident ship's engineers would be how fast would it take to reverse the pitch of the propellers specifically.  For instance, while manouvering at the pier, how quickly would the captain be able to say through the port in forward and starboard in reverse to aid in pivoting the ship?

Not an engineer, but a Deck Officer. It was almost instantaneous, maybe a second or 2 slower.
There was really very little point in doing such a thing with the engines however. The props were so close together that doing that was pretty much useless, hence the reason tugs were used pretty much everywhere. Anyone who has been to Flaam (before the days of the tug following us) can testify how long it takes to swing the ship on it's own!

[Isabelle Prondzynski]

Anyone who has been to Flaam (before the days of the tug following us) can testify how long it takes to swing the ship on it's own!

I sense there is a story here! What is this about the "tug following us"?

[skilly56]

The rate of application of pitch is usually controlled by a pitch rate controller for each hub system. The rate of application and reduction on some systems can be set individually with a small potentiometer in the electronic systems cabinet, or, if it an older system with pneumatic controls, the application rate is set using pitch rate restrictors.

The pitch application rate for each type of vessel will be different (except maybe for sister ships), and will depend on the size of the hubs, the area of the blades, the hub servo piston diameter, the hydraulic pressures involved, and the main factor will be the type of engine(s), the drive system (diesel-electric, geared diesel, or gas turbine), how many engines are running, and whether the shaft is operated in the combinator mode, the constant-speed mode, or is switchable between both modes like the ship I have just come off last week.

However, the pitch change when testing the gear (ie, with the shaft stationary) can be as little as 10-15 seconds from Full Astern to Full Ahead, mainly because the application rate controllers on a lot of installations are not looped in the pitch control circuit until the shaft rotation is actually started. If the maximum pitch application rate was available when the shafts are rotating, the sudden application of pitch can easily be enough to stall the engines and cause overload trips and auto shutdowns - not a very nice occurrence, especially if the ships electrical power is being supplied from a shaft alternator.

Cheers

Skilly