QE2's Variable Pitch Propellers

[skilly56]

Not forgetting that if you put QE2's 135,000 shp (Correction required - the DG output figure is 130,000 hp, and the actual shp would be considerably lower as approx. 14,450 hp went to ships load)  through 4 shafts, then you also get the heat & windage losses of four propulsion motors (which would be smaller than the present two motors), plus the increased friction from the pedestal/thrust bearings of four shafts and not two would also increase those losses.
If QE2 had four props, their diameter would be much smaller than the current two props, and the propeller slip for 4 props would be greater than for two props as the smaller props would have to rotate faster. To be able to utilise the horsepower she did through only two shafts/props certainly kept the driveline losses down and resulted in better efficiencies. QE2's propeller blade area ratio is about the highest I have ever seen, and for maximum efficiency (ie., less slip) you want your shafts to rotate as slow as possible, and with the optimum blade pitch angle. Once you get beyond a certain pitch on the blade angle you start to lose thrust as well.

Skilly

[Isabelle Prondzynski]

Did it ever happen that QE2 lost power in one of the props and had to keep going on the other on its own? How did that work out?

[June Ingram]

Not forgetting that if you put QE2's 135,000 shp through 4 shafts, then you also get the heat & windage losses of four propulsion motors (which would be smaller than the present two motors), plus the increased friction from the pedestal/thrust bearings of four shafts and not two would also increase those losses.
If QE2 had four props, their diameter would be much smaller than the current two props, and the propeller slip for 4 props would be greater than for two props as the smaller props would have to rotate faster. To be able to utilise the horsepower she did through only two shafts/props certainly kept the driveline losses down and resulted in better efficiencies. QE2's propeller blade area ratio is about the highest I have ever seen, and for maximum efficiency (ie., less slip) you want your shafts to rotate as slow as possible, and with the optimum blade pitch angle. Once you get beyond a certain pitch on the blade angle you start to lose thrust as well.

Skilly

Thanks very much, Skilly, for all of the information that you have presented.  I found it particularly interesting that QE2's propeller blade area ratio is about the highest you have seen.   

[Bob Abbot]

Very interesting comments and photos regarding QE2's Variable Pitch Propellers.

I've also just looked at all Rob Lightbody's photos taken on board in 2011- brought back lots of happy memories!

[Adam Hodson]

That wouldn't double the speed; you'd be dividing the horsepower amongst twice as many propellors and with a bit extra loss through natural inefficiences within twice as many transmissions and shafts.  You probably would get a little bit more speed but it would depend on how efficient the design of the propellors was - she was optimised for the two she had.  A ship with four would be optimised for that many; it's not easy to compare or estimate directly.

There is also the factor that extra speed would involve extra drag, so again you wouldn't end up gaining much - what extra speed you could claw from her that way would almost certainly be at the expense of significantly higher fuel consumption.

Not forgetting that if you put QE2's 135,000 shp (Correction required - the DG output figure is 130,000 hp, and the actual shp would be considerably lower as approx. 14,450 hp went to ships load)  through 4 shafts, then you also get the heat & windage losses of four propulsion motors (which would be smaller than the present two motors), plus the increased friction from the pedestal/thrust bearings of four shafts and not two would also increase those losses.
If QE2 had four props, their diameter would be much smaller than the current two props, and the propeller slip for 4 props would be greater than for two props as the smaller props would have to rotate faster. To be able to utilise the horsepower she did through only two shafts/props certainly kept the driveline losses down and resulted in better efficiencies. QE2's propeller blade area ratio is about the highest I have ever seen, and for maximum efficiency (ie., less slip) you want your shafts to rotate as slow as possible, and with the optimum blade pitch angle. Once you get beyond a certain pitch on the blade angle you start to lose thrust as well.

Skilly

Really interesting physics behind this!

[skilly56]

In starting to empty the house in preparation for sale, I stumbled across hundreds of my old marine engineering journals from my time as a member of the Institute of Marine Engineers in London. I happened to flick through one that covered the development of Merchant Ship Propulsion Machinery from 1964 to 1989.

On one page I found the attached photo, with the editorial remark that they would "watch the performance of this propulsion system with considerable interest".
And well they might - I have attached the related photo of one of QE2's 44 MW propulsion motors actually being assembled, with the rotor being introduced into the windings & casing. I think I have pointed out before that my photos taken of these motors actually in the ship are hard to appreciate dimensionally as they cover five levels. The attached photo gives a much better idea of their actual size.
Just a bit bigger than the average washing machine motor??

ps - Have added photo of a complete motor being lowered into position as well.
Skilly

[Alan Snelson]

Great photos, a good find.

It is easy to forget the sheer scale of the engineering involved so it's good to have a reminder.

[cunardqueen]

another view of the props.... on a diferent topic, might this be the viewing hole that is often spoken about..

[June Ingram]

Hi Skilly -

Thanks very much for posting the photos - amazing to see the size !! 

Do you by any chance have  a copy of the following ?

International Maritime and Shipping Conference (IMAS)
1988
Conference Proceedings

I believe there were three papers presented during that conference about QE2.

Thanks !

June   

[skilly56]

A very clear photo and highlights the blade area ratio. There is very little of the propeller disc area that is not filled with blade.

Sorry June - I don't think I have any of those issues. Mainly Motorship magazines & Institute of Marine Engineers Transactions and papers

Skilly

[June Ingram]

Thanks, Skilly, for checking.

Are QE2's propellers unusual in their blade area ratio ?

June   

[skilly56]

June,

The blade area ratio is the ratio of the area of the disc from the shaft centre to the outermost blade tips, compared to the total area of the blades themselves. Because of the design of QE2's CPP blades, they have a very large area when compared to the total disc area of the propeller.

The attached CPP photos show blades with more space between the blades, and overall, compared to the total disc area, they have a lower blade area ratio.

The 1st attached photo shows two propellers, both having exactly the same blade area and diameter, but having totally different blade profiles.
The closest one has a very basic blade design (Mickey Mouse ears!), and when in the zero pitch position as shown, the maximum chord of the blade is at mid-height. This propeller vibrated a lot, and wasn't very efficient. Also, the small blade necks were prone to fracturing, and actually did so one evening in August 1984, at about 1712 hrs (just after I sat down for dinner) - 2nd photo. (Cost me a lot of money over the years, as we were towed the last 130 miles to Wellington, where my wife was staying with her parents - she got pregnant and had twins!. I still blame the propeller manufacturer for that result!! )

The second prop in the background has a 'skewed' blade design, and the maximum chord is further out toward the perimeter, thus giving a larger thrust area toward the outer extremity of the blade. As the further you get from the shaft centreline, the faster a given point will be rotating, then the added area further out toward the circumference means the propeller is developing more thrust than the first design does at the same 167 rpm that this installation operates at. This later design also has bolt-on blades with substantially stronger root sections than the earlier propeller.

The change in propeller installation resulted in a gain in speed and very noticeable vibration reduction, plus the added security of knowing there is less likelihood of a blade snapping off. It lets you sleep better!!

Skilly

ps - Added a couple of photos showing things that break and things that are stronger!

[Bruce Nicholls]

Interesting to compare the blade area on our 60 inch diameter Hundested variable prop on Lone Gerd.

[Bruce Nicholls]

Another view

[June Ingram]

Thanks very much, Skilly, for all of the information you gave and for the photos. 

How does an engineer go about deciding and designing the kind of propellers to put on a ship ?

Is there a difference in designing propellers for a propeller shaft as opposed to a propulsion pod some of which have propellers on both ends of the pod ?

Thanks, Bruce, for your photos ?  How is Lone Gerd doing ?

June