QE2 Technical Questions

[Clydebuilt1971]

Heres one for the marine engineers amongst our throngs (especially ones who sailed on steam powered ships)

The only experience I have of steam propulsion is ps Waverley's triple expansion diagonal and ss Shieldhall's triple expansion "up & dooners"

Both have a device called the air pump which is used to draw the exhaust steam from the Low Pressure cylinder through the condenser and then move the resultant condensate back to the "hot well" which is effectively a holding tank before re-joining the boiler feedwater loop once again.

I assume that larger steam propulsion had a similar system in place? What was in place on QE2 when she was a steam ship?

Cheers!

Gav

[Chris Shaftoe]

clydebuilt1971: As I recall, QE2s main engine turbines sat on huge condensers which used a vacuum to draw down the steam/condensate, but this at the time was beyond my scope as I was only an Engine Room Boy at the time. (1972-74)

As the condensers drew sea water for cooling the steam, we had to open them up and clean them out by hand which was pretty disgusting because they would collect all kinds of unmentionable items of the sort that really needed surgical gloves to handle.

[Clydebuilt1971]

Thanks for the response Chris,

Condenser cleaning sounded like a horrible task!!

I am wondering what generated the vacuum? In the case of the examples I mentioned in my message it was the air pump that generated that vacuum.

I wonder if the surface area of the condenser was enough...

Hmmm
Gav

[Isabelle Prondzynski]

Here is an opinion piece from David L Smith in the Herald (Scotland) dealing with weighty matters on which I am no expert :

https://www.heraldscotland.com/opinion/17285237.letters-a-weighty-matter-concerning-the-qe2/

[Thomas Hypher]

Here is an opinion piece from David L Smith in the Herald (Scotland) dealing with weighty matters on which I am no expert :

https://www.heraldscotland.com/opinion/17285237.letters-a-weighty-matter-concerning-the-qe2/

QE2's displacement weight is indeed far less than her GRT likely down to the extensive use of aluminium but also how she was built (being welded and built with box sections but still on a traditional slipway - a junction between old and new shipbuilding techniques). The original Queens had a displacement weight around the same as their GRT (although I suspect QM in Long Beach no longer has such a displacement weight given her "conversion" from 1968 to 1971) however QM2's displacement weight is far lower than her GRT (76,000 tons compared to a GRT of around 148,000) so even in all-steel ship construction the displacement weight and GRT are not likely to be similar these days which could be down to modern shipbuilding techniques such as box sections so there are no overlapping plates to increase weight and of course welding instead of riveting. Modern cruise ships also have a GRT far above their displacement weights but aluminium is used on a small scale for the likes of deckhouses on the upper decks although I suspect it wouldn't make much difference in the scheme of things.

One wonders if the modern cruise ships or QM2 for that matter would float (in terms of stability mainly) if their displacement weights and GRT were so close together, or whether they'd be practical to build or commercially viable in terms of build costs and operating costs?

[Peter Mugridge]

If I recall correctly for passenger ships the GRT is in fact a measure of volume based on cubic metres, rather than a true weight measure so a lot of the apparent discrepancies will be due to the large areas which are enclosed but virtually empty spaces.

Think of all those extra decks on top of modern ships - those are mostly cabins, so effectively empty boxes.

If you bridged the gap between the twin accommodation blocks of one of the Oasis class vessels with a lightweight plastic covering that would perhaps weight a couple of hundred tonnes, you would be enclosing all that empty space between the two blocks and you would immediately get a GRT increase of several tens of thousands of tonnes as a result.

As to why it is done this way rather than a measure of displacement, i.e. the true weight, I am not sure.

[tramscape]

When evaluating a ship, how much it can carry - cargo space - was (and still is) of much more importance than its actual weight, so it is a suitable means of classification

GRT and NRT have now been superceded by Gross tonnes / Net tonnes based on a calculation using the outside dimensions of the vessel

[Peter Mugridge]

When evaluating a ship, how much it can carry - cargo space - was (and still is) of much more importance than its actual weight, so it is a suitable means of classification

GRT and NRT have now been superceded by Gross tonnes / Net tonnes based on a calculation using the outside dimensions of the vessel

Interesting...  I thought the standard for cargo ships was that they did measure the actual displacement?

As for passenger ships - I would have thought the best measure of capacity, if we are basing things on how much can be carried, is the passenger ( "self loading freight"  ) capacity rather than any weight based measure?

[tramscape]

Yes, tonnage as such is not so relevant for passenger ships ....but with so many ways of defining a ship it was probably best not to devise another for such "cargoes" . I suspect that it is impossible to define a standard measure for people-carrying capacity

I think it goes back to the days to assessing how much a cargo ships could carry - "tuns" (ie barrels), which later became tonnes of water which could theoretically be transported in the cargo spaces

Taxation and fees were determined on cargo capacity as commerce was the original main reason for having ships

[Peter Mugridge]

I think it goes back to the days to assessing how much a cargo ships could carry - "tuns" (ie barrels), which later became tonnes of water which could theoretically be transported in the cargo spaces

Ah!  So is that why the passenger ship measure is 1 tonne per enclosed cubic metre then?

[tramscape]

The precise detail escapes me ....... so it is a matter of resorting to wiki for that !

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