Ocean liner vs Cruise ship

[highlander0108]

Mr. B,

I've had several discussions regarding the confusion with flat bottoms of current cruise ships and QE2's hull.  During a heated discussion onboard among several "old timers"  who insisted that all the new cruise ships are flat bottomed and aren't sea worthy compared to QE2's full keel, I did suggest that they go look at that silver model in the midships lobby to check out the bottom configuration. 

I do have this observation which can further explain the differences.  QE2's and QM2's (to a somewhat lesser extent) hulls are tapered more at each end than current cruise ship.  In the bow sections, this tapering allows for greater speed through rougher seas.  This tapering runs aft for quite a distance on QE2 and to a lesser extend on QM2.  This resulted in cabins of varying dimensions at the bow areas of QE2.  Modern day cruise ships have many standardized cabins, built as modules off site.  It looks like most modern day ships taper to a standard hull shape that extends most of the length of the ship quite rapidly as compared to QE2.  This mazimizes interior space, with the tradeoff being speed, beauty, and sea keeping abilities.  The result of this is the typical blunt nose that we see in the QV/QE hull shape compared to the beautiful, graceful, classic hull shape of QE2.

Regarding the center of gravity,  I would argue that although these new monstrosities may look dangerously top heavy, rest assured that the calculated center of gravity, or metacentric height, is probably better than that of the original Queens.  Back in the day, before stabilizers were fitted on her, Queen Mary rolled ALOT to the discomfort of all onboard in heavy seas.  She had bilge keels as well as QE2, to help in minimizing the rolling.  Ships must maintain adequate stability in the hull design without the effects of stabilizers factored in.  Would I want to be on the new NCL Epic in a storm on the Atlantic...no way, but no cruise line can operate a ship without meeting the IMO regulations in place.  I had a discussion regarding this very topic with a registered Naval Architect friend and he offered to answer any other questions I had on the current state of ship design.  He did mention that the QE2 design is regarded in his field as one of the best overall in blending beauty and functionality of design.

Ken

[Clydebuilt1971]

The issue of liner hulls cropped up elsewhere on this forum with the question of whether QM2 is a proper liner like QE2.

I posted https://www.theqe2story.com/forum/index.php/topic,968.msg14177.html#msg14177 in response which may be of interest here.

Sorry if I've "contaminated" this thread!

I've got pics somewhere of a cruise ship in drydock which when compared with QE2 might be useful.

Gav

[skilly56]

It all comes down to economics.

The more the 'full beam' can be extended forward and aft, the more cabins that can be squeezed in, the more 'punters' that can be carried, and the more money that will be spent! This is why the cruise ships resemble a 'shoe box' shape rather than carrying the beautiful lines of most of the earlier trans-Atlantic liners. More PAX = more $$$. (but then also requires more crew)

The 'full body' shape forward is also why, on the tandem crossing, the QV was punching into the swells and trying to stop, whilst the QE2 just sliced through them with little impedance to her forward motion. (Just ask any tanker or bulk carrier engineer how hard the engines & engine governors have to work when the ship continuously buries it's blunt bow into a big swell for a couple of days).

Also, QE2's draft was deeper, so the props were operating in slightly deeper and more dense water, were more effective, and also didn't tend to cavitate as much as those on a shallower-draft ship (ie, cruise box) would when pitching into head seas. The result of the props being deeper in the water means they didn't lift towards the surface and become as ineffective when the ship buried it's nose down into a big trough. The only drawback was that QE2, with a deeper draft, had to go into Trieste (a deeper water port) rather than Venice, where the shallower draft ships can go.

I'm off to join the OV in the Caribbean in a couple of weeks, so I'll see how that compares to the above.

Skilly

[Twynkle]

That's interesting - my next question was going to be about draft!
 - and is it correct to think that in the case of QE2 this is measured between the lowest and highest (deepest) point of the hull? I wonder where on her hull this point might be.   
On from there - once the ship's purpose had been designated, then in QE2's case, would it have been the hull that was designed first?

(qV's draft is something far less than QE2's! - Maybe, 'these days' the shape of the superstructure will need to be carefully designed, before the hull can be made to accommodate the dimensions of the superstructure...
Skilly56 - you refer to the qV's time ploughing through the rough Atlantic - from experience, would you expect that the actual shape of her hull might cause the C/E  to inform the Bridge that heaving -to, could be the best option?
I wonder whether engines use much more fuel, if ploughing is as arduous as it looks?!)

Hope you'll enjoy your time on qV! You'll have probably found the Topic for her in the Virtual Chart Room by now!

[Mr B]

Great posts above for sure !

Er, I think Highlander we are saying the same thing, although you word it better !  Apart from perhaps a difference of opinion on being 'Top heavy', it goes without saying that ships must meet stringent stability regulations & criteria which obviously includes not having to have continuous stabiliser deployment.

Skilly's point about the econmics and potential future profits for the ship operator is very relevant indeed, just look at 'Oasis of the Seas' for ideas on how to pack in as many passangers as possible, and your mention of draft and prop depth brings us nicely on to...
..Clydebuilt's thoughts (see link above).  Perhaps Queen Elizabeth 2's traditional fixed propeller tubes and rudder setup, her streamlined curvaceous deep hull profile and ocean liner superstructure layout, makes her indeed the last of the world's great liners.


Oh, we haven't even started on bulbous bows yet...  *hee hee* !

[skilly56]

Rosie,

I'm going on the OV (Ocean Village), not the QV. No penguin suits required on the OV - just jandles, shorts, and 'T' shirts from some of the photos I have already seen. Might get to QV one day though.

Skilly

[skilly56]

Ah, Rosie, I missed half the question - to keen to get into a motionless bed for a change.

The draft is the measurement from the waterline to the deepest immersed part of the ship - generally the aft draft will be greater than the fwd draft when at sea, and the 'squat' at the rear of the ship when it gains speed actually increases the draft even further when under way.

Regarding the heaving-to in the lumpy stuff - the engine room machinery will generally handle the conditions far better than the passengers and the equipment up top (eg, last years incident, when a good portion of the un-restrained casino machines went walk-a-bout on a cruise ship in a South Pacific storm and numerous people were injured).

Normally the load is taken off the engines when punching into heavy seas so as to reduce the stresses & strains on the hull, so this also reduces the stresses & strains on the machinery as well (and if it is a ship with an unmanned engine room like I work on, then the duty engineer can sleep soundly right through the night without any alarms going off to break his beauty sleep).

Having nine 'smaller' engines with a total of 81 cylinders like QE2 enables the ship to maintain speed better in adverse weather than a similar sized ship with only one large engine and thus fewer cylinders. The many smaller engines have a better ability to recover and re-deliver power as the load comes back on than does one larger engine. Also, being diesel electric, QE2's engines are running at a faster speed than if they directly coupled to the propeller like a single large engine would be, so this fact also contributes to the 'quicker' ability to re-deliver power, and thus maintain speed.

Anyway, must off to bed. Cheers

Skilly

[highlander0108]

Bulbous bows.....here we go!  QE2 has the beginnings of one, but no where near any resemblance to the appendages on QM2 or QV/QE.  They are designed to "trick" the water into making the ship a bit longer, which in theory alone would increase hull speed. (another discussion here) They reduce the bow wave created, which means less energy is used to propel the ship.  Unfortunately, they do have some tradeoffs.  In heavy seas, the added area upfront can "slap" the water as the ship rises out of the water and then back down, sending shudders throughout the ship.  QE2, on the other hand, pretty much just sliced through the water with her very minimal bulbous frontal area.  The larger the appendage, the greater the chance of bow slap.  This was a major concern on the QM2 when Stephen Payne decided to lengthen the bulbous bow to increase hull speed to meet the design parameters.  To minimize the effects while in seas, the ship must slow down, not something you would want to do say if you had a schedule to meet.   

I believe that shuddering had been experienced on QV on her transatlantics with heavy seas.  I felt this firsthand while on the Costa Magica in heavy swells on our trip to Bermuda from our cabin way up front and down low in the ship.  The noise and shuddering felt were not welcome at all.  In fact, it was downright disconcerting, at times we wondered if we hit something.  Contrast that with our rather silky smooth ride through the heavy seas on QE2 on our tandem transatlantic with QV. 

Ken

[skilly56]

OK - bulbous bows! I will have to try hard to prevent this getting too technical, but here goes

In 2000 I spent some weeks at the Aust Maritime College testing facility in Launceston, Tasmania. I had a full-bodied bulk carrier that was really chewing through the fuel, plus, it had some very undesirable wave-making abilities (ie, it produces a very big bow wave, which generates much wash on the shore, plus gives little boat owners a big fright when they don't realise what is coming.)

So, I had a 2 metre long model of the hull lofted from the ship's lines plans, and we had a supercomputer doing 94 computational fluid dynamics options on the bulb sizes and shapes that should be tested. Much info was obtained before the 2 trial bulb sizes were determined. One statement below (Para 8.) could be directly related to why the QE2 does NOT have a large bulb - those Scottish naval architects knew what they were doing:-

Aspects of Bulb Design (Pp 208, Col 2, para 2 & 3)

7.   “In the preceding sections it has been shown that a well-dimensioned bulbous bow improves the performance of a ship in many ways by smoothing the flow around the forebody and by reducing wave-making resistance.”  

8.   “In general it may be stated that a hydrodynamically good main hull with low wave making does not need a bulbous bow in any case. (This would appear to be applicable to QE2)

                 But ships with pronounced bad wave making should always be fitted with a bulb. For ships already built, an additive bulb will in general be the best solution, while for a new design, an implicit bulb might be an advantage”.

This last statement refers almost directly to the ship I was having problems with (also a well-built Scottish-born vessel, and at 30 years old, has now carried over 7 million tons of bulk cement and is still going strong.)

When a vessel's forward-facing bow plating pushes into the seas due to the forward motion of the ship, it creates huge resistance on that plating while pushing the water out around the ship's bow. So much so that the seas actually ride up the plating (forming the bow wave) before falling away to the side.

By fitting a correctly shaped bulb (and they are all different shapes, depending the the beam-to-draft ratio of the particular ship, it's speed, it's beam, etc) the bulb can actually create a 'depression' in the water flow. If the bulb is sized correctly, then that 'depression' in the water flow will coincide with the the forward-facing area of the bow plating where the area of maximum resistance to flow is normally experienced, and will reduce the bow wave to almost nothing. This can result in up to a 7% reduction in fuel consumption, or an increase in speed for the same consumption, if it is designed correctly.

However, a bulb only works well over a very limited speed range, and it ONLY works when FULLY submerged. When not submerged, it actually INCREASES the fuel consumption! (Think of all those ships you see steaming around with their bulbs sticking out, and how much excess fuel they are burning!!)

The bulbs trialled on the previously-mentioned bulk carrier worked very well (the larger one worked better) and showed fuel savings of 7+%, but ONLY over 13 knots - below that speed it actually created a fuel penalty.
Everybody was happy with this result, then I told them I wanted the trials repeated with the ship in the ballast condition (as this ship only carries bulk cement, it is in ballast for 50% of it's travels). The resulting trials showed the large bulb gave a 23-27% INCREASE in fuel consumption when not submerged (which it wouldn't be when the ship was in ballast). Project instantly cancelled, and the bulb was never fitted!!!
So, those naval architects at Robb Caledon Shipyard in Dundee really knew what they were about, and had designed the best bow and hull shape for ALL conditions.

Incidently, the inside of a bulb is normally part of the forepeak ballast tank, so is often full of water. Come survey time, it is often only the skinniest people who can wriggle inside it to carry out a structural inspection, so the bigger the bulb, the happier people will be.


I have all the test photos somewhere in my files and will post a couple of the better ones.

Incidently, if you ever want to have everyone staring at you in Launceston, Melbourne, and Auckland airports, try walking around with a 7-foot long, bright yellow ship's hull standing upright in the trolley in front of you!

Cheers

Skilly

[Twynkle]

This is such a good Topic
Thank you everyone!
Skilly56 - It's really interesting stuff!
This probably sounds really stupid - but worth a try!
Given certain conditions as you mention above,
could be a need for a retractable bulb?
Or even a 'changing-shape' one?

QE2's bow
https://www.flickr.com/photos/watch_keeper/4188042709/
In Queen Elizabeth 2: The Authorised Story
Potter and Frost 1969: Harrap.


Does anyone know whether the shape of QE2's bulbous bow
was 'modified' at any time?
Is there a difference that you can see between this photo and the black and white one above?
https://www.theqe2story.com/forum/index.php/topic,872.0.html - Top post
Maybe it's just the angles... or my getting-older eyes!!

[highlander0108]

Thanks Skilly for the excellent write-up and first hand experience with a bulbous bow.  At least the designers of current cruise ships do not have to deal with ballast conditions like bulk carriers need to.  I did see QV's appendage clear out of the water on several occasions.

[skilly56]

Ok, I said I would find those elusive photos, so here are a few of them to help explain 'flat bottoms' and 'big bulbs'.
It must be remembered that with a deadweight (combined weight of pax, stores, baggage, caviar, bubbly, bunkers, lubricants, etc, etc) of only around 11,500 tons, QE2's draft did not change very much in relation to her displacement, so the small bulb that she has would always be submerged, and thus was always effective.

The attached photos are of a hull that has a large variation in immersion up fwd between loaded & ballast condition. The broadness of the trial bulbs was dictated by the wide beam-to-draft ratio. If this hull had a deeper draft, the bulbs would have been more 'tubular'-so-to-speak.

1.  Shows hull (definitely flat-bottomed) being fitted with strain gauges on setup table.
2.  Shows the two variations of bulb to be tested.
3.  Side elevation of the bulbs.

[skilly56]

Further to the above:-
4.  Shows hull being ballasted to correct (scale) loaded draft in the wet dock before the 65 test runs begin.
5.  Shows hull at scale speed of 14 knots in the test tank.

The electronic telemetry on the strain gauges delivers an incredible amount of data - right down to exactly how many shaft horsepower are required to push the hull at each speed.

6.  Had to get the RNZAF to send an Orion to get this last photo yesterday (well, maybe not, but it shows what the weather is like here today).

The large bow wave and wake pattern are typical of a full-bodied hull with no bulb – although only doing 14 knots, the bow wave is almost pronounced enough for a vessel twice the size of the one shown, and doing twice that speed.
A good hull with a smaller relative-sized bulb fitted could be doing 28 knots with a lot less wave resistance than this hull – eg, QE2.
Hope you all have a Merry Xmas
Cheers
Skilly

[highlander0108]

Merry Christmas Skilly and thanks for finding the pictures.  That is one serious bow wave!

One other thing to point out in the QV photo I posted....you can see the water dumping out of the bow thruster cavities.  There were times when I could actually see daylight right through the ship as the bow came completely out of the water.  I bet the ship was shuttering and banging alot.  QE2's ride was silky smooth through the same seas...plenty of movement, but SMOOTH!  I read somewhere that they decided not to provide doors, ala QE2/QM2, since the cruising speeds were not high enough to justify the expense and complexity.  Skilly, do you know at what hull speed it makes sense to fit doors on the thrusters to reduce drag?

Ken

[Matt]

Thankyou everyone for all this great information! I feel quite knowledgeable now!

Regards,
Matt