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quote:Originally posted by LeBarryboat:...Her superstructure alone didn't make her top heavy, but the materials put into that superstructure had something to do with it...
Huh?
quote:Originally posted by joe at travelpage:Huh?
Even today not everything can be considered in the calculations/plans (-> air conditioning of Disney ships...) not to talk about some decades ago. - another prominent example is the Canberra, where the ceeling of a public room had to be removed after the sea trials, as the ship turned out to be too heavy - Of course the hull of Queen Mary had a higher centre of gravity, and her superstructure was much, much heavier than on nowadays ships. I do not know, wheter they did test examining her rolling (...and what woud they could learn from such "test"), but even if they did that, there was not that much "play" back then.
quote:Originally posted by Noordam:Does the QE2 roll?
All ships pitch and roll in a storm, but some more than others. The QE2 has very good sea keeping qualities - far better than the original QM.
It amazes me that the great Ocean Liners like the QM has so little superstructure compared to ALL modern ships. 80% of their cabins and public rooms are within the hull and do not sit on top of it.
One other note contributing to her stability is that the QM had significant machinery installation low in the ship, 24 Boiler, quadruple main machinery sets.. all of which is considerablely heaver than todays diesel installation found in the modern cruise ship.
just some thoughts.
Then when the QM was launched about 1/2 century latter........again the builders stated her size would reduce rolling (there werent even hand rails fixed to corridoors and such) didnt take long for Cunard to order those soon needed hand rails and more heavy furniture to be bolted down.Linerdan
quote:Originally posted by VDK:[...] I really don't think the QM was much different in her inherent stability than most ships of today, infact I would say she was probably a bit better. One other note contributing to her stability is that the QM had significant machinery installation low in the ship, 24 Boiler, quadruple main machinery sets.. all of which is considerablely heaver than todays diesel installation found in the modern cruise ship. just some thoughts.
The most dominant parameter for stability is the width - the uprighting torque scales with the third power of the width - which is why nowadays ships are so boxy: They are wider at a much longer fraction of their length (they are "boxy") than e.g. the Queen Mary.So modern ships are more stable not only because they are "lighter". (It`s actally a problem that the heavy cabins are in the superstructure today - compared to the hollow public rooms)Gernerally, the "retaring forces" of modern ships are higher (raked bows etc.), not only because they are higher etc, but one usually tries to stay below the resonance frequency of a system -> they try to increase the eigenfrequency of the ship, and nowadays "materials" allow that. This often causes on the other hand "modern ships" to be a "rougher ride", and there might be problems due to these high accelerations that might occur.
A ships stability depends both on its centre of gravity in relation to its centre of buoyancy and its righting lever which are all variables depending on how the ship is loaded.
The Metacentre is the intersection of vertical lines through the centres of buoyancy in an uprigt ship and a slightly inclined ship. The Metacentric height is the distance between the metacentre and the centre of gravity. - This is the GM and is what gives a righting lever, GZ when the ship is inclined.
The bottom line is that Queen Mary was no less stable than modern ships, she simply did not have stabilizers until later. We put the stabilizers out almost automatically on modern cruise ships as if someone fell over and they weren't out, the master could be negligible.
If you have been on a modern ship when the stabilizers were not working, and the ship was light (low on fuel and water and not ballasted properly) and the weather was from the quarter, you would soon see how a modern ship can roll.
For those of you that do no know, Gerry worked with Stephen Payne on the QM2 project. He was also involved in the QV/Arcadia, amongst other projects. So he knows a bit about ships!
quote:Originally posted by Gerry:[..]The bottom line is that Queen Mary was no less stable than modern ships, she simply did not have stabilizers until later. We put the stabilizers out almost automatically on modern cruise ships as if someone fell over and they weren't out, the master could be negligible.
I am not an expert, but isn`t the shape of the GM curve of nowadays ships different, due to the "stricter" criteria for the intergral over the roll angle? Of course ships roll less with active stabilizers, but isn`t it required today that under no circumstances the panic angle is reached? (I am not sure, but were such regulations already around when QM was built) What actually is the more dominant function of the stabilizers - increasing the uprighting momentum or damping?
quote:Originally posted by lasuvidaboy:...How much does hull design have to do with this issue? ...
To simplify a lot and all other parameters identical (width, draught, position of "B" center of buoyancy in upright position of the ship, no stabilizers or anti-roll keels and so on... a hull with more "squared" transversal section in its widest part (some hulls are even widder near their bottom than at the floating line) has a bigger uprighting moment than a hull with a more "rounded" transversal section... precisely because the position of the center of buoyancy will be now rather different between the two hulls as soon as the angle of rolling starts to grow.
quote:Originally posted by Ernst:...What actually is the more dominant function of the stabilizers - increasing the uprighting momentum or damping?
The dominant function is damping.
If the story of the QM rolling on her side after being hit by a wave during the war is true than I would submit she had very good righting arms and thus was a fairly stable ship.
quote:Originally posted by VDK:The bottom line is that all ships are going to roll. Some will roll more than others. But it should be understood that roll itselft is not a measure of stability. However the period of roll is an indicator as to whether as ship is stiff or tender and a tender ship will generally have a longer roll period and thus smaller righting arms and thus can be considered to be somewhat less stable. If the story of the QM rolling on her side after being hit by a wave during the war is true than I would submit she had very good righting arms and thus was a fairly stable ship.
The stability / uprighting momentum and roll motion ARE related to each other, as generally the resonance frequency / Eigenfrequency of an (harmonic) oscillator is defined as the square root of the restoring force or in this case torque per unit displacement (which would be the roll angle in this case) - so a higher uprighting torque per moment of inertia results in a higher roll frequency.
To analyse the stability of a ship it is not enough to require an uprighting torque for certain roll angles. (as I get the impression this it is what is usually done, and only "recent" regulations consider e.g. the integral of the "GM" curve over the roll angle) To investigate the stability of this oscillator, it is necessary to analys the Eigenvalue spectrum of the roll motion, and to examin wheter the resonances are damped sufficiently.
But I am only a physicist, having attended some shipbuilding lectures and read some books. Can anyone reccomend good literature on regulations / rules considering shipbuilding? (e.g. The Principles of Naval Architecture are very nice books explainig the basics, but I would like to know more about why things are done how they are done)
quote:Originally posted by OCEANSDEVINE:Thanks Ernst for your expertise. Very interested in the subject myself. A website I find much information called The Mother of all Maritime www.boat-links.com/boatlink.html Hope it's technical enough.
Thank You for the link! (...wil take some time to browse trough it...) The only thing on naval architecture I found on the Internet are the hand-outs of the MIT. (But we shouldn´t get to technical in this forum)
quote:Originally posted by Vaccaro:The dominant function is damping.
As I have seen in photos, Normandie's hull flared out below the waterline amidship. This design feature seems to be the reason for her lack of 'holding onto' a roll as QM1 did.
Once stabilizers are used all bets are off. Stabilizers do not work at <15 knots and have little effect of pitching.
quote:Originally posted by lasuvidaboy:As I have seen in photos, Normandie's hull flared out below the waterline amidship. This design feature seems to be the reason for her lack of 'holding onto' a roll as QM1 did.
Johan
quote:Originally posted by desirod7:It is called tumblehome. The SS United States has very pronounced tumblehome. The Loveboats do too. The Regal Empress does not. Those 3 ships have a lot of Sea motion.Once stabilizers are used all bets are off. Stabilizers do not work at <15 knots and have little effect of pitching.
Tumblehome is th "widening" near/at the water "line" (I know, it`s an area, not a line ) and not "below". Nearly all Fincantieri built ships have a it, and also the "boxy" Europa of 1981, but if (only if!) I remember right not the Normandie.
quote:Originally posted by Ernst:Tumblehome is th "widening" near/at the water "line" (I know, it`s an area, not a line ) and not "below". Nearly all Fincantieri built ships have a it, and also the "boxy" Europa of 1981, but if (only if!) I remember right not the Normandie.
The photos of Normandie I have seen shows a portion of her hull (amidships) below the waterline that flares out and curves under. It looks as if her hull is pressing outward due to extreme weight but it is the way that portion of the hull was designed. It is in addition to the tumblehome of her above water hull. I believe the author John Maxtone-Graham mentioned this design feature in one of his books.
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