Was the Titanic's Rudder Large Enough?
Titanic Research
There have been several times when the question has been raised about whether the Titanic’s rudder was large enough. It has been suggested that if the rudder had been larger she would have turned more quickly and thus missed the iceberg.
The usual way of determining the proper size of a rudder is to compare the area of the rudder to the longitudinal area of the ship’s hull on the centerline ( LBP x Draft).
On page; 207/208 in Modern Ships, La Dage says the “usual ratio for a cargo ship is about 0.015, while … a usual ratio for a tugboat would be about 0.03 or 0.04.” In Reed’s Naval Architecture on page 149, Stokoe says rudder area for fast ships should be 1/60th of hull area, and for slow ships 1/70th. In Ship Design and Construction the authors say “For merchant ships, the area of the rudder is usually about 2 percent of the product LT for ships 120m long and over”; L is length between perpendiculars and T is draft.
Titanic’s LBP was 850’ and her full load mean draft was 34.5’, so her longitudinal area on the centerline was 29,325ft2; this must be reduced by 455 ft2. This is the area of the cutaway forefoot (13ft high by 70 ft. long). Thus her effective hull area on the centerline is 28,870 ft2. Her rudder area ( using Simpson’s Rule) was 401.63ft2. Dividing through one gets a ratio of 0.014, compared to La Dage’s 0.015. Using Mr. Stokoe’s method, a rudder that was 1/60th of the hull area would be 481.75ft2 and 1/70th would be 412.43ft2 . Using the method in the SNAME book, a rudder that was 2% of the hull area would be 577.4 ft2 ;1.5% would be 433.1ft2
So Titanic’s rudder would be very slightly too small. In each case, the amount the rudder is too small is minor, so it probably didn’t influence the outcome significantly. Particularly when you take into account other activities like stopping or reversing the engines and lag time for the steering engine to put the rudder over.
References
La Dage, John H. Modern Ships 2nd Ed. Centerville, MD. Cornell Maritime Press, 1979.
Stokoe, E. A. Reed’s Naval Architecture for Marine Engineers 4th Ed. London: Thomas Reed, 1991.
Taggart, Robert Ship Design and Construction. New York: The Society of Naval Architects and Marine Engineers, 1980.
------------------------------------------------------
DISCUSSION:
Mark Chirnside
Just a chain of thought…
It has often been reported that the rudder of the ‘Olympic’ class was undersized, considering the size of the vessels.
Maritime Historian John Maxtone-Graham cites that the rudder design was twice in question: when Titanic failed to clear the iceberg, and during 1934 when Olympic rammed the Nantucket lightship.
However, to me this seems unfair: Titanic’s engines had at least been stopped at the time of the collision, if not been put astern, as some people think, and in any case the central propeller had surely slowed considerably, reducing the slipstream that ‘fed the rudder’s turning power.’
Olympic had been running at a reduced speed of ten knots when the Nantucket light vessel was spotted from the liner. Her helm was put hard over for a port turn, then the port engine was reversed to assist the turn, its starboard counterpart soon following. Captain Binks – a ‘splendid seaman’ by all accounts, who would ‘never take a risk’ unnecessarily, nearly sixty and due to retire at the end of December 1934 – estimated that by the time of the collision, Olympic’s speed had been as little as three knots; the engines had clearly been doing hard work, taking seven knots off the ship’s speed. It must be admitted that she had failed to miss the 133-foot light vessel (if my memory serves), so Olympic could not have turned more than one or two points. (One point is 11¼ degrees.) But the engines were working astern at the time, and although reversing the port engine first would have some turning effect, the slipstream that fed the rudder had certainly been severely reduced…
There is a comparison to be made as well… I am no expert on the Imperator, but this 909-foot-long vessel had a rudder of ninety tons, that, judging from photographs and the 16½-foot propellers, was about fourteen feet at its widest point. It was not below the waterline, as on the ‘Lusitanias,’ but partly above water underneath the counter stern. (Imperator’s sisters’ rudders were entirely below water, if memory serves.)
The ‘Olympic’ class’s rudder: ‘The total weight of the rudder is 101¼ tons, while its length over all is 78 feet eight inches and its width fifteen feet three inches. The diameter of the rudderstock is 23½ feet.’
Therefore – and I may be wrong on this – the rudder on the German liner was even smaller, yet the German vessel was larger. It would be interesting to know whether it was ever questioned that her rudder was undersized.
During Titanic’s trials, it was reported that Carruthers was impressed at her turning circle: at 20½ knots, her turning circle diameter was 3,850 feet while the ship moved 2,100 feet.
I would greatly appreciate and like to hear thoughts on the matter from the numerous experts out there…
--------------------------------------------
Erik Wood
You have delved into one of the many mysteries of maritime travel. It is my belief that width is more important then length when it comes to rudders. Mainly because if you turn the rudder hard over it is basically covering one entire propeller making the turn promptly. But that is just my thought on that.
While Titanic did miss the berg (as in not hitting it broadside or head to) she still hit. Part of the reason I believe is due to the speed change. As you stated rudders need free water to make them effective and while they will work with the gliding power of the ship it is preferred to not use it that way. There is much other debate on that but the key to your question is what do you think the key use of the rudder is other then turning?
The rudder needs to be small enough to be able to keep a steady course. The larger the rudder and the larger the ship the harder it will be to keep a steady course. When you turn the rudder slightly it will cover more of the screw space which will result in the ship turning further in one direction. You have more horsepower and bigger screws.
If the ship has a smaller rudder but is bigger it is to aid in it's ability to keep a straight course in open seas. The smaller the ship the bigger the rudder but the wider the props means the ship will turn promptly with more power but when free water is taken away then the ship will slow.
Forward momentum only works for so much. Twin screw ships can turn faster when they apply one of the engines to a stop or reverse mode while turning. As Mark pointed out above.
These are just some ramblings that don't make a lot of sense but those of you seafares out there you know what I tried to say and hopefully you can say it in a way that is better understood.
-------------------------------------------------
Parks Stephenson
I'm at work at the moment and do not have access to my library at home. However, I have at least two period Naval Architecture manuals for use by Royal Navy and Merchant Marine officers that describe the style of rudder as used in the Olympic class as one of the most common in use at that time. If I remember correctly, most of the capital ships in the Royal Navy used the same style rudder. Later tonight, after the kids have been put to bed, I will go through those texts and extract the relevent discussion for you. If not tonight, then hopefully sometime this weekend.
My impression after reading those sections is that there was nothing lacking in the design or size of Titanic's rudder, as viewed by expert opinion of that time. I think debate over the adequacy of the rudder stems from people trying to come up with new reasons why Titanic failed to avoid contact with the iceberg. Hindsight is not always 20/20, especially when one is not aware of the original reasons as to why that particular shape was selected for use.
---------
I read through the extracts on rudder shape of W.H. White’s Manual of Naval Architcture (London, 1900) and W.J. Lovett’s Class-Book of Naval Architecture (London, 1905) and compared those with the same section in Gillmer’s textbook on Naval Architecture (Annapolis, 1982) for any differences. Basically, here is what I found:
Where rudders are concerned, bigger is not always better. It’s true that the larger the rudder, the more surface area there is to generate hydrodynamic torque, but larger rudders also generate more drag and require more pressure from the steering engines to turn them effectively. British naval architects during the first part of the century appear to have preferred the unbalanced rudder, where the blade of the rudder is entirely aft of the stock. This places the centroid of pressure (CP) relatively far out on the blade, increasing the pressure required by the steering engines to move the rudder. The balanced rudder was known (one that places the CP on the stock by having a portion of the blade ahead of the stock), but the drag that design induces was considered too excessive for merchantile use. Other factors affecting a rudder’s design will be familiar to aviators...tip vortices (similar to cavitation), induced drag and stall. Another consideration is protection against grounding damage.
So what was the ideal design? To quote Lovett, "Even the highest authorities are at variance in respect to the best form of rudder." The White manual discusses four of the more common rudder shapes in use by the Royal Navy (one balanced, three unbalanced) and weighs the pros and cons of each, comparative to the hull to which they are normally attached. For the rudder shaped like Titanic’s, White mentions that it is "a form now commonly used in the steamships of the Royal Navy," and that one major advantage of its shape is that "by tapering the rudder, the power required to put the helm over is made considerably less...in screw steamers where the rudder is placed abaft the screws...then the form [of the rudder here under discussion] is to be preferred." The rudder shape accepted by the H&W architects therefore appears to be a compromise (as most rudder designs are) between weight and surface area, while taking advantage of the position of the centre screw and providing protection against potential grounding.
So, was Titanic’s rudder big enough? White states that "for steamships...the extreme breadth of the rudder [is often] from one-fortieth to one-sixtieth of the length...in merchant ships much smaller rudders are used, and values as low as one-hundredth have been met with". Without running a model in a tow tank, I can only judge by dimension and compare to White’s stated guidelines. Titanic was 850’ long along the waterline, her rudder was about 15’ wide at the fullest part of the blade. That’s makes it about one-fiftyseventh of the length and therefore follows White’s rule of thumb.
Would a Titanic II have a differently-shaped rudder? According to Popular Mechanics, it will be. However, the shape of an enlarged rudder not only requires more powerful steering engines, but also introduces the risk of stalling the rudder at extreme rudder angles. Again, going back to White, he cautions that (in a given example) a "broad rudder, with an area 37 per cent. greater than the narrow one, has therefore less turning effect by about 11 per cent."
There’s no set standard for determining what the optimal shape for a rudder for Titanic ought to have been. Oftentimes, rudder shapes are determined by copying a shape that worked well for another ship of similar dimensions (I kid you not). But, given the methodology laid out in the contemporary Naval Architecture books, it appears that Titanic’s rudder was of adequate design to effectively maneuver the ship. Comparing that design to rules laid out in the more modern textbook, I see no glaring deficiencies, especially considering the capability of the three-crank steam-driven steering engines.
------------------------------------------------------
Mark Chirnside
Sorry for this short post, I’ve had trouble with my computer recently, damaging by authorial progresses with editing of the manuscript…The noise in this place doesn’t help.
Then the rudder was not undersized, contrary to popular belief. One thing that I had not really thought about would be that a larger rudder could make it harder to steer a straight course. And that a broader rudder could actually reduce turning effect is also a serious design consideration.
Your thoughts Eric that a rudder could cover nearly a whole propeller got me thinking about a photo I had seen of Aquitania; her rudder is hard over, covering three-quarters of her propeller. In fact, her two middle propellers are very close to each other. This certainly aids manoeuvring. Aquitania was partly built to Admiralty specifications like her two ‘near sisters.’ All vessels had semi-balanced rudders, possible because of their quadruple screws rather than the triple-screw design of the ‘Olympics.’ I hope this sounds coherent. A loud hammering is continuing from next door and so I am having trouble thinking straight.
Then again, a thought about those vessels is that because they were propelled by turbines, these are slower to reverse and therefore they cannot do emergency stops as well. But, on the other hand, there are other advantages…
------------------------------------------------------
Six Seconds to Disaster - the Death of Titanic
Titanic Research
by Jim CurrieSome have concentrated on the engineering aspects of the ship... her engines, boilers and auxiliary machinery. Some find fascination in the lives of the people who were on board her on that fateful maiden voyage to New York. Yet others are interested in the aesthetics... her basic design, furnishings and fittings etc. As a result of all the digging and delving, there is now a huge database covering every single aspect of Titanic. Without doubt, all this information will be put to good use, resulting in a plethora of books, pamphlets, articles and short stories. All of these, scheduled to see the light of day at or near April 14, 2012... the centenary of that dreadful moment when the great ship struck an iceberg in the cold North Atlantic Ocean and plunged over 2000 fathoms down to where she now lies.
I am not about to produce a book or try and emulate all those clever people who have spent years minutely examining the circumstances surrounding the disaster and writing books about it. By April, 2012, there will be enough Titanic books to build a staircase to the moon thus avoiding the huge expense of using a rocket!
I am a relatively latecomer to this arena so have a very narrow field of interest in the subject.
I first joined this excellent web-site a couple of years ago and was astounded at the wealth of information contained within its pages. I was a struck by the depth of knowledge by many of the contributors. However, one particular part of the story fascinated me.
As a professional mariner and Marine Accident Investigator, I was irresistibly drawn to the detailed information available concerning the few minutes before Titanic began her death throes.
Like most people, I had sat through the movies and television programmes covering the accident. While these were excellent in their construction and production, I could not but chuckle at the artistic licence taken by those who marketed such entertainment.
The most glaring error concerned the time interval between the moment the iceberg was sighted by the lookouts Fleet and Lee and the moment the ice penetrated Titanic’s hull below the water line.
In various film versions of the accident, the officers on Titanic’s bridge could have sent out for pizzas while waiting for the crunch to come. That is understandable; such films were made to entertain... not educate.
Almost every paper and article I read concerning the final moments before Titanic’s original course was altered, caused me to doubt what I was reading. With few exceptions, they promoted a 37 seconds period to turn the ship 2 points... 22½ degrees to the left of her original course...the period from the time of the three bell lookout warning to the moment of impact.
Such a conclusion in itself is unremarkable but when that same 37 second interval of time is used to support other theories then a closer examination is necessary. One such theory connects the use of a second emergency helm order to the positions of the Leyland Liner SS Californian and that of the sinking Titanic.
The most important part of the period between the lookouts warning and the moment of impact is the part starting with the first helm order. Specifically, the moment the ship’s head started to turn left. I firmly believe that the time taken for this to happen did not exceed 6 seconds. Consequently there was no time to give or execute a successful hard-a-port helm order. But let’s be fair and have a look at the evidence for the 37-second duration.
The 37-second time to turn before Titanic hit the iceberg was based on evidence given by Robert Hitchens, the Quartermaster who was steering Titanic at the time.
Hitchens informed the US Inquiry that the ship’s head had altered 2 points to the left between the time he was given the emergency turn order and the moment the ship hit the ice. Since Titanic was at the bottom of the ocean, there was only one way to find out just how long it would take for Titanic’s bow to turn 2 points; by simulating the turn using Titanic’s sister ship Olympic.
The simulation showed that a 2 point emergency turn would take 37 seconds to complete. And so the 37 seconds myth was born.
This test could not be an exact replica of the events that night. Never-the-less, it supported the theory thatFirst Officer Murdoch’s initial hard-a-starboard helm order was immediately followed by an order to turn the ship the other way... hard-a-port. Let us consider the evidence put forward to support a second helm order!
Quartermaster Frank Olliver told the US Inquiry that he distinctly heard First Officer Murdoch give a second helm order to turn the ship to the right
Able Seaman George Scarrott said that when he saw the offending iceberg, it was out from the starboard side of the ship and agreed that this indicated that she was swinging away from it thus the ship was turning rapidly to the right.
A passenger stated that the iceberg was about 50 feet off the starboard side of Titanic confirming Scarrott’s observation
Conversely, Quartermaster George Rowe who was located at the ship’s stern told his questioners that the offending iceberg was 8 to 10 feet off the ship’s side. But when it passed his position, it was so close, he could almost touch it. If Titanic ’passed’ the iceberg, she did not swing away from it, as would be the case with a hard-a-port helm order given in sufficient time.
So how to treat these bits of conflicting evidence?
The evidence of Joseph Scarrott and that of the passenger points to the stern of Titanic swinging away from the iceberg as her bow turned rapidly to the right. But did the bow act in this way as the result of a helm order? Was there time to give a second emergency helm order?
There is no reason to disbelieve the evidence of Frank Olliver relative to the second helm order however there is enough hard evidence to state that such an order was not part of the iceberg avoidance manoeuvre. This being so, Titanic did not turn to the northward. Subsequently, the moving ship seen on her port bow in the early hours of April 15 was not and could not have been the SS Californian. So how to go about proving it?
Let us first look at the time to turn 2 points to port and the experiment to prove it.
The experiment made on the Olympic was fatally flawed. Simply because it was made by conducting an emergency left turn at speed without considering any other contributing factors. On the other hand, theTitanic emergency turn was not simple but extremely complicated. Olympic did not have the added problem of a very big chunk of ice virtually pushing on her starboard bow. Additionally, although the Olympic’s bow took 37 seconds to turn 2 points, Titanic’s bow did it in about 6 seconds!
The Six Second Turn
Titanic was steering a course of 265 True. Barring accidents or emergencies, she would maintain that course until she got close to her destination. As we know, a dire emergency in the form of an iceberg caused her First Officer William Murdoch to shout to the helmsman to put the rudder hard over to the left... hard-a-starboard!
Quartermaster Hitchens, the man steering the ship, immediately obeyed this order and spun the steering wheel over to the left as far as it would go. He had barely got the wheel over to it’s maximum when the ship hit the iceberg.
By experiment, it takes 4 to 6 seconds to turn a ship’s steering wheel hard over from the mid-ship neutral position. It follows that Titanic had changed from her normal course for a mere 6 seconds when she hit the iceberg... not 37 seconds!
Hard-a-Port
Now that we know that Titanic had changed direction for 6 seconds before she hit the iceberg, was there time for an effective reverse helm order to be given? The physical evidence of Able Seaman Scarrott and the passenger suggest that such an order was given. How else could the iceberg be 50 feet off the ship’s starboard side?
Let’s examine the possibilities.
The ship’s speed was close to 36 feet per second and we know from other evidence that she was damaged from just before the Forepeak bulkhead to a point just aft of the watertight bulkhead in boiler room 5... a distance of about 206 feet. This meant that the iceberg was in contact with Titanic for close to 6 seconds. Five (5) seconds after that the iceberg would be mid-ship. Ten, Seconds (10) later, it would pass very close to Quartermaster Rowe. So how was it that Scarrott and the passenger saw the berg clear of the ship’s side? I suggest the answer lies with the complicated physics involved when a very large ship travelling at speed, brushes against an immoveable object.
If we consider the iceberg in a pushing role...rather like a tug pushing on her bow then we might just have an answer to the mystery,
If, when a ship is turning, a tug pushes on the bow opposite to the direction of turn, the ship tends to turn back towards the tug doing the pushing. If the pushing effort is removed, the ship resumes her original direction of turn. It is all to do with an imaginary point on a ship called the ‘pivot point‘...the point about which a ship turns...much like the fulcrum of a sea-saw. Until recently, people thought that the pivot point was fairly fixed depending on whether the ship was going ahead or astern. Turns out, this is not the case. In fact, in certain circumstances, it actually changes position fairly quickly. The following rough sketch substituting Titanic’s iceberg for a tug might explain it better. The black arrows represent the sideways-pushing currents generated.
At C, the bow moves into clear water. As more of it moves ahead of the pushing point, the bow swings to starboard and the stern moves to port.
At D, the contact with the ice is lost... no more relative push and the bow resumes it’s turn to port and the iceberg closes with the ship’s side. However, the beam of the ship reduces toward the stern so the ice passes clear... just!
The foregoing is one explanation as to why Titanic seemed to be turning under a hard right helm order given immediately after the initial hard-left one. But was there time to give such a second order? More important... was there time to observe the effects of it?
Earlier I explained that it took a maximum of six (6) seconds to apply full left or right rudder from the mid-ship position. Titanic’s rudder was hard left when she hit the iceberg. If, at that moment, Murdoch had ordered a hard right application, it would have taken about 3 seconds to return the wheel to mid-ship then six seconds to spin it hard over the other way. A total of nine seconds! In that time, Titanic would have moved on another 324 feet and the berg would be just over 300 feet from the stern. Five or six seconds later, it would pass Quarter Master Rowe. All of these estimates depend on Mr. Murdoch giving instant orders... without a second’s delay in his decision making. While this is possible, it is just not practical! Apart from the time factor, the rudder was acting in disturbed water and the ship speed was dropping rapidly. A second helm order would not have been effective enough.
Summary
There is no doubt that a second helm order was given. However, the physical evidence discounts the possibility of it having been given as part of an emergency iceberg avoidance manoeuvre. Consequently, it is highly unlikely that Titanic was deliberately turned toward the north.
As to that second helm order:
According to the transcript of the US Inquiry, Quartermaster Olliver stated that the second helm order was given when the iceberg was ‘away up stern'. According to the same transcript, part of his duties was to attend to ‘the lights in the standing compass’.
In fact, I believe that Olliver was indicating that the berg was away astern and that he was attending to the Standard Compass. The terminology used in the transcript is totally inaccurate!
There is a perfectly reasonable explanation for the second helm order.
When it is a captain’s intention to put people in lifeboats, he will stop his ship and point her in the most favourable direction before doing so. He will take into consideration the prevailing conditions of wind and weather. Captain Smith had ideal conditions; he could point his ship in any direction. However, he would not do this or consider putting people in boats until it was absolutely necessary to do so. There was only one other reason why... after he had taken the way off his ship... he would start his engines once more and at the same time give a helm order. That would be while he still had hopes of resuming the voyage. In that event, it would be while he waited for departmental reports, he would turn his ship back to her original heading and be ready to carry on. To do this, he would order a brief half-ahead on his engine and if Titanicwas pointing south; hard-a- port the helm. As soon as the ship‘s head started turning he would order stop engines and then steady the ship‘s head on her former course. At that time, the iceberg would be somewhere off the ship’s starboard quarter. This would be about ten minutes to quarter of an hour after impact. Shortly after that, Boxhall’s mystery ship was approaching Titanic from a westerly direction. It was not, nor could it have been the SS Californian.
No comments:
Post a Comment