1. Welcome to Encyclopedia Titanica
    or subscribe for unlimited access to ET! You can also login with , or !
    Dismiss Notice

Rudder

Discussion in 'Technical Construction Design' started by Mark Chirnside, Feb 2, 2001.

Tags:
  1. 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…

    Best regards,

    Mark.
     
    Tags:
  2. Erik Wood

    Erik Wood Member

    Mark,

    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.

    Erik
     
  3. Mark,

    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.

    Parks
     
  4. 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.

    Parks
     
  5. Paul Rogers

    Paul Rogers Member

    Parks,

    Really interesting stuff, this. Thanks for taking the time to post it. As many people believe that T's rudder was too small, (largely thanks to Cameron's film), perhaps your posting should be copied to the FAQ thread?

    Regards,
    Paul.
     
  6. A tip o' the slide rule to Parks. His work should be the definitive answer to questions about the size of rudders on Olympic class ships. Of particular interest is his second-last paragraph regarding the loss of efficiency in a wider rudder.

    --David G. Brown
     
  7. Eric, Parks, Paul and David,

    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…

    Best regards,

    Mark.
     
  8. Erik Wood

    Erik Wood Member

    Good Job Parks!!

    I thought that I had it right. You just threw all the right mumbo jumbo in there. You are a great researcher.

    Erik
     
  9. Nigel Hampson

    Nigel Hampson Member

    Hello everyone,
    I am new here, but I thought I would add my humble POV to this discussion.

    If someone has touched on this above then I apologise for going over it again, although I haven't noticed anyone mentioning it.

    For a ships rudder to be most effective, it must be directly behind the wash of the propellor. This is one of the problems that faces Paddle steamers - no prop wash, they usually have a second rudder up near the bow somewhere.

    When the Olympic class were built, they were designed with a low pressure turbine to power the centre screw - the screw directly in front of the rudder. But they were constructed in such a way that this turbine was not capable of running astern. When the Bridge rang down on the telegraph for full astern, the centre screw would simply stop, this is shown to good effect in Camerons movie. With no prop wash over the rudder, it's effectiveness was cut by some 40% - as trials with Olympic later showed.

    You could have a huge rudder on a ship, but put it in the wrong place - ie not in the prop wash, and it's effectiveness will be very limited indeed.
    Nigel Hampson
    RNR
     
  10. Cal Haines

    Cal Haines Member

    Hi Nigel,

    Welcome aboard! No need to apologize, we're always happy to have another set of hands on the oars!

    Have a look at the Reversing Engines discussion, further down in this section. You will find a lengthy discussion of the engine orders.

    I'm curious about the Olympic trials that you mention. Could you provide some additional details?

    Warm Regards,

    Cal
     
  11. Sam Brannigan

    Sam Brannigan Member

    Hi all!

    Just how powerful was the steering engine on the Olympic and Titanic. Is there any record of how it performed under emergency conditions during trials?

    Sam
     
  12. Sam,

    This may be of interest, but Britannic's steering gear failed after brief movement when the ship was listng by some twenty degrees. They used the propellers to turn her.
    _________________________________________________
    Nigel,

    Thanks for your post. I am also curious like Cal about the trials, could you tell us the source as well? Thanks.

    Best regards,

    Mark.
     
  13. Senan Molony

    Senan Molony Member

    As Parks said:
    "So, was Titanic’s rudder big enough?"

    I dunno, because I have techie-difficulties, but I did notice today a piece in the Waterford News of June 1912 saying that the Titanic's steering gear could have played a role in the disaster because "American marine engineers are nearly universally of the view that the Titanic's rudder was too small"...

    This is surely the earliest ever airing of this familiar chestnut... wherever the truth might lie.

    The Waterford News piece, which was only a few pars, then went on to report that British warships of the same tonnage as large passenger vessels routinely had rudders *twice* the size of their civilian counterparts.

    The argument was that warships naturally needed greater manouevrability in a tight spot. The corollary, of course, is that passenger liners would be less manouevrable.

    As I say, I have no idea whether rudder size played any significant role in the impact - obviously speed was the prime culprit - but it was very interesting to see the rudder question raised as early as June 1912.

    I came across it when looking for something else, a little theory Hermann Soeldner and I are working on, but I can dig it out again and post it if it's of galvanising interest to anyone.
     
  14. Funny thing about subject matter experts, like those "American marine engineers"...where were they before the fact? It was accepted practice then, as it is today, that maneuverability is more crucial for warships than it is for merchants. Shipping line owners, and this would include the White Star Line, only pay for what they have to.

    I'd wager that the crew of the U-103 had wished that Olympic's rudder could have been smaller still.

    Parks
     
  15. Speaking of that, Lusitania and Mauretania had bigger rudders and more advanced hull forms, and they were built to Admiralty specifications.

    However, I've read that their hulls had a hidden defect, costing Cunard thousands of pounds of extra fuel consumption over the years and robbing one knot off the ship's speed. It was in the article in 'The Great Ocean Liners.' Can anybody elaborate?

    Best regards,

    Mark.
     
  16. Mark,

    I'm not aware that Lusitania's rudder was significantly larger than Olympic's, in surface area below the waterline. Olympic used an unbalanced design, while Lusitania used a semi-balanced rudder. That means that Olympic had more rudder up the stock, while Lusitania had more rudder before the stock. Just eyeballing the plans, it looks to me that Lusitania's rudder is slightly larger, but Olympic has the advantage of having a screw directly in front of her rudder. As Bill Sauder would explain, the Admiralty was concerned primarily with Lusitania having the entire rudder surface under the water, so that it would not be vulnerable to gunfire.

    Eric Sauder explains in his book how the "deadwood" was cut away in Lusitania's keel to enhance her turning characteristics, but I haven't heard of any hidden defects. If there was a defect, it didn't keep Mauretania from surpassing 30 knots later in her life.

    Parks
     
  17. Parks,

    I was unclear before, I meant to indicate that her rudder was deeper and as all was below the waterline it seemed to me that it was larger. Then again, as you point out Olympic had a centre screw behind her rudder to help it.

    I found it hard to believe the 'hidden defect' information in this article, as the Admiralty assisted with the hull, but then we know what rumours there are on popular historical subjects!

    Best regards,

    Mark.
     
  18. Debate topic:
    Think about the logic of this question.

    Was it large enough for what?

    Since ship was not designed with dodging icebergs
    in mind, that can't be the reason why the question is asked.
    So what else is there?
     
  19. If memory serves, the concern was that the Titanic's rudder was too small for the job and in some way, may have contributed to the ship's demise. For a lot of reasons, I have difficulty buying into that one. I've seen Fr. Brown's photos of the ship doing turns and the tightness of these turns suggests to me that the ship may have been a lot more nimble then generally believed.

    Still, you might as well read up on what people more competant then I am in such matters have to say about this. Go to Was the Titanic’s Rudder Large Enough?
    by Capt. Charles B. Weeks Jr.

    This one requires an Adobe Acrobat reader.

    Also, go to the Cunard-Star Research Forum and click on "Sparks’s Titanic FAQs". When you get there, click on Page 7.
     
  20. That's what I mean, saying it was "too small for the job".
    Capt. Weeks has a brilliant paper there, but my whole point is even asking the question in the first place.
    It kind of falls in with the "inferior steel" lark (see the great FAQ by Parks).
    That some have doubt that Titanic was a worthy sea going vessel just because she couldn't get out of the way of the iceberg in time or that if she was "stronger" that she would have stayed afloat, like I said she wasn't designed for that.
    The ship was desinged with three things in mind, luxury, comfort and safety... but in that order of priority!
    That we go so much into what if's and if onlys with construction, most do it with a present day state of mind and not really considering the mind set of 1912 or the operating human element.
    I'm just ranting but my point is that asking those questions (and I'm not saying don't) sort of labels the people with a shroud of stupidity when it was really ignorance.
    The ship was fine for what she was designed for, the people in charge however are really the ones to blame.
     
Loading...