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    Given the interest sometimes shown on this forum for piano wire, the following might be of interest.

    I have an interesting book "Memoirs of a Marine Troubleshooter" by G. C. Volcy (available from The Institute of Marine Engineers). The author was a marine engineer and spent his life investigating vibration and associated problems on ships and he explains how he used piano wire as one of his essential on-board tools.

    Mr Volcy worked for the French classification society Bureau Veritas and used the latest electronic aids in his work, including the world’s most powerful computers at the time. However at times he also used piano wire and feeler gauges in preference to laser, hence the nickname "The Volcy Laser" given to his piano wire by the IHI Company in Japan in the 1970's.

    The book gets too technical for me in places, but it has a series of interesting accounts of diagnosis and repair of propulsion machinery.

    The story begins in the 1960's when shipbuilding entered a revolutionary period extending up to the present day - a time when ship and engine sizes increased hugely. In 1961 the first “super tanker" was built (The Tina Onasis, 50,000 tdw), much larger than any existing vessel. Within 3 years size had doubled to 100,000 tdw and within 7 years (1968) a six-fold increase to 326,585 tdw. There were not only huge tankers, but fast container ships and very large methane carriers. The closing of the Suez Canal in 1967 prompted the need for very large tankers able to travel around longer routes.

    The author developed new ways of dealing with the vibration problems which beset ships as they grew in size; however it is the engine and shafting problems which I will mention here.

    Welded construction (previously rivets), combined with improved methods of calculation (e.g. a bit later computers allowing use of Finite Element Method calculations) led to reduction of steel work required in the ships. Ships became more flexible as their size increased, yet their engines became more powerful requiring stiffer line shafts going to the propeller.

    The basic problem was that inflexible shafting was incompatible with flexible hulls.

    Stiffness of line shafting (for the same span between bearings) is exponential to the diameter by the power of four - so doubling the shaft diameter makes it 16 times stiffer.

    Meanwhile the double bottoms of ships had increased in length. As a ship is loaded the hull is subjected to increasing water pressure as the draft increases - the deforming of the engine room floors is a function of the length of the floors to the fourth power, so doubling the floor length results in a 16-fold increase in deformation.

    The result was all sorts of engine and shafting problems, evident as soon as these large ships went to sea - severe vibrations, diesel engines with crankshaft main bearing problems, crankshaft breakages, stern tube and shaft bearing wear, and in the 1960's and 1970's when most of the large tankers were steam turbine powered (up to 60,000 hp per shaft), they had very serious problems with reduction gearing. There was wear and pitting on the reduction gear teeth, even broken teeth and gear wheel rims - this was happening on ships all around the world and was costing millions of dollars. The massive gearing on a steam turbine is designed to last a long time - in some cases it was being damaged immediately after entering service causing desperation amongst the industry.

    The first problem was how to fix existing ships - it was not possible to stiffen machinery foundations on these ships, this would have been far too difficult and expensive. Bureau Veritas began to investigate, and Mr Volcy was their specialist in vibration and interaction problems.

    The problems seemed to all stem from the line shafting. Volcy measured vibrations in shafts, bearings, crankcases etc to build up a picture which convinced him that some bearings were running without load (hence allowing vibration), others were overloaded and failing. (He also used a simple feeler gauge when stopped to detect bearings which were not loaded).

    There was nothing obvious, for example it was sometimes the 2nd to last main crankshaft bearing that was failing on the first ships he investigated (yet the last main bearings showed no wear at all). The huge weight of propellers caused the tailshaft to bend, the massive flywheels fitted to some diesels caused crankshaft bend, thrust bearings moved on their mountings to add yet more bending. Bedplates were flexing as the ship loading changed - it seemed like an impossible mess.

    In some cases intermediate shaft bearings were removed so as to increase shaft flexibility, but more interestingly, Volcy introduced a radical concept of rational curved alignment for shafts. Instead of using classical 'straight-aligned' shafting, software was developed that allowed on-board shafting to be 'curved', while still not exceeding allowable pressures on bearing shells. This included not just the line shafting but the crankshaft as well - sagging pre-deformation was applied.

    Mr Volcy re-tells his first attempts to put his ideas into practise - they were greeted with shock and great distrust by many (ship owners, ship builders, marine engineers), but the situation was so desperate he was able to try out his theories. This took great courage on his part, and he is quick to say he was backed by Bureau Veritas (although his new ideas fell outside their standards of alignment!) and he was supported by some key people.

    The first ship he worked on was vibrating so badly binoculars couldn't be used on the bridge, it was destroying main bearings and stern tube bearings in short order. Vibration was so bad the flooring and double bottom below the engine and shafting showed deformation and cracking. The three intermediate bearings for the line shaft showed no wear on their lower halves - the line shaft had been floating freely supported only by the stern tube bushing and the crankshaft.

    Volcy introduced a sagging pre-deformation of 0.6mm to this 8 cylinder diesel engine crankcase (with lightly loaded ship), this being worked out previously from measurements taken on board. By the way, Taylor Hobson optical devices were used by the ship yard for the crankshaft bearing alignment; however Volcy preferred a "gap and sag" technique when setting up the line shafting and couplings. The thrust bearing also needed chocking, so that when it tilted under full load it didn't influence the engine bearings (this being why the 2nd to last crankshaft bearing had been damaged).
    The result was a cured problem - the oil filters remained clear of white metal, vibration diminished and the engine could run at maximum revs, which it did for many more years after.

    The "Volcy Laser" nickname came about later when the author was asked to help IHI in Japan with some huge new tankers (the largest in the world at that time). These new ships had steam turbines which were showing very heavy contact, then wear, on the meshing teeth of the pinions and main wheel (0.5mm wear, and pitting).

    By attaching piano wire to the bulkheads, Volcy was able to measure the floor deformation while the ship was lightly loaded, fully loaded and under way. He found about 3mm deformation between the loaded and unloaded conditions.

    IHI would not accept these results, and repeated the tests using their laser equipment. They were attempting to measure the alignment of 3 bearings with their laser attached to bulkheads. Unfortunately, as the ship was being loaded, the bulkheads moved, and the laser lost its target. (Also the halo of the laser made precise measurements difficult). The Japanese engineers struggled for a long time, and eventually had to admit that the piano wire they had scoffed at was preferable for this sort of work. The shifting of the bulkheads had little effect on the piano wire.

    The upshot of this job was that Volcy recommended rational misaligning of the second reduction gearing and also rational aligning of the lineshaft - it gave good results, ending the wear on the gearing.

    Naturally ship and engine design changed as a result of these problems.

    Basically, a tail shaft (the portion of shafting carrying the prop) should be stiff, while intermediate shafts needed to be flexible so that hull deformation through loading conditions or sea swell doesn't influence the tail shaft, turbine gearing or diesel crankshaft.

    Engine design was changed as a result of these problems, box-type main engine frames evolved.

    Double bottom structures beneath the engine rooms were stiffened.

    The curved alignment of crankshafts was universally adopted.

    As regards vibration, Volcy says it was necessary to renounce the old-fashioned approach to ship vibrations based on hull girder vibrations and introduce the idea of forced vibration resonators an idea he took from electrical theory. Bureau Veritas built powerful vibrators (exciters) which could be fixed to parts of a ship, and vibrations induced and monitored. Quite a bit of the book deals with these vibration problems, how problems were solved, structures de-tuned etc.

    I don't fully understand what this book describes, but I hope I have managed to describe some of this story without too much error. As the president of IHI (Dr Shinto) said of Mr Volcy one day in the midst of those pioneering times - "you see, he's right. I've already told you that a ship is a morass!"

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    Very interesting. I expect the book will be over my head but I will look for it anyway.

    "Good" design which fails once scaled up seems a common theme in many fields.

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    Peter,

    Very interesting, thanks.

    Surprising that they’d been aiming for straight alignment of prop shafts. Established practice with steam turbine generators had long been to set bearing heights to accommodate the natural catenary of the rotors.

    The problems you mention seem to echo the problems encountered in the 19th century, both with engine vibration and shaft failure. Failure of crankshafts and main shafts seemed to have been a fact of life, especially with wrought iron shafts. Wise ship owners equipped their vessels with suitable spares and ‘Thomson Couplings’ for emergencies. Others relied on the ingenuity of the crew to carry out repairs using hand drills, hand rails, firebars, wire rope, sweat, etc. As far as vibration was concerned, something was developed with the snappy title the ‘Yarrow-Schlick-Tweedy system of balancing’. I’ve never troubled to look into it, but it attempted to address the interaction of the system as a whole – reciprocating engine, shaft, and hull.

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    Pretty neat to be the guy who can cut thru all the chaos and confusion with a simple and wildly effective approach. Nice post, Peter.

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    Great post, thanks for the time put into telling a good story.

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    Thank you for a very interesting post, Peter. I was a USN machinist mate in a previous lifetime, so this was right down my alley. Fascinating.

    Orrin

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    Great post. I just ordered a copy $58.00 from amazon uk.

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    Thanks for the comments, you guys did well to read that considering I didn't include any ad breaks, or prizes if you reached the end. I must learn to be more concise....

    Asquith,

    I have read a bit about the Yarrow-Schlick-Tweedy system over the years, but have only seen it in reference to the engines, not to the shaft or hull (but I am sure all was considered).

    One explanation I have is in "Power Of The Great Liners" by Denis Griffiths (an excellent book!!) He has an appendix describing the system.

    Quote:

    "Reciprocating engines caused vibration in the early steamers and the situation was most severe in triple expansion engines where three pistons of different weights set up large unbalanced forces and couples.

    Balancing of the masses would avoid or minimize these forces and couples, but that proved to be difficult with three cranks.

    A four crank arrangement, whether triple or quadruple expansion, allowed use of the Yarrow-Schlick-Tweedy system of balancing which eliminated all primary and secondary forces as well as the primary couples.

    It is not necessary to understand the detail of dynamic balancing to be able to appreciate its importance, the mathematics being rather involved.

    The Yarrow-Schlick-Tweedy system required a symmetrical arrangement of four cranks, but it was possible to divide the low pressure stage of a triple expansion engine between two equal smaller cylinders, thus giving four cranks. From aft the connections would be aft LP, IP, HP and forward LP.

    With a quadruple expansion engine the sequence from aft would be first IP, secon IP, LP and HP.

    Essentially the low masses were connected to the outer cranks with the higher masses in the middle. For engines having tandem LP and HP stages these were connected on the middle cranks and the IP stages to the outer. In such cases these tandem pairings had identical masses.

    Crank positionings were symmetrical about engine mid-length, whilst the crank angles were symmetrical about a vertical centreline.

    Masses angles and lengths had to satisfy the three equations shown below....." end of quote(equations not included here unless someone desperately wants them!)

    NB, a diagram would simplify things, but note that the cranks pins are not at equal angles around the crank circle. They are symmetrical about the engine mid-length though.

    Apparently there were other ideas, but the Y-S-T system was the most common. It could not guarentee no vibration however as there were other factors involved.

    The German "Kaiser Wilhelm der grosse" of 1897 is a sucessful example using this system - twin quadruple expansion engines of huge size (15,000 ihp each engine) with "absence of any noticable vibration even at higher powers".

    "Deutschland" of 1900 however used twin engines, six cylinder quadruple expansion on four cranks according to the Y-S-T system (up to 18,500 ihp each engine), and had very bad vibration problems which caused much passenger discomfort. The ship would vibrate "from stem to stern" at anything approaching full speed. It seems that the ship structure was at fault in this case, not the engines - however the only solution was to re-engine her a few years later with less powerful machinery.

    [ 12-08-2006, 12:34 AM: Message edited by: Peter S ]

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    Asquith sent me this photo a while ago - one of the crankshafts used on "Kaiser Wilhelm Der Grosse". Four-crank triple expansion engines.

    Note, while it applies the Yarrow-Schlick-Tweedy system of balancing, the cylinder layout is different from that in the explanation above, being HP (52") and IP (90") in forward group, two LP (96") aft.


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    Very interesting. I worked for a time under Sam Smith in 1962 on establishing the bore centers for the main reduction gear and propuslion shaft bearings, stern tube bearings and strut bearings for several vessels under construction.

    We used a combination of piano wire and optical tooling to establish the bore from design data taken from the arrangement drawing. The amount of sag bow deflection underload and light for different conditions were tabulated along with the coordinates for the departure of the vaious bores from a theoretical centerline extended from the reduction gear axis.

    Pre establishing propulsion alignments to accout for hull deflections under various conditions and using shaft deflection to advantage for the vessel's working at sea is old stuff used by the Navy long before WW II and probably before WW I. It was certianly used in England because I recall seeing an account included in a description of the installation of the first Parson turbine.

    I can see where single shaft vessels can get into propulsion alignment problems given the very short coupling of propellor to engine. Given the gereral availability of the topic I'm quite Volcy's claim ot fame is to bring all the elements together and complie them int a defintive work. I salue him for that.

    The need for allowances for ships deflection and working has been known for probably a century now and for that I salute the generations of fellow crafsmen log gone and nameless but whose contribution still lives in daily use in shipyards ofver the whole world.

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    Just to confirm Asquith's comment, from this side of the pond: Power plant turbogenerators shafts are usually set up to the natural catenary curve. Here the total length of shaft is of the order of 100 feet or so, and the TG set is on a massive concrete foundation, supported by a huge number of pilings. No foundation movement here. Weight of shaft, turbine rotor, and generator rotor is on the order of hundreds of tons.

    Thermo1

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    I guess it is quite true that all these problems had been around for many years, and solutions had been found as well.

    This book is just one mans memoirs, and doesn't look at much historical back ground and doesn't describe what else was going on in the ship building world, so it is a bit narrow in that sense. Interesting as one mans life in the industry and someone who evidently had some interesting and sucessful ideas. Would be nice to have his work put into context of the industry at that time - but not sure where to find such an account.

    I get the impression (but it is not explicitly stated) that the ships he was working on were pushing the boundaries on construction and were quite flexible compared with what had been built before (and maybe later). So there may have been other vessels which worked quite well without his attention - I guess he got to see the troublesome jobs.

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    Peter,
    Apologies for any impression that we were diminishing the achievements of M. Volcy, and for hijacking the thread away from modern technology!

    I’ve been looking at a short account of vibration problems, presented in a lecture by Mr Yarrow in 1892. Yarrow and Thorneycroft amongst others built fast warships, whose nightmarish engine room scenes were so vividly described by Kipling.

    You are right that the balancing was applied solely to the engines, but the problems were due to the response of the system as a whole. Specifically, the hull has a number of natural frequencies waiting to be excited into a resonant condition at certain engine speeds. Yarrow was unimpressed by the unscientific stiffening of hulls to try and move resonant frequencies away from engine speeds, and he undertook a lot of studies. In 1886 Yarrow’s developed a clockwork vibrometer which recorded vibration amplitudes on a rotating chart.

    Yarrow described a sleepless Atlantic voyage on a high speed liner, with the vibration rising to a crescendo each time pistons in the two engines moved in synchronism (the engine speeds being slightly different).

    In the lecture he showed working models mounted on springs, and also ‘high speed’ photographs of a warship on test in London’s West India dock. These were done at a troublesome engine speed (248 rpm) with the propeller removed, and with various balance weights added. The photographs showed the ripples set up in the water due to the resonant vibration of the hull. With the engine balanced properly, no ripples were evident. To illustrate how easy it was to excite the hull into vibration and produce ripples, Yarrow also included a photo of the effect of a man jumping up and down at the stern!

    To digress further, but staying with the marine connection, I went to listen to a guitarist last night, who’d sneaked in an accordionist to accompany him. While he was tuning his guitar to the squeezebox, the accordionist explained the difficulties caused by his ‘musical’ instrument emitting a beating note rather than a single frequency, due to each metal reed having two prongs of slightly different length. He likened the beating effect to the periodic ship-shaking vibration that occurs when on cross-channel ferry boats’ engines are running at slightly different speeds. Art and science together in one evening.

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    Asquith, good stuff about Mr Yarrow, thanks.

    I have read about ships that kept their passengers awake for five Atlantic nights through vibration - they certainly became very unpopular!! Mr Volcy reckons that some particular vibrations helped him to sleep at sea (likened them to being in a cradle)!

    I have a book (Steam at Sea by K.T. Rowland) which mentions (without much detail) the work done by both Yarrow and Thornycroft on balancing (I presume because they were trying to use such high outputs/high revolutions in their torpedo boats and destroyers). It mentions a paper given by Yarrow where the revolutions were 248 and were synchronised with the hull. That is certainly high revolutions for a steam engine. The Thornycroft torpedo boat compound engine he mentions ran at 450 rpm but was quite small (390 ihp) unlike the extremely powerful destroyer engines. Yarrow was proposing the use of bob weights opperated by eccentrics on the crankshaft (I wonder if the author has this correct?)

    By the way, the author notes that incorrect balancing and failure to minimise torsional stresses resulted in many crankshaft failures in the late 19th century, and not just with high-speed naval boats.

    "Between 1881 and 1884 it was reported that 224 merchant vessels were disabled through broken crankshafts and that the average life of these components was under four years. In 1890 built-up crankshafts began to be favoured in place of single forgings but the trouble persisted and of the 173 steamships reported disabled in 1898, a broken shaft was responsible in the majority of cases".

    I came across a German Dr Otto Schlick in the same book - he patented something like a gyroscope between 1903 and 1908. Its purpose was to dampen ships rolling motion, and seemed fairly sucessful. I wonder if he was the crankshaft man as well? (hmmm, should try a patent search).

    I looked in my Sotherns "Verbal" Notes and Sketches for Marine Engineers - his drawing of the Yarrow-Schlick-Tweedy system differs again in that the crank angles are not symmetrical about the engine centre line. There is a different angle between each of the four cranks. I guess each engine was worked out according to its own sizes and weights.

    I also note some of the pistons on the Kaiser Wilhelm Der Grosse were weighted to help with balance.

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    Speaking of Yarrow, and their high powered engines, I like this photo. I think it comes from the frontis of an early 20th century book on engines.

    Both engines by Yarrows of Poplar, London. Both the same power. I would need to check to be sure, but from memory the big triple was used for pumping water in London.


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    In case there is anyone not thoroughly bored yet, I came across this on the internet, taken from the 1911 Encylopaedia Britannica:

    http://www.1911encyclopedia.org/Steam_Engine see under "Influencing of the inertia of reciprocating masses"

    "The most usual arrangement adopted in marine engines, when questions of balance are taken into account, is to have four cranks, and consequently four sets of reciprocating masses.

    In the " YarrowSchlick-Tweedy " system of balancing engines four cranks are employed, and by adjusting the relative weights of the four pistons, as well as their distances apart, and by selecting suitable angles for the relative positions of the cranks (differing somewhat from 90°), a close approximation to complete balance is obtained.

    In triple expansion this arrangement is readily applied when two low-pressure cylinders are used instead of one, the steam from the intermediate cylinder being divided between them, and it is also of course applicable to quadruple expansion engines".

    And this interesting bit about what I assume are Manhattan-type engines:

    "In this connexion mention may be made of a type of engine which has been used in various electric power stations, especially in America, in which a revolving mass might be employed to balance completely the inertia effects of two pistons.

    This is a compound engine in which the cylinders stand at right angles to one another, one being horizontal and the other vertical. If the piston masses were made equal it is clear that the inertia effect of a revolving mass could be resolved into two components which would balance both.

    It does not appear, however, that advantage has been taken of this property in the design of actual engines of this type. In the London County Council power station at Greenwich, where the engines are of this class, the unbalanced effects of inertia are so considerable as to affect the instruments at the Observatory half a mile away".

    Also mentions destroyers running at 400 rpm, 18" stroke, 6000 hp!! I guess this may be where the stories started about marine engineers requiring rain coats when attending the engines??

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    Peter,

    Your reference to bobweights and eccentrics has forced me to find out more, so here’s a picture of the model that Mr Yarrow took to his lecture:-

    Yarrow's model

    It’s a 3 cylinder engine, cranks at 120 degrees. This arrangement can be made to give quite a good state of balance of the rotating masses (including part of the mass of the con rods). This leaves the reciprocating masses to be dealt with. This is addressed by the bobweights: these are the dummy pistons at front and rear which are moved up and down by eccentrics. These are 180 degrees out of phase with each other. Quite how you balance three reciprocating masses with two others is a question for another day. Now where are my wire coat hangers, pliers, and springs?

    The Kaiser’s crankshaft doesn’t appear to have such provision. Mind you, it doesn’t appear to have eccentrics for the valve gear, either. Perhaps that’s why the gent in the photos is wondering why all the workers have scarpered.

    An extract from one of Kipling’s accounts of a high speed marine engine here (there's more to be found somewhere on the web):-

    Kipling and the oily engine room


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