The Cutty Sark as a ship of her times and part of the introduction of the International Load Lines.

While examining the maritime world of the Cutty Sark I was struck by the developments and events that happened before, during and after the time of her construction. I did write about how Load Lines developed into the International Load Line Convention but, a book recently came into my possession that told the story of Lloyd’s, the Classification Society. In response to a couple of requests for more about the famous ship, I decided to re-model this narrative.

The text on the history of Lloyd’s makes it clear that the presence of the Cutty Sark is a miracle, not just for what this vessel achieved but that no other Clipper vessel survives. Behind this narrative is another on Load Line development as a means of determining the maximum loading of a vessel. The Lloyd’s story makes it clear that Samuel Plimsoll, thought to be the only man responsible for Load Line introduction, achieved what he did by ‘agitation.’ Lloyd’s had introduced a rule on Load Lines when Plimsoll was in Primary school but it is clear that Plimsoll knew members of the Classification Society and made no secret of this in his parliamentary speeches.

The Cutty Sark is at a point in ship construction development when timber was giving way to composite in which Iron Framing was used. She is also at a point when new timbers were introduced because historical supplies were diminishing. John Harrison, inventor of the first Marine Chronometer produced his solutions when navigational errors in the navy caused huge losses of men and ships that the Naval Comptrollers knew would lead to a shortage of naval tonnage which in turn would lead to a diminished naval presence around the world.

Midships section for the Cutty Sark. All vessels in the Clipper Class had this form.

Further, increases in trade following the ending of the Napoleonic Wars happened because seas were safer for navigation and international voyages undertaken by the East India Company and others was leading to an enrichment of a Britain that sought to consolidate its position as a leading trader the world over.  The years of 1850 to 1900 saw the biggest increase in trade undertaken by Britain as the Industrial Revolution advanced in many areas. The Navy was watching how ship construction was changing. Because of the increase in sea trade the first Merchant Shipping Acts were introduced and these were instrumental in forcing shipowners to reduce loads carried by their ships.

Common riveted sections from a text on engineering drawing. Above are drawings of Composite ship construction using Transverse Framing methods.

The fate of the Clippers was sealed by the opening of the Suez Canal. The almost complete absence of wind there made it off limits to Clippers. The Clippers needed winds in excess of 30 knots and some of her Captains sailed further south, closer to the ice fields of Antarctica, to reach the strongest winds that blew from west to east.

If we look at the Cutty Sark as just another vessel in the development of ship design, we should also consider the momentous events that became design features that determined her form because, in that golden period of vessel construction ships had to possess to things. Speed and beauty. The Clippers, as a world class of vessels, had this in spades.

General Arrangement drawing of the Cutty Sark, a drawing still used today.

Stability Data for the Cutty Sark, with the top drawing showing shapes of frames as they ran fore to aft. These give an idea of her incredibly fine form that made itself known as a reduced Block Coefficient.

A stone bust of Samuel Plimsoll stands on one side of the river in Bristol, gazing with petrified authority upon the graving dock where the SS Great Britain sits in its state-of-the-art preservation dock on the other side.  He was active in this area during the transition from wooden hulls to Iron. The full transition is wood to composite, composite to iron, iron to steel. Reproductions of drawings of the Cutty Sark in my possession show a vessel built in 1869 with tonnage marks in the form of the first Plimsoll line on the hull. These appear in the forerunner of the general arrangement drawing that became standard in vessel design. To anyone looking at them now the lines of the vessel can be clearly discerned along with the dimensions that can be calculated from the scales drawn out.  His career as an MP stands out as an example of the sort of thing that statesmen politicians ought to do. Engage in the development of workable legislation that improves the lot of the greater number of working men and women.

Lloyds the Classification Society grew in a coffee house in London, one among many where well-known businesses started. 

Lloyd’s of London had what some might describe as dodgy beginnings. As a coffee house in London it served the new and fashionable beverage that had caused so much trouble in Europe after the Moors abandoned the siege of Vienna leaving sacks of beans behind them. The Viennese picked them up, sniffed them, ground them and stewed them. 

The coffee in Lloyd’s was stewed to oblivion and served to men in powdered wigs smoking clay pipes while discussing the insurance risks on vessels trading in and out of London. They had classifications which, in altered guise, still hold true today. They were Good, Middling and Bad. Hulls were classed through the sequence of vowels in our alphabet; A, E, I, O, U. These were assigned according to information received, known or suspected. It could be anything from the vessel’s observed condition to the quantity of liquor loaded for the Master’s consumption before the voyage.

Plimsoll’s activity led to the first Merchant Shipping Act of 1876 but even before he was ten, Lloyd’s had a rule (1835) on a mark to be used that was determined by one of the vessel’s principal dimensions, the hold depth. The Freeboard calculation was 3” for every foot of depth in the hold.

Lloyd’s was following in a tradition begun by the Venetians, Phoenicians and Hanseatic traders who all had methods of ship insurance. There was the same provision in the Laws of Justinian in Rome (AD 533) which addressed the legal rates of Usury. It followed that if an underwriter was to take on a financial liability for the loss of a vessel then a vessel inspection was necessary and this was the precursor to the many who were known as Lloyd’s surveyors who work all over the world looking at and assessing the suitability of the vessel for the purpose intended by its owner.

From one book in my possession, here is the original wording of the definition of the Load Line.

“That the centre of the disc shall indicate the maximum load line in salt water to which the owner intends to load that vessel for that voyage.”

Two points emerge from this. The Owner is now legally liable. The second is that the load line makes no allowance for a change of the water during the voyage.

It is worth quoting the lines from my book on Load Line calculations, published in 1945 and used by my Father from 1950.

“To restore to life the dead bones of history from the valley of despair would only still further confuse the mind of the reader whose business brings him into contact with Government Regulations.”

Who said books on topics as dry as this were not entertaining?

Then comes an astonishing admission.

“The Load Line Regulations have no claim to be based upon scientific investigations.”

This is a statement made against a backdrop of increasing use of mathematical analysis for the solution of many problems, even in the 19th century. The origins of the 1835 rule on Freeboard may, as you read on, become clear.

This is a tacit admission that the history of Load Lines is tortuous so, I will keep the story as succinct as it can be made.

The 1835 rule applied by Lloyds was not universally enforceable. Its use was confined to vessels on a list of vessels that became Lloyd’s list.  A vessel could only remain on the list for as long as the mark was there.

The application of the rule led Lloyds straight into litigation with shipowners. The first case was connected with the use of what was known as an Awning Deck. Many shipowners were using vessels with passenger accommodation and the decks where the passengers were accommodated were Awning Decks. Even now, freight vessels can carry up to 12 passengers.  This limit is imposed because, above this number, the vessel has to conform to Passenger Vessel construction rules which are far more stringent than those applicable to freight vessels.

Lloyds argued that if a vessel with Awning Decks was used to carry cargo then those decks should have scuppers to free the decks of water. It came to the attention of the Lloyds committee that many vessels were closing these ports permanently and action was taken by the committee that led to the de-listing of the vessels where this was done. The shipowners took Lloyds to court and lost.

The history of the Load Line is not complete if new legislation for Merchant Shipping is not included.

In response to the need to regulate Merchant Shipping Activity an Act emerged that regulated the conditions under which seafarers worked. The first all-encompassing but had nothing in it about a Load Line. It did contain a requirement about the Articles which are the conditions of service. Essentially this said that from signing that a man was legally bound to serve two years before the breaking of the articles two years later. The two-year period could not be altered. The Act was introduced when ships were on world-wide trading routes and rarely touched a home port. A man could not be held on board if the Master knew that the ship would be in port shortly before the due date for the breaking of the Articles. This meant that Articles had to be broken in a home port and all men who had served up to two years at that time could, if they wished, leave the vessel.

Timeline of Merchant Shipping Legislation.

1868; Plimsoll elected as member for Derby.

1786; First Act, repealed by later enactments.

1850; Mercantile Marine Act.

1873; Plimsoll publishes his famous pamphlet alerting the general population to the parlous conditions of Merchantmen. This probably is the event that induces Gladstone to instigate a Royal Commission.

1876; Revision with first reference to Load Lines and called the Unseaworthy Ships Bill. The Bill required Load Lines to be placed on the sides of vessels but owners were not compelled to place them where they were effective. Vessels with Load Lines so placed were not permitted on Lloyd’s Registers.

1877; New Act with limitations on loads to be carried.

1890; Revision with corrections on Load Line placement, generally in line with Lloyd’s requirements.

In 1875 a Bill was read Parliament after a Royal Commission instigated by Gladstone but Disraeli dropped it. Many believed that the Bill had been stifled by the Shipowners (a very powerful lobby) and it was re-introduced as an Act of 1876 (Unseaworthy Ships Bill). The older Acts were revoked because they did not address Load Lines. The new one was enforced by the Board of Trade but even this had to be revoked by a later 1890 Act because the 1876 Act was not clear about the Load Line position on the vessel. The 1890 Act corrected this and clarified the issue of Load Line position.

While the narrative on Lloyds describes Plimsoll as an “agitator” his efforts in getting the Load Line accepted cannot be denied. He was up against Disraeli who clearly capitulated under pressure from the shipowner lobby. 

Initially, Freeboard Tables were drawn up in 1886. The requirements for the load line, as rules in some form, did not become compulsory until 1890 with the introduction of the third Merchant Shipping Act. In other words, guidance was available before the rules were introduced. These rules, including the 1835 rule, were later incorporated into an International Load Line Convention.

The term “Freeboard” is the distance at longitudinal ‘midships from the Freeboard deck to the water line. This is the first mention of a datum, in any form, about which Plimsoll may not have been clear. When the first Merchant Shipping Acts were introduced in 1850 and 1876 the Load line position on the hull was unclear. This meant that the Lloyd’s rule of 1835 was difficult to enforce but it was this construction rule that led to litigation between a shipowner and Lloyd’s and the Judge’s summing up shows how, even though the rule was unclear in some respects, the application of the rule and the inclusion of a vessel on Lloyds list implied the existence of a contract and the shipowners had broken the contract by altering the appearance of the vessel and therefore its original design to which the listing referred.

A cartoon that probably was on the wall of every Marine Surveyor's office in Britain.

Here is a quote from a book I have about International Load Lines.

“The Freeboard tables originally introduced in 1886 were formulated on the assumption that the ship was strong enough for the freeboards assigned, and that the scantlings used were in accordance with the 1885 Rules of Lloyd’s Register for the 100A, spar or awning Class, as the case might be.”

Two points come from the quote above. The assumption is that the vessel is strong enough and not “scant” in its constructional features. The second is that the vessel has been built to a set of Scantlings that had been established by experience. By now you might have some idea how this came about. The scantlings used are the first indication of what we now understand to be the Construction Rules for a vessel. Every vessel type has them. Even Cross Channel Ferries.

The term “Scantling” is a curious word, still in use and meaning the dimensions of principal construction features. The word origin is possibly Norse. Not even my huge Chambers Dictionary lists it.

Here is the argument laid bare; That the Freeboard Tables as written are based on an assumption that the vessel construction is up to the mark. How can this be achieved?

The only way to ensure that a vessel IS strong enough is to use or employ people with the right experience in ship construction who possess sufficient knowledge on vessel construction who can make a valid judgement on the strength of the design and its execution in the construction yard. This is how a department of Surveyors within Lloyd’s began. It set the pattern of operations for every Vessel Classification Society for years afterwards.

I have no doubt that the early surveyors took and used guidance from Naval construction methods. These methods entailed sourcing and cutting timber from areas local to the shipyard slipways or ‘Hards’ as the Navy had it. It is no accident that one famous slipway, Buckler’s Hard in Hampshire, totally exhausted the stock of timber from what is now the New Forest.

The Cutty Sark was completed in 1869, before the position of the Load line on the side of the vessel was far from clear either by legislation or by Lloyd’s rulings. The remarkable feature of this and other Clipper vessels is that they were so successful, even when Load Line position had not been finally determined.

One reason, possibly, is that all cargo was under deck, completely secured and could not shift in transit. Another reason is that there was no expense spared in the quality of the timber used for her principal features. This arose out of the fierce competition between yards that built the Clipper class. Each was out to outdo all others in producing the most beautiful of vessels that made the passages in the shortest times. The name ‘Clipper’ arises out of the capacity these ships had in ‘clipping’ days and then hours off journey times, pilot to pilot. One major factor for this success which all yards employed was the transition from all wood to composite construction. In essence this was the use of an Iron frame and the beauty of this material is that it will cast easily and forms a framework onto which timber sections can be attached. The volume of the Iron meant that the material volume used for framing was reduced from that of timber and this method was adopted because of diminishing timber supplies. The Cutty Sark used Teak for the main deck and the Thermopylae used Yellow Pine. Each had its own characteristics but, a major consideration for wooden decks is cleaning. For this a ‘holy stone’ was used. Essentially a small frame with a hinged pole that enclosed a soft stone, this was dragged over the decks with plenty of water as a cleaning operation but, it can be imagined that timber replacement was necessary and some timbers did not need Holystoning.

So sharp was the competition that even the opening of the Suez Canal did not deter ship constructors from building them. Here they are, all built around the same time.

Caliph.

Normancourt.

Wylo.

Ambassador.

Eme.

Duke of Abercorn.

Osaka.

Doune Castle.

City of Hankow.

Oberon.

Blackadder.

Others included the Ariel, Titania, Golden Fleece and the famous Otago, a small clipper that had none other than Joseph Conrad for a Captain.

It is at this time that passenger movement in the form of emigration trade was expanding but the Clippers had no need of this. They could not carry the passengers in the numbers required so they transported out the choicest of general cargoes and brought back wool, hides and Tallow.

One may imagine why the many points of issue between Plimsoll and the owners on Load Line position led to them, almost universally, wanting him to be stopped. Plimsoll did not give in. Here is a speech in Parliament he made during debates about the safety of Mariners.

I beg, Sir, to move the adjournment of the House. Sir, I earnestly entreat the right hon. Gentleman at the head of Her Majesty's Government not to consign some thousands of living human beings to undeserved and miserable death.……………Under the Board of Trade, since 1862, when unhappily the commercial marine of this country was committed to their care, matters have been getting worse and worse, with shipowners of murderous tendencies outside the House, and who are immediately and amply represented inside the House, and who have frustrated and talked to death every effort to procure a remedy for this state of things…… a ship…..which was bought for about ￡780, and being of about an equal amount of tonnage, and having had about ￡800 spent upon her in repairs—making the total value about ￡1,500—the owners, immediately on the vessel being repaired, entered into a contract which would have recouped them that sum total of the cost in one half of the first voyage. I entreat you to consider it…………..The Secretary of Lloyd's tells a friend of mine that he does not know a single ship which has been broken up voluntarily by the owners in the course of 30 years on account of its being worn out. Ships gradually pass from hand to hand, until bought by some needy and reckless speculators, who send them to sea with precious human lives.  On the 3rd of this month I had a list carefully prepared of 15,000 vessels on Lloyd's Register; and on (examining) these what does the House think was the result? It was found that no fewer than 2,654 of the classed ships had gone off their class and forfeited their position. And what is the consequence that ensues? It is that continually, every winter, hundreds and hundreds of brave men are sent to death, their wives are made widows and their children are made Toggle showing location of Column 1824orphans, in order that a few speculative scoundrels, in whose hearts there is neither the love of God nor the fear of God, may make unhallowed gains. There are shipowners in this country of ours who have never either built a ship or bought a new one, but who are simply what are called "ship-knackers," and I accidentally overheard a Member of this House described in the Lobby by an ex-Secretary to the Treasury as "a shipknacker." ["ORDER! ORDER!]

1707 was the year when a solution to the parlous state of navigation in the Navy was needed. This story is told brilliantly by Dava Sobel. The loss of men under the command of Sir Clowdisley Shovell led to the formation of the Longitude Board that put up a prize for the first man who could solve the problem of calculating longitude in global navigation. It was not only the loss of men and a very popular admiral that led to this pass. Prime timber, needed for ship construction, was becoming scarce. By about 1770 the first clocks were in service in the fleet. By 1860 the Admiralty owned about 800 Chronometers.

I remember these devices kept in a glass covered case in the chartroom. Always in pairs, they kept GMT and a small book in the case, filled in every day recorded Chronometer error, the difference between the two. I remember a conversation relayed to me by a Second Mate who almost berated a Superintendent on the matter of sextants, insisting that there be two on every vessel which, in the past, was accepted practice. The Superintendent, being from the engineering department, did not agree. His argument was that with Satellite Navigation, Decca, Loran and sundry other pieces of electronic wizardry, there was no need of a sextant at all, let alone one. This flew in the face of older conventional wisdom expressed to me by a senior Master who, in the genial manner of a Grandfather with children, explained the difference between a Navigational Method and a Navigational Aid.

The ransacking of the timber reserves in Britain was suspended when trees were marked for the Admiralty by its surveyors. Harrison, who made his first clocks out of wood, was one of them. Another transition, that being the fuel source for domestic heating, also took place when coal began to be used instead of wood. The Cutty Sark and others like her were perfectly equipped to transport this new commodity.

The overlap between wood and composite construction ran from 1850 to 1870. By about 1870, almost all the lessons about wooden vessel construction had been learned. The period produced some of the most graceful ships ever built and was the high point of Composite ship design.

The use of an iron frame with timber attached to the ribs meant that the timber was still responsible in large part for accepting the stresses imposed on the vessel when at sea. The framing of the vessel is still what we would now describe as Transverse and the Longitudinal framing necessary for longer vessels was not to emerge until the 20th century.

The top drawing of these three is mine from years ago. It shows the Isherwood Longitudinal Framing system and how it differs from the Transverse Framing of the Cutty Sark and earlier vessels. Isherwood was a Lloyd's Surveyor who produced the solution to vessels of increased length like Oil Tankers and Bulk Carriers.

A running joke I heard about the transition from wood to iron hulls centred upon a jibe about men of iron sailing ships of wood which transmuted into men of wood sailing ships of iron. The stresses imposed upon modern seafarers never entered the conversations I enjoyed. In general it was understood that a good sense of humour, in some abundance, was all that was needed for sanity. I had learned many years before that, according to one writer in the Theatre of the Absurd, sanity was the most prevalent form of lunacy.

Iron ships solved the problem of Teredo Navalis but produced another in that sudden hull fractures sealed the fate of the vessel where before, wooden construction creaked and groaned, informing all on board to lower sail. It is clear that all the Clippers were driven hard to achieve incredible speeds and this explains why only the Cutty Sark survived and so many were lost.

In summary, Composite vessel design allowed less timber to be used because the frames that used heavier timber sections were no longer necessary. In addition, the method allowed the use of shorter planks in the strakes of timber needed. One could argue that Composite design came not a moment too early.

One book I have on the origins and development of International Load Lines has, with calculations, the story of how the rules were formulated.

“The Merchant Shipping Act of 1876 made it compulsory to place a Load Line on the hulls of Foreign Going ships, such that the centre of the disc shall indicate the maximum Load Line in salt water to which the owner intends to load the ship for that voyage.”

Even then, this applied only to ships on foreign voyages and not to home trade. It was only in 1890 that these anomalies were cleared and the government made it obligatory to place the line at a defined position on every vessel.

Among the rules was an assumption that a standard reserve of buoyancy existed that was provided by an intact portion of the hull above the summer load water line. The importance is that the vessel will float at an increased draft in warmer water at summer time.

The other main assumption is that the Freeboard Deck is fitted with a standard thickness of wood and ‘round of beam’. This is another term for the camber of the deck, measured as the difference of deck height at the longitudinal centre line above deck height at the shear strakes. The ‘midship cross section shows how this looks. The Freeboard Deck has now become the datum from which the Load Line position is calculated and it is to be measured from the longitudinal ‘midships, that being half way between the fore and aft perpendiculars of the vessel.

Then comes a paragraph that explains how the 1886 Board of Trade Rules stand in relation to the later Regulations on Load Lines.

“The foregoing explanation of the 1886 Board of Trade Rules is considered essential to enable the reader to realise that the entire fabric of the present International Load Line Regulations has been constructed upon the basis of experience accumulated since the introduction of the original rules, the underlying principles of which have not been altered.”

This might look obtuse but all ships are built to Construction Rules. The difference between this and a standard is that a rule or set of rules has arisen out of a body of collective experience that has influenced the direction of rule-based design development. In any standard there is evidence that the standard under scrutiny is based upon an older standard which itself is based upon empirical laws established by investigation and/or experimentation.

This means that anyone active in assigning Load Lines to vessels has to know not just current rules used to calculate them but, how the earliest assessments were made, even if the sum of experience accumulated that produced them is not known. It could be compared to asking a schoolboy to explain how triangulation of land evolved in Egypt before Pythagoras discovered it and took his findings home to Athens where the practice became a Theorem attributable to him and him alone.

The Freeboard Deck now has considerable significance. All openings below and above it are subjected, by virtue of their distances above or below, to serious design scrutiny. Here is how the Freeboard Deck is defined.

“It is the deck from which freeboard is measured. If the deck is continuous, it can be identified as a freeboard deck. If not, it must have permanent means of closure for all openings where the deck is exposed to weather. This includes all such openings as hatches, water tight doors that open outwards, that would permit persons to enter parts of the vessel from exposed decks.”

This shows how the freeboard deck changes profile along the vessel with the deck arrangements.

The wording takes into account the changes in profile of a vessel and also determines where the watertight openings have to be located. For the Cutty Sark, this was simplicity itself. The main and exposed deck was the Freeboard Deck.

This is why the shipowners, in litigation with Lloyds, lost their case because the Freeboard Deck needs sufficient scuppers and freeing ports on it to clear the deck of water quickly and the shipowners decided they were not necessary and closed them up.

The story, from Lloyd’s, runs like this;

“The Society’s rules insisted that, in such cases, there should be scuppers through the sides of the Awning ‘tween decks and sizeable ports on the deck below, to allow free escape of water in a seaway. It came to the knowledge of the committee that some shipowners, wishing to load their vessels more heavily, were permanently closing the scuppers and ports on the main deck. Firm action was taken in 1873.”

The rule of three inches freeboard for every foot depth of the hold had already been enforced which permitted a vessel to be identified in the existing Lloyd’s register. Shipowners began to exploit this by building awning decks for passenger vessels in warmer seas. The Society’s view was that the additional weight or material might not be great but that this and the height above the water level could have a bearing on the vessel classification.

The judge took the view that a contract already existed between the shipowner and Lloyd’s and that the shipowner was now seeking to alter it by changing the design after the fact of registration a vessel bult to a design that conformed to the three inches per foot rule.

So while Plimsoll had a role as an ‘agitator’ it would also be true to say that the Classification Society already had rules that the shipowners chose to violate.

I referred earlier to practices used by older seafaring nations. I searched for anything on this that might give me a clue on how Lloyd’s developed their first rule of 3” freeboard per foot of hold depth. I found a document in the Max Planck Institute on the history of scientific development.

Archimedes of Syracuse is credited with an explanation of floating bodies. An immersed body experiences an upthrust which is determined by the weight of the fluid displaced. The body floats when that upthrust equals the weight of the fluid displaced.

Look how similar this is to modern methods of finding the Metacentric Height.

Archimedes was involved in vessel design and while most of his work appears to have been lost in library fires, vessel designers of his day and after were not slow to realise just how the vessel shape below the water line (the ‘midship cross section) was so critical to the stability of the ship. Ship builders all over Europe adopted very similar methods of construction and the rapid spread of these ideas can only be attributed to trade patterns. 

The Gokstad Viking ship complete. A remarkable vessel that has none of the intricate ornamentation seen on funeral boats of the same design that were buried.

The Gokstad Ship and the Takwon below it have a great deal in common. Both are remarkably stable and show a rapidly broadening of the water plane at midships with increased immersion which imparts increased stability when loaded.

Viking ships show precisely how a remarkably stable ship can be built. Herodotus, in his histories, warns anyone who will listen that knowing the meanings of different vessel shapes can inform on the likelihood of invasion. Broad beam vessels (high Block Coefficient), slower in the water, were for trade. Narrow beam vessels with a fine form (low Block Coefficient) were for war.

I alluded earlier to the manner in which the builders of the Cutty Sark made every effort to reduce the area of the underwater form the while increasing sail area. Earlier designers were certainly aware of what every Naval Architect and Mariner knows about now.

The height of the Transverse Metacentre.

At this point I turn to the Naval Architect who lectured me years ago on Vessel design.

Edward Stokoe was a Naval Architect known, as the saying went, “from Swan’s to Smith’s”. These were two dockyards on the Tyne; Swan Hunter at the Newcastle end and Smith’s on the north bank close to the estuary. He made a deep impression on me. His book states that there are only two occasions when a ship can be considered to be NOT moving and UPRIGHT. Before launching and in dry dock.

He briefly introduces the three equilibrium states but makes it clear that a vessel can move from stable equilibrium to unstable almost on the turn of a pin.

In a stable state, the vessel is floating upright and G, the centre of gravity is directly above B, the centre of buoyancy. The weight is exactly countered by the upthrust from the displaced weight of water. Upon heeling to a given angle, the centre of gravity remains in the same position but the centre of buoyancy moves to a new position, laterally from B to B . The buoyancy now acts upwards in the same direction BUT the weight still acts downwards in the same direction through G and the two forces now create a turning moment.  An upward projection from Z to the centreline of the vessel intersects at M, the Metacentric Height.  It is this turning moment that constitutes the force that returns the vessel to the upright condition. The Righting Moment is Δg x GZ and is properly named the Righting Lever. It is only while this moment can act and right the vessel that the vessel can be described as stable, and is thus in a state of Stable Equilibrium. This holds ONLY for small angles of heel, around 10?. It is the height of the Transverse Metacentre GM that determines how stable the vessel will be and, for modern tonnage, how stiff the vessel will be in a seaway. A small value of GM will mean that the vessel is stable but is susceptable to rolling. A large value of GM will mean that the vessel is resistant to rolling and the period of roll will be small. This means that roll accelerations can be large and structural damage may occur. 

In an unstable vessel G will be above M, meaning that the Metacentric Height could be considered to be negative and the turning moment that once righted the vessel will now operate to capsize it.

Examining the drawings that Stokoe produces for modern students of Naval Architecture and comparing these to the drawings in the document from the Max Planck institute shows that men concerned with vessel stability then were thinking about pretty much the same thing. Even then, they had the concept of a “centroid” of an area. In a three-dimensional shape of irregular density and uniform thickness the centre of gravity is the point from which all of the weight can be considered to act. Stokoe describes Centroids as follows;

“The centre of gravity of a uniform lamina is midway through the thickness. Since both the thickness and density are constant, moments of area can be used. This system may also be applied to determine the centre of gravity or, more correctly, the centroid of an area.”

So the centroid distance from an axis becomes; 

Stokoe then goes on to explain how the height of the centre of gravity above the keel is calculated by taking moments of the centres of gravity of individual masses above the keel.

The Centre of Flotation is the point about which the vessel can be considered to float. The TCF (Transverse Centre or Flotation) thus remains stationary when the vessel rolls to one side or the other. 

The LCF (Longitudinal Centre of Flotation) is the point at which weight can be added and the vessel will sit lower in the water without changing trim (the difference between immersion at the forward end and aft end).

The Righting Moment, as shown above, depends upon Metacentric Height.

In the legal case when the shipowners took Lloyd’s to court over their decision to use Awning Decks, Lloyd’s would have used evidence of this nature to support their argument.

Isaac Newton published his Principia Mathematica in 1687. There were later editions in the following century. Even at the time of the later editions it is highly likely it was not widely understood so at the time when Lloyd’s began to insist on their first Classification Rule this is was still very much the case.

Lloyd’s would have needed evidence of this sort to show the judge that there was some scientific base for their arguments.

In essence, Lloyd’s showed that a vessel HAD to have a defined distance from the deck to the water line because if a vessel was excessively loaded, the vessel shape would not contribute to the presence of the Righting Moment and would thus turn over at a low angle of heel. This explains why the Freeboard is measured at a point half way between the two perpendiculars. It is at this point, in traditional ship design (Cutty Sark included), that the beam is widest.

So the first Construction Rule used by Lloyd’s intended to preserve the stability of the vessel, the method being enforcing a distance (Freeboard) from deck to water line so that the vessel ‘midships cross section remained effective in maintaining and increasing a Righting Moment that would counter the force that initiated the heel in the first instance. This can only be done by ensuring that a reserve of buoyancy exists after the vessel is loaded. Loading the vessel to a point where instability may occur means that G moves vertically to a point where GM is negative, or G is above M and not below it.

The final section I include is a deadweight scale I sketched out years ago. The Deadweight Scale shows the Tonnage marks and Load line in the context of the hull characteristics when immersed. This is hydrostatic data, not stability data.  The distances of the freeboard deck and the keel from the Plimsoll mark are given. The Freeboard shown is about 9’ 4”. Adding these figures gives the total depth of the hold or tank. This is 38’ 2”. 

If the first rule that Lloyds applied in 1835 to calculate a Freeboard we have a surprising result. Applying the 3” rule of freeboard per foot of hold depth we have a result only an inch away from the freeboard already assigned. The remarkable thing is that this type of vessel did not even exist at the time the 1835 rule was drawn up.

We can look at earlier designs and see that the lessons learned about designing vessels for increased stability were learned he world over. The picture is of a loaded Takwon operating in the Far East. This working vessel has many features in common with Thames barges. Broad in the beam at ‘midships, the vessel sits lower in the water with increasing loads but, the immersing water plane at the water line changes its outline and remains pointed at the ends and widening at the middle. This confers increasing stability with increasing load. These vessels were frequently loaded until the sides were just above the water line and the crew had wet feet moving around the sides from forward to aft. 

Lloyd’s Surveyors.

I had a few experiences with these men as I went about my business and turned up in this dockyard or that. I found them to be remarkably patient and highly intuitive men.

In one dock yard I heard about an incident. One of them came very close to being killed. He was looking at something on the vessel in the adjacent basin and, after this, came out from under the ship’s hull to the “turn of the bilge”. He placed his safety helmet on his head immediately but did not walk more than a few paces when something hit his helmet making him and his colleague stop dead in tracks. To his total astonishment, a pipeworking spanner with an open jaw at one end and a spike at the other had embedded itself in the helmet, spike down.

After a quick visit to the local hospital he was back at work a couple of days later. When he turned up on my vessel I spoke to him and asked him how he was. He was not in the least bit shaken. He put his hand on my shoulder, smiled and said that nothing good came of lying around the house all day worrying about what might happen when venturing outside.

“When your number is up, it’s up and there is nothing you or anyone else can do about it.”

With that he shrugged his shoulders, smiled broadly again and got on with signing off our safety valves.

Then there was the assiduous and (rather) mischievous electrical surveyor with whom I worked at close quarters. He gave me a valuable inside view on how he carried out his work.

Looking at the main electrical circuit breakers for the two 1MW alternators in the Main Switchboard, he asked me what had been done. I told him that I was present noting how the examination had been carried out. I made sure that he knew in what state the devices that controlled the release of the overload mechanism had been found.

“Oh…..” he said. “Were they totally seized up?”

“Yes. Badly”

“Free to operate now, I take it?”

“Yes.”

“Who carried out the work?”

I opened my note book and told him. He made one last visual around the circuit breaker.

“I’m happy” he said. “Box them up.”

Then there was the quiet and unassuming Dutch Surveyor. He walked onto the deck of our Capesize Bulker and enquired, in the manner of asking about the cricket score, of the Chief Engineer if he had seen the cracks in the deck plating originating from the hatch corners in the doubler plates.

Summary.

Events in ship construction moved fast from 1870 onwards. The Composite vessel was a short transition to Iron hulled vessels and steam powered ships acquired more Horse Power per shaft and engines acquired more Horse Power per Cylinder. Steam reciprocating engines had their limits and these were soon discovered. 

Turbinia was launched in 1894 and solved two problems at the same time. The first was a simpler engine for marine operations with no apparent limit on speed and the second was a source of mechanical energy that could turn shafts faster for electricity generation at the higher speeds needed for an emerging technology. Alternating Current electricity.

End Notes.

The narrative on Lloyd’s Registry ends in 1960. It does not include the events that took place at the end of that decade. By this time, VLCC’s (Very Large Crude Carriers) were in service that reached a Deadweight Tonnage unthinkable in the late 1950’s. Three exploded in two weeks at the end of 1969.

They were the Mactra, Marpessa and the Kong Haakon VII. The Mactra exploded in the Mozambique Channel. The Kong Haakon VII exploded off Liberia and the Marpessa off Senegal.

The factors uniting these events were as follows;

Same activity at the time. (Tank cleaning; methods used were very similar; high pressure hot water jetting with sea water)

Same cargo. (Persian crudes)

Same deadweight tonnage.

Similar construction methods.

It is clear that if Inert gas systems were in use at the time on these vessels the events above would never have happened. American experience with tankships in 1932 led, after similar explosions on American owned ships, to the universal adoption of Inert Gas systems which was adopted quickly by the American Bureau of Shipping, the American counterpart to Lloyd’s of London. The story of Lloyd’s mentions the American Bureau of Shipping (ABS) as working closely with Lloyd’s at the end of WW2. Lloyd’s had been using ABS as an agent when their own representation was not geographically possible. But it is clear that the experience on American Tankship vessels was not shared with Lloyd’s and therefore other Classification Societies such as Bureau Veritas and DET Norske Veritas. Yet, it is clear that tankship explosions and Inert Gas systems were understood before, during and after WW2.  During WW2 there was a pivotal event in the battle for supremacy of the Mediterranean Sea. Malta was under siege when it was critical as an air base for operations in the Eastern Sahara. The Ohio was a Liberty Tanker that had been requisitioned for supply from America. It was attacked by the Luftwaffe and, because of the efforts of the men aboard and the design it became known as the ship that refused to die. Another factor that contributed to her survival was the use of Inert Gas plant that had been adopted by her constructors years before. It would not be incorrect to suppose or surmise that had this not been in use, the vessel would have been sunk and events in the Middle East may have been very different as a result.

After the 1969 explosions on the three vessels named above, Inert Gas systems were enforced on such tonnage and, over the ensuing years, the Dead Weight tonnage of vessels on which Inert Gas had to be used to remain registered dropped. This led to vessels of 100,000 tons deadweight having them fitted as a retrospective measure. Even today, the reverberations of those events are still felt.

In 1963 the world saw the first commercial transport of LNG (Methane) by sea. Many thought this would never be possible. In large part the development of Natural Gas transport methods was an Anglo-French project very similar to Concord. It was the close associations that key people made during this time that made LNG and LPG gas transport by sea possible and an activity that has an enviable safety record. It may have been this and Concord that lay at the roots of the arguments supporting Britain’s application to join the European Common Market. One man, a Naval Architect, is pivotal in the development of this technology. Roger Ffooks was deeply involved as a Naval Architect at the forefront of design for both the vessels and the cargo containment systems. While the story of Lloyd’s ends in 1960 and the story of LNG transport begins in the 1950’s, there is no mention of it. It has been by far one of the most challenging of technologies ever developed in Sea transport.

Without the knowledge of Freeboard calculation and Load Line assignment neither the development of VLCC’s nor that of LNG carriers would have been possible. The story of gas transport and Roger Ffooks shows that open collaborations are necessary for effective solutions. These left the squabbling and combative days of Plimsoll, Disraeli and recalcitrant shipowners behind.

The last days of the Clippers, the opening of the Suez Canal, the open feuds in Parliament where vested interests pressurized politicians into making decisions that some today might label as immoral, set against the backdrop of shipowners challenging the validity of rule-based decisions, however amateur these may have appeared, were also the days before a dreadful conflict that clawed many nations into a bloodbath.

Disraeli’s direct intervention in 1875 secured a 40% stake in the Suez Canal project and this would later draw Britain into direct conflict in 1956 (along with France) with Gamel Abdul Nasser when he nationalized the Canal and took tonnage receipts as cash for a dam project that may have been ill-advised.  The Suez conflict gave General de Gaulle all the justification he needed to ensure that Britain only entered the European Common Market over his dead body.

In conclusion, the days of the Cutty Sark, Plimsoll and the troubled transitions from wood to steel for ship construction were peppered with events that resonate from their days to ours and the Clippers and their intrinsic beauty as nautical construction were high points in this technology when a needed function was combined with a subtle art form in a manner we will not see again.