FOOTNOTES:

JAMES LAING,

EX-PRESIDENT OF THE CHAMBER OF SHIPPING OF THE UNITED KINGDOM; MEMBER OF THE INSTITUTION OF NAVAL ARCHITECTS; OF THE IRON AND STEEL INSTITUTE; AND MEMBER OF COMMITTEE OF LLOYD’S REGISTER.

Mr Laingwas born at Deptford House, Sunderland, on 11th January, 1823, and is the only son of Mr Philip Laing, who, as early as 1793, in partnership with his brother John, commenced the business of shipbuilding which, nearly a century later, is still carried on, under greatly transformed conditions, by his son. MrLaing’searliest impressions and associations were connected with what was afterwards to become his life’s vocation, his boyhood having been spent in a home contiguous to his father’s yard. While a youth, he served as an ordinary workman in the shipyard, and in 1843, his father, on launching the “Cressy,” signalised the jubilee of a singularly successful career by handing over to him the care and titles of the business. MrLaingcontinued to build wooden vessels until 1853, in which year the “Amity,” his first iron ship, was launched. In 1866 he entirely ceased building in wood, and since then has built a very large number of iron vessels for various owners, amongst others for such well-known companies as the Peninsular and Oriental Steam Navigation Company, the Royal Mail Company, the Union Steamship Company of Southampton, etc. In 1883, he built for the last-mentioned company the Mail Steamer “Mexican,” of 4669 tons. Besides the shipyard, he is the owner of graving docks connected therewith, as well as extensive copper and brass works, and is principal proprietor of the Ayres Quay Bottle Works, which are capable of turning out 33,000 bottles per day. For upwards of thirty years MrLainghas served as a member of the River Wear Commission, and as chairman since 1868. For years he has taken a leading position among shipbuilders and shipowners, not only in his own district, but throughout the country. In 1883 he was chosen President of the Chamber of Shipping of the United Kingdom, and as official representative of that interest has performed signal service, both with reference to the Shipping Bill introduced to Parliament by Mr Chamberlain and the recent agreement come to between the shipowners and the Suez Canal Company, of which company he has since been appointed a Director. For twenty years MrLainghas acted as a member of the Board of Lloyd’s Register of Shipping, and at present is Vice-President of the Load Line Committee, appointed by the Board of Trade for the settlement of a most important and intricate question. In the shipbuilding and other cognate businesses MrLaingis now ably assisted by his three sons, Philip, Arthur, and James.

HandwrittenJames Laing (signature)INK-PHOTO, SPRAGUE & Co. LONDON.

James Laing (signature)INK-PHOTO, SPRAGUE & Co. LONDON.

FOOTNOTES:[1]Since the above was written, theAuraniaand theOregonhave resumed their services on the Atlantic, the results in the case of the latter vessel being extraordinarily successful. On Saturday, the 5th April, she arrived at Queenstown, having left New York on Saturday, the 29th March, making the trip in 7 days, 2 hours, 18 minutes, her daily runs being:—45, 407, 396, 400, 302, 410, 384, 412, and 60; total, 2816 knots. Leaving Queenstown on Sunday, the 13th April, she arrived at New York on Saturday, the 19th April, in the unprecedentedly short period of 6 days, 9 hours, 22 minutes.[2]While these sheets were passing through the press, theAmericawastried unofficiallyon the Clyde, and attained a speed of 17 knots, with about 6,500 indicated horse-power. On her passage from the Clyde to the Mersey she maintained, it is stated, 18¼ knots over the whole distance.[3]This list with those which follow other chapters, have been compiled at considerable trouble in the hope that they may be of use to technical readers in directing them at once to accurate and detailed information. In this connection also, the excellent work by Mr A. S. Seaton, “Manual of Marine Engineering,” and that by Mr W. H. White, “Manual of Naval Architecture,” may be referred to with every satisfaction.[4]For full and excellent treatment of this subject, see the paper on “Causes of Unseaworthiness in Merchant Steamers,” by Mr Benjamin Martell, Chief Surveyor to Lloyd’s Register, with the ensuing discussion: Trans. Inst., N.A., vol. xxi., 1880.Several of the causes above named it is doubtless the province of the scientific shipbuilder, and the duty of the shipowner, to obviate by furnishing the captain and officers—especially in the case of entirely new vessels—with particulars and data of the vessel’s technical character, such as are now left to be found out by slow and sometimes bitter experience. Of these it may be sufficient to instance:—Stability, steadiness, trim, carrying capability, and steaming powers. Mr William Denny, of Dumbarton, has recently publicly declared his firm’s intention of supplying such particulars to the vessels built by them. It is to be hoped this worthy example may be extensively followed.[5]In this, as in other matters dealt with, the full appreciation of which involves careful technical study, readers are referred to the papers enumerated at the end of chapter, as well as to the “Manuals” already referred to in this work.[6]The principle which underlies the experiment is this:—If any one body forming part of a system of heavy bodies be moved from one position in the system to another, the weight of the body moved multiplied into the distance through which it is moved, is precisely equal to the weight of the whole system of bodies multiplied into the distance through which the common centre of gravity of the whole has moved. If in a ship, therefore, a movable weight of known amount is moved across the deck through a given known distance, the centre of gravity of the ship itself, with all on board, has been moved in a line parallel to that through which the small weight has been transferred, and through a distance inversely proportioned to the weight of the whole ship to the weight moved. If, for instance, a weight of five tons should be moved through a distance of twenty feet, then multiplying this weight into this distance and dividing by the total weight of the ship, the distance through which the ship’s centre of gravity has travelled parallel to the deck is obtained. If, at the same time, an exact measure of the angle through which the ship has been inclined by moving the five tons through the distance named has been taken, and the position of the ship’s metacentre has been obtained, then the elements of a triangle are known—namely, the degrees in each of its angles, and the length of one of the sides—and from these the length of the remaining sides of the triangle is easily deduced. One of these sides will be the distance between the metacentre of the ship and its centre of gravity, and, consequently, the metacentre being known from calculation, the position of the centre of gravity becomes known also.[7]The classification of strains here given is as contained in White’s “Manual of Naval Architecture.” To this authoritative source readers must turn who wish a full exposition of the several problems go shortly dealt with in these pages.[8]This will be more fully referred to further on, but it may be stated here that the need for independent calculation is largely obviated, owing to the existence of “co-efficients,” deduced from investigations made by experts. Further, the existence and influence of the Registration Societies are such that the codes of scantling and the structural supervision instituted by them together constitute the only guarantee of structural strength generally desiderated.[9]Suppose the dimensions of a proposed vessel to be 320 × 36 × 26½ feet, then, according to a method of approximation largely in use, the sum of these dimensions divided by 100 gives what is known as the “cubic number”—(320 × 36 × 26½ ÷ 100) = 3052 cubic number. Suppose that for a vessel already built, similar in type and dimensions, or of similar proportions, to the one proposed, the cubic number, when divided into the ship’s actual weight (i.e., the displacementminusthe weight of machinery and the dead-weight carried), gives say ·53, then this figure represents the “co-efficient” of ship’s weight, and applying it in the case supposed gives:—3052 × ·53 = 1620, the weight of hull for proposed vessel. This example illustrates the manner in which the weight of machinery is estimated, and indicates the nature and use of the general term “co-efficient:” frequently employed in this chapter.[10]One such method, devised and followed by Mr C. Zimmermann in his daily practice as chief draughtsman to the Barrow Shipbuilding Company, and described by him before the Institution of Naval Architects in 1883, gives with very little preliminary calculation, and at once, a close approximation to the correct displacement. Another system, originated and used in practice by Mr Chas. H. Johnson, chief designer to Messrs Wm. Denny & Brothers, consists of an analysis of the lines of vessels of various degrees of fineness and fulness previously built, formulated for daily use in a series of curves of areas, giving, for sections at certain fixed distances from midships—in terms of percentage to the midship area—the particular area specially suited to afford the required displacement; and at the same time to maintain the general form of hull which in actual practice has proved satisfactory with respect to speed. In his later practice, Mr Johnson has found it preferable to use the block form of analysis of Mr A. C. Kirk (considered further on in matters relating to speed), using the three sides of that form as a basis upon which to group the water-lines.[11]For illustrated descriptions of this and other improved calculating instruments referred to in this chapter, seeAppendix.[12]This experimental method, it may be explained, has long been practised in connection with ships built for the Royal Navy, and for a considerable number of years it has been systematically followed in some leading merchant shipyards. Messrs A. & J. Inglis, Pointhouse, Glasgow, and Messrs Wm. Denny & Bros., Dumbarton, were amongst the earliest firms to systematically adopt the practice. With the former it has been customary to incline every vessel of distinctive type built by them since 1871, and with the latter the practice has been constantly followed from a date somewhat subsequent. For some years past other firms on the Clyde and elsewhere have adopted the method, the data so accumulated being found an admirable basis from which to estimate the height of the centre of gravity in proposed vessels. Tables giving the results of inclining experiments made on various types of merchant steamships and sailing vessels will be found in “White’s Manual of Naval Architecture,” pages 82-87.[13]From the first volume (1860) of the Transactions of the Institution of Naval Architects, it is seen that Dr Inman, Samuel Read, and Dr Woolley had each already found different methods of simplifying Atwood’s calculations.[14]Various other methods of simplifying the calculations based on Atwood’s theorem were subsequently proposed, and one or two different methods also brought forward—notably one in 1876 by the late Mr Charles W. Merrifield, afterwards improved by the late Professor Rankine, and one by Mr J. Macfarlane Gray, of the Board of Trade, described by that gentleman in 1875, but since considerably improved. Most of them were laid before the Institution of Naval Architects in papers which will be found enumerated in the list at end of chapter. While such propositions did not contribute directly to bring the problem of stability to its presently accepted form, they deserve to be remembered as tokens of the great labour and skill which have been expended in founding and developing this branch of scientific naval architecture.[15]“On Cross-Curves of Stability; their Uses, and a Method of Constructing Them, Obviating the Necessity for the Usual Correction for the Differences of the Wedges of Immersion and Emersion.”[16]A detailed description of this valuable instrument will be found inAppendix.[17]Space forbids any detailed reference to these, but the names of the papers and their respective authors will be found enumerated in the list at end of chapter.[18]An obvious means of dealing approximately with stability, to which limits of space will not permit more than simple reference, consists in so manipulating the data obtained by calculation for known ships that it may be made available, either in the form of curves or of tables, for determining the stability of proposed vessels. Methods of accomplishing this may of course vary to suit the ideas and convenience of designers. A well-arranged system was brought forward, jointly by Mr F. P. Purvis, head of Messrs W. Denny & Brothers’ scientific staff, and Mr B. Kindermann, one of his assistants, in a paper (see list at end of chapter) read before the Institution of Engineers and Shipbuilders in April last. While the results exhibited in the paper are immediately applicable to ships of one particular form, whatever the length, breadth, depth, or draught may be, this method still requires much development to make it at all universally applicable.[19]It is the usual practice to assume vessels to be laden with homogeneous cargo of such a density as to fill the holds, and for this condition to estimate the position of centre of gravity to be used in calculation.[20]See paper by Mr Kirk “On a Method of Analysing the Forms of Ships and Determining the Lengths and Angles of Entrance.”—Trans. Inst. N.A., vol. xii., 1880.[21]With the view of effecting an economy in time, and to enable the trials at progressive speeds to be carried out while vessels are in a lengthened run out to sea, a method has been proposed by Mr J. H. Biles, naval architect to Messrs J. & G. Thomson, and adopted on board the vessels tried by that firm, and also experimented with on some of the vessels turned out by Messrs W. Denny & Bros., by which the necessity for running with and against the tide on the measured mile is entirely obviated. The principle of the method is to measure the time that a certain part of the length of the ship takes to pass an object thrown from the bows of the vessel well clear of the side. For full particulars, both of the apparatus employed and of the results of actual trials by this method compared with trials made on the measured mile, see paper on “Progressive Speed Trials,” by Mr Biles, in the Transactions: Institution of Naval Architects, vol. xxiii., 1882.[22]A general outline of the operations conducted in Messrs Denny’s tank will be found in the description of their large works inChap. VI. For a detailed account of themodus operandiin the same establishment, see abstract of a paper delivered in Dumbarton by Mr E. R. Mumford, of Messrs Denny’s Experimental Staff, printed in theEngineerfor 15th February and theSteamshipfor 15th February of the present year.[23]From experimental data obtained by Mr Froude, this correction can be made with certainty. The reasons for it may be explained as follows:—If an extremely thin short plane is drawn through the water it meets a certain resistance due entirely to surface-friction; that is, supposing the plane to be thin enough to eliminate wave-making and eddy-making. If the length of the plane is doubled while the depth is kept the same, the resistance at the same speed is not, as might at first appear to be the case, doubled accordingly. Owing to the friction of (say) the first half of the plane, the water is made to partake of the motion of the plane, so that the second half of the length, rubbing not against stationary water, but against water partially moving in its own direction, does not experience so much resistance from it. Adding a third equal length, it would have less surface friction than the second, and so on to infinity.[24]See papers by Mr Mansel, enumerated in list at end of chapter.[25]For description of apparatus, see Trans. Inst. Mechanical Engineers, 1877.[26]A body which shortly afterwards joined with a kindred society in forming the “Institution of Engineers and Shipbuilders in Scotland,” hereafter noticed.[27]Following the methods laid down in the Treatise on Shipbuilding, edited by Prof. Rankine, Mr John Inglis, Pointhouse, instituted calculations in 1873 of the longitudinal strains of two steamers built by his firm, the form of the waves being assumed trochoidal. The result of these calculations—which, under Mr Inglis’ directions, were got out by Mr G. L. Watson, subsequently distinguished as a yacht designer, and then in the employ of Messrs Inglis—appeared in the form of curves of hogging moments inEngineeringfor 1st May, 1874. Mr Inglis found that entering upon the work of calculation had a very decided effect in giving him clearer ideas of how distribution of weight and buoyancy affected the structure of a vessel.[28]The substance of this paper is contained in a series of three articles on the Strength and Strains of Ships given in “Naval Science” (vol. i. and ii., 1872-3), a high-class journal ably edited by Sir E. J. Reed, but unfortunately abandoned after the fourth year of publication.[29]It should be stated that under certain circumstances of lading and support the value assigned by Mr John for the maximum bending moment may be exceeded in merchant vessels, and that in some special classes of ships—particularly light-draught vessels in certain circumstances of lading and support—the sagging moment may prove of most consequence. Instances are indeed on record of light-draught vessels giving way completely under the excessive sagging strain brought upon them at sea.[30]The Institution of Engineers and Shipbuilders in Scotland was formed in 1865 through the amalgamation of two separate bodies—“The Institution of Engineers in Scotland” and “The Scottish Shipbuilders’ Association.” The former of these was founded in 1857 and the latter in 1860, the same year in which “The Institution of Naval Architects” was established. The membership of the Institution at the present time numbers nearly seven hundred, and comprises honorary members, members, associates, and graduates: the latter being a special section of the Institution, designed to embrace students or apprentices in the profession, and fulfilling a very useful end. The various offices have long been filled by gentlemen more or less actively engaged in the practice of shipbuilding or of engineering on the Clyde, and the proceedings have assumed, on this account alone, a richer practical interest. Scientific subjects have also received their share of attention, and of the members taking the lead in this connection the names of Mr J. G. Lawrie and Mr Robert Mansel are worthy of special mention. Along with Mr Robert Duncan and Mr Lawrance Hill, these gentlemen have, from the foundation of the Institution, taken a specially warm interest in its prosperity, and have contributed not a little thereto by the numerous valuable papers they have brought before its meetings. The secretary of the Institution is Mr W. J. Millar, C.E., himself the author of numerous papers, and the editor of the Transactions.[31]For interesting and reliable information on this head, as well as on other matters dealt with in this and the preceding chapter, see Sir E. J. Reed’s excellent treatise on “Shipbuilding in Iron and Steel.”[32]This method of graphically representing tonnage output was applied for the first time by the author to the Clyde district from the figures supplied by theGlasgow Heraldfor each of the years since 1860, and appeared, with much of the descriptive matter now given, in the issue of that journal for March 4th of the present year.[33]The following fragmentary returns have, through the kindness of a friend engaged in shipbuilding on the Tyne, been forwarded while those sheets were in the press. They have been gathered from occasional records in the local press, supplemented by personal knowledge, but may only be taken as approximate:—Year.No. ofVessels.Tons.Year.No. ofVessels.Tons.18649749,82018688645,390186512377,5001869———186611051,80018709586,42018678134,0801871———[34]These instruments, and the others here noticed, are supplied in this country by Mr W. F. Stanley, the noted scientific instrument maker of Great Turnstile, Holborn, London. They are described in his treatise on “Mathematical Drawing Instruments,” from which work, it should be stated, some of the present notes concerning them are derived. A source of accurate information on the theory of planimeter, to which Mr Stanley himself expresses indebtedness, is the paper by Mr —now Sir—F. J. Bramwell, read before the British Association in 1872, and contained in the Association Reports for that year.[35]The following is a list of the multipliers for converting the planimeter readings to square feet for any required scale:—1/16-in.scale=2565/16-in.scale=10·241-in.scale=1·00⅛-in.do.=64⅜-in.do.=7·111½-in.do.=·443/16-in.do.=28·44½-in.do.=4·003-in.do.=·111¼-in.do.=16¾-in.do.=1·77

FOOTNOTES:

[1]Since the above was written, theAuraniaand theOregonhave resumed their services on the Atlantic, the results in the case of the latter vessel being extraordinarily successful. On Saturday, the 5th April, she arrived at Queenstown, having left New York on Saturday, the 29th March, making the trip in 7 days, 2 hours, 18 minutes, her daily runs being:—45, 407, 396, 400, 302, 410, 384, 412, and 60; total, 2816 knots. Leaving Queenstown on Sunday, the 13th April, she arrived at New York on Saturday, the 19th April, in the unprecedentedly short period of 6 days, 9 hours, 22 minutes.

[2]While these sheets were passing through the press, theAmericawastried unofficiallyon the Clyde, and attained a speed of 17 knots, with about 6,500 indicated horse-power. On her passage from the Clyde to the Mersey she maintained, it is stated, 18¼ knots over the whole distance.

[3]This list with those which follow other chapters, have been compiled at considerable trouble in the hope that they may be of use to technical readers in directing them at once to accurate and detailed information. In this connection also, the excellent work by Mr A. S. Seaton, “Manual of Marine Engineering,” and that by Mr W. H. White, “Manual of Naval Architecture,” may be referred to with every satisfaction.

[4]For full and excellent treatment of this subject, see the paper on “Causes of Unseaworthiness in Merchant Steamers,” by Mr Benjamin Martell, Chief Surveyor to Lloyd’s Register, with the ensuing discussion: Trans. Inst., N.A., vol. xxi., 1880.Several of the causes above named it is doubtless the province of the scientific shipbuilder, and the duty of the shipowner, to obviate by furnishing the captain and officers—especially in the case of entirely new vessels—with particulars and data of the vessel’s technical character, such as are now left to be found out by slow and sometimes bitter experience. Of these it may be sufficient to instance:—Stability, steadiness, trim, carrying capability, and steaming powers. Mr William Denny, of Dumbarton, has recently publicly declared his firm’s intention of supplying such particulars to the vessels built by them. It is to be hoped this worthy example may be extensively followed.

Several of the causes above named it is doubtless the province of the scientific shipbuilder, and the duty of the shipowner, to obviate by furnishing the captain and officers—especially in the case of entirely new vessels—with particulars and data of the vessel’s technical character, such as are now left to be found out by slow and sometimes bitter experience. Of these it may be sufficient to instance:—Stability, steadiness, trim, carrying capability, and steaming powers. Mr William Denny, of Dumbarton, has recently publicly declared his firm’s intention of supplying such particulars to the vessels built by them. It is to be hoped this worthy example may be extensively followed.

[5]In this, as in other matters dealt with, the full appreciation of which involves careful technical study, readers are referred to the papers enumerated at the end of chapter, as well as to the “Manuals” already referred to in this work.

[6]The principle which underlies the experiment is this:—If any one body forming part of a system of heavy bodies be moved from one position in the system to another, the weight of the body moved multiplied into the distance through which it is moved, is precisely equal to the weight of the whole system of bodies multiplied into the distance through which the common centre of gravity of the whole has moved. If in a ship, therefore, a movable weight of known amount is moved across the deck through a given known distance, the centre of gravity of the ship itself, with all on board, has been moved in a line parallel to that through which the small weight has been transferred, and through a distance inversely proportioned to the weight of the whole ship to the weight moved. If, for instance, a weight of five tons should be moved through a distance of twenty feet, then multiplying this weight into this distance and dividing by the total weight of the ship, the distance through which the ship’s centre of gravity has travelled parallel to the deck is obtained. If, at the same time, an exact measure of the angle through which the ship has been inclined by moving the five tons through the distance named has been taken, and the position of the ship’s metacentre has been obtained, then the elements of a triangle are known—namely, the degrees in each of its angles, and the length of one of the sides—and from these the length of the remaining sides of the triangle is easily deduced. One of these sides will be the distance between the metacentre of the ship and its centre of gravity, and, consequently, the metacentre being known from calculation, the position of the centre of gravity becomes known also.

[7]The classification of strains here given is as contained in White’s “Manual of Naval Architecture.” To this authoritative source readers must turn who wish a full exposition of the several problems go shortly dealt with in these pages.

[8]This will be more fully referred to further on, but it may be stated here that the need for independent calculation is largely obviated, owing to the existence of “co-efficients,” deduced from investigations made by experts. Further, the existence and influence of the Registration Societies are such that the codes of scantling and the structural supervision instituted by them together constitute the only guarantee of structural strength generally desiderated.

[9]Suppose the dimensions of a proposed vessel to be 320 × 36 × 26½ feet, then, according to a method of approximation largely in use, the sum of these dimensions divided by 100 gives what is known as the “cubic number”—(320 × 36 × 26½ ÷ 100) = 3052 cubic number. Suppose that for a vessel already built, similar in type and dimensions, or of similar proportions, to the one proposed, the cubic number, when divided into the ship’s actual weight (i.e., the displacementminusthe weight of machinery and the dead-weight carried), gives say ·53, then this figure represents the “co-efficient” of ship’s weight, and applying it in the case supposed gives:—3052 × ·53 = 1620, the weight of hull for proposed vessel. This example illustrates the manner in which the weight of machinery is estimated, and indicates the nature and use of the general term “co-efficient:” frequently employed in this chapter.

[10]One such method, devised and followed by Mr C. Zimmermann in his daily practice as chief draughtsman to the Barrow Shipbuilding Company, and described by him before the Institution of Naval Architects in 1883, gives with very little preliminary calculation, and at once, a close approximation to the correct displacement. Another system, originated and used in practice by Mr Chas. H. Johnson, chief designer to Messrs Wm. Denny & Brothers, consists of an analysis of the lines of vessels of various degrees of fineness and fulness previously built, formulated for daily use in a series of curves of areas, giving, for sections at certain fixed distances from midships—in terms of percentage to the midship area—the particular area specially suited to afford the required displacement; and at the same time to maintain the general form of hull which in actual practice has proved satisfactory with respect to speed. In his later practice, Mr Johnson has found it preferable to use the block form of analysis of Mr A. C. Kirk (considered further on in matters relating to speed), using the three sides of that form as a basis upon which to group the water-lines.

[11]For illustrated descriptions of this and other improved calculating instruments referred to in this chapter, seeAppendix.

[12]This experimental method, it may be explained, has long been practised in connection with ships built for the Royal Navy, and for a considerable number of years it has been systematically followed in some leading merchant shipyards. Messrs A. & J. Inglis, Pointhouse, Glasgow, and Messrs Wm. Denny & Bros., Dumbarton, were amongst the earliest firms to systematically adopt the practice. With the former it has been customary to incline every vessel of distinctive type built by them since 1871, and with the latter the practice has been constantly followed from a date somewhat subsequent. For some years past other firms on the Clyde and elsewhere have adopted the method, the data so accumulated being found an admirable basis from which to estimate the height of the centre of gravity in proposed vessels. Tables giving the results of inclining experiments made on various types of merchant steamships and sailing vessels will be found in “White’s Manual of Naval Architecture,” pages 82-87.

[13]From the first volume (1860) of the Transactions of the Institution of Naval Architects, it is seen that Dr Inman, Samuel Read, and Dr Woolley had each already found different methods of simplifying Atwood’s calculations.

[14]Various other methods of simplifying the calculations based on Atwood’s theorem were subsequently proposed, and one or two different methods also brought forward—notably one in 1876 by the late Mr Charles W. Merrifield, afterwards improved by the late Professor Rankine, and one by Mr J. Macfarlane Gray, of the Board of Trade, described by that gentleman in 1875, but since considerably improved. Most of them were laid before the Institution of Naval Architects in papers which will be found enumerated in the list at end of chapter. While such propositions did not contribute directly to bring the problem of stability to its presently accepted form, they deserve to be remembered as tokens of the great labour and skill which have been expended in founding and developing this branch of scientific naval architecture.

[15]“On Cross-Curves of Stability; their Uses, and a Method of Constructing Them, Obviating the Necessity for the Usual Correction for the Differences of the Wedges of Immersion and Emersion.”

[16]A detailed description of this valuable instrument will be found inAppendix.

[17]Space forbids any detailed reference to these, but the names of the papers and their respective authors will be found enumerated in the list at end of chapter.

[18]An obvious means of dealing approximately with stability, to which limits of space will not permit more than simple reference, consists in so manipulating the data obtained by calculation for known ships that it may be made available, either in the form of curves or of tables, for determining the stability of proposed vessels. Methods of accomplishing this may of course vary to suit the ideas and convenience of designers. A well-arranged system was brought forward, jointly by Mr F. P. Purvis, head of Messrs W. Denny & Brothers’ scientific staff, and Mr B. Kindermann, one of his assistants, in a paper (see list at end of chapter) read before the Institution of Engineers and Shipbuilders in April last. While the results exhibited in the paper are immediately applicable to ships of one particular form, whatever the length, breadth, depth, or draught may be, this method still requires much development to make it at all universally applicable.

[19]It is the usual practice to assume vessels to be laden with homogeneous cargo of such a density as to fill the holds, and for this condition to estimate the position of centre of gravity to be used in calculation.

[20]See paper by Mr Kirk “On a Method of Analysing the Forms of Ships and Determining the Lengths and Angles of Entrance.”—Trans. Inst. N.A., vol. xii., 1880.

[21]With the view of effecting an economy in time, and to enable the trials at progressive speeds to be carried out while vessels are in a lengthened run out to sea, a method has been proposed by Mr J. H. Biles, naval architect to Messrs J. & G. Thomson, and adopted on board the vessels tried by that firm, and also experimented with on some of the vessels turned out by Messrs W. Denny & Bros., by which the necessity for running with and against the tide on the measured mile is entirely obviated. The principle of the method is to measure the time that a certain part of the length of the ship takes to pass an object thrown from the bows of the vessel well clear of the side. For full particulars, both of the apparatus employed and of the results of actual trials by this method compared with trials made on the measured mile, see paper on “Progressive Speed Trials,” by Mr Biles, in the Transactions: Institution of Naval Architects, vol. xxiii., 1882.

[22]A general outline of the operations conducted in Messrs Denny’s tank will be found in the description of their large works inChap. VI. For a detailed account of themodus operandiin the same establishment, see abstract of a paper delivered in Dumbarton by Mr E. R. Mumford, of Messrs Denny’s Experimental Staff, printed in theEngineerfor 15th February and theSteamshipfor 15th February of the present year.

[23]From experimental data obtained by Mr Froude, this correction can be made with certainty. The reasons for it may be explained as follows:—If an extremely thin short plane is drawn through the water it meets a certain resistance due entirely to surface-friction; that is, supposing the plane to be thin enough to eliminate wave-making and eddy-making. If the length of the plane is doubled while the depth is kept the same, the resistance at the same speed is not, as might at first appear to be the case, doubled accordingly. Owing to the friction of (say) the first half of the plane, the water is made to partake of the motion of the plane, so that the second half of the length, rubbing not against stationary water, but against water partially moving in its own direction, does not experience so much resistance from it. Adding a third equal length, it would have less surface friction than the second, and so on to infinity.

[24]See papers by Mr Mansel, enumerated in list at end of chapter.

[25]For description of apparatus, see Trans. Inst. Mechanical Engineers, 1877.

[26]A body which shortly afterwards joined with a kindred society in forming the “Institution of Engineers and Shipbuilders in Scotland,” hereafter noticed.

[27]Following the methods laid down in the Treatise on Shipbuilding, edited by Prof. Rankine, Mr John Inglis, Pointhouse, instituted calculations in 1873 of the longitudinal strains of two steamers built by his firm, the form of the waves being assumed trochoidal. The result of these calculations—which, under Mr Inglis’ directions, were got out by Mr G. L. Watson, subsequently distinguished as a yacht designer, and then in the employ of Messrs Inglis—appeared in the form of curves of hogging moments inEngineeringfor 1st May, 1874. Mr Inglis found that entering upon the work of calculation had a very decided effect in giving him clearer ideas of how distribution of weight and buoyancy affected the structure of a vessel.

[28]The substance of this paper is contained in a series of three articles on the Strength and Strains of Ships given in “Naval Science” (vol. i. and ii., 1872-3), a high-class journal ably edited by Sir E. J. Reed, but unfortunately abandoned after the fourth year of publication.

[29]It should be stated that under certain circumstances of lading and support the value assigned by Mr John for the maximum bending moment may be exceeded in merchant vessels, and that in some special classes of ships—particularly light-draught vessels in certain circumstances of lading and support—the sagging moment may prove of most consequence. Instances are indeed on record of light-draught vessels giving way completely under the excessive sagging strain brought upon them at sea.

[30]The Institution of Engineers and Shipbuilders in Scotland was formed in 1865 through the amalgamation of two separate bodies—“The Institution of Engineers in Scotland” and “The Scottish Shipbuilders’ Association.” The former of these was founded in 1857 and the latter in 1860, the same year in which “The Institution of Naval Architects” was established. The membership of the Institution at the present time numbers nearly seven hundred, and comprises honorary members, members, associates, and graduates: the latter being a special section of the Institution, designed to embrace students or apprentices in the profession, and fulfilling a very useful end. The various offices have long been filled by gentlemen more or less actively engaged in the practice of shipbuilding or of engineering on the Clyde, and the proceedings have assumed, on this account alone, a richer practical interest. Scientific subjects have also received their share of attention, and of the members taking the lead in this connection the names of Mr J. G. Lawrie and Mr Robert Mansel are worthy of special mention. Along with Mr Robert Duncan and Mr Lawrance Hill, these gentlemen have, from the foundation of the Institution, taken a specially warm interest in its prosperity, and have contributed not a little thereto by the numerous valuable papers they have brought before its meetings. The secretary of the Institution is Mr W. J. Millar, C.E., himself the author of numerous papers, and the editor of the Transactions.

[31]For interesting and reliable information on this head, as well as on other matters dealt with in this and the preceding chapter, see Sir E. J. Reed’s excellent treatise on “Shipbuilding in Iron and Steel.”

[32]This method of graphically representing tonnage output was applied for the first time by the author to the Clyde district from the figures supplied by theGlasgow Heraldfor each of the years since 1860, and appeared, with much of the descriptive matter now given, in the issue of that journal for March 4th of the present year.

[33]The following fragmentary returns have, through the kindness of a friend engaged in shipbuilding on the Tyne, been forwarded while those sheets were in the press. They have been gathered from occasional records in the local press, supplemented by personal knowledge, but may only be taken as approximate:—Year.No. ofVessels.Tons.Year.No. ofVessels.Tons.18649749,82018688645,390186512377,5001869———186611051,80018709586,42018678134,0801871———

[34]These instruments, and the others here noticed, are supplied in this country by Mr W. F. Stanley, the noted scientific instrument maker of Great Turnstile, Holborn, London. They are described in his treatise on “Mathematical Drawing Instruments,” from which work, it should be stated, some of the present notes concerning them are derived. A source of accurate information on the theory of planimeter, to which Mr Stanley himself expresses indebtedness, is the paper by Mr —now Sir—F. J. Bramwell, read before the British Association in 1872, and contained in the Association Reports for that year.

[35]The following is a list of the multipliers for converting the planimeter readings to square feet for any required scale:—1/16-in.scale=2565/16-in.scale=10·241-in.scale=1·00⅛-in.do.=64⅜-in.do.=7·111½-in.do.=·443/16-in.do.=28·44½-in.do.=4·003-in.do.=·111¼-in.do.=16¾-in.do.=1·77

[35]The following is a list of the multipliers for converting the planimeter readings to square feet for any required scale:—

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