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deprived of such erections, have likewise received our careful attention, and have had their due influence upon the tables submitted herewith. The same may be said with reference to the freeboards assigned to vessels of extreme proportions and to vessels of very fine forms. The Board of Trade distinction between winter and summer freeboards has" likewise, after the fullest consideration, been adopted.
The tables as now submitted involve only such limited modifications of the freeboards assigned by the latest tables of Lloyd's Register Office as Mr. Benjamin Martell is able to freely accept and cordially concur with. The same may be said of the extension of the tabular forms by the addition thereto of corrections for changes of length and for voyages in summer and in the North Atlantic in winter.
In the tables submitted the definitions of length, breadth, depth, sheer, round of beam, and freeboard have undergone revision.
The changes introduced have been made for the purpose of simplifying the assignment and marking of freeboards, and although they modify in one or two points the directions of the fourth section of the Merchant Shipping Act of 1873, and may therefore render legislation necessary, the measure required would be of so brief, simple, and non-contentious, a character as to render its passage easy.
It will be observed by the tables that they refer exclusively to cargo-carrying vessels. E. J. Reed (Chairnian), W. Denny, Robt. Duncan, James Dunn, Frans Elgar, Thomas Gray, William Gray, James Laing, B. Martell, Digby Murray, T. B. Royden, Thos. Sutherland, Reginald Bingham (Secretary). Explanation of the following Tables of Freeboard for the various
Types of Steam and Sailing Vessels. In the following tables the word Freeboard denotes the height of the side of a ship above the waterline at the middle of her length, measured from the top of the deck at the side, or, in cases where a waterway is fitted, from the curved line of the top of the deck continued through to the side. The freeboards and the corresponding percentages of reserve buoyancy necessary for flush-deck steamers not having spar or awning decks, for awning deck steamers, and for flush-deck sailing vessels, are given in Tables A, C, and D for vessels of these classes and of various dimensions and proportions. The freeboards necessary for spar deck steamers are given in Tables B. The latter are determined by considerations of structural strength, and they denote the limitations to depth of loading which are thereby imposed upon firstclass vessels of this type. The free. boards and percentages of reserve buoyancy thus obtained being in excess of what would otherwise be required, the amounts of such percentages are not given in tables B.
The exact freeboard required for a given ship belonging to any of the classes comprised in Tables A, C, and D, may be calculated by constructing a displacement scale to the height of the deck to which the freeboard is measured, so as to give the whole external volume up to the upper surface of that deck. The percentage of the total volume which is given in the tables as the reserve buoyancy for a vessel of given type and dimensions will be the amount of volume that must be left out of the water. If a water-line be drawn upon
the displacement scale aforesaid to cut off the given percentage of total volume, the height of side above this line will be the freeboard required.
In order to simplify and reduce the work that would be involved by the above mode of determining the water-line and the consequent freeboard, that correspond to a given percentage of reserve buoyancy, an approximate method is adopted in the following tables, which enables the freeboard of a vessel to be calculated with a sufficient degree of accuracy for all ordinary working purposes. The use of this method not only saves the time and labour that would be involved by making a complete displacement scale for the whole external volume of a ship, but, what is much more important, it makes the tables easily and directly applicable in cases where such a displacement scale for a vessel is not at hand, or where the data requisite for constructing one is not procurable.
In this approximate method the form of the ship is taken into account by means of proportionate quantities, which are termed coefficients of fineness, instead of by the exact volumes that a displacement scale would give. It is found that the whole internal volume of a ship as measured for register tonnage divided by the product of the length, breadth, and depth, measured as described in the following clauses 1, 2, and 3, gives a fractional quantity or coefficient which bears a nearly constant relation to the quantity that would be obtained by dividing the whole external volume below the upper surface of the deck by the product of the length, breadth, and depth. This fractional quantity is called the “coefficient of fineness” for freeboard purposes; and it serves the same practical object, when combined with the dimensions of the ship in the manner explained in the tables, as the volume itself would do.
İn applying such an approximate method as the above, it is necessary to connect the coefficients of fineness given in the tables with a standard sheer and round of beam. The standard scales for sheer and round of beam that have been adopted for this purpose are given in clauses 16 and 17 hereafter. Descriptions are also there given of the corrections that should be made for deviations from these standard amounts.
The freeboards given in the tables are for Aush-deck vessels in all cases. Such reductions in freeboard as may be allowed for deck erections of various kinds and sizes in steamers not having spar or awning decks, and in sailing vessels, are described in paragraphs II, 12, 13, 14, and 15.
No reduction of freeboard should be allowed on account of deck erections in spar-deck and awning-deck steamers.
Tables A and D give the minimum freeboards for first class iron and steel vessels, the strength of which is at least equal to the requirements of the 100A class in Lloyd's Register for three-deck and smaller vessels. The freeboard of all other iron and steel vessels, classed or unclassed, should be regulated by the same standard; the increase of freeboard required in each case being determined by the limit at which the stress per square inch upon the material of the hull amidships shall not exceed that of the standard class, of the same proportions, form, and moulded depth, when loaded to the freeboards required by Tables A and D. Tables B and C give the free. boards for vessels built in accordance with, or equal to the require. ments of Lloyd's Register for the spar and awning deck classes ; and are subject to the conditions just stated for any modifications of
strength in excess or diminution of the requirements of their respect tive classes.
1. Length. The length of the vessel is measured on the loadline from the fore side of the stem to the aft side of the stern post in sailing vessels, and to the aft side of the after post in steamers.
2. Breadth. The breadth used in obtaining the coefficient of fineness is the extreme breadth measured to the outside of plank or plating as given in the Register Book, or on the certificate of the ship's registry.
3. Depth of Hold. The depth used in obtaining the coefficient of fineness is the depth of hold as given in the Register Book, or on the certificate of the ship's registry. This dimension is subject to modification in determining the coefficient of fineness as explained in clause 4.
4. Coefficient of Fineness. The coefficient of fineness in one, two, and three deck and spar-deck vessels, is found by dividing 100 times the gross registered tonnage of the vessel below the upper deck by the product of the length, breadth, and depth of hold. In awning-deck vessels the registered depth and tonnage are taken below the main deck.
(a) It is of importance in the application of the rules and tables of freeboard that the coefficient of fineness deduced from the under-deck tonnage, and the principal dimensions should be a correct index to the vessel's relative fulness of form, and that a change in any of those elements which affect the coefficient, determined in accordance with the rule set forth should be considered, and the necessary correction, having regard to the special circumstances of the case, introduced. Among the cases that have from time to time come under notice are the following:
(6) Vessel having a cellular bottom throughout, or floors of greater depth than those usually fitted.--In such a case the coefficient as determined from the under deck tonnage is in most instances slightly greater than it would be if the vessel were framed on the ordinary transverse system with floors of the usual depth. No general rule can be given for guidance, but it is not difficult, if the depth and slope of the top of the cellular bottom or floor be compared on the midship section with the depth and slope of an ordinary floor, to determine very closely the amount of the correction necessary.
(c) Vessels constructed with floors of the ordinary kind, but with a cellular bottom for a part of the length amidships under the engines and boilers.-In such a case the registered underdeck tonnage is smaller than it would be if the vessel were framed with ordinary floors throughout, the difference being the tonnage of the space between the top of the cellular bottom in the part amidships, and the level of the ordinary floor. The depth of hold is also measured by the Customs officials to the top of the cellular bottom, and this depth is inserted in the register. Under such circumstances, in order to arrive at the coefficient of fineness the vessel would have, is built on the ordinary system throughout, and for which the tables are framed, the tonnage of the volume between the top of the cellular bottom and the level of the ordinary floor should be calculated and added to the registered under-deck tonnage. The tonnage so corrected, used in conjunction with the depth of hold to the top of the ordinary floor, gives the coefficient to be used in the tables.
(d) Vessels constructed with a cellular bottom throughout the fore and after holds, but with floors of the ordinary kind fitted for a part of the length amidships under the engines and boilers.In such a case the tonnage of the space between the top of the ordinary floors in the part amidships, and the top of the cellular bottom, if made continuous, should be estimated, and de. ducted from the registered under-deck tonnage, and the remainder employed in conjunction with the depth of hold to the top of the cellular bottom in determining the coefficient of fineness.
(e) Other cases may in practice arise in which the registered under-deck tonnage, or the registered depth of hold, or both, require modification before being used in the determination of the coefficient of fineness, but little difficulty will be experienced in making the necessary correction, if it be remembered that the coefficient sought is the coefficient the vessel would have if
framed on the ordinary transverse system. 5. Moulded Depth.—The moulded depth of an iron or steel vessel, as given in the tables, is the perpendicular depth taken from the top of the upper deck beam at side, at the middle of the length of the vessel, to the top of the keel and the bottom of the frame at the middle line, except in spar and awning deck vessels, in which the depth is measured from the top of the main deck beams. In wooden and composite vessels the moulded depth is taken to be the perpendicular depth from the top of the upper deck beam at the side of the vessel amidships to the lower edge of the rabbet of the keel.
(a) The form at the lower part of the midship transverse section of many wooden and composite vessels being of a hollow character, as in cases where thick garboard strakes are fitted, the moulded depth in such instances should be measured from the point where the line of the flat of the bottom continued
cuts the keel. 6. Freeboard.—The moulded depth, taken as above described, is that used in the tables for ascertaining the amount of reserve buoyancy and corresponding freeboard in vessels having a wood deck, and the freeboard is measured from the top of the wood deck at side, at the middle of the length of the vessel.
(a) On the same principle, in fush-deck vessels, other than spar or awning decked, and in vessels fitted with short poop and forecastle, having an iron upper deck, not covered with wood, the usual thickness of a wood deck should be deducted from the moulded depth of the vessel measured as above, and the amount of reserve buoyancy and corresponding freeboard taken from the column in the tables corresponding with this diminished moulded depth: Example.-In a steamer fitted with an iron upper deck, not covered with wood, and having a moulded depth of 19ft roin, 4 inches, or the usual thickness of a wood deck, must be deducted from this, leaving a depth of 19st 6in. The freeboard of such a vessel with a coefficient of fineness of 0.76, taken from the column under 19ft bin, is 3st 8in, which should be measured from the top of the iron upper deck.
(6) In spar-deck vessels having iron spar decks, and in
awning-deck vessels having iron main decks, the freeboard required by the tables should be measured as if those decks were wood covered. Also in vessels where 7-10ths, or more, of the main deck is covered by substantial erections, the freeboard found from the tables should be measured amidships from a wood deck, whether the deck be of wood or iron. In apply, ing this principle to vessels having shorter lengths of substantial enclosed erections the reduction in freeboard in consideration of its being measured from the iron deck, is to be regulated in proportion to the length of the deck covered by such erections. Thus, in a vessel having erections covering 6-10ths of the length, the reduction is 6-10ths of 3) inches, or 2 inches. 7. For vessels which trim very much by the stern, through the engines being fitted aft, the freeboard, as ascertained from the tables, if set off amidships would not cut off the amount of surplus buoyancy deemed necessary, and in such cases the suitable freeboard amidships could only be determined after full information is obtained regarding the vessel's trim.
8. The following example will illustrate the general application of the tables :
In a steamer of the following dimensions, viz., length 204ft; breadth extreme, 29ft ; depth of hold 16'oft ; registered tonnage under deck, 682 tons; and moulded depth, 17 oft ; the under deck capacity in cubic feet is 68,200 ; by dividing this by 94,656, that is, the product of the length, breadth, and depth of hold, the quotient is o*72, or the coefficient of fineness.
If we now refer to Table A at 17.ost moulded depth, and trace the line opposite the coefficient 0*72 to the column corresponding with this depth, it is found that the winter freeboard given for a first-class steam vessel without erections, whose length is twelve times the moulded depth, is 2st urin, corresponding with a reserve buoy. ancy of 25 per cent. of the total bulk.
9. Vessels of Extreme Proportions.-For vessels whose length is greater or less than that of the vessel of the same moulded depth for which the tables are framed, the freeboard should be increased or diminished as specified in the footnote to the tables. Thus, if the vessel in the example, clause 8, were 224ft long, the winter free. board required would be eft in plus zin, or 3ft iin, For steam vessels with top-gallant forecastles, having long poops or raised quarter decks connected with bridge-houses, the whole extending over 6-10ths, or more, of the length of the vessel, the correction for length should be one-half that specified in Tables A.
10. Breadth and Depth.-In framing the tables it has been assumed that the relation between the breadth and depth is such as to ensure safety at sea with the freeboard assigned when the vessel is laden with homogeneous cargo; for vessels of less relative breadth, the freeboard should be so increased as to provide a sufficient range of stability, or other means adopted to secure the same.
11. Erections on Deck. For steam vessels with top-gallant forecastles having long poops, or raised quarter decks connected with bridge-houses, covering in the engine and boiler openings, the latter being entered from the top, and having an efficiently constructed iron bulkhead at the fore end, a deduction may be made