US2054011A - Construction of floating vessels - Google Patents

Description

Sept; 8, J w SHERWOOD CONSTRUCTION OF FLOATING VESSELS Filed Jan. 1933 4 Sheets-Sheet 1 Invezz for Sept. 8, 1936. J. W. ISHERWOOD CONSTRUCTION OF FLOATING VESSELS 4 Sheets-Sheet 2 Filed Jan.- 6, 1933 JW sberWoocZ Invezz for Attorney Sept. 8, 1936. i J. w. ISH'ERWOOD 2,054,011

CONSTRUCTION OF FLOATING VESSELS Filed Jan. 6, 1933 4 Shets-Sheet 3 .IWIsherWoacZ hr Inventor Sept. 8, 1936. J. w. ISHERWOOD CONSTRUCTION OF FLOATING VESSELS Filed Jan. e, 1955 4 Sheets-Sheet 4 .J. lshefwood nven tor Patented Sept. 8, 1936 UNITED STATES PATENT OFFICE Joseph William Isherwo'od, Chislehurst,

. Kent, England Application January 6, 1933, Serial No. 650,554 In Great Britain July 26, 1932 6 Claims.

This invention relates to improvements in floating vessels of the mercantile form which normally have horizontal sections producing approximately parallel sides over a substantial pro- 6 portion of the ship's length and relates in particular to floating vessels of the type having a floor which is either fiat or has a slight rise (for drainage purposes) i. e. it does not include floating vessels having a central portion of cylindrical, oval or elliptical cross section.

It is well known that in ancient days sailing ships, which were built of wood and which are the precursors of the modern ship of today, were built within a moulded breadth line having a midship cross sectional form with a substantial rise of floor and with what is known as 'easy bilges, i. e. curved in approximately the arc of a circle of large radius, the side walls of the ship up to the load water line being either straight or slightly curved and then curved inboard from about the load water. line to the deck. Such vessels might be broader at the load water line than at the bilge but always within the moulded breadth line and still be regarded as vessels of normal form.

This midship section contour wassimilar in either cargo carrying vessels or in ships of war, with the exception that the ships of war were constructed with finer lines forward and aft for 30 the purpose of attaining comparative greater speed.

The tendency for many years past has been gradually to lower the rise of floor line and to make shipswith flatter bottoms and the bilges 35 sharper and sharper, i. e. substantially an arc of a circle of small radius. At the present time the normal form of a vessel of mercantile form is one having a middle body portion with little or no rise of floor, vertical wall-like sides, and very sharp bilges. It is the general practice to design the midship section within the moulded dimensions of the vessel, viz. breadth, depth and base line or rise of floor line, and the normal form is des iged' to give the maximum displace- 45 ment in these conditions, the midship section area being such as would be contained in 9. rectangle the upper horizontal line of which corresponds to the load water line, the lower horizontal line of said rectangle being the base or bottom of the vessel (whilst in cases in which the vessel is provided with a rise of floor line, this rise of floor line is considered as the base line of the rectangle), and the sides of the rectangle being the moulded breadth lines of the vessel. Such a rectangle is clearly indicated in each of Figs. 1, 2 and 3.

The result of the sharpening of the bilge for the purpose of increasing the midship section area or displacement, has increased the welted 5 surface by a greater percentage than the percentage increase in displacement.

The above, being a development of the previous types, has produced a type of vessel to which, in the following, I have applied the term normal form for the sake of brevity of description and it is in comparison with this type of vessel obtaining today that my invention particularly applies.

The object of my invention is to provide a vessel of the type described of such fcrm that the wetted surface is considerably reduced and is such as to provide an optimum. value when all other qualities of the ship are considered, such as reduced frictional and wave making resist- 2 ance, reduced propelling power, reduced weight of hull, increased cubic capacity, reduced water ballast capacity for the same comparative, draft, increased dead-weight carrying capacity, increased stability, these results being obtained Without additional first cost.

According to the present invention in a floating vessel of the mercantile type and having a middle body portion extending over at least 40% of the vessel the breadth of the frame moulding line in the vicinity of the load water line is increased beyond the breadth of a rectangle whose area is equal to therequired midship section area of the. vessel, at the upper turn of the bilge the widths of the vessel are less than the rectangle, the mean widths of both between the load water line and the upper turn of bilge being approximately the same, whilst the frame moulding line descends from the load water line for a comparatively short dlSl :nce almost vertically or with a constant slope then in a fair curve of decreasing slope until it joins the flat of bottom or floor line without a sharp turn of bilge, the width of the fiat of bottom of the vessel being substantial and notless than one third of the maximum beam thus maintaining approximately the same displacement or midship section area as that of the rectangle, whilst the wetted surface is substantially reduced, all sharpness or abruptness of bilge eliminated, the flow lines of water are rendered easier and frictional, and wave making resistance of the min are reduced.

The term middle body portion means that portion of the vessel wherein cross sections are. 5

of approximately the same shape as the amidship cross section. Practically all normal vessels have an easily recognizable middle body portion which varies in length according to the size and the type of vessel and may be from about 15% of the length on either side of the amidship section in a vessel with fine lines up to about 40% of such length on either side of the amidship section in a vessel of full lines.

As an example, if the middle body portion be 40% of the length of the vessel the cross sections I taken at any part within the said middle body portion would include sections which are not less than of the area of the amidship section area. As another example, if the middle body portion be taken as 60% of the lengthof the vessel, cross sections taken at any. part within the said middle body portion would include sections which are not less than 55% of the area of the amidship section area. The term flat of bottom as defined in the body of this specification and in the appended claims is to be understood as that part of the bottom plating below or joining the lower turn of the bilge.

It has previously been proposed to build vessels with a semi-circular midship contour or having each half of the midship section in the form of an arc of a circle so that despite the relatively small displacement compared with normal ships of substantially rectangular midship section, it will carry its weights for a voyage'of the desired length, owing to the decrease in power (and consequent decrease in weight of machinery) required being greater than the decrease in displacement. In contradistinction to this proposal, according to my invention I do not reduce the displacement of the vessel as compared with a vessel of normal form and I provide a sufliciently wide and flat bottom frame line with not greater,

a bilge of small radius in order to reduce the wetted surface but with much greater percentage reduction in displacement.

The curves of the sides of transverse sections of the middle body portions of a vessel according to my invention are preferably arcs of circles or approximating thereto. The are is not necessarily tangential to the base line or rise of floor line, the end of the arc, (where such is employed) being joined by a fair curve to meet the baseline. In a vessel constructed in accordance with this invention the point, where the frame moulding line intersects the bilge diagonal, is located a distance in along the bilge diagonal which is never less than 14% of the length of such diagonal.

Preferably the increase in beam at the load water line is approximately 10% of the width of the rectangle whose area is equal to the required midship section area of the vessel as previously defined. The efliciency is increased up to say 15% increase in beam dependent on the resultant ultimate beam and its effect on the economic permissible an le of entrance of the forward lines,

and the run of the after lines. Beyond 15% increase in beam the efi'iciency of the vessel tends to fall off on account of the limitations previously mentioned, and it will be obvious that the increasing percentage in increase in beam as compared with similar vessels of normal form will ultimately find its maximum by simple comparative illustration. If the increase in beam is less than 10% the advantages decrease, and in practice I do not employ a beam in which the increase is reduced below 5%.

'I'he midship section contour above the load water line may be of any desired form to meet therequirements of design.

The width of the midship section of a vessel made in accordance with this invention (hereinafter called the new section) exceeds the width of the rectangle (whose area is equal to the re-- quired midship section area, as defined above) for a distance below theload water line that varies according to the size and type of the vessel. In general such distance would be from.% to %rds.the draft of the vessel. At the lower extremity of this distance the width of the new section" is the same as the .width of the rectangle. Below this point the width of the "new section" is less than that of the rectangle. The curvature of the "new section is easy and progressive and the normal sharp bilge is eliminated.

The curved sides of the new section will join the base line or rise of floor line at a point nearer the keel than in the case of a normal vessel. The base line or rise of floor line itself will be simi larly situated as in the case of a normal vessel but the bottom frame or floor line will be narrower. At the same time it will be of sumcient width to aid stability of the vessel and provide for easy dry docking conditions.

With the same displacement and with ties wetted surface as compared with the normal form of vessel the angles of entrance and/or run of the load water line can be the same or similar as for those of normal form, whilst the angles 01' entrance and/or run of the lower water lines may be somewhat less than normal, giving finer lines in the region of the bottom of the vessel without any reduction in displacement. From tests carried out at the National Physical Laboratory, Teddington, it has been ascertained that the forward water line can be made fuller than in a vessel of normal form, thus increasing the displacement and carrying capacity of a vessel of my new section without loss of efliciency, as compared with a vessel of normal form. The reduced angle of run of the lower water lines provides for easier flow lines of water past the bottom of the vessel and is particularly beneficial in providing an easy flow of water to the propeller or propellers.

The invention is illustrated by way of example in the accompanying drawings in which Figures 1, 2 and 3 are diagrams illustrating the comparison between prior art vessels and vessels according to this invention,said diagrams illustrative of the contour of the middle body portion of the vessels; Figures 4 and 5 are diagrams illustrating the comparison between prior art vessels, and vessels according to this invention, said diagrams illustrative of the contour of the horizontal body portions of said vessels taken at the load water line and lower water line in way of the bilge respectively; whilst the Figures 6 and '7 are diagrams taining the contour of the middle body portion of a vessel made according to this invention. Figs. 8 and 9 show the distance in along the bilge diagonal of the point of intersection between this latter and the frame moulding line of the vessel. In the drawings showing transverse sections, the weather deck is approximately in the plane of the uppermost dashed line, as W Z in Figs. 8 and'9.

Referring now to Figures 1 to 3, in each case there is shown a rectangle which approximates,

except for a slight turn of bilge, the contour of the section of the middle body portion of a vessel of normal form, that is to say a vessel built in accordance with modern practice said contour represented by the dotted lines I. The area of the rectangle is made equal to the required midship section area of a vessel built according to this invention the contour of which is represented in full lines 2. The load water line which is the same height above the base line as the upper horizontal line of the rectangle is, in each case, indicated at 3-3, 4-4 representing the center line of the vessel. In Figure 1 there is indicated a vessel having no rise of floor in which case the base line of the vessel forms part of the base line of the rectangle; in Figure 2 a vessel with medium rise of floor, and in Figure 3 a vessel with large rise of floor.

In all cases in which the vessel is provided with a rise of floor, the rise of floor line is to be considered as the base line ofthe rectangle.

55 represents the lower water line in way of the bilge. It will be noticed that the additional area or space 6 provided in the vessel constructed in accordance with this invention is the same or approximately so as the area or space I which is in a vessel of normal form and not in the vessel according to this invention.

Referring now to Figures 4 and 5 the vessel of normal form is indicated in dotted lines I and the vessel according to this invention in full lines 2. 99 represents the normal moulded breadth line; lB--I0 and ll-H are lines drawn tangential to the load water line and lower water line, thus showing respectively the angle of entrance G and run H at the load water and lower water lines. The middle body portion of the vessel is indicated as extending between the lines l2|2 in Figure 4 at load water line and the lines I3--I3 Figure'5 at the lower water line.

For a given'displacement the girth of the section of the middle body portion of a vessel according to this invention is less than as compared with a vessel of normal form, and therefore, there is a reduction in wetted surface area and, of course, of frictional and wave making resistance; the invention also provides for easier flow lines of water past the bottom of the vessel.

The reduction in girth and reduction in widths of bottom at double bottom if one be employed,

along with the raising of the neutral axis of the structure, all effect a saving in weight of steel with a corresponding increase in the deadweight carrying capacity.

For instance in a vessel 400 feet long and with 10% increase in beam at load water-line, the estimated reduction in weight of steel would be from about 70-120 tons dependent on the system of construction.

The increase in reserve buoyancy (represented by the area or space 8 in Figures 1, 2 and 3) enables the vessels to be loaded deeper than would be the case of a comparable vessel of normal form, and so further increase the deadweight carrying capacity to an estimated total of 220-270 tons. Obviously the deeper immersion would not be obtained in vessels having a finer block coeflicient of displacement than .68 because of the legal limitations laid down by International Convention Load Line Rules.

The breadth of the lower part (neighbourhood of bilge) of the vessel being less than normal, causes greater immersion at light drafts, also greater immersion at the ballast draft, with the same or less weight of ballast which is, as is well known, of particular advantage.

From the load water-line upwards to the deck the side of the vessel may continue in the same curve form as shown in full lines in Figures 1, 2 and 3 or it can be extended up, to the deck in a straightened curve, or made wallsided as indicated in dotted lines Figures 1, 2 and 3 if it is desired to provide "for increased cubic capacity, increased reserve buoyancy or increased deck area.

Referring now to Figures 6 and 7, as in the previous figures there is shown the rectangle whose area is equal to the required midship section area of the vessel, which rectangle is substantially the contour of the section of a vessel of normal form is indicated in dotted lines I whilst two different forms of vessel according to this invention are indicated in full lines 2. In order to determine the radius of the arc of a circle forming the contour of the side of the vessel according to this invention the formula set out below can be applied for a vessel having any desired increase in beam percentage or to any ratio of beam to draft. Whilst I do not bind myself to any particular formula or shape, the examples shown in Figures 6 and 7 illustrate the principles of the invention.

In order to determine the formula:

1. Starting from the rectangle mentioned above, which rectangle approximates the contour of a section of a vessel of normal form, the beam is increased to the point A (Figures 6 and 7) on each side of the rectangle to the desired amount.

In Figure 6 this increase, which hereinafter is termed a, is

of the beam, and it is in Figure 7.. As stated before, the arrangement shown in Figure 6 is preferable, although the increase .1: may vary according to the type of vessel it is desired to build.

2. Mark off point B on the line of the rectangle, or the vertical normal breadth line I, at

a distance below the load water-line equal to A;

the distance d between load water-line and the base-line. I

3. Draw a straight line through points A and B meeting the base-line at point D.

7. From point E downwards a fair curve is drawn to meet the base line.

In vessels in which a: is small, say

the point E is preferably! at a vertical distance above the base line equal to 20% d and the versed sine is preferably 1:.

In vessels having a rise of floor the words base line" used in determining the above formula should be replaced by the words rise of floor line.

It is obvious that an arc of a circle might be made to any assumed width at load water line beyond that actually required and the are moved inboard to such desired increased beam, until the same approximate midship section displacement is obtained.

The invention can be applied in the construction of all kinds of mercantile vessels, either for overseas trading, or for trading in limited waters and is advantageous in the construction of either general cargo vessels or passenger liners.

Referring to the arrangement illustrated in ure 8, one form' of vessel having a 10% increase in beam according to the invention is shown in full lines 2. KOLNPMK (shown in dotted lines) is a rectangle bounding the same area as the required midship section area of the vessel to be built, the line K L being the load water line and the line MP N the bottom of the vessel. The increase in beam at the load water line is 10% greater than the width KOL of the rectangle. RS TU represents a second rectangle which shows the maximum beam and draft of the vessel according to the invention, whilst U 0 and TO represent the bilge diagonals. 'The frame moulding line of the vessel intersects the bilge diagonal at V, the distance in along the line U0 or T0 of the point V being 19.0% of the length of the diagonal.

In Figure 9 there is shown a similar vessel (having a 10% increase in beam at load water line) but with a rise of floor. In this case the area bounded by the figure KOLNPM'K is the same as the midship area of the vessel to be built and the bilge diagonals are represented by the lines U 0 and T O, R. S T' U being an approximate rectangle similar to the rectangle R S T U (Figure 8). The frame moulding line of the vessel intersects the bilge diagonals at the points V the distance in along the lines U 0 or T0 of the points V being 19.0% of the length of the diagonal.

In order to avoid -a sharp bilge, an excessive rise of floor and an excessive width of flat of bottom (such as are shown in the British patcut to Cassap No. 21,177 of 1897) the distance inv alongthe bilge diagonal should not be less than 14% of the length of the bilge diagonal. V

The invention can advantageously be applied in the construction of all kinds of mercantile vessels, either for overseas trading, or for trading in limited waters, and is advantageous in the construction of either general cargo vessels or passenger liners.

The invention is advantageous for vessels constructed for the carriage of liquid in bulk either with a centre longitudinal bulkhead, with two longitudinal bulkheads or with three or more longitudinal bulkheads, and it may also be adapted in suitable designs of vessels without a longitudinal bulkhead, and is equally adaptable to longitudinal, transverse or combined methods of framing.

One of the advantages for the bulk liquid carrier is that the vessel can be more readily adapted for the ballast condition and considerably less ballast is necessary to load a vessel to-the same ballast draft as in the comparable normal vessel. For instance, a vessel of say 10,000 tons deadweight in the loaded condition will carry in the ballast condition for the same draft as the normal vessel some hundreds of tons less water ballast.

Furthermore, by forming the sides of the vessel in the shape of the arc of a circle or approximating thereto, a further advantage is obtained inasmuch as preliminary information can be given by the technical staff as to the radius of this are and thus enable the frame benders to commence bending the side frames in the middle body. portion without having to wait for information from the mould loft or the scrieve boards.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

1. The method of determining the arc of the Side of the transverse sections of the middle body'portion of a vessel comparable to a ship having straight wall sides, i. e., comparable transverse sections having similar displacement or area, but wherein the beam of the former is approximately to 15% greater thanthat of the latter, which consists in establishing a straight line defined by the points A and B, the point A being located on the load water line beyond the contour of the side of the wall-sided ship a distance equal to one-half the total increase in beam, and the point B being located on the contour of the side of the wall-sided ship one third the distance from the load water line to the base line; establishing a point E on said line located no greater than one eighth of the vertical distance from the base line to the load water line; and employing the portion AE of said line as .a chord of the desired arc, said chord having a versed sine equal substantially to one half the total increase in beam.

2. The method of determining the arc of the side of the transverse sections of the middle body portion of a vessel comparable to a ship having straight wall sides, i. e., comparable transverse sections having similar displacement or area,

but wherein the beam of the former is approximately 5% to 15% greater than that of the latter, which consists in establishing a straight line defined by the points A and B, the point A being located on the load water line beyond the contour of the side of the wall-sided ship a distance equal to one half the total increase in beam, and the point B being located on the contour of the side of the wall-sided ship one third the distance from the load water line to the base line; establishing a point E on said line located between one tenth and one eighth of the vertical distance from the base line to the load water line; and employing the portion AE of said line as a chord of the desired are, said chord having a versed sine equal to from eight twentieths to nine twentieths the total increase in beam.

3. The method of determining the arc of the side of the transverse sections of the middle body portion of a vessel comparable to a ship having straight wall sides, 1. e. comparable transverse sections having similar displacement or area, but wherein the beam of the former is approximately 5% to 15% greater than that of the latter, which consists in establishing a straightline defined by the points A and B, the point A being located on the load water line beyond the contour of the side of the wall-sided shipa distance equal to substantially one-half the total increase in beam, and the point B being located on the contour of the side of the wall-sided ship substantially one-third the distance from the load water line to the base line; establishing a' point E on said line located no greater than oneeighth of the vertical distance from the base line to the load water line; and employing the portion A E of said line as a chord of the desired arc, said chord having a versed sine equal substantially to one-half the total increase in beam.

4. A floating vessel of the mercantile type and having a middle body portion extending over at least 40% of the length of the vessel, in which load water line and the upper turn of bilge being approximately the same, whilst the frame moulding line descends from the load water line for a comparatively short distance in a constant slope which is substantially vertical and then in a fair curve in a decreasing slope until it joins the flat of bottom or floor line, the area which is lost as compared with the rectangle of equal area in the region of the bilge which joins the bottom without a sharp curve is added by the arcuate form of the frame moulding line outside the rectangle oi equal area, the width of the flat of bottom of the vessel being substantial and not less than A; of the maximum beam. and the width of the weather deck corresponding substantially to the width of the rectangle, and the distance in along the bilge diagonal at which the frame moulding line and bilge diagonal intersect being at least 14% of the total length of said diagonal, thus maintaining approximately the same midship section area as that 01' the rectangle whilst the wetted surface is substantially reduced, all sharpness or abruptness of turn of bilge is eliminated, the flow lines of water are rendered easier, and frictional and wave making resistance of the hull are reduced.

5. A floating vessel of the mercantile type and having a middle body portion in which the maximum breadth of the frame moulding line is in the vicinity oi the load water line and is increased substantially 5-15% beyond the breadth of a rectangle of equal area, below water of the same depth, the width of the flat 'of bottom of the vessel being substantial and not less than one third of the maximum beam, the frame moulding line being characterized by the use of an arc form main transverse section with avoidance of sharp curvature running into the bottom, and the width of the weather deck corresponding substantially to the width of the rectangle. Y

6. A floating vessel of the mercantile type and having a middle body portion in which the maximum breadth of'the irame moulding line is in the vicinity of the load water line and is increased substantially 5-l5% beyond the breadth of a rectangle of equal area below water of the same depth, the width of the flat of bottom of the vessel being substantial and not less than one third of the maximum beam, the frame moulding line being characterized by the use of an arc form main transverse section with avoidance of sharp curvature running into the bottom, and the beam at a distance of one third

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