US 3842771 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Murata SHIPS LINES  Inventor: Yoshiaki Murata, 2-17-19 Ofuna Kamakura, Kanagawa Prefecture, Japan  Filed: May 30, 1972 21 Appl. No.: 257,510
 US. Cl. 114/56, 114/122'  Int. Cl. B63b 1/32  Field of Search 114/56, 122
 References Cited UNITED STATES PATENTS 1,133,928 3/1915 Cahill [14/122 1,780,970 11/1930 Campbell 2,892,435 6/1959 .Ljungstrom 114/122 .Oct. 22, 1974 3,303,809 2/1967 Ross; 114/56 3,369,512 2/1968 Music ll4/56 Primary Examinef-Trygve M. Blix Assistant Examiner-Galen L. Barefoot Attorney, Agent, or Firm-Anthony A. OBrien [5 7] ABSTRACT Ships lines or hull contour having side shell platings slanted in the midship section such that lower portion of the side shell platings are directed toward the longitudinal central plane of the ship below the full load water line and upper portion of the side shell are directed away from the longitudinal central plane of the ship, so as to obtain a relatively large value of the rolling period even under light load conditions.
2 Claims, 3 Drawing Figures 1 SHIPS LINES The present invention relates to a hull for a ship, more particularly hull for a ship providing a prolonged period of roll at sea, while maintaining a sufficient stability thereof.
It is heretofore known that a metacentric height GM must be enlarged in order to increase the stability of the ship while it must be reduced for obtaining a sufficiently long period of rolling motion to prevent people aboard the ship from becoming sea sick, and that the stability and the rolling period will present a conflicting problem in determining a value of GM. The value of GM is normally determined by compromising requirements presented from the standpoint of stability and from that of the rolling period. However, the value of GM selected by such a step will be after all deemed unsatisfactory in terms of either one or both standpoints. In the case of bulk carriers, shoulder tanks are provided on the hull for the purpose of regulating the value of GM. However, those shoulder tanks do not prove sufficiently effective since the amount of ballast water loaded into those tanks is limited. Some ships have been designed to have a sufficiently large value of stability, with the problem of rolling period being solved separately, for instance, by providing some sort of roll damping means. However, such roll damping means have not been found sufficiently effective. For instance, a fin type stabilizer is not effective in increasing the rolling period, although it may reduce an angle of roll of the ship at high speed. The roll damping means is not necessarily advantageous since it will involve an increase of ship's horse power and initial cost.
Accordingly, a primary object of the present invention is to overcome disadvantages of conventional ships as described hereinabove.
Another object of the present invention is to provide ships lines producing an improved stability over the prior art lines and a prolonged period of roll in both light and full load condition. I I
According to the present invention, a hull for a ship is formed of a pair of opposed side shell platings slanted with respect to the longitudinal center plane of the ship such that lower portions of the shell platings are directed toward the ships longitudinal center plane below a full load water line and upper portions of the shell platings are directed away from the ships longitudinal center plane above the full load water line in a midship section of the ship.
A preferred embodiment of the ships lines according to the present invention will be described hereinafter in detail with reference to accompanying drawings, in which FIG. 1 is a midship diagrammatic sectional view showing the ships lines according to the present invention in full line and conventional lines in dotted line,
FIG. 2 is a horizontal sectional view taken along a line ll- 11 in FIG. 1 showing a half breadth of the ship according to the present invention in full line and that of the conventional ship in dotted line, and FIG. 3 is a graphical representation showing a variation of the center of buoyancy, the center of gravity and the position of metacenter in horizontal axis with a change of ships draft taken in vertical axis. j
Referring to FIG. 1, there is shown a hull structure incorporating ships lines according to the present invention floating at a full load draft 6-6. The feature of the present invention resides in that side shell platings 3 are slanted with respect to the ships longitudinal center plane XX such that a lower portion 3 of the shell platings will be directed toward the latter below the full load water line 6-6 and an upper portion 2 of the shell platings away from the latter above the full load water line. The hull 10 is provided with upper deck 1, bridge deck 5 and superstructure decks 8, all of which are superposed one above the other. Bottom shell platings of the hull are shown at 4, and the ships light load water line is designated at 7-7. A box-shaped conventional ship form 9 is shown in dotted line.
As known conventionally, the metacentric height GM and the period T of the roll of ship will be defined where C is a constant value.
by following formulae;
T= 2.01 x K/B X B0] GM where K denotes upper surface of keel plates, that is, a datum line for measuring the heightof various points,
G the position of center of gravity of the ship in any loaded condition, thus giving the height thereofby KG,
- varies proportionally with a draft d of the ship, KB may be expressed as follows;
KB C X d Also, as known in the prior art, a distance between the center of buoyancy B and the metacenter M is defined by following formulae;
where 1 denotes a moment of inertia of the water line plane, at which the ship floats, with respect to the longitudinal central axis of the ship,
V a volume of immersed portion of the ship,
Cb a block coefficient of the ship, and
m a coefficient of constant value.
The present invention contemplates the reduction of the ships breadth B in the above formula (4) as the draft d becomes smaller, such that the metacenter M will come closer toward the center of gravity G when the draft d is reduced by'unloading of the cargo placed on or above the upper deck and by consumption of water and fuel loaded below the upper deck and consequently the height of the center of gravity KG becomes smaller. Since the breadth of the ship becomes smaller as the water line plane comes down, the side shell platings will be slanted toward the longitudinal center plane of the ship. The inclination of side shell platings with respect to the vertical will vary to the cargo and route of the ship. However, the inclination will be preferably in a range of 12 to 28"v to the vertical, assuming that the ship would have a predetermined breadth B at the full load draft. When the side shell platings are constructed in this manner, the value of KM will be reduced considerably as the draft d becomes smaller, thereby maintaining the value of GM substantially at a constant. Therefore, the rolling period T will not be reduced even in a light load condition. That is to say; the rolling period T will be maintained at a constant, regardless of the change of draft of the ship. A ship incorporating the ships lines according to the present invention .will roll at sea at a period twice that of the conventional ship in various loaded conditions. The rolling period T can be prolonged to the extent that no one aboard the ship can feel the rolling of the ship. In this manner, passengers and crews aboard the ship may become free from sea sickness, and various cargo, for instance, fully loaded trucks aboard the ship can be prevented from becoming upset.
Conversely, for the conventional box-shaped hull structure 9, since the center of gravity G will come downwardly with the ships breadth unchanged asthe draft d becomes smaller, the value of Km, that is, the height of metacenter above the top'surface of the keel plate, will be considerably increased in accordance with the formula (4), as shown clearly by a dotted line KM in FIG. 3. Therefore, the value of GM will become conspicuously larger, thereby reducing the rolling period T, as thedraft d decreases.
Further, according to the present invention, the side shell platings are considerably slanted upwardly and outwardly above the full load water line. Accordingly, the side shell platings 2 will have a conspicuous flare extended outwardly similarly to a horizontal flange of a washing bowl.
The flare portion of the side shell platings 2 according to the present invention will increase the breadth of ship considerably, enlarge the value of BM in accordance with the formula (4), raise the'position of the Y metacenter M, and increase the value of GM, thereby improving the ships stability. That is to say, the flare portion will act as a supporting lever'for preventing the ship from becoming upset. a
In the prior art hull structure, when the rolling period T is larger, the ship will become more pleasant to ride. However, such ships are relatively weak against the side wind. The ship may be easily upsetwhen she, is fully subjected to a heavy wind from one side at rough sea.
When the ships breadth Bo at the full loaddraft is reduced by l0 percent, as compared with a normal type ship, for thepurpose of improving the rolling period, the ships length may have to be increased, say, by 10 percent to compensate for reduction of the breadth for securing the same amount of deadweight or gross tonnage. In this case, a ships depth D and the draft d are naturally taken into consideration for determining the length L. The height of the center of gravity, the metacentric height GM and the rolling period T willbe taken into account when determining the value of breadth B0. I a
FIG. 2 shows a contour of the water line plane of the ship incorporating hull lines according to the present invention floating in a light load condition, together with that of the ship having conventional lines in dotted line. As shown in the drawing, the ship's length is rendered greater in the ship incorporating the lines according to the present invention than that of the conventional ship, although the ship 5 breadth is considerably reduced as compared to that of the conventional ship due to the inclination of side shell platings.
In FIG. 3, 3 curves, that is, KB-, KG-, KM-curve, are delineated by taking the draft d in the vertical axis and taking the height respectively of the center of buoyancy B, the center of gravity G, and the metacenter M above the top of keel plate in the horizontal axis. The feature of the present invention will be clearly understood by comparing the KM-curve of the lines according to the present invention with that of the conventional lines. That is to say, in case of the lines according to the present invention, KM-curve (full line) will increase at a large gradient, thereby increasing the value of GM, above the full load water line 6-6, as the draft d increases. However, below the full load water line 6-6, the KM-curve will come closer to the KG-curve in intermediate load condition 7-7 as well as in a light load condition, as shown in the portion l2of the KM-curve having a conspicuous curvature, and both KM- and KG-curve are delineated substantially in parallel. Accordingly, the value of GM ismaintained at a constant below the full load conditiom'regardless of the value of d. In this manner, the period T of rolling will not be reduced even in light load condition for a ship having lines according to the present invention. Conversely, a KM-curve (dotted line) comes closer to the KG-curve such that the value of GM will be reduced, thereby degrading the stability, above the full load water line 6-6 in case of the conventional ships lines. Moreover, the KM-curve (dotted line) is coming away from the KG- curve such that the value of GM will be increased .thereby reducing the rolling period to the extent that people aboard the ship will feel sea sick, below the full load water line 6-6. It is ideal to have the value of metacentric height GM varied as shown in full line in FIG. 3 as the draft 21 changes. The variation of the metacentric height GM as shwon in dotted line in FIG. 3 is deemed undesirable.
In case of the ship incorporating the lines according to the present invention, area available for carrying cargo on the upper deck will be considerably increased. The deck cargo may be loaded on the upperdeck at a level relatively lower than that of deck cargo on the conventional ship. Therefore,'the center of gravity of the ship will be lowered, thereby eliminating the ballast water in the double bottom tanks. Thus, the cargo carr'ying capacity of the ship can be increasedas much as the ballast water is saved.
On the other hand, since the center of gravity of the ship is not lowered unduly inthe ship according to the present invention-for the reason of increased cargo loaded on theupper deck, the breadth of which is particularly increased above the full load water line, a vertical distance. 00 from the center of gravity G to the center 0 of the water line plane can be maintained at a suitably small value, thereby reducing an angle of roll 0 of the ship. it is appreciated that the angle of roll will be reduced also by the increased value of GM which is attributable to a sudden increase of the ships breadth immediately below the upper deck.
The ships lines according to the present invention will be suitable for carrying timber or wooden chips,
since the cargo carrying capacity above the upper deck is increased. However, the present ships lines are more preferable for so-called car ferry" carrying automotive vehicles on the upper deck particularly for the reason of the rolling period T being not reduced even in the light load condition, since all the passengers aboard the ship are free from sea sickness.
Since the breadth of the ship in the water line plane is reduced and the length is increased so as to produce a water line form more smooth and fine than that of the conventional ships lines in the present invention as shown in FIG. 2, the wave-making resistance of the ship will be reduced thereby substantially saving the horse power of main engine and the fuel consumption and hence reducing the initial cost of the ship.
What is claimed is:
1. A hull for a ship configured to define a vertical longitudinal center plane and a full load water line, said hull comprising a pair of opposed side shell platings having lower portions slanted relative to said vertical longitudinal center plane and directed from said full load water line toward said vertical longitudinal center plane at an angle to lower the metacenter when the draft of the ship is reduced such that metacentric height is maintained substantially constant as the draft varies, said side shell platings having upper portions slanted relative to said vertical longitudinal center plane and directed from said full load water line away from said vertical longitudinal center plane to form a protruding flared'structure for a midship section of the ship, the included angle between each of said upper portions of saidside shell platings and said vertical longitudinal center plane being greater than the included angle between each of said lower portions of said side shell platings and said vertical longitudinal center plane but less than 2. A hull for a ship as recited in claim 1 wherein the included angle between each of said lower portions of said side shell platings and said vertical longitudinal center plane is within a range of from twelve to 28.