Ship Hull

This invention relates to a ship hull adapted for operation in ice-filled waters.

As a ship moves through an ice field, chunks of ice in front of the ship are forced below the surface of the water by virtue of the ship's forward movement. The chunks of ice then slide along the external suface of the underwater part of the hull. Some of the chunks of ice slide along the bottom surface of the hull, thereby easily obstructing the ship's propeller. This reduces propeller efficiency, and the chunks of ice can also cause damage to the propeller. The chunks of ice which slide along the side surfaces of the ship can also get into the ship's propeller, particularly in twin or triple propeller ships.

The purpose of the invention is to create a favorable hull form for a ship operating in icy waters, so that chunks of ice will be directed in such a way as to have as small an adverse effect as possible on the forward movement of the ship.

The configuration of the hull of a ship is conveniently illustrated by means of its so-called frame form, which shows the external cross-section of the hull at a defined location along the length of the ship. Several frame forms may be illustrated in a single figure (such as FIG. 1 of the accompanying drawings). The main frame form is the frame form midway along the hull's design waterline length.

For convenience of nomenclature, the "side surfaces" of the hull are those portions of the hull, extending downwards from the top of the hull at port and starboard respectively, which are vertical or are inclined to the vertical at a smaller angle than to the horizontal, and the "bottom surface" of the hull is that portion of the hull, beneath the side surfaces, which is inclined to the horizontal at a smaller angle than to the vertical.

It will be appreciated that in order to maximize the internal volume, or cubic capacity, of a ship's hull, within given overall dimensions, the hull is normally constructed so that its middle section is of substantially uniform beam, and the hull's bottom surface, within the middle section, is made as wide as possible within the limits determined by the sides of the ship.

According to a first aspect of the present invention, there is provided a ship having a hull defining a bow having a substantially V-shaped form in the waterline plane of the ship, and having a general frame form defining a bottom surface and two side surfaces, the bottom surface of the hull having a bottom section that is horizontal in a cross-section of the hull and extends longitudinally of the hull midway between the two side surfaces of the hull, and the bottom surface of the hull also having two inclined bottom sections that are located entirely below said design waterline plane and are joined to the horizontal bottom section along respective sides thereof and to the side surfaces respectively, each such join being along a clearly defined longitudinal intersection edge, whereby each side of the hull is divided into at least three clearly defined portions, the width of said horizontal bottom section of each of the inclined bottom sections being at least 20% of the maximum beam of the hull, and the inclined bottom sections extending over a substantial part of the length of the hull.

According to a second aspect of the present invention there is provided a ship hull defining a bow having a substantially V-shaped form in the design waterline plane of the hull, and having a general frame form defining a bottom surface and two side surfaces, the bottom surface of the hull having a bottom section that is horizontal in a cross-section of the hull and extends longitudinally of the hull midway between the two side surfaces of the hull, and the bottom surface of the hull also having two inclined bottom sections that are located entirely below said design waterline plane and are joined to the horizontal bottom section along respective sides thereof and to the side surfaces respectively, each such join being along a clearly defined longitudinal intersection edge, whereby each side of the hull is divided into at least three clearly defined portions, the width of said horizontal bottom section and of each of the inclined bottom sections being at least 20% of the maximum beam of the hull, and the inclined bottom sections extending over a substantial part of the length of the hull.

In the case of a ship embodying the first aspect of the invention, or a ship having a hull embodying the second aspect of the invention, very few chunks of ice go under the horizontal bottom section of the hull because it is quite narrow. Owing to their buoyancy, the chunks of ice which go under the inclined bottom section move towards the sides. Since the bow of the ship is substantially V-shaped in the waterline plane, the bow's main section has a wedge-shaped form in horizontal cross section, and this pushes the ice to the sides. However, it is not essential to the invention that the very front part of the bow at the design waterline be sharp. The bow can be designed in the manner described in U.S. Pat. No. 4,351,255.

In a preferred embodiment of the invention, which is intended for operation in extremely difficult ice conditions, the lower part of each side surface is inclined. It is also important for the horizontal bottom section and the inclined bottom section together to extend over a considerable proportion of the length of the ship. In practice this means that the length of that part of the ship which has the defined general frame form extends over at least 20% and preferably at least 30% of the ship's design waterline length. It is most desirable that the defined general frame form applies to the form of the main frame of the ship. If the ship has a middle section of uniform beam whose length is at least 25% of the ship's waterline length, it is preferred that the defined general frame form should apply at a point whose distance to the rear from the foremost point of the ship's middle section of uniform beam is 20% of the design waterline length, provided that this point is forward of the main frame.

As indicated previously, if the horizontal bottom section is made too narrow, the hull will have an unfavorable cubic capacity because the ship's internal volume is small in relation to the ship's overall dimensions. Owing to this, it is most advantageous for the horizontal bottom section to be at least 30% of the ship's maximum beam. If the ship only has a single propulsion propeller, the width of the horizontal bottom section should preferably be at least as large as the diameter of the propulsion propeller. If twin propellers are used for the ship's propulsion, the total width of the horizontal bottom section should preferably be at least 80% of the distance between the axes of these propellers. The horizontal bottom section may be of uniform beam for at least part of its length forward of the point where the bottom line of the ship begins to rise towards the stern of the ship. The horizontal bottom section may even become wider towards the stern. In the latter case, a more favorable hull form in terms of cubic capacity is obtained and at the same time more effective steering of the chunks of ice towards the sides is achieved. The horizontal bottom section may then advantageously be narrow at the forward narrowing section of the ship, for instance having a width of no more than 15% of the maximum beam of the ship. At the point of the bow section, where the bottom line of the hull proper of the ship rises in the forward direction, the horizontal bottom section may be at the bottom of a wedge-shaped structure protruding downwards from the hull proper of the ship.

If the ship has side surfaces that are inclined to the vertical, the angle of inclination should not be made too large because the hull's cubic capacity is then adversely affected.

The angle of inclination of the side surfaces is preferably smaller than the angle between the inclined bottom section and the horizontal plane. This too favorably affects the guiding of the chunks of ice. The angle of inclination of the inclined bottom section in relation to the horizontal plane is preferably between 5 and 30 degrees, more preferably from 8 degrees to 20 degrees. In a particularly preferred embodiment of the invention, the side surface has an inclined section that extends upwards from the outer edge of the inclined bottom section so far above the ship's design waterline that its end point remains above the waterline even when the ship heels to the maximum angle for which the ship is designed. The inclined bottom section preferably extends in the longitudinal direction of the ship both backwards and forwards at least to the point where the ship's bottom line begins to rise and in the aft direction preferably extends a considerable distance farther than that point.

In a hull embodying the invention it is very advantageous to use the air bubbling system described in U.S. Pat. No. 3,580,204. Air discharge openings are located at the lower edge of the inclined bottom section, whereby the hull form enhances the beneficial effect of the bubbling and the bubbling also enhances the beneficial effect of the hull form. It is advisable to provide the air discharge openings over that longitudinal section of the hull for which the ship's bottom line is substantially horizontal. It is also advantageous to arrange air discharge openings forward of this section. This can easily be done, if the bow section of the ship has a structure that extends downwards from the hull proper as has already been described. A hull form with an inclined side surface below the waterline best enhances the effect of air bubbling.

The invention will now be described in detail, referring, by way of example, to the attached drawings, in which

FIG. 1 represents schematically the frame forms of a first ship hull in such a way that the left side shows the hull as a rear view and the right side shows the hull as a front view,

FIG. 2 is a schematic side elevation of the ship hull shows in FIG. 1,

FIG. 3 is a bottom plan view of the ship hull shown in FIG. 1,

FIG. 4 is a bottom plan view of a second ship hull,

FIG. 5 is a side elevation of the ship hull shown in FIG. 4,

FIG. 6 is a front elevation of the ship hull shown in FIG. 4, and

FIG. 7 is a rear elevation of the ship hull shown in FIG. 4.

The frame form lines 0 to 10 shown in FIG. 1 correspond to the eleven cross sections 0 to 10 shown in FIG. 2. Sections 0 and 10 are at the end points of the ship's design waterline. The distance L from cross sectional plane 0 to cross sectional plane 10 is thus the ship's design waterline length. The distance between each two adjacent cross sectional planes in FIG. 2 is 10% of the ship's design waterline length. The cross-section 5 is the ship's main frame. The cross-sectional diagrams should not be taken to imply that there would necessarily be a structural frame member at the cross section location in question.

In the drawings, 11 denotes the ship's hull, 12 its horizontal bottom section, and 13 its inclined bottom section. The maximum width of the horizontal bottom section 12 is A and the maximum width of the inclined bottom section 13 is B. The dimension B is measured in horizontal plane. Both dimensions A and B are at least 20% of the ship's maximum beam C. Dimension A is also no less than 30% of the maximum beam C at least in the position of main frame 5. Dimension A in a single propeller ship is at least as large as the diameter D of the propeller 17 and in a twin propeller ship at least 80% of the distance 2F between the axes of the propellers 17. Between the frames 2 and 7, the side of the ship consists of two parts, the upper vertical side part 14 and the lower inclined side part 15, which extends a distance H above the ship's design waterline plane 16. The distance H should preferably be such that part of the inclined side section 15 remains above the waterline even when the ship heels to the maximum angle of inclination b taken into account in the ship's design.

Between the frames 2 and 7, the ship's frame form has four discontinuities, which are at the junctures of the bottom sections 12 and 13 and of the bottom sections 13 and the side sections 15. Preferably, these junctures are sharp, but it might be necessary, especially in the ship's bow, for the junctures at least between sections 13 and 15 to be somewhat curved. The radius of curvatures is at any rate kept as small as possible taking into account the general design of the hull. The cross sectional form of the inclined bottom section 13 and/or the side section 15 may be somewhat curved, but this usually increases the ship's construction costs without countervailing improvements so far as performance in ice conditions is concerned.

In the case of the ship shown in FIG. 1, the angle d between the inclined bottom section 13 and the horizontal plane is greater than the angle e between the inclined side surface 15 and the vertical plane. Angle d is generally between 5 degrees and 30 degrees and preferably from 8 degrees to 20 degrees.

When the ship is viewed in the design waterline plane and at other horizontal sections, it has a substantially V-shaped bow section 18 and a narrowing stern section 19. The ship's midsection 20 is of uniform beam and occupies the distance M between the bow and stern sections. That part of the ship where its bottom line 22 is substantially horizontal when viewed from the side (FIG. 2) is indicated by the letter P. The horizontal bottom section 12 extends backwards with a uniform width to the end point 21 of section P, where the ship's bottom line 22 begins to rise. The inclined bottom section 13 also extends backwards beyond the point 21.

FIGS. 4-7 show a ship in which the width of the horizontal bottom section 12 increases in the direction towards the stern of the ship. In this case, the horizontal bottom section is substantially triangular in shape, as viewed in bottom plan (FIG. 4). In the case of FIGS. 4-7, dimension M, or the ship's middle part 20 having a uniform beam, is long. In this kind of ship, where dimension M is at least 25% of the ship's design waterline length L, the most important portion where the frame form that is characteristic of the invention should be applied is the portion that is to the rear of the forward end 23 of the section 20 by a distance equal to 20% of the ship's design waterline length L. This theoretical checkpoint is shown as number 24 in FIG. 4. However, this checkpoint is never located to the rear of the midpoint of the design waterline length L, that is, to the rear of the ship's main frame.

The ship shown in FIGS. 4-7 has two propulsion propellers 17 fitted in respective nozzles 25. The rudders 26 are behind the two propellers.

In the case of FIGS. 1-3, the horizontal bottom section 12 ends at that point in the forward part of the ship where the bottom line 22 starts to rise. The ship shown in FIGS. 4-7 can be constructed in a similar manner, where the horizontal bottom section 12 would end approximately at the position of section plane 23. It is, however, possible to continue the horizontal bottom section 12 forwards in such a way that a protruding wedge-shaped structure 27 is formed, extending downwards and forwards from the hull proper. The bottom surface of the wedge-shaped structure forms the forwardmost part of the horizontal bottom section 12. When the horizontal bottom section widens towards the rear, it is preferred that its forward end is narrower than 15% of the ship's maximum beam C.

It is very advantageous to use the previously mentioned air bubbling system in a ship embodying the invention in such a way that the air discharge openings 28 are arranged at the lower edge of the inclined bottom sections 13. In FIG. 1 these openings and the air discharging through them are symbolized by means of arrows 28a. It is advisable to locate the openings 28 as close to the junctures of the inclined bottom section 13 and the horizontal bottom section 12 as structural considerations permit. As FIG. 2 shows, there are air discharge openings 28 over the entire length of the section P.

In a ship having a wedge-shaped structure 27 protruding downward and forward from the hull proper toward the bow, it is advantageous to locate air discharge openings 28 also in this part of the vessel. This makes it possible to bring air discharge openings located at a low level nearer the ship's bow, which otherwise is impossible because the underwater bow line of a ship designed for use in icy conditions is generally very strongly inclined to the vertical.

It will be appreciated by those skilled in the art that the present invention is not restricted to the particular hull configurations that have been shown as described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims, and equivalents thereof.