US3306243A

US3306243A - Cargo ship hull

Info

Publication number: US3306243A
Application number: US397172A
Authority: US
Inventors: William O Gray; Bryant A Hilliard
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1964-09-17
Filing date: 1964-09-17
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28

Description

Feb. 28, 1967 w. o. GRAY ETAL CARGO SHIP HULL Filed Sept. 17, 1964 FIG. 1

TOTAL AREA FIG. 4

HALF BEAMM FIG. 3

(EEL

INVENTORS WILLIAM o. GRAY BRYANT A. H ILL'IARD he n,Chosan,Li'rro Marx BxWright United States Patent Ofiice 3,306,243 CARGO SHIP HULL William 0. Gray, Pratt Island, Darien, and Bryant A. Hilliard, Norwalk, Conn., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Sept. 17, 1964, Ser. No. 397,172 1 Claim. (Cl. 114-56) The present invention relates to full form ships such as oil tankers and like bulk cargo carriers and, more particularly, to a new and improved hull shape therefor.

Naval architects have long designed the lines of vessels in forms having the tendency to reduce the wave making resistance and to improve overall efiiciency, i.e., reduction of power requirements for given speeds. A recent development in the solution of the excessive wave making problems of full form ships (i.e., ships with a Block Coefiicient greater than 0.75 and with speed to length ratio (VA/L) of less than 0.8, as distinguished from the relatively fine lined, sleek passenger liners and warships having Block Coefiicients of less than .75) ha involved the enlarging of the lower part of an otherwise conventional bow of the ship into a substantially bulbous form or so-called bulbous bow. The novel placement and p-roportioning of the bulbous bow enables its advantages, heretofore known in connection with passenger and warships with relatively fixed drafts, to be realized in connection with tankers and the like, having a full form and a highly variable water line.

The bulbous bow as heretofore designed for tankers has proved effective in substantially reducing wave making of full form ships. However, the advantages of such construction are realized to a lesser extent when such full form ships travel in a fully laden rather than in a ballast condition. Accordingly, an important object of the present invention is to further improve the efliciency of a full form ship by providing a hull that has a reduced wave making resistance at all conditions of draft, from fully laden to ballast.

Another and more specific object of the invention is to improve the shape of the bow structure of a full form ship having a substantial difference between its designed Load Water Line and Ballast Water Line (as contrasted with a fine lined ship which sails at a comparatively constant draft) by providing a predetermined hollow or concavity at intermediate bow portions of the hull, in conjunction with a protruding bulb at the lower bow portions of the hull in a predetermined relation with the hollow. The hollow reduces the entrance angle at the Load Water Line and serves to increase the efiicacy of the bulbous bow portion when the ship is traveling under load.

The above and other objects and attendant advantages of the present invention will be more fully understood by referring to the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a fragmentary side elevational view of a full form ship with a new and improved bow structure, embodying the principles of the invention;

FIG. 2 is a fragmentary, cross-sectional view of the hollow bow structure of the new ship taken along line 2-2 of FIG. 1 with the outline of a conventional bow superimposed in broken lines;

FIG. 3 is a series of conventional naval architectural representations of the transverse half sections of the ship of FIG. 1, with broken lines representing the corresponding sections of the bow of a conventional ship superimposed; and

FIG. 4 is a graphical plot of the cross-sectional areas of the hollow bow at the water lines of the forwardm-ost stations of the ship as contrasted with those of a conventional ship shown by broken lines.

3,306,243 Patented Feb. 28, 1967 With reference to FIG. 1, a carbon hull 10 is shown with the inventive structure in its bow 11, which is advantageously slightly raked as is typical for most tankers. The cargo ship 10 is a full form ship having a relatively high Block Coefficient (C which is, in effect a measure of the extent to which the shape of the ship approximates a long rectangular box, and having a relatively low speed to length ratio (VA/T.) in comparison with fine lined, passenger ships and warships. More specifically, the full form ship hull 10 has a Block Coefficient greater than 0.75 and a designed speed to length ratio of less than 0.8.

The hull structure from the rearmost stern stations (not illustrated) through the intermediate stations is conventional for ships of this type. Hence, the transverse sections a a a taken at intermediate stations (FIG. 3) of the hull, correspond to those of conventional ships and are relatively smoothly shaped having a gradually sloped, regular contour.

In accordance with an important aspect of the invention, a new hull shape for full form ships is formed by creating a hollow or concavity 12 in the sides 13 of the bow 11 of the full form cargo ship, which ship, as a cargo carrier, has a substantial separation between the designed Ballast Water Line (BWL) and the designed Load Water Line (LWL) at the forwardmost portions of the ship (the Ballast Water Line usually being disposed above the keel 14 at a level 30-60% of the level of the Load Water Line above the keel). Accordingly, the transverse sections b b b at the forwardmost stations include changes in shape in the side of the ship at a knuckle 15 or the like, which defines the upper limit of a hollow 12 above the Load Water Line, as shown in FIG. 1. The concavity 12, defined in the sides 13 of the ship extends vertically from the knuckle 15 at points above the Load Water Line to points slightly above the Ballast Water Line where the sides defining the lower limits of the hollow are faired into the lower portions 16 of the hull. The rearmost extremities 17 of the hollow are faired into the general lines of the ship at sections of less than full beam (B), as shown in FIGS. 2 and 3. The longitudinal extent of the hollow will normally be less than 20% of the length of a conventionally proportioned hull between its forward perpendicular (PP) and its aft perpendicular (the perpendiculars intersecting the forwardmost and rearmost portions of the hull along the Load Water Line).

As an important aspect of the invention, the entrance angle 0 (by definition the angle between the center line and the tangent to the ship profile at the point where it is intersected by the water line) of the hollow portions 12 of the bow between the Load Water Line and Ballast Water Line is significantly reduced from the entrance angle 0 of a conventional ship of similar overall proportions, whose conventional bow profile is represented in the dotted outline superimposed on the profile of the new ship hull 10, as shown in FIG. 2. More specifically, a conventional ship has a substantially constant entrance angle 0 at levels below and above the Load Water Line, for example, whereas a ship constructed in accordance with the present invention has a significantly reduced entrance angle 9 at the water lines adjacent the Load Water Line within the hollow 12 and a different and larger entrance angle corresponding generally to the conventional wider entrance angle 0 at bow portions without the hollow 12. Thus, the hollow form of the bow significantly reduces the transverse vertical crosssectional areas of the bow structure at intermediate water lines as compared with corresponding cross-sectional areas of conventional ships, as illustrated graphically in FIG. 4.

In cooperative association with the-hollow 12 in the bow, and as an important aspect of the invention, a protruding bulb 18, extending forwardly of the forward perpendicular (PP) and constructed in accordance with the principles set forth in more detail in the copending application of Ernst Eckert, Serial No. 389,157, filed August 12, 1964, for Improved Ships Hull Construction, is formed at the forward end of the keel 14. Specifically, a bulb constructed in accordance with the principles of the copending application protrudes forwardly of the forward perpendicular of the hull at the Load Water Line, has a substantial although minor portion above 60 percent of the height from the keel line to the Load Water Line, and has it forwardmost portion or nose located at a level in the range between 30 percent and 40 percent of the height from the keel line to the Load Water Line. Reference may be had to that application Serial No. 389,157 for further, more specific details of the placement and proportioning of the bulb. A shown in the transverse sections of FIG. 3 and in the side elevational view of FIG. 1, the bulb 18, as a further important aspect of the invention, extends slightly above the Ballast Water Line and is faired into the concavity of the hollow 12 to provide smoothly molded hull form.

In accordance with the principles of the invention, the efficiency, in terms of power requirements, of a full form ship of predetermined dimensions and displacement embodying the inventive structure and sailing at any draft between ballast and full load is improved substantially at normal speeds due to a substantial reduction in wave making resistance in comparison with a ship of conventional shape having similar dimensions and displacement. While the specific hydrodynamic theory for this significant improvement in operation is not fully understood, the creation of a hydrodynamic sink in the hollow 12 cooperating with the effects of the bulb has been empirically determined to be unusually effective in reducing the wave making resistance of full form ships at all draft conditions. More specifically, the beneficial resistance-reducing effects of the bulb 18, which tend to predominate at ballast conditions of draft, and the beneficial resistancereducing effects of the hollow 12, which tend to predominate at fully laden draft conditions, synergistically combine, in a full form ship, to provide significantly improved performance at all conditions of draft from full load to ballast. Thus, it should be appreciated that a full form ship provided with both a hollow, creating a reduced entrance angle at the Load Water Line, and a protruding bulb in the bow structure, in accordance with the principles of the invention, will have a substantially reduced wave making resistance and a markedly increased etficiency.

It should be understood that the specific construction herein illustrated and described is intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claim in determining the full scope of the invention.

What is claimed is:

A full form ship hull having a substantial difference between its designed Ballast Water Line and Load Water Line at its forward end including,

(a) a bulbous bow protruding from the lowermost portions of said hull forwardly of the forward perpendicula of said hull,

(b) forwardmost sides of said hull at the bow of said ship defining an elongate concavity having upper and lower extremes,

(c) said concavity extending rearwardly and terminating at a point of less than full beam,

((1) said concavity being disposed below said Load Water Line and extending to slightly above the Ballast Water Line at the forward perpendicular and at least partly above said Load Water Line and cooperating with said bulbous bow to provide minimum wave making resistance, the lower extreme of said concavity defining a line substantially parallel to said Load Water Line,

(e) said hull having a first predetermined entrance angle at said Load Water Line and Ballast Water Line at said forward perpendicular and a second predetermined entrance angle above said concavity and said Load Water Line,

(f) said first entrance angle being less than said second entrance angle.

References Cited by the Examiner UNITED STATES PATENTS 5/1963 Costanzi 114-65 4/1965 Inui 11456