WO2012007035A1

WO2012007035A1 - Ship with bulbous bow

Info

Publication number: WO2012007035A1
Application number: PCT/EP2010/060119
Authority: WO
Inventors: Hans Christian Nielsen
Original assignee: Hans Christian Nielsen
Priority date: 2010-07-14
Filing date: 2010-07-14
Publication date: 2012-01-19

Abstract

A ship designed to operate at service speeds in excess of 20.5 knots comprising a slender hull having a block coefficient below 0.72 and a Froude number above 0.28 and a design draft defining a design water line is disclosed. The hull is defined inter alia by an aft part and a forward part comprising a bulb and a bow profile extending upwards above the bulb and design water line. The bow profile defines flare which, in a vertical central and transverse plane of the hull, extends, in a longitudinal direction of the hull, between 0% and 50% of the longitudinal length of the bulb.

Description

SHIP WITH BULBOUS BOW

The present invention relates to the form of a fore ship of a ship. The form of the fore ship will provide a bow which, due to its distinct form, is less susceptible for deformation and damage due to high sea conditions. Further, the form of the fore ship according to the present invention is, e.g., able to reduce the wave or sea resistance inflicted on the bow of a ship sailing at relatively high speeds.

According to a first aspect, the present invention relates to a ship designed to operate at service speeds in excess of 20.5 knots. The ship comprises a slender hull having a block coefficient below 0.72 and a Froude number above 0.28 as well as a design draft defining a design water line of the hull. The hull is further defined inter alia by an aft part and a forward part comprising a bulb and a bow profile or bow line extending upwards above the bulb and the design water line. A bulbous bow is, according to common shipbuilding practice, a protruding bulb arranged at the bow, or front, of a ship just below the waterline. The bulb modifies the way water flows around the forward part of the hull reducing drag and thus increasing the ship's speed, range and fuel efficiency.

In this specification, the expression bulbous bow denote a bulb which do not necessarily protrude beyond, in a longitudinal direction of the ship, the ship's forward perpendicular, however the bulb may, according to certain aspects of the present invention, protrude beyond certain parts of the hull in the area of the forward perpendicular.

The forward perpendicular is a vertical line drawn through the point of inter- section of the design water line and the stem of the ship.

The block coefficient is the ratio of the volume of water displaced by a ship to the product of the ship's length, breadth, and draft. Gains in fuel efficiency, rendered by the bulb, are often between 12-15%.

In a conventionally shaped bow, a bow wave forms immediately ahead of the bow. When a bulb is placed below the water ahead of this wave, water is forced to flow up over the bulb. If a wave formed by water flowing off the bulb coincides with the bow wave, the two waves partially cancel out and thereby greatly reduce the vessel's wake.

Another explanation of the bulb's effect focuses on the fact that water flowing over the bulb depresses the ship's bow and keeps the ship's at optimum trim, allowing the engines to be more efficient. Trim is the relationship between a ship's draughts forward and aft.

A sharp bow also produces waves and low drag like a bulbous bow, but waves coming from the side would strike the hull harder. Also, when the bow moves up and down in heavy seas, the water has to flow around the bulb, damping the movement like a squiggle keel. The expression "aft", "after" or "rear" is throughout this specification intended to denote a portion of a ship lying behind the middle portion of the ship.

The expression "fwd" or "forward" is throughout this specification intended to denote a portion of a ship lying in front of the middle portion of the ship. Background

The first bulbous bows appeared in the 1920s with the introduction of the Bremen and Europa, two German North Atlantic Ocean liners. Bremen, which appeared in 1929, was able to win the coveted Blue Ribbon of the Atlantic with a speed of as much as 27.9 knots. Smaller passenger liners such as the American President Hoover and President Coolidge of 1931 began to appear with bulbous bows although they were still viewed by many ship owners and builders as experimental.

In 1935 the French superliner Normandie made use of a bulbous bow with a radically redesigned shape and was able to achieve speeds in excess of 30 knots. At the time Normandie was famous for (among other things) her clean entry into the water and her greatly reduced bow wave. Normandie's rival, the British liner Queen Mary achieved equivalent speeds with a non-bulbous and traditional stem and hull design; however, the crucial difference lay in the fact that Normandie achieved these speeds with approximately 30% less engine power than the Queen Mary.

Today's classical bow shapes are greatly inspired by the design of the abovementioned ship's provided with bulbous bows, i.e. the forepart of the ship's is provided with a bulb which, when the ship is submerged at design draft, protrudes below the waterline and forward the hull's intersection with the design water plane, i.e. the ship's forward perpendicular. According to the classic design, the bow profile or bow line extends, above the design water line, further forward from the forward perpendicular and the bow profile terminates at a longitudinal position which substantially corresponds to the lon- gitudinal position of the extreme forward of the bulb. As the longitudinal distance between the forward perpendicular and the extreme forward of the bulb typically is in the range of, or even above, 5-12 meters, the forward part of the hull, i.e. the bow profile, defines a significant flare under which waves are formed upon contact with the hull making way. Flare is the outward curve of a ship's hull near the bow.

Modifications to the classical "bulbous bow" with large flare was suggested by the applicant of EP 1 314 639 A2 which hereby is incorporated by reference. The reference discloses an alternative bow form of a medium speed cargo ship. According to the reference, a vertically and upwardly extending forefront end line, or bow line, of a bow forming a bow profile will, on ship's having a Froude's number in-between 0.18 - 0.23, reduce wave resistance inflicted on the bow of a ship travelling at medium speed.

The Froude number is a ratio of inertia and gravitational forces. It may be used to quantify the resistance of an object moving through water, and to compare objects of different sizes. Named after William Froude, the Froude number is based on the speed/length ratio as defined by him.

The Froude's number (Fn) is generally expressed as Fn = v/ (LwL χ g), where LwL represents the horizontal distance from a point at which the de- signed load waterline crosses the front end of the ship to a point at which the designed water line crosses the rear end of the ship, g is the acceleration due to gravity and v is the velocity of the ship.

Brief description of the invention

One object of the present invention, according to the preamble of this specifi- cation, is to set forth an improved ship with a fore ship which is significantly less disposed for damage caused by the bows slamming in heavy seas.

Another object of the present invention is to set forth an improved ship with a fore ship which increases the internal volume within the confines of the ship's hull.

Another object of the present invention is to set forth an improved ship with a fore ship which increases the ship's fuel efficiency by reducing wave induced resistance to the hull.

According to the present invention, the above objects are met by providing a ship according to the introductory part of this specification, wherein the bow profile defines a flare which, in a vertical central and transverse plane of the hull, extends, in a longitudinal direction of the hull, between 0% and 50% of the longitudinal length of the bulb.

By providing the abovementioned bow line, the hull preferably should be pro- vided with a sharp angle of entrance above the bulb. Test has shown that the bulb will, with a hull form having a relatively sharp angle of entrance, preferably below 30°, show effects similar to the abovementioned classical hull forms comprising bulbous bows having bow profiles which define flares which, in a vertical central and transverse plane of the hull, extends, in a lon- gitudinal direction of the hull, in about the entire length of the bulb.

According to one embodiment, the bulb may constitute a bulb arranged below the design water line. The bulb may have a first transverse thickness which, at a first point on the bulb lying forward of a second point on the bulb, is larger than a second transverse thickness of the bulb at the second point, and where the forward part of the hull, together with the designed water line, defines a forward perpendicular lying forward of the first point.

According to one embodiment, the bow profile may extend upwards above the bulb from a point lying, in a longitudinal direction of the hull, forward of the first point.

According to one embodiment, the bow profile may define a flare which, in a vertical, central and transverse plane of the hull, extends, in a longitudinal direction, between 0% and 30% of the longitudinal length of the bulb. According to one embodiment, the bow profile may define a flare which, in a vertical, central and transverse plane of the hull, extends, in a longitudinal direction, between 5% and 20% of the longitudinal length of the bulb.

According to one embodiment, the bow profile may extend substantially verti- cal above an extreme forward position of the bulb. According to one embodiment, the bow profile may be configured such that the forward part of the ship comprises, in a vertical, central and transverse plane of the hull, no flare. Further, the bow profile may be configured such that the forward part of the ship may comprise, in a vertical, non-central and transverse planes of the hull, flare.

According to one embodiment, the bow profile may extend continuously upwards from the bulb to an upper deck or forecastle and/or mooring deck of the ship.

According to one embodiment, an intersection of the design water line and the forward part of the hull may define a forward perpendicular lying, in a longitudinal direction of the hull, between 0% and 50% of the longitudinal length of the bulb.

According to one embodiment, an intersection of the design water line and the forward part of the hull may define a forward perpendicular lying, in a longitudinal direction of the hull, between 0% and 30% of the longitudinal length of the bulb.

According to one embodiment, an intersection of the design water line and the forward part of the hull may define a forward perpendicular lying, in a longitudinal direction of the hull, between 5% and 20% of the longitudinal length of the bulb.

According to one embodiment, the forward part of the hull may have an angle of entrance, measured at the water line, above a maximum width of the bulb, below 30° or even below 18°.

According to one embodiment, the ship according to the present invention may have a Froude number below 0.32. According to one embodiment, the ship according to the present invention may be a cargo ship such as a container ship or a reefer ship.

Brief description of the figures Figure 1 is a perspective view of one embodiment of a part of a ship according to the present invention.

Figure 2 shows certain waterlines, or horizontal sectional planes, of a part of a ship according to one embodiment of the present invention.

Figure 3 shows certain buttocks, or longitudinal vertical planes parallel to the central longitudinal vertical plane of a ship, of a part of a ship according to one embodiment of the present invention.

Figure 4 shows certain buttocks of a part of a ship according to one embodiment of the present invention.

Figure 5 shows certain buttocks of a part of a ship according to one embodi- ment of the present invention.

Detailed description with reference to the figures

Figure 1 discloses a three-dimensional view of a part of a ship according to the present invention. Numeral 50 denote spaced apart waterline sections, numeral 30 denote spaced apart buttocks and numeral 40 denote spaced apart stations also known as transverse sections.

The forward portion of the ship according to figure 1 is shown with transverse flare only, hence the forward perpendicular 60 is located at the extreme forward 101 of the bulb 100.

As can be seen in the figure, the bulb 100 is arranged below the design water line 20 and above the baseline 1 of the ship. Further, from the buttocks 30, the stations 40 and the waterlines 50, it is clear that the transverse width of the bulb 100 is, starting from the extreme forward 101 of the bulb 100 and moving aft., increasing continuously until a maximum width is obtained, see figure 2 point 1 15, where after the width of the bulb 100 decreases to a smaller width as illustrated also in figure 2 pos 120. According to certain embodiments of the present invention, the forward perpendicular may lie anywhere in-between the extreme forward 101 of the bulb 100 and the point 1 15 of maximum width of the bulb 100.

Further as can be seen in the figures, the point of maximum width of the bulb 100 may be placed, vertically, in a central portion of the bulb 100, e.g. in the range of 20 - 80 % of the bulbs height or the ship's design draft, however according to certain bulb shapes, it may be preferred to provide the height of the maximum width of the bulb 100 in an upper part of the central portion of the bulb such as shown throughout the figures. Figure 2 shows, as per the above, certain waterlines 50, 51 , or horizontal sectional planes, of a part of a ship according to one embodiment of the present invention. Waterlines lying below the level of maximum width of the bulb are for illustrative purposes not shown in this figure; hence the lowest water- line shown is the waterline 51 passing through the maximum width of the bulb 100.

Figures 3 - 5 show certain buttocks, or longitudinal vertical planes parallel to the central longitudinal vertical plane of the ship, of a part of a ship according to one embodiment of the present invention.

In the embodiment according to figure 3, a substantially vertical bow line 10, departing or extending substantially from the extreme forward 101 of the bulb 100, is shown.

In the embodiment according to figure 4, a substantially vertical bow line 10 is shown, however here, the bow line 10 departs or extends from the bulb 100 at a location slightly aft of the extreme forward 101 of the bulb 100. The distance between the extreme forward 101 of the bulb 100 and the location from where the bow line 10 departs or extends from the bulb 100 may, in certain embodiments, constitute a distance lying anywhere from 0.2% - 10% of the ship's overall length behind the extreme forward 101 of the bulb 100.

Figure 4 further illustrates that the location from where the bow line 10 extends from the bulb 100 may lie forward of the maximum width of the bulb.

In the embodiment according to figure 5, a bow line 10 defining limited flare is shown. Again the bow line 10 departs from the bulb 100 at a location slightly aft of the extreme forward 101 of the bulb 100. The distance between the extreme forward 101 of the bulb 100 and the location from where the bow line 10 departs or extends from the bulb 100 may, again and in certain embodiments, constitute a distance lying anywhere from 0.2% - 10% of the ship's overall length. Although not shown in figure 5, the sloped bow profile 10 may connect to the bulb 100 via a relatively small and substantially vertical section as is common shipbuilding practice. Such vertical section of the bow profile typically defines the abovementioned forward perpendicular.

Figure 5 further illustrates that the location from where the bow line 10 ex- tends from the bulb 100 may lie forward of the maximum width of the bulb.

This invention may be embodied in several forms without departing from the scope of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within meters and bounds of the claims, or equivalence of such meters and bounds thereof are therefore intended to be embodied by the claims.

Claims

1 . A ship designed to operate at service speeds in excess of 20.5 knots comprising a slender hull having a block coefficient below 0.72 and a Froude number above 0.28 and a design draft defining a design water line (20) of said hull, said hull is defined inter alia by an aft part and a forward part comprising a bulb (100) and a bow profile (10) extending upwards above said bulb (100) and said design water line (20) characterized in that said bow profile (10) define a flare which, in a vertical, central and transverse plane of said hull, extends, in a longitudinal direction of said hull, between 0% and 50% of the longitudinal length of said bulb (100).

2. A ship according to claim 1 , wherein said bulb (100) constitutes a bulb (100) arranged below said design water line (20) and having a first trans- verse thickness (1 10) which, at a first point (1 15) on said bulb lying forward of a second point (125) on said bulb, is larger than a second transverse thickness (120) of said bulb (100) at said second point (125), and where said forward part of said hull, together with said design water line (20), defines a forward perpendicular (60) lying forward of said first point (1 15).

3. A ship according to claim 2, wherein said bow profile (10) extends upwards above said bulb (100) from a point lying, in a longitudinal direction of said hull, forward of said first point (1 15).

4. A ship according to any of the previous claims, wherein said bow profile (10) defines a flare which, in a vertical, central and transverse plane of said hull, extends, in a longitudinal direction, between 0% and 30% of the longitudinal length of said bulb (100).

5. A ship according to any of the claims 1 - 3, wherein said bow profile (10) defines a flare which, in a vertical, central and transverse plane of said hull, extends, in a longitudinal direction, between 5% and 20% of the longitudinal length of said bulb (100).

6. A ship according to any of the claims 1 - 3, wherein said bow profile (10) extends substantially vertical above an extreme forward position (101 ) of said bulb (100).

7. A ship according to any of the claims 1 - 3 or 5 - 6, wherein said bow profile (10) is configured such that said forward part of said ship comprises, in a vertical, central and transverse plane of said hull, no flare, and where said bow profile (10) is configured such that said forward part of said ship comprises, in a vertical, non-central and transverse plane of said hull, flare.

8. A ship according to any of the previous claims, wherein said bow profile (10) extends continuously upwards from said bulb (100) to an upper deck of said ship.

9. A ship according to any of the previous claims, wherein said bow profile (10) extends continuously upwards from said bulb (100) to a forecastle deck of said ship.

10. A ship according to any of the previous claims, wherein an intersection of said design water line (20) and said forward part of said hull defines a forward perpendicular (60) lying, in a longitudinal direction, between 0% and 50% of the longitudinal length of said bulb (100).

1 1 . A ship according to any of the previous claims, wherein an intersection of said design water line (20) and said forward part of said hull defines a forward perpendicular (60) lying, in a longitudinal direction, between 0% and 30% of the longitudinal length of said bulb (100).

12. A ship according to any of the claims 1 - 3 , wherein an intersection of said design water line (20) and said forward part of said hull defines a forward perpendicular (60) lying, in a longitudinal direction, between 5% and 20% of the longitudinal length of said bulb (100).

13. A ship according to any of the previous claims, wherein said forward part of said hull has an angle of entrance below 30°, measured at said design water line (20) and above a maximum width of said bulb (100).

14. A ship according to any of the previous claims, wherein said forward part of said hull has an angle of entrance below 18°, measured at said design water line (20) and above a maximum width of said bulb (100).

15. A ship according to any of the previous claims, wherein said Froude number is below 0.32.

16. A ship according to any of the previous claims, wherein said ship is a cargo ship such as a container ship or a reefer ship.