US3433194A

US3433194A - Bows of ships

Info

Publication number: US3433194A
Application number: US625512A
Authority: US
Inventors: Denis Csupor
Original assignee: Maierform Trust Registered
Current assignee: Maierform Trust Registered
Priority date: 1966-03-26
Filing date: 1967-03-23
Publication date: 1969-03-18
Anticipated expiration: 1986-03-18
Also published as: NL6704335A; NO127700B; BE696057A; DE1506190A1; NL164236C; DE1581125B1; ES338289A1; GB1141954A; NL164236B; SE384659B; JPS527239B1; NO127700C; FI48694B

Description

D. CSUPOR BOWS OF SHIPS March 18, 1969 Sheet of 3 Filed March 23, 1967 March 18, 1969 v D. CSUPOR 3,433,194

BOWS 0F SHIPS Filed March 23, 1967 Sheet g of 5 In venfor DEN/s 417 0? BY M- March 18, 1969 CSUPOR 3,433,194

BOWS 0F SHIPS Filed March 23, 1967 Sheet 3 of 3 fig. 40

In venfor Dems ($0002 av K24 0 7 Ava/tum United States Patent 3,433,194 BOWS 0F SHIPS Denis Csupor, Vernier, Switzerland, assignor to Maierform Trust Reg, Schaan, Liechtenstein Filed Mar. 23, 1967, Ser. No. 625,512 Claims priority, application Germany, Mar. 26, 1966,

M 68,925; July 7, 1966, M 70,152 US. Cl. 114-56 14 Claims Int. Cl. B63b 1/06 ABSTRACT OF THE DISCLOSURE The bow of a ship with a forwardly projecting bulb, the stem having below the load waterline an arcuately forwardly projecting portion and a maximum width wherein this most forward point and this maximum width are located above the ballast waterline but below the point to which the water is banked up when the ship travels at its normal speed. The stem tapers from its maximum width in the form of a wedge down to the keel line. The invention also relates to such bulbous bows for ships travelling in frozen seas.

The invention relates to a bow for ships of all kinds, having a forwardly projecting bulb or bulge, wherein the stem has below the load waterline an arcuate, forwardly projecting part and whose underwater rib has at the point of the forward perpendicular a maximum width, wherein the part below the same tapers substantially in the form of a wedge to the keel point.

The load waterline of a ship may be defined as that waterline which applies when the ship carries the load for which it has been constructed. The ballast waterline is the waterline which applies when the ship is in the unloaded, ballasted state.

It is known to provide the stem line of ships below the waterline with a forwardly projecting portion, forming a bulbous bow. Thus, for example, in Report No. 718 of the Netherlands Research Centre T.N.O. for Shipbuilding and Navigation of May 1965, entitled, Research on Bulbous Bow Ships Part II-A, later reprinted in International Shipbuilding Progress, vol. 12, No. 136, December 1965, by Professor Dr. Ir. Ven. Lammeren, M.P.A. and Muntjewerf 1.1., a stem line has been described with results in a reduced resistance between 15 and percent, in the ballasted condition. However, no improvement in the resistance in the loaded state has been achieved by the known bulbous bows, and the cited publication stresses particularly that bulbous bows constructed for the loaded state would scarcely yield the required results.

Hitherto it has not been possible to construct and arrange a bulbous bow so that it considerably improves the economy of the ship both in the ballasted and in the loaded state thereof, that is to say, reduces the power input for the same speed or improves the speed for the same power input, without incurring the risk of shocks in the vessel or damage to the bow bulb during slamming thereof on to the water in the case of rough seas.

The invention therefore relates to a bow for surface ships of the kind hereinbefore described, resulting both in the loaded and in the ballasted state of the ship in a reduction of the travelling resistance with a certain, given, speed range, wherein at the same time the forces generated with rough seas in the case of slamming of the fore part of the vessel on to the water are reduced to as low and undangerous a value as possible.

According to the invention, this object may be realized in that the leading point of the arcuately projecting portion and the maximum width are located above the ballast "ice waterline and in the upper half of the draught and in that the part below the said maximum width is constructed after the manner of a ship with V-type frame. It has been shown by tests that this configuration of the bow leads to a substantial reduction of the travelling resistance of the forepart of the ship in the loaded state, whilst also in the ballasted state there are no difiiculties with the projecting bulb in rough seas. In the ballasted state, a ship equipped with this type of bow behaves like a normal, slightly longer, ship, a fact which is known to affect the travelling speed beneficially.

Particularly preferably, the stern intersects the load waterline at a negative angle. This condition may be achieved by a suitable positive trim of the ship.

Particularly with slower ships, with Froude-Number of up to about 0.28, the stem projects to its maximum forward dimension preferably at the level of the maximum width.

With faster ships, with Froude-Numbers above 0.29, the maximum width is preferably below the said forward point. Generally, the said forward point and the maximum width should be spaced in the vertical direction by an amount equal to about 5 to 15 percent of the distance between the maximum width and the keel line. With fast ships, the maximum width may also be near the half level of the draught.

The effect of the bulge reducing the travelling resistance is obtained not only in the loaded state, but also in the ballasted state of the ship, if the front point is arranged above the ballast waterline only by such an amount that, with normal travelling speed the water is raised above this forward point and flows around surfaces of the bulbous bow located above its most forward point. By means of this configuration water will flow around the bulbous bow despite the fact that its most forward point is above the ballast waterline, resulting in a substantial reduction in the travelling resistance.

The height of the most forward point of the bulbous bow above the ballast waterline is preferably one half to one third of the water damming height present in a ship with V-type frame, in which the bow proceeds from the keel line beyond the most forward point without being recessed according to the invention towards the top. This value can be determined by calculation or empirically, by tests, by means of a model.

The effect of the bulbous bow in the ballasted state is further improved in that the mean radius of curvature of the stem at the most forward point amounts to between one half and one third of the water damming height.

Optimum conditions are obtained with regard to the travelling resistance during travel under ballast, if the sum of the height of the most forward point above the ballast waterline and the radius of curvature of the stem at this most forward point is substantially equal to the height of the banked-up water.

Especially with ships travelling in ice-carrying water, the invention may be further developed in that the water line inlets between the ballast waterline and the load Waterline are sharpened and the half of the waterline inlet angle is smaller than 35, wherein the stem following the line according to the invention is constructed after the manner of a conventional, stable ice stem. In its sharpened form, the upper, rearwardly inclined part of the bulbous bow is particularly suitable for breaking ice under favourable conditions in that it engages the sheet ice from the bottom and breaks from the bottom upwardly. During this process, the lower part of the ice, which is wetted with water, makes contact with the hull of the ship, which has the advantage, compared with the upper, usually snow-carrying surface of the ice, that the frictional resistance between the ice and the hull is reduced to about one fortieth of the resistance existing between the dry surface of the ice and the steel hull.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatical, vertical, longitudinal crosssection of a bow according to the invention;

FIG. 2 shows the left half of a cross-section along the line II-II in FIG. 1, the right half being symmetrical thereto;

FIG. 3 is a cross section corresponding to that of FIG. 1, indicating the banking up of water in the zone of the bulbous bow during travel under ballast;

FIG. 4 is a first embodiment of a cross-section along the line IVIV in FIG. 1, and

FIG. 4a is another embodiment of the cross-section along the line IVIV in FIG. 1, with a definition of the angle b with the how not sharped in the shape of a wedge, wherein both FIG. 4 and FIG. 4a show only one half of the cross-section, and the other half extends symmetrically thereto.

FIG. 1 shows diagrammatically the stem line of a ships bow constructed according to the invention, consisting of the under-water stem 16 and a stern above the water, shows in shortened form at 17. The drawing indicates the load waterline 18, that is to say, the line up to which the ship dips into the water when carrying the load for which it has been built.

The figure also shows the ballast waterline 19, that is the line to which the ship sinks into the water when unloaded and carrying only ballast. Owing to a positive trim, the ballast waterline 19 is frequently slightly inclined towards the front.

FIG. 2 is a vertical cross-section, normally to the keel line, at the point of the forward perpendicular 12. The forward perpendicular is the perpendicular at that point of the ships hull at which the load water line 18 intersects the

stem

16, 17. As may be seen from the drawing, in the bow according to the invention, the forward perpendicular 12 is slightly in front of the most rearward part 21 of the stem above the forwardly projecting bulb.

It results from the FIGURES 1 and 2, that both the most forward point 20 of the underwater stem 16 and the widest point 22 of the underwater frame 11 at the point of the forward perpendicular are above the ballast waterline 19 and in the upper half of the designed draught, shown at T. This configuration of the bow is relevant for solving the object of the invention.

Together with the arrangement of the maximum width in the upper half of the designed draught, this configuraward point 20, a smaller absolute mean value of the resistance with the ship in the loaded condition, but also in a substantial improvement of the conditions at rough seas, because the forces acting on the forecastle during impact on the water are substantially reduced.

It may be seen from FIG. 1 that the underwater stem 16 has, relative to the keel line, above the most forward point 20, a smaller absolute mean value of the inclination than below this point. In consequence of this configuration, the ribs in front of the underwater frame 11 in FIG. 2 are geometrically similarly formed, which is important in order to achieve the advantages according to the present invention and has also additional structural advantages.

The levels of the most forward point 20 of the underwater frame 16 and the maximum width 22 of the underwater-frame 11 above the keel line may be equal.

This configuration is to be preferred for slower vessels mum width 22 and the keel line 15. With faster vessels, F

the maximum width may be at about half the draught T 2.

It should be stressed, that generally the most forward point 20 should exceed the forward perpendicular by not more than 4 percent of the length of the ship, because otherwise the classification length of the vessel will have to be assumed to be longer. Generally, the forward point 20 will be in front of the forward perpendicular by about 2-3 percent of the length of the ship.

According to the invention, the height h of the forward point 20 of the bulbous bow above the ballast waterline should be less than the level of the banked-up water as it occurs with a V-frame travelling at standard speed, and the stem of which extends from the keel line 15 substantially rectilinearly at 23 and further on towards. the top, as known in the art. With this configuration and when travelling under ballast, the conditions shown diagrammatically in FIG. 3 occur, i.e. the Water 25 rises at the bulbous bow beyond the ballast waterline 19 and floods also the forward point 20 and zones on the top 24- of the bow bulb or bulge. Towards the rear, the water drops gently over the side faces of the bulb towards the ballast waterline 19.

In this manner, the bulb effect is produced, reducing the travelling resistance also during travel under ballast.

The height h is preferably one half to one third of the banking-up height defined hereinbefore, which may be found by tests with a model, or may be calculated by means of the formula:

t h 1.774: m g si in which:

hz{/(mm.)=the banking-up height in millimetres v=The speed in knots rp=the angle of the straight portion 23 as shown in FIGURE 1 T =The front draught in metres =Half the water line inlet angle (FIGS. 4 and 4a) tgh=Tangens hyperbolicus FIG. 4 shows the definition of the angle 1/ with pointed bow.

FIG. 4a shows the definition of this angle if the stem is rounded. Here, the angle is defined by the following relation:

tg !/=2-F/(L/20) where L is the length of the ship in metres between the forward and after perpendiculars, and F is the half surface of the waterline over the length L/2O of the forecastle. In other words, the shaded surface F and the right-angled triangle in FIG. 4a have equal areas The radius of curvature r (FIG. 1) of the stem at the most forward point 20 is preferably equal to one third to one half of the banking-up height. Generally also, the sum of h and r should be equal to the banking-up height. Hence, optimum conditions are achieved, with regard to the bulb effect when travelling under ballast, if the following applies:

According to FIG. 1, the underwater stem 16 has underneath the most forward point 20 a straight or substantially straight portion 23, forming an angle of 20 to 40 with the vertical.

The part of the stem extending on the upper side of the bulbous bow has also a straight or substantially straight portion, forming an angle of 15 to 30 with the horizontal. At any rate, the angle should not be larger than 35. Since the stem has, on the upper side 24 of the bow bulb, always a reversing point, the inclination of the tangent of reversal may be regarded as a measure of the inclination of the stem on the upper side 24.

The bow according to the invention is also particularly suitable for ships travelling in frozen seas.

In this case, the waterline inlets are formed sharp in order to cut the ice reliably. This sharpened portion, shown, by way of example, in FIG. 4, is required only between the ballast waterline and the load waterline. Between these two waterlines, the stem, having the profile according to the invention, is constructed after the manner of a conventional icebreaking stem.

The part of the bulbous bow according to the invention extending along the upper side 24, is particularly suitable in its sharpened shape for breaking ice under favourable conditions in that it engages underneath the ice sheet and breaks from the bottom upwardly. During this operation, the ships hull makes contact with the wetted underside of the ice float and this has the advantage, compared with the usually dry and snow-carrying upper surface, of reducing the friction between the hull and the ice to about one fortieth of the value which would exist if contact were made between the upper surface of the ice and the ships hull.

The improvements made according to the invention, namely the lower input required with constant speed, or the higher speed with the same power input are far above percent with deep loading. If a ships model equipped with a bow according to the invention is given a larger positive trim, a further, surprising saving in power is achieved, resulting in an improvement of up to almost 30 percent, compared with a known model.

This fact that a large positive trim at which the bulbous part projects out of the water achieves a further reduction of the resistance, must be regarded as very surprising, since with known models an opposite effect of the large positive trim could be observed. Hitherto it has already been regarded as favourable, if a large positive trim did not cause a deterioration of the resistance conditions.

Hence, the stern according to the invention offers the following advantages, compared with conventional constructions of bulbous bows, known in the art:

It is particularly effective when travelling under load, but reduces the travelling resistance also considerably when travelling under ballast.

The V-shaped construction of the front stem eliminates excessive impacts during the slamming on the surface of the water.

Owing to its high centre of lift it has a beneficial effect on the stability of the vessel.

In view of its high degree of efficiency, a smaller volume bulb is sufiicient, so that trimming diificulties are eliminated even in the case of subsequent installation.

I claim:

1. An improved bow for ships of all types, having a forwardly projecting bulb or bulge, wherein the stem has in the zone below the load waterline an arcuately forwardly projecting part and the underwater frame has a maximum width at the point of the forward perpendicular, and wherein the part thereunder tapers substantially after the manner of a wedge towards the keel point, wherein the improvement comprises the arcuately projecting part having a forwardmost point; said forwardmost point and the maximum width being located above the ballast waterline and in the upper half of the draught so that the part located under the maximum width has the form of a V-shaped frame ship.

2. A bow as set forth in claim 1 wherein the stem intersects the load waterline at a negative angle.

3. A bow as set forth in claim 1, wherein the load waterline intersects the stern immediately in front of the most rearward point of the portion of the stern located above the load water line.

4. A bow as set forth in claim 1, wherein said forwardmost point is substantially horizontally aligned with the maximum width.

5. A bow as set forth in claim 1, wherein the maximum width is below said forwardmost point.

6. A bow as set forth in claim 1, wherein said forwardmost point and the maximum width are spaced from each other in the vertical direction by an amount within the range of 5 to 15% of the distance between the maximum width and the keel line of the ship.

7. A bow as set forth in claim 1, wherein the maximum width is substantially horizontally aligned with /2 of the draught.

8. A bow as set forth in claim 1, wherein the portion of said stem below the load-water line has a substantially rectilinear portion below said forwardmost point and extending at an angle within the range of 20 to 40 degrees relative to the vertical.

9. A bow as set forth in claim 1, wherein the stem below said load-water line has a retracting portion above said forwardmost point having a rectilinear range, determined by the reversing tangent of the side profile curves, with an inclination to the horizontal of between 15 and 30 degrees.

10. A bow as set forth in claim 1, wherein said forwardmost point is located vertically above the ballast water line, and said stem is so constructed as to constitute means for backing the water up substantially above said forwardmost point when the ship is travelling at its normal speed under designed ballast so that the water flows above said forwardmost point and upwardly around the bulbous bow above the forwardmost point.

11. A bow as set forth in claim 1, wherein the height of said forwardmost point above the ballast water line is between one-half to one-third of the level of the back-up water that would be produced by a V-frame type ship having a bow extending from the keel line beyond said forwardmost point rectilinearly without the shape according to the present invention.

12. A bow as set forth in claim 10, wherein said stem has a mean radius of curvature at said fordwardmost point that is between one-third and one-half of the backed-up water level.

13. A bow as set forth in claim 10, wherein said stem has a mean radius of curvature at said forwardmost point the sum of the height of said forwardmost point above the ballast water line and said mean radius of curvature being substantially equal to the backed-up water height.

14. A bow as set forth in claim 1, wherein said stem is reinforced for ice-breaking and has Water inlet portions presenting a sharp cutting surface between the ballast water line and the load water line with at least one half of the portion above said forwardmost point having an angle with respect to the horizontal smaller than thirty-five degrees.

References Cited UNITED STATES PATENTS 3,302,603 2/1967 Eckert 114-56 3,306,244 2/1967 Schneekluth et al. 11456 ANDREW H. FARRILL, Primary Examiner.