US1831643A - Trace of ships' lines - Google Patents

Description

NOV. 10, V YQURKEVITCH 1,831,643

TRACE FOR SHIPS LINES Filed Oct. .3, 1929 I V I' 1.

[Ll U 2 g 2 r 2 i3 E mama Nov. 10, 19 1 PATENT orrlcs i VLADIMIR YOURKE' VITCE, OF PARIS, FRANCE TRACE or sn'rrs' LINES Application filed October 3, 1929, Serial No. 397,007, and in Germany Kay 7, 1828.

Fig. 3 is a half-breadth'plan of the/hull The invention relates to certain improvements in the trace of ships" lines. Its object is to provide a hull whose resistance to forward motion is reduced for a 'ven dis 5 placement, whereby a saving in t e power necessary to pro el the ship is effected, assuming that the is lacement, the length and the speed remain t e same. J As is known, the resistance to forward motion in ships is made up of two factors.

1. A general frictional resistance. 2. A direct resistance to forward motion termed hereinafter residuary resistance.

The general frictional resistance is due to 5 the rubbing of the water against the ships hull; this resistance is proportional to the immersed surface of the hull, to itscleanliness, its general condition and the like; it is scarcecing this resistance. On the other hand, the residuary resistance may be decreased. This resistance is produced in great part by the wake which depends on the form of the hull. Shi s of the same length and dis lacement may ave residua2ry resistances iflering in the ratio of 1 to The object of the resent invention is to provide a trace for 's ips" lines enabling the duced.

Other advantages and peculiarities of the mg to usual design and according to de-- sign in conformance with the invention. "A

ships hull and the profile of the wave which is formed in the case of the usual design and in the case of the design according to the invention, has likewise een illustrated diagrammatically in this figure.

ly possible to find means for substantially reresiduary resistance to be considerably re-.

of a ship at the water line according to the usual design and to the present invention.

Fig. 4 is a graph illustrating the resistance curves of different ships according to the usual design and to the present invention. a

In the different figures of the drawings,

.the fine line refers to the usual design and the thick continuous or dotted line refers to the design according to the present invention.

As is apparent from the law of comparison which is applied to similar ships when their dimensions have the same linear ratio, the speeds vary'as the square root of the linear dimension; speeds are'generally compared by using the ratio A Y 41 where L is the length of the ship.

From the tests. which were carried out in the experimental tank, it' has been found that the form and height of the wake which, as

has been stated above, is the principal cause of the residuary resistance, are de endent to a great extent on the trace of t e forepart of the ship. When the coeflicient is comparatively low, equal to 1 for. example, hardly any wave is formed at the stem, the stream lines can adapt themselves to the profile of the shi so that they produce neither aves nore dies. On the other hand, when t e speed increases, the fore-part of the ship so to speak pushes the water before it so that the latter has not time to adapt itself to the profile of the ship and the wake is produced.

The thrust of the wake has a centre of pressure oneither side of the ship which is displaced more and more towards amidships 'as the speed increases. It gradually reaches amidships for a value of This resistance is the resistance to forward movement excluding the frictional resistance.

4 the centre of pressure r i the centre of pressure is amidships. It may x be taken for granted that the displacement of the centre of pressure isroughly proportional to the speed and by uniforml dividing up the space from 1 to 3, the 'fl'erent positions of the centre of pressure for the corresponding values of may be obtained. The distance, in meters, of the center of ressure from the bows of the ship is there ore given by the formula where L is the length ofthe ship.

7 Assuming that it is desired to build a ship having a definite displacement, length and speed, the position of the centre of pressure for a given ship can be immediately read ofi the diagram ofFig. 3.

The method 'of tracing in conformance with the invention consists in making the hull of the ship as narrow as possible in the neighbourhood of the centre of pressure, the internal arrangements being of course allowed for. In this manner, since at this point the hull makes a very acute angle with the direction of motion, the residuary resistance will be considerably reduced. The diminution in the breadth of the hull in the neighbourhood of the centre of ressure is compensated by widening it in other places so as to maintain the displacement unchanged.

For example, if it be desired to build a liner 225 ms. long to steam at 25 'knots, the ratio which is at 37.5 ms. from the bows of the is right forward and ship to be located. lhe form of the ship is then traced and is made as narrow as possible at this point.

Thus the trace illustrated in heavy lines is obtained, the usual form of trace being illustrated by the thin line.

The ships half-breadths at this point will be respectivelya and b. For either case, the residuary resistances may be taken to be proportional to the squares of these lengths;

the resistance ratio will therefore be 5( As will be realized, a'verysubstantial reduction in the residuary resistanceis efiected by tracin the hull in'accordance with the design 0 the invention. This resistance may,'1n certaln cases, behalved; As it has been assumed that ships'having the same displacement, length and speed were-being compared, the diminution ofresistance thus obtained results in a corresponding decrease in the power necessary to drive the ship.

In the diagram of Fig. 4 the resistance curves of two ships, one according to our- I rent design, the other according'to'the present invention have been plotted in terms of the speeds of the ships. These curves are obtained by taking the values in kilograms of the resistances as ordinates and the values oftheratio r resistances, r in the case of the usual design a 10s as abscissae. It will be seen from this diand r for the one in conformance-with the invention, very soon diverge; 7 may be less than half 13.

In order to decrease the residuary resistance, not only may the trace of the hull be modified in the horizontal direction as has been indicated above, but also in the vertical direction. p

In Fig. 1, the various transverse frames starting from the fore-part of the shi have been illustrated on the right, and the rames of the aft portion of the ship on the left. As has been stated above, thethin lines 1,

2, 3 illustrate the frames according to existing design, the heavy full lines A, B, C and chain dotted lines a, b, 0 illustrate two alternative forms of the case of the frames 1 and 2 which are the nearest to the fore-part of the ship.

but also, all along the upper immersed portion of the frame, a thrust perpendicular to the curvature of said frame, that is to say the frame 1 tends at each point of its length to thrust the 'water below the horizontal plane passing through such point, if, of course, the frame is inclined to the vertical at this point. It is this action which increases the height of the wake, which, as has been previously indicated, is due to the direct resistance to the forward motion of the ship.

By designing the different frames of the ship, and, in particular those situate near the fore-part thereof, in such manner that they shall always be practically vertical as far as the portion lying below the water line is concerned, as is the. case for the frames A, B, C of the drawing, this particular resistance is further reduced to an appreciable extent.

By even making said frames distinctly concave as illustrated in Fig. 1 in the case of the frames a, b, 0, the height of the wave is lowered to a very appreciable extent, the concavity so to speak choking the wave.

A ships hull has been illustrated in longitudinal section in Fig. 2; in this figure as well as in Fig. 1, the heights of the wakes a: and 3 which are produced in the two cases under consideration and which are the efin a hull designed in conformance with the present invention the surface areas of the frames are much greaterfthanusual amidships and very much smaller at the ends.

To sum up, with the present design, the concavity in the fore-part of the ship makes its presence felt both in the vertical and in the horizontal direction in each of the horizontal planes cutting the ship below the water line. This has moreover been expressed in the diagram of Fig. 2, in which, as has been pointed out, the areas of the vertical sections perpendicular to the longitudinal axis of the I ship have been. plotted as ordinates.

has been pointed out previously, by

adopting the design indicated above, the residuary resistance which produces the wake is reduced to a marked extent, and, consequently, less power is required to drive a ship of given displacement and length at a given speed.

It is obvious that the invention has only been described above in conjunction with the accompanying drawings for a narrow speed range and merely in an explanatory but by no means limitative manner, and that it ma include all alternatives in conformance wit the spirit of the invention.

I claim:

1. A ships hull having transverse frames reduced in breadth in the vicinity of the position of the center of pressure of the residuary resistance which varies with the ratio of the speed of'the vessel to the square root of its length, the center of pressure being in the f0re-part of the ship when the ratio is 1 and amidships when the ratio is approximately 3.

2. A ships hull having transverse frames reduced in breadth in. the vicinity of the position'of the center of pressure of the residua-ry resistance which varies with the ratio of the speed of the vessel to the square root of its length, and other transverse frames which are increased in breadth to maintain the ships displacement unchanged.

VLADIMIR YOURKEVITCH.

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