US1491499A - Parallel-stern vessel - Google Patents

Description

April 22 1924.

D. w. TAYLOR PARALLEL STERN VESSEL Filed Jan.

D. W. TAYLOR PARALLEL STERN VESSEL Apg'il 22 1924.

Filed Jan. 31. 1925 3 Sheets-Sheet 2 April 22 1924.

D, W. TAYLOR PARALLEL STERN VESSEL Filed Jan. 51 1923 3 Sheets$heet 3 I n ,I

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3 w uw xw NS MN Patented Apr. 22, 1924.

DAVID W. TAYLOR, OF W'A SHINGTON, DISTRICT OF COLUMBIA.

PARALLEL-STERN VESSEL.

Application filed January 31, 1923. Serial No. 618,140.

To all whom it may concern:

Be it lniown that I, DAVID WV. TAYLOR, a V

citizen of the United States, residing at lVashington, in the District of Columbia, have invented certain new and useful Improvements in Parallel-Stern Vessels, of which the following is a specification.

This invention relates to boats, ships or other vessels which are provided with screw propellers at the stern for moving them through the water and is adapted and intended to cause the effective action of the propellers in moving the vessel to be much greater than has been possible with the arrangement of arts on vessels heretofore in general use. ine of the efiects of the operation of a screw propelleris to reduce the natural or normal pressure of the water on that portion of the stern of the vessel directly in front of the propeller and that of course tends to retard the forward movement of the vessel and thus reduces the effective action of the propeller in movingforward. This tendency of the propeller action to suck the vessel astern is eliminated or reduced to a minimum by the use of my present invention which consists in making that portion of the vessel in front of the propeller which would normally be affected by the suction of such shape or form longitudinally that substantially none of the re duced pressure or suction will-have effect in a sternward direction. Broadly it consistsin a parallel stern vessel. The invention will be more fully understood from the following description and claims taken with the accompanying drawings:

In the drawings:

Fig. 1 shows in plan the actual water lines (on sections of the surface by horizontal planes) of the aft portion of'an actual existing twin-screw vessel of known type. i

Fig. 2 shows the water lines of a similar twin-screw vessel as modified in accordance with m invention.

Fig. 3 shows in plan the actual water lines of the aft portion of a single screw vessel in use heretofore.

Fig. 4: shows the water lines of asimilar single screw vessel as modified in accordance with my invention; and

Fig. 5 shows in outline a side view of a practicable arrangement of the aft part of a single screw vessel embodying my invention.

In order that the functions and advantages of my present invention may be easily and fully understood the operation'of the propeller and its effect in moving a-vessel 0f the ordinary tyipe now in use will be first referred to and explained.

A ship propeller in action produces the thrust by which a ship is propelled by driving sternward the water upon which it acts, the thrust being measured by the sternward momentum impressedupon the water. The sternwardvelocity of'the water is produced partly as a result of' excess pressure upon the sternward or driving faces of the propeller blades and partly as a result of re duced pressure or suction upon thebacks of the propeller blades. latter action there is a condition of reduced pressure in the water immediately forward of a propeller that is driving a ship. This reduced pressure, moreover, extends forward and outward from the propeller and embraces the rear portion of the ship forward of the transverse plane of the propeller. The further we goforward of the propeller. the less the reduction of pressure. so that at a reasonable distance in front of the propeller the reduction of pressure caused by it is negligible. The effect of the reduction of pressure acting over the rear portion of the ship is to suck the vessel astern, as it were. thereby increasing its natural resistance. so that a part of the thrust of the propeller is absorbed in overcoming the extra resistance of the ship resulting from the action of the propeller itself. This is a complete waste of power and seriously reduces the possible efliciency of propulsion. 7

While the suction above referred to can be modified somewhat by modifying propeller blades. it cannot be'materially 'reduced thus and. indeed. considering the propeller apart from. the ship, it is believed that the larger the proportion of the thrust. due to the suction upon the water. ahead of As a result of this the propeller, the greater the efficiency of. l

the propeller propera In considering what can be accomplished by changes in the ship itself. however. I

found that it is possible to so shape or form that portion of the ship in the region of the suction that the suction will have no material prejudicial effect on or resistance to forward movement. The thing to be avoided is suction upon the hullin the fore and aft direction. If the side surfaces of the pertion ofthe hull in the region of suction GX tend directly fore and a'iter are parallel to a fore and aft line, no matter how great the suction may be upon it, the resultantforce upon the ship due to suction is trr verse and the fore and aft component is zero. In practice the suction in front or" a propeller decreases steadily and fairly rapidly at successively greater distances forward from the plane of the blades and is virtually negligible for a propeller not too deeply imme..s..d at a distance from the propeller center of about two diameters oi the propeller. It therefore follows that it the aft part of the hull is so shaped that the portion which is submerged when underway, although having sh ape in transverse planes, has side surfaces on lines parallel to the center line for a distance "forward of the propeller equal to about two diameters of the propeller. the harmful suction will be virtually nullified. However even where the rear portion of the hull havingits sides parallel to fore and att line extends for a less distance forward the rearward suction will still be materially reduced thus securing the benefits of the present invention. the amount of the reducth'in depending upon the extent of the fore and att portion hav ing the parallel sides.

In the case of twin-screw vessels there are no serious practical diiliculties in the wav of making the rear underwater portion oi the hull forward of the plane oi the propellers practically fore and aft. i. e. a true parallel stern. For single screw vessels considerations of strength render it inadvisable to shape the rear portion of the hull side surfaces exactly parallel to a fore and aft line: but by giving a slight divergence to the water lines in this part of the ship at a small angle. preferably not exceeding 5. my invention may be applied to single screw vessels with but slightly less effectiveness than in twin screw vessels. In pra tice. ships are now usually built. it. is the water lines near the surface which diverge at large angles to the fore and aft line, as compared with those well under water. and the greatest benefit will follow from the reduction of these water line angles to zero or to a small angle.

In order to make clear the meaning of the drawings by inspection. descriptive words and abbreviations and numbers have been placed on each figure the letters V7. L. being used to indicate waterline and the numeral with an apostrophe to indicate feet. By comparing Figures 1 and 2 it will be seen that in applying my invention to the vessel the deck line is not changed. Below the deck line the horizontal lines are drawn in gradually until the most radical change in the angle to the fore and aft line is at the actual water line of the vessel underway menace as indicated in Figure 2 labeled Load water" line 236. Below that line the changes are much less radical as the keel is approached. The lines of Figures 1 and 2 indicate a vessel with a thick stern post where the rudder is of substantial thickness and carries on the water lines abai't the stern post as indicated by the dotted lines in Figure 2 abaft the six-foot and twclve-foot water lines.

The dotted lines 11 in Figures 1 and Q indicate the transverse plane of the propellers and a dotted line 12 in Figure 2 indicates the transverse vertical plane of the vessel where the drawn in water lines forming the parallel portion commence to curve outwardly from the central fore and aft line towards their normal positions. It will be noted by comparison of Figures 1 and 2 that the water lines above the propeller and parallel portion and in front of it and even above the actual water line under load are drawn in to a. material extent for structural reasons.

It will be observed by inspection of Figure a that in applying the invention to a single screw vessel the water lines of that portion of the vessel directly in front of the propeller are not exactly parallel to a fore and aftline but diverge at very small angles increasing from the lower edge to an angle of about 5 at the upper portion. This results in comparatively little change from the normal water lines near the keel but there is a radical change near the actual load water line of the vessel. As in the case of the twin screw vessel however there is little or no change at the upper deck. In Figure 3 the dotted lines 13 represent the propeller shaft bossing. 14: represents the stern post and the rudder post of the ordinary vessel. The propeller is mounted and operates between stern post 14 and rudder post 15.

lnapplying the inv-nliion to a single screw vessel it is desirable. although not necessary, to carry the stern overhang a little further bacl: than is usual in order to make it strong enough to carry with safety a rudder of the balanced spade type which is supported entirely in the hull above it as illustrated in Figure 5. This obviates the necessity for fitting the rudder post behind the Screw propeller and reduces the strain on the stern of the ship below the stern tube.

Figure 5 shows in outline one desirable general arrangement by which this may be done. It will be noted from an inspection oi Figs. 4 and 5 that the upper part of the hull in the rear of the stern post 18 is supported by what may be called a shelf 19 which is in a straight horizontal plane at the 20 water line and which forms the bottom surface of that portion of the hull and which is rigidly connected to and supported by the portion of the hull next forward. This shelf provides a fiat downwardly facing surface and carries the bearings 24 which support the rudder and it adds strength to the upper part of the hull. In this case the angle of divergence of the 24 water line from the fore and aft line is reduced from about in the usual type of vessel illustrated in Figure 3 to about 5 in the one embodying my invention as shown in Figure 4:. This angle is so slight.

even at the water line that the vessel has a substantially parallel stern. The propeller 20 is below the shelf and between the stern post 18 and the rudder 25 as shown in Fig. 5.

It will be seen by reference to Figure 4 that the 20 water line 21 below said shelf terminates at the stern post 18 and from that pointforward is at a very slight angle to the center fore and aft line until at the dotted line 22 it curves outwardly and joins the 20 water line above the shelf at the point 23. There are thus narrow side sections of the shelf from the stern post 18 to the points 23 on opposite sides. Since a parallel stern vessel such as described above greatly reduces the sternward suction on the vessel and thus secures the advantages of my invention whether the propeller is mounted on the central fore and aft line or at one side my invention is not limited to any particular numb-er of propellers and the reference to propeller in the claims is intended to means one or more.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

l. A propeller operated vessel so shaped that the corresponding port and starboard water lines of the submergedportion immediately forward spaced apart laterally a short distance sufficient to accommodate the stern post or other necessary structural features between them and extending forward substantially of the propeller are.

parallel to a fore and aft line for a material distance from the propeller and then diverging on outward curves.

2. A propeller operated vessel so shaped that the corresponding port and starboard water lines mediately forward of the propeller are spaced apart laterally, a short distance sufficient to accommodate the stern post or other necessary structural features between them and extending forward substantially parallel to a fore and aft line for tance from the transverse center line of the propeller approximately equal to twice the diameter of the propeller and then diverging on outward curves.

3. A propeller operated vessel so shaped that the corresponding port and starboard water lines of the submerged portion immediately forward of the propeller are spaced apart laterally a short distance sufficient to accommodate the stern post or.

other necessary structural features between them and extending forward at an angle to a fore-and aft line not greater than approximately 5 for a materialdistance from the propeller and then diverging on outward curves.

1. A propeller operated vessel so shaped that the corresponding port and starboard of the submerged portion ima dis water lines of the submerged portion immediately forward of the propeller are spaced apart laterally a short distance sufficient to accommodate the stern post or other necessary structural features between them and extending forward at an angle to a fore and aft line not greater than approximately 5 for a distance from the center transverse line of the propeller approximately equal to twice the diameter of the propeller and, then diverging on outward curves. 7

In testimony whereof I hereunto afiix my signature. 1

DAVID W. TAYLOR.

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