US 2666406 A
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Jan. 19, 1954 a v. c. BABCOCK BOAT HULL s Shets-Sheet 1 1 a l. i Q
Filed March 22, 1950 INVENTOR Vdi'li Cffiacock r ATTOR Jan. 19, 1954 y. c. BABCOCK 2,666,406
BOAT I -IULL Filed March 22, 1950 5 Sheets-Sheet 2 INVENTOR Vaz'ne C Bacock BY M/ r ATTOR Jan. 19, 1954 I v, c, A K 2,666,406
v BOAT HULL Filed March 22, 1950 3 Sheets-Sheet 3 INVENTOR Varne c. BaaW/C' WL.--- m Mp 25 I 26 ATTORN Y Patented Jan. 19,1954
BOAT HULL Vearne C. Babcock, Deland, Fla., assignor to Kattu Project, Inc., Forest Hills, N. Y.
Application March 22, 1950, Serial No. 151,147
This invention relates to boat hulls, and particularly hulls for motor-driven boats, but not necessarily being limited thereto.
1 It is among the .objects of the invention to provide a boat hull having the several advantageous characteristics of good stability, longitudinal, lateral andjdirectional; capability of relatively high speeds at low power; maneuverzrbility'; shallow draft; and susceptibility to economical manufacture, operation and mainteriance. a
These, and other desirable objects apparent hereinafter, are accomplished by the present invention, a suitable embodiment of which is described herein and shown in the accompanying drawings, in which:
Figure 1 is a lateral elevation of a boat whose hull embodies features ofthe invention;
Figures 2, 3 and 4 are diagrammatic lateral elevations of the boat underway, illustrating the variation in forces acting upon the boat when itis, respectively, in normal attitude; inbowdown attitude, i. e. at low angle of attack; and in bow=-up attitude, i. e. .athigh angleof attack.
Figures 5 and '6 are respectively top plan and front elevational views of the boat;
Figure 7 is a bottom plan view of the boat, at slightly reduced scale;
Figures .8 and 9 are respectively top plan and front elevational views of another hull showing an alternative arrangement. of. driving propeller within the scope of theinvention.
.As shown particularly injFigures 6, and 'Lthe hull comprisesa pair of laterally .spaced floats, generally. indicated at l0 and [0, with a continuous bridge structure, generally indicated at I 2 extending therebetween. Thelaspect ratio (i. e., the ratio of waterline length to beam)v of the floats is low enough to allow the floats to fplane on the waterryetj high enoughto give the craft good directional stability. Ratios ranging from 6:1 to'1 0: 1 have been found satisfactory; The, keel ,line runs .substantially parallel to the waterline; for approximately twothirds of the length from the stern forward,
' then has a gradually increasing'upward sweep to the stem' It; the chine line [3 startsat approximately'the same elevation as the keel at the stern, and runsi'orward with a slight rise for the first half portion of the. hull and then with gradually increasing rise to the stem 16. This arrangement makes the bottoms of the hulls Ill-Ill, substantially flat at the' s tern, of shallow V section throughout the center portion, and with deeper v'sectiontoward the stem '16. As
shown in Figures 5 and 7, the floats Ill, H) are of substantially uniform width throughout the major portion of their length, gradually tapering in their forward portions to relatively sharp prows I6, l6. Advantageously, the displacement of the floats is suflicient that the waterline of the hull when at rest is below the bottom wall l8 of the bridge structure l2.
Referring now to Figure 1, it may be seen that, the bottom wall [8 of the bridge structure I 2,
which extends between the floats I 0, l0 throughout a major portion of their length, is substantially straight and horizontal throughout most of its length, with a forward portion |8a having a gradual upsweep. From the forward end ofthis upswept portion of the bridge structure I 2 projects an overhanging deck or brow 29 which serves, among other functions, as a spray shield.
Thus, referring to Figures 5, 6 and 7, the inner walls 22, 22 of thefloats ill, in and the bottom [8 of the bridge structure 12 form through the hull a tunnel of generally rectangu lar cross-section extending fore and aft. The sides of a tunnel, which are formed by the in,- ner walls 22, 22' of the floats l0, it, are substantially vertical and parallel to each other throughout a major portion of their length.
The ceiling of the tunnel, which is formed by the bottom wall I 8 of the bridge structure 12, is substantiallyhorizontal and'therefore sub.-..
stantially perpendicular to the sides of the tun nel throughout a major portionof its length The forward end of the tunnel has a pronounced funnel or bell-mouth shape, by virtue of the tapering of the floats I 0, l0 and the'upsweep of the forward end l8a of the bottom l8 of the bridge structure l2, an effect further accentuated by the overhanging brow v2ll.
Substantially the entire beam of the hull above the line o f th'e bottom of the bridge structure l2 is available as utility space. In Figure l'there has been illustrated a cockpit for the craft, with a suitable arrangement of seating and controls.
' In the particular embodiment shown, twin engines (not shown) are employed, one located astern in; each of theflo ats It, It, These engines, through offset shafting, drive screws 24, 24fwhich are mounted in fin and rudder assemblies 26 26' projecting beneath the centerlin'es of the floats l0, ID. V I
' When the boat is'under way, the bottoms I 4, I 4 of the floats I 0, I 0' have a planing action, which causes the-craft to ride extremely high in the water. The lines WL throughout the figures indicate the approximate position of the waterline when the boat is under way at normal cruising speed. Thus it can be seen that the tunnel under the hull is completely clear under such circumstances. As the boat moves forward, the funnel-shaped forward end of the tunnel scoops in air which is forced or rammed aft into the portion of the tunnel of lesser cross-section, where it is compressed and exerts an upward pressure or lift against the bottom wall 18 of the bridge structure 12. This serves to raise the hull even farther out of the water, so that the craft literally skims across the surface, with only a few inches of the floats l0, I submerged.
The particular novel structural features of a hull made in accordance with the present invention give it the additional and important advan tage of extraordinary stability. The dual orcatamaran type of hull, the general principle of which has been heretofore known and employed, inherently possesses excellent lateral stability, due to th concentration of hydrodynamic lift near its outboard extremities. The present invention provides structural features which add to this inherent lateral stability uncommon degrees of longitudinal and directional stability.
Figures 2, 3 and 4 diagrammatically illustrate the manner in which the longitudinal stability is accomplished. In these figures, th arrowG indicates the longitudinal position of the center of gravity of the boat, the arrow Hthe longitudinal center of hydrodynamic lift force efi'ectiv'e upon the boat, and the arrow A the longitudinal center of aerodynamic lift. 7 The center of gravity G of course remains fixed despite changes in attitude of the boat. The center of hydrodynamic lift H and the center of aerodynamic lift A, however, shift longitudinally with changes in attitude.
When the boat is in its normal attitude, as shown in Figure 2, the hydrodynamic lift, which is a composite of the effects due to displacement Qf water by the floats l0, Ill and the upwardforce exerted by the planing of the floats upon the water, has its longitudinal center Hslightly abaft the longitudinal center of gravity G. The longitudinal center of aerodynamic lift A, whichlift, as above described, is produced by compression of air in the tunnel beneath the boat, is considerably forward of the center of gravity G, While the hydrodynamic lift has greater magnitude than-the aerodynamic lift, the moment arm of the hydrodynamic lift-that is, its longitudinal distance from the center of gravity-4s shorter than that of the aerodynamic lift so that the effective moment of force or torque of the two lifts exactly cancel and the craft tends to remain in perfect balance.
Figure 3 illustratesthe shift of the centers of the aerodynamic and hydrodynamic lift when the craft is momentarilyfin a bow-down position, that is, a position of lower angle of attack than shown in Figure 2. Th center-0f hydrodynamic lift H has moved considerably forward of the center of gravity G, due to a shift in the longitudinal center of displacement, and in the effective longitudinal center of the planing surface, as can be seen. Also, since the ceiling of the tiirinel is new inclined downwardl toward the bow, it has in the portion near. the :bow. a-
markedly reduced cross-sectional area, which results in locally increased aerodynamic pressure. Accordingly, the center of aerodynamic lift has instantaneously moved forward along the boat an appreciable distance. Both the centers of hydrodynamic lift and of aerodynamic lift are now well forward of the center of gravity and augment rather than cancel each other to exert a considerabl torque which tends rapidly to restore the craft to its normal position of balance.
In Figure 4, the boat is shown in a momentary bow-high position or at greater angle of attack than shown in Figure 2; The center of hydrodynamic lift H, as would be expected, has now shifted well abaft the center of gravity G, because only the after portions of the floats ill, Ill are submerged. Also, since the tunnel now has its smallest cross-sectional area in the stern portion, thecenter of aerodynamic lift A has moved some distance-aft from its normal position as in a Figure 2. While the center of aerodynamic lift percent of the length of erait'at the water- 1 a run site test boat, the longitudinal sta- A is still forward of the center of the center of gravity G, the magnitude of aerodynamic lift has been considerably diminished by virtue of the fact, that the forward portions of the floats 10, It" are now clear of "the" water, allowin some of the air which would otherwise be rammed into the tunnel to "*spill? out of the tunnel to either side between the bottoms l4 and M of the floats and the surface or. the water; Thus, the torque produced by the diminished aer'o dynamic lift, acting upon a shortened moment arm, is greatly reduced, while the" undiminished hydrodynamic lift operating on a substantial level arm aft or the cent-seer gravity G, strongly urges the stern of the boat upwardly and tends to restore the boat to its normal attitude.
It will thus be seen hat change in iongit'udinal attitude of the boat, however slight, causes an instantaneous shift in the center or magnitude of lift, producing a force which tends immediately to restore the boat to normal attitude. The result is a longitudinal stability not previously possible. a a V 1 The effect or the shifting of aerodynamic lift will be beneficial no matter new small its magnitude. However, for best results it has been found advantageous tornaiiitain a ratio. of aerodynamic to hydrodynamic lift of-at least l to 20. This is accomplishedby proper proportioning 'of the cross-sectional area of the tunnel at its mouth and at its major portion, and by the proper proportioning of the aieaor the bottom wall l8 ofthe bridge srtructiire 12, with respect to the displaeeiiie or the boat. Also, to afford a substantial shift of the center of aerodynamic lift with change ifrattitiid of the beat, it has been found preferable to extend the uniform reotangular portion of the tunnel for at least bility was so good that the iial tendency to nose up when power is applied or increased. or to nose down power is suddenly out on; was su'b staiitiau over Further, the inherentlateral-stab"lity that it did not meet over on and a large maiicouid ump from one gunv'vale to the other without producing noticea, aele rocking motion. 2
As the bot picks up speed, it mer ly rises in the water with little change or attitude until the bottoms 14, I4 ofthe floats 'r'r' erelysliifn or skid on the surfacofthe' water. This allows the-boat to move forward witheutthe necessity ofmovingl vast voli-i'rns ti water aside, as is necessaryw'ith the usual displamer'it typeti nun; the boat leaves but the slightest were eastern. Thus, it can attain surprising speeds at low power.
arsed-10o Moreover, since the'aerodynamic lift increases as the quantity of air passing through the tunnel is increased, the boat actually makes as good or better speed upwind as downwind. The lower power requirement reducesthe initial cost of the boat, as well as lowering fuel consumption and increasing its operating range. 7 Its points of deepest draft, the tips of the fin and rudder structures 26, 26, are only of the order of one foot below the surface in a boat of the size illustrated, so that it can negotiate extremely shallow waters with safety. This light draft confers the additional advantage of rendering steering unusually easy.
The light draft and the conformation of the floats l0, III which adapt them for planing both longitudinally and laterally also provides the advantage of excellent static directional stability. It is well known that a quartering sea, wherein the horizontal wave motion has a component transverse to the boat, causes a boat having the conventional displacement type hull to yaw, because such a hull presents a large area to the waves and is necessarily carried with them to some extent. With the present hull, however, the transversely moving waves slide beneath the shallow bottoms of the floats I 0, l, and the craft is not carried off course.
The slight V shape of the bottoms I4, I 4' of the floats illustrated give the craft sufficient bite to afford good dynamic directional stability and allow the craft to make good a straight track through the water. The flattening of the bottoms M, M toward the after ends of the floats keeps the center of hydrodynamic lift well aft and overcomes the usual difliculty of excessive drag in hulls with high aspect ratio (relatively long and narrow hulls).
Figures 8 and 9 illustrate an alternative embodiment having a single driving screw 28 mounted at the lower end of a streamlined column 30 projecting downwardly from the bridge structure I2 at the lateral center of the after end thereof. The screw 30 may be powered by an engine 32 mounted on the upperside of bridge structure l2 directly above the screw 28 and coupled therewith by means of a shaft extending through the column 30. A driving arrangement of the general type illustrated in Figures 8 and 9 may be readily provided by means of a conventional outboard motor. Such a system has exhibited extraordinary effectiveness and efliciency. When an outboard motor is used, the craft may be steered by bodily rotation of the motor and its propeller, or, alternatively, by a separately movable rudder mounted directly behind the propeller, or by a pair of rudders in assemblies 26, 26' on the two floats, as already described.
It will be appreciated that the present invention accomplishes the aforementioned as well as other desirable objects. It should be emphasized, however, that the embodiment shown and described is intended as merely illustrative and not as restrictive of the invention.
1. A boat hull comprising a pair of laterally spaced floats and a continuous bridge structure extending between the upper portions of said floats, said floats and said bridge? structure shaped and arranged so as to provide below the operating waterline of said hull two discrete hull portions, and above the operating waterline forming a longitudinally extending tunnel throughout a major portion of the length of said floats, the top of said tunnel being formed by the bottom wall of said bridge structure and having a generally smooth surface which is substantially parallel to the operating waterline for a distance from its after end in the order of magnitude of two thirds of its length and with its remaining portion forward expanded upwardly and forwardly to a cross-sectional area at least twice that of its said after portion, the longitudinal elements of the sides of said tunnel, formed by the inner walls of said floats, being substantially p'arallel'to each other throughout a major portion of their length, whereby said tunnel has substantially uniform cross-sectional area throughout a major portion of its length and a portion opening to at least double such cross-sectional area at its forward end.
2. A boat hull as claimed in claim 1, wherein the ratio of length to width of said floats is between 6:1 and 10:1.
3. A boat hull as claimed in claim 1 wherein the bottoms of said floats are formed in their forward portions to the transverse shape of a shallow V, gradually blending to a generally flat transverse hape at their after extremities. 4. A boat hull as claimed in claim 1 wherein said floats are of suflicient displacement that the waterline of the hull when at rest is below the bottom wall of the bridge structure.
5. A boat hull as claimed in claim 1 wherein the bottoms of said floats are relatively flat transversely and have an upswept portion forward, whereby to give said floats a planing action on the water.
6. A boat hull as claimed in claim 1 wherein the bottoms of the floats are relatively flat longitudinally whereby a relatively small increase in the angle of attack of said hull causes a substantial forward portion of the bottoms of the floats to clear the water.
7. A boat hull according to claim 1 wherein the bottom wall of the bridge structure is substantially horizontal for at least seventyg-flve percent the length of said hull at the waterline.
8. A boat hull comprising a pair of laterally spaced floats having inner walls approximately vertical and disposed substantially parallel to one another throughout a major portion of their length with a tapered portion forward, and a continuous bridge structure extending between the upper portions of said floats to form a tunnel throughout a major portion of their length, said bridge structure having a bottom wall substantially horizontal from its after end throughout about two-thirds of its length and with its remaining forward portion upswept to provide an entering cross-sectional area of said tunnel at least double that of its after portion, thu forming above the operating waterline of said hull a clear tunnel having substantially uniform rectangular shape and size throughout a major portion of its length with a flared portion forward.
9. A boat hull as claimed in claim 1 wherein the top of the forward portion of said tunnel extends upwardly and forwardly for a portion of its length and then forwardly approximately parallel to the operating waterline for the remainder of itslength.
10. A boat hull comprising a plurality of laterally-spaced floats and a continuous rigid connecting structure extending between the upper portions of said floats, said floats and said connecting structure forming longitudinallyextending tunnels between said floats throughout a major portion of their length, the longisubstantially pairane to each other throughout a; major portion 01'; their length, the tops of said tunnels being tornicl by the bottom wall of said connecting structure and having generally smooth surfaces which are Substantially parallel to the operating waterline for a distance from the after ends of said. tunnels in the order of magnitude of two-thirds of their length and with their remaining portions forward opening upwardly and forwardly to cross sectional areas equal to at leist twice that or their uniform after portions. M I V U C. BABCOCK.
. Retereneee Gitedin the file o thi patent UNITE-D sjIATEs PATENT-5 Number Number I Name 7 Date S'chmitt July 1'7, 1928 Adelm'ann Dec. 10, 1929 Rippen Sept. 26, 1933 Creed -1 Aug. 6, 1946 FOREIGN PATENTS Country Date France Oct. 15, 1920 France ..7, Apr. 23, 1946