A mid-planing hull for a fast, sea-going vessel in which the centers of buoyancy, gravity, and hydrodynamic lift at planing speeds substantially coincide amidships. In a preferred embodiment, the hull includes a full forefoot of conically developed forward sections, a straight and level keel in a vee-bottom of constant deadrise, with planing surfaces distinctly decreasing in area in the afterbody to trailing edges at the stern.

BACKGROUND OF THE INVENTION 
The present invention relates to a hull capable of performance in a 
combination of speed and seakeeping heretofore found separately in 
displacement and planing hull types. The two qualities have always been 
difficult to combine because they depend on decidedly different hull 
forms. 
The seakeeping characteristics of displacement hulls are well known. They 
are most evident in the classic lines of traditional sailing vessels with 
graceful curvature fore and aft to move easily under sail through the 
water and follow the waves. Those lines are little changed in the 
ocean-going ships of today, with their pointed bows, round bilges, rounded 
sterns, and amidships balance to ride as level as possible in meeting seas 
under all weather conditions. 
More recently, hull speed has been increased by use of a very different 
hull form from that of displacement vessels, enabling such planing hulls 
to rise bodily towards the water's surface and move at higher speed 
because of less water resistance. Typically, planing hulls have 
sharp-cornered chines, flat bottom surfaces aft, and square transoms. For 
the sake of speed, they have given up some of the seakindly configuration 
of their predecessors, tending in a seaway to leap from the crest of each 
wave and to slam violently into the next. 
The development of fast planing hulls began with the design of racing 
hydroplanes in the early 1900s, and they set the style for all speed boats 
with wide, flat planing surfaces aft. Morever, powerboats have been 
inclined to settle by the stern as they pick up speed; and that tendency 
is often aggravated into a bad squat as a fast boat rises up to plane. A 
typical planing hull then assumes an ungainly attitude, with its bow 
riding well up out of the water at high speed, an attitude safely 
maintained only in calm water. 
Numerous inventions over the years have tried to correct the problem of 
poor planing trim, usually by adding some leveling or stabilizing device. 
For example, Weiland's U.S. Pat. No. 988,437, dated July 18, 1911, and 
Prosser's U.S. Pat. No. 1,075,726, dated Oct. 14, 1913, both attached 
something like water skis to either side of a small, narrow boat. More 
recent attempts to improve trim were in having slightly concave bottom 
lines aft to keep the stern up by deflecting passing water downward, as 
disclosed in the Burgess U.S. Pat. No. 2,185,430, dated Jan. 2, 1940, and 
the Troyer U.S. Pat. No. 2,342,707, dated Feb. 29, 1944. 
The introduction of fiberglass boatbuilding in the 1950s boosted mass 
production of planing hulls by the use of molds to provide hulls in almost 
any shape or form. Since then, extruded panels, steps, and chine lips have 
become common in multiple horizontal surfaces added to the basic 
vee-bottom. In what has been popularly accepted as modern styling, the 
extra angles and curves seem to create an illusion of speed, but speed is 
actually reduced by the increase in wetted surface. Improvement in trim 
may be claimed or implied, but there has actually been little change in 
planing performance. Examples of such modern design in fiberglass planing 
hulls include those disclosed in the Becker U.S. Pat. No. 2,634,698, dated 
Apr. 14, 1953; the Canazzi U.S. Pat. No. 2,980,924, dated Apr. 25, 1961; 
and the Schoell U.S. Pat. No. 4,193,370, dated Mar. 18, 1980. 
A significant improvement in planing hull design occurred in 1959 when the 
so-called "deep vee" for ocean racing put a definite dihedral or deadrise 
angle in a planing hull bottom. The change became popular and was widely 
copied as it greatly improved directional stability for open ocean 
operation. However, the improvement had little efect on planing aspect or 
trim and thus did not minimize slamming or pounding by the forward portion 
of the hull. The latest models are still characterized by hard chines, 
vee-bottoms, and broad transoms to carry maximum planing surfaces farthest 
aft; and planing hulls still ride on their afterbodies, being notoriously 
rough in any waves. 
While there has been no fundamental change in planing hull lines to achieve 
a desirable minimum angle of trim, trim tabs are commonly installed at the 
transom to offset an extreme squat. Similar to the former use of 
wedge-shaped blocks under the transom to force the water down and push the 
stern up toward a more horizontal position, external contrivances like 
trim tabs have only a limited effect, as they function at some expense of 
economy or speed. Any such projections from the hull proper, whether in 
attachments or extrusions, will reduce speed by adding to wetted surface 
and parasitic drag. Reverse curves or warped planes have the same adverse 
effect by increasing the area of skin friction and distorting the free 
flow of water past the hull. 
Riding trim is largely a matter of innate balance, something primarily in 
hull form not very well managed by simply adding to or changing hull 
surfaces. A slow and well balanced displacement vessel accepts sea 
conditions most agreeably without pounding or slamming; but a fast hull, 
riding on her after planes with a high bow, can only meet the waves with 
violent impact. 
SUMMARY OF THE INVENTION 
Two vessels that admirably exemplify the respective qualities of seakeeping 
and speed combined in this invention are the Hawaiian Sampan and the Navy 
Patrol Torpedo boat. The two hull types are strikingly similar in having a 
fairly deep and sharp forefoot, hard chines, vee-bottom, and transom 
stern; but a difference in their underbodies aft clearly distinguishes 
their characteristic performance. The Sampan has an upward run of her 
underwater lines aft to the stern; while the PT has chines and buttocks 
lines that run parallel with the keel straight aft to the transom. 
The Sampan is a traditional, sturdy vessel of displacement type, able to 
maintain little more than ten knots, but very seakindly. Being almost 
perfectly balanced with buoyancy and weight amidships, it rides the waves 
on a fairly level keel as bow and stern successively rise and fall in no 
more than half the vessel's length. 
The typical PT Boat is a lightweight planing hull, capable of more than 
forty knots when planing, but rough riding in a seaway. The bow of the PT 
Boat at speed inclines up and the hull is lifted farther out of the water 
to ride on her after planing surfaces. Coming off a large wave at speed, 
the airborne bow of an 80-foot PT will slam down into the next wave, often 
with such force as to bring the vessel momentarily to a shuddering stop. 
The principal object of the present invention is to improve seagoing 
performance by combining, as best possible, the seakindly character of a 
Sampan and the planing speed of a PT Boat, enabling the vessel to drive 
through the crest of a wave, and then coast down the wave slope at speed 
with little change in level of trim. The improvement is accomplished by 
embodying the balance of underwater volume in the Sampan for seakeeping 
and the parallel buttocks of the PT boat bottom for speed. This 
combination provides a more level planing trim and tends to reduce both 
slamming or pounding by the bow and squatting by the stern. That balance 
in the hull of the present invention is derived from the marriage of 
forward presentation with planing surfaces to locate the centers of 
buoyancy, gravity, and lift amidships rather than at the extreme stern. 
For better seakeeping at speed, the present invention more specifically 
includes a bow portion that will drive through the waves and is less 
susceptible to being tossed high and plunging precipitously down. The 
forebody, having a sharp entry at the stem and full-bodied sections under 
the bow, provides buoyancy forward to carry the center of gravity more 
amidships and also to cushion the impact of oncoming waves. 
To improve speed in seagoing, the present invention provides lift amidships 
by planing surfaces that taper aft to be no more than trailing edges, and 
the chine lines converging aft toward the keel to at least half of their 
maximum beam amidships, lessening both wetted surface and body drag. 
Manueverability is improved by the more streamlined form overall that 
allows better directional stability, smaller turning circle, and banking 
on high speed turns without slewing by the stern. 
Efficiency is improved by hull lines designed to provide better trim for 
better utilization of propulsion thrust to gain more lift. 
The instant invention finds an exceptional fore and aft balance in a 
surprisingly simple modification of underwater lines that enables a vessel 
to plane on her midsection. The convex forward sections are not only 
shaped to lessen the severity of wave impact but streamlined to improve 
speed. More subtly, but very definitely, they enhance the effectiveness of 
planing lift amidships and trim at the stern. The resultant seagoing 
balance is obtained with smooth and clean planing hull lines without any 
need for any attachments, extrusions, or concave surfaces. And the 
advantages in more stable riding, improved speed, and better handling in 
rough seas have been verified in prototype model tests. 
While this invention has particular application to off-shore patrol and 
fishing vessels in the range of eighty feet in overall length, it may 
generally be applied to smaller craft that aspire to meet rough water 
conditions and to larger vessels in size up to and over 250 feet in length 
where a semi-planing condition can improve their speed. The preferred 
embodiment shows the lines of an eighty-foot vessel with a length-beam 
ratio of 4:1; but larger vessels may have a normal proportion up to 7:1, 
and smaller craft where the usual ratio may go as low as 3:1. The present 
invention is not limited to the particular embodiment shown in the 
drawings or described in the foregoing specification, and modification of 
details can readily be considered by those skilled in the art without 
departing from the invention as defined in the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The hull structure of the present invention may be more readily understood 
by reference to the drawings. Since hull performance is primarily a 
function of the underwater lines, particular attention is given to the 
underbody. The topsides may be conventional except where the hull sides 
toe in downwardly as they go aft to form an unconventional transom that is 
broad at the deck and narrow below the waterline. 
As shown in FIGS. 2 and 3, a raked stem (1) at the bow goes deep before it 
curves into the keel (2), which runs straight and level aft to the transom 
(3) and parallel to the designed waterline (4). The two chines (5) and 
(6), outlining respectively the bottom to port and to starboard, begin 
forward at a point more than halfway up on the stem (1) to angle out and 
down to either side befor curving back to run nearly parallel to each 
other and the keel (2) amidships. Thereafter they continue to the stern by 
converging toward the keel while remaining in the two planes of the 
vee-bottom. 
The two dashed lines (7 and 8) shown in both profile FIG. 2 and in plan 
FIG. 3, angling straight out to either side from forward on the keel to 
aft at the chines, mark the joint along which the conically developed 
forward surfaces flow smoothly or "fair" into the flat planing surfaces 
going aft. In plan view, the forward portion of the planing bottom is 
triangular in area before its two planes are narrowed toward the stern by 
the converging chines. 
FIG. 4 shows the corresponding port and starboard conical development of 
the convex forward sections below the chines (5 and 6); and FIG. 5 shows 
how the vee-bottom, with its constant deadrise of about 14 degrees 
dihedral, narrows in going aft to the transom (3), as the hull sides 
gradually toe in and the chines converge toward the longitudinal 
centerline or keel (2). FIGS. 4 and 5 also show clearly how the chine, 
marking the joint between bottom and hull sides, gradually "soften" in 
going forward to the point of disappearing as they reach the stem but 
become sharp-cornered or "hard" where they define the planing surfaces 
aft. 
The fullness of the forefoot that adds buoyancy forward is also evident in 
the rounded development of the bottom sections of the forebody shown in 
FIG. 4. The shape of the transom (3), as seen from aft in FIG. 5, is the 
most visible change from conventional hull form, showing neither a stern 
post nor a square stern of other vessels. More significantly, being wide 
at the deck but narrowed at the waterline, it indicates a bottom having 
planing surfaces reduced to at least half-breadth in breadth at the stern. 
Two sets of lines that further help delineate the shape of the hull bottom 
are usually a number of buttocks lines and several waterlines, marking the 
intersections where evenly spaced vertical and horizontal planes pass 
lengthwise through the hull. Both sets of lines indicate relative speed or 
the ease with which a vessel moves through the water. In the profile and 
plan view drawings (FIGS. 2 and 3), a typical buttocks line (9) and the 
designed waterline (4) show the advantage of a fairly streamlined contour 
where they cross the chines forward with a minimum of "knuckle" or sharp 
angle for least disturbance of water as the vessel moves ahead. Good 
seakeeping is evident in the streamlining of the waterline forward and 
aft, and planing speed is indicated by the parallel buttocks line where it 
runs straight aft to the transom. 
FIG. 1 shows best how the hull bottom distinctly differs from that of a 
conventional transom-type planing hull, and how the converging chines 
affect performance. A simple analysis of the hydrodynamics involved makes 
it easy to see from the drawings how a real improvement in planing hull 
balance means better seakeeping with speed. Having the vital centers of 
volume, weight, and lift moved from the extreme after end of the vessel to 
a point nearly amidships, the fulcrum of response to wave action has also 
been moved forward about half of the vessel's length. Because the vessel 
then pivots on her midsection, the successive up and down movement of the 
bow and the force of impact in reaction to waves can be visualized as 
reduced by about one half. The planning hull with bottom or underbody 
configuration includes a forefoot, a midsection, and an after portion. The 
forefoot has conically developed surfaces in convex forward sections that 
provide a sharp entry to part waves in laminar flow with sufficient 
fullness under the bow to cushion the impact of oncoming waves and add 
approximately ten percent buoyancy forward to thereby effectively move the 
center of overall buoyancy forward. Buttocks lines and waterlines cross 
the chines forward with minimum knuckle to result in more streamlined 
form, whereby bow wave resistance is lowered by a better forebody 
presentation. 
The midsection has vee-bottom planing surfaces beginning in a triangle 
forward with greatest breadth at its base amidships from which the 
surfaces begin to narrow between the chines that curve continuously inward 
toward the keel in going aft. The planing surfaces follow a straight and 
level keel line that begins at a point about one-eight of the load 
waterline length aft of the stem and runs all the way to the stern. The 
planing surfaces are in a moderate vee-bottom of about fourteen degrees 
constant deadrise. The planing surfaces join the conic surfaces forward 
along lines that slant out and aft at an angle of about twenty degrees to 
either side of the keel to reach the chines at amidships. The midsection 
planing surfaces taper forward and decrease aft and have the center of 
their total area practically amidships to provide a mid-planing 
hydro-dynamic lift. 
The after portion has planing surfaces that continue to decrease in width 
between the chines converging aft to at least half of their amidships 
distance apart to provide no more than trailing edges at the transom for 
fore and aft trim. The underbody aft approaches streamlined form in the 
waterlines that converge with the chines as they go aft, resulting in a 
lower wake due to less wavemaking resistance from afterbody drag. The aft 
underbody has buttocks lines running aft between the chines parallel to 
the keel and straight to the transom to maximize planing. The converging 
chines reduce the area of the after planing surfaces by about twenty 
percent, thereby lessening frictional resistance due to wetted surface. 
The converging chines also reduce the aft underbody volume by 
approximately ten percent, effectively moving the center of overall 
buoyance further forward to approximately amidships. The trailing edges of 
the planing surface at the semitransom have a span that is not more than 
half of the maximum beam of the planing surfaces amidships. 
The average hull for an eighty-foot planing hull has a ratio of load 
waterline length to load waterline beam of about 4:1. This ratio would 
normally be higher for a larger vessel and lower for a smaller craft, 
maximum beam being amidships. 
The vital centers of buoyancy, gravity, and lift practically coincide 
amidships of the hull to provide an exceptional balance that locates the 
axis of response to waves in the midsection, thereby reducing the violence 
of impact in pitching or pounding by nearly half while maintaining planing 
speed in a seaway.