Note: Descriptions are shown in the official language in which they were submitted.
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BOAT HULL DESIGN FOR OUTBOARD JET MOTOR
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention pertains generally to the design of hulls for watercraft. More
specifically, the
invention relates to hull designs that improve the efficiency of propulsion
systems that are used to
power watercraft over waterbodies.
(2) Description of the Related Art
Powered watercraft that are used for a variety of applications like fishing,
racing, recreational
boating, rescue operations, etc. generally use propulsion systems comprising
an inboard
motor/engine or an outboard motor/engine or a sterndrive with different drive
configurations. The
motors/engines are used to drive a propeller or jet drive in many commonly
used configurations.
Inboards, wherein the engine or motor is located inside of the watercraft, are
extensively used in
high-powered applications since they generate higher power than outboard
motors. However,
outboard motors are cheaper, less expensive to maintain, and easier to service
than inboard motors.
Further, the outboard motors can be easily mounted and dismounted from
watercraft whereas
inboard motors are installed inside boats and cannot be easily
mounted/dismounted as needed.
Moreover, inboard motors/engines are quite difficult to service since they are
not easily accessible.
These and other advantages have made outboards very popular. However, the
efficiency and power
output of outboard motors/engines is significantly less compared to inboards
of the same size or
capacity.
Jet drives are used with both outboard and inboard motors. Jet drives are
becoming increasingly
popular due to their inherent safety advantages over propellers since there
are no moving blades in
the water. Moreover, they can also operate in shallower water than propellers.
Watercraft with
propellers can get stuck when operating in shallow water due to debris
clogging the intakes and the
blades, or the blades dragging through the riverbed or lakebed, or the
motor/engine overheating
due to insufficient water at the intake, etc. and may need to be lifted out of
the water by helicopter
in a worst-case scenario.
BRIEF SUMMARY OF THE INVENTION
According to an exemplary embodiment of the invention there is disclosed a
method of increasing
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efficiency of a propulsion device of a watercraft. The method comprises
drawing water from a
waterbody into a tunnel and channeling the water through the tunnel towards
the propulsion device.
The method further comprises forcing the water in the tunnel to be compressed
by a solid surface
before the water reaches the propulsion device and feeding the propulsion
device with the water
from the tunnel after the water has been compressed by the solid surface.
According to an exemplary embodiment of the invention there is disclosed an
apparatus for
increasing efficiency of a propulsion device of a watercraft. The apparatus
comprises a tunnel for
drawing water from a waterbody and channeling the water towards the propulsion
device. The
apparatus further comprises a solid surface for forcing the water in the
tunnel to be compressed
before the water reaches the propulsion device, wherein the propulsion device
is fed with the water
from the tunnel after the water has been compressed by the solid surface.
These and other advantages and embodiments of the present invention will no
doubt become
apparent to those of ordinary skill in the art after reading the following
detailed description of
preferred embodiments illustrated in the various figures and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail with reference to the
accompanying drawings
which represent preferred embodiments thereof:
FIG. 1 shows a bottom view of a watercraft with a tunnel and a delta pad
according to an exemplary
embodiment.
FIG. 2 shows a side view of the watercraft with an outboard motor mounted on
to a transom of the
watercraft according to an exemplary embodiment.
FIG. 3 shows a rear perspective view of the watercraft illustrating the
transom, tunnel, and delta
pad of the watercraft according to an exemplary embodiment.
FIG. 4 shows a perspective view of a partially constructed watercraft showing
the transom, exit-
opening of the tunnel, side walls, and delta pad according to an exemplary
embodiment.
FIG. 5 illustrates the tunnel of the watercraft in operation wherein the
propulsion device is fed with
water from a waterbody through the tunnel according to an exemplary
embodiment.
FIG. 6 shows a perspective view of a simplified tunnel design with a narrow
delta pad that does
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not extend across the width of the watercraft, according to an exemplary
embodiment.
FIG. 7 shows a bottom view of the watercraft with two tunnels and associated
delta pads, one tunnel
and delta pad located on either side of the center line of the watercraft
according to an exemplary
embodiment.
FIG. 8 shows components of a kit that can be used to transform an existing
watercraft to incorporate
the tunnel and delta pad according to an exemplary embodiment.
FIG. 9 illustrates side views of some exemplary shapes of the tunnel of the
watercraft.
FIG. 10 shows top-down views of some exemplary shapes of the tunnel of the
watercraft.
DETAILED DESCRIPTION
Outboard motors coupled to jet drives, also known as outboard jets, are a very
popular
configuration. However, a significant problem affecting jet drive performance
is the phenomenon
of cavitation, wherein cavitation bubbles consisting of air or vacuum form in
the water and explode
at the blades of the impeller of the jet drive resulting in cavitation damage
to the blades. Further,
cavitation results in a lowered efficiency of the jet drive. Insufficient
volume or pressure of water
at the intake due to low water depth or debris at the intake increases the
occurrence of cavitation
and also further reduces efficiency.
FIG. 1 shows a tunnel 100 and delta pad 102 installed on a watercraft 104. The
tunnel 100 is located
in a middle section of the hull 106 of the watercraft 104 and runs along a
length of the watercraft
104 towards an aft or rear end of the watercraft 104. The delta pad 102 is
affixed to the hull 106 at
the aft end of the watercraft 104. The delta pad 102 is a flat surface,
constructed generally out of a
material like aluminium, steel, carbon fibre, fiberglass, etc. The delta pad
102 also forms a lower
wall 202 of the tunnel 100. FIG. 2 shows a side view of the watercraft 104 of
FIG. 1. In this
embodiment, the tunnel 100 has a curved shape in side-view as can be seen from
the figure. The
curved shape is due to the curvature of an upper wall 204 of the tunnel. The
tunnel 100 has an
entry-opening 206 on its lower surface that is in contact with the water body.
Water is drawn into
the tunnel 100 from the waterbody through the entry-opening 206.
An outboard motor/engine 208 connected to a jet drive is affixed to a transom
210 of the watercraft
104 as shown in FIG. 2. The outboard motor 208 is attached to the watercraft
104 with no part of
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the outboard motor 208 immersed in the waterbody, in an exemplary embodiment.
A water intake
212 of the jet drive is located adjacent to an end of the tunnel 100 through
which water exits the
tunnel. The jet drive is included within the representation of the outboard
motor 208 and is not
shown separately in FIG. 2. In this embodiment, the jet drive propels the
watercraft 104 over the
waterbody by drawing water from the waterbody through the tunnel 100 and
shooting out the water
through a nozzle 214.
FIG. 3 shows an exit-opening 302 of the tunnel 100 located at the aft end of
the watercraft 104.
Water that is drawn from the waterbody enters the tunnel 100 through the entry-
opening 206, flows
through the tunnel 100 and exits the tunnel 100 through the exit-opening 302.
The tunnel 100 passes
through a hole cut into the transom 210 and extends a few inches beyond the
transom 210. In FIG.
3, the exit-opening 302 of the tunnel 100 is viewed head-on. The entry-opening
206, the upper wall
204 with a deflector plate 308 and the side walls 304 of the tunnel can also
be seen in FIG. 3. A
pair of sponsons 306 are shown, one on either side of the tunnel. In the
embodiment illustrated in
FIG. 3, the overall length of the watercraft is increased by the length of the
extended delta pad 102
beyond the transom 210. The delta pad 102 provides a platform that extends
across the width of
the watercraft 104 at its rear end. This arrangement allows the tunnel 100 and
outboard motor 208
to be installed in a manner that provides protection to the motor and
contributes to making the ride
less bouncy. In some embodiments, the sponsons 306 are part of the structure
of the hull 106 itself.
In some other embodiments, the sponsons 306 may be supplied as part of a kit
to form an additional
structure affixed to the transom 210. The hull design with sponsons 306
increases the buoyancy of
the watercraft 104 and improves stability of the watercraft while in motion on
the waterbody. In
some embodiments, the sponsons 306 are closed, box-like structures that may be
hollow or filled
with foam or other material.
A watercraft that is being modified to incorporate the tunnel 100 is shown in
FIG. 4 illustrating the
exit-opening 302 of the tunnel and side walls 304 of the tunnel. The delta pad
102 is shown
extending beyond the transom and providing a platform for the tunnel. The
deflector plate 308
located at an end section of the upper wall 204 of the tunnel 100 has a curved
edge in order to
accommodate the curved surface of the outboard motor, allowing the motor to be
manoeuvred
easily. Only the end section of the tunnel 100 that extends beyond the transom
210 is shown in
.. FIG. 4. The rest of the tunnel 100 along with the entry-opening 206 is
omitted for simplicity.
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FIG. 5 illustrates the flow of water through the tunnel 100 during operation
of the watercraft 104.
An outboard motor 208 incorporating a jet drive is installed on the watercraft
104 as shown in FIG.
5. In this embodiment, an impeller 502 of the jet drive functions as a
propulsion device. The
impeller 502 of the jet drive is driven by the motor through a shaft (not
shown). The rotational
motion of the impeller 502 creates a suctional force that draws water from the
waterbody through
the tunnel 100 into the intake 212. As water flows through the tunnel 100, the
water is compressed
due to collision with the walls of the tunnel 100 that are not parallel with
the direction of flow of
the water, as well as due to the changing width or circumference of the tunnel
100 at various
sections. In this embodiment, the upper wall 204 of the tunnel 100 is curved
as shown in FIG. 5.
Within the curved tunnel, the water reaches a high point of the tunnel 100 and
then drops towards
the lower wall 202 formed by the delta pad 102. When the water hits the delta
pad 102, it undergoes
further compression. The water is also compressed due to collision with the
side walls 304 of the
tunnel 100 and walls of the intake 212 before reaching the impeller 502.
As a consequence of the compression of water caused at least in part by the
collision of water with
the solid surfaces, the formation of cavitation bubbles in the water is
reduced and the pressure of
water and flow rate of water at the intake 212 of the propulsion device 502 is
increased. This
reduces the possibility of cavitation damage to the propulsion device 502 and
may help in
improving efficiency of the jet drive. In this embodiment, the entry-opening
206 and shape of the
tunnel 100 allow the volume of water flowing through the tunnel 100 to be
greater than needed by
the propulsion device 502. Having a greater volume of water than needed also
helps with increasing
the water pressure, compressing the water and reducing the likelihood of
cavitation. Water flowing
through the tunnel 100 that is not drawn into the intake 212 flows along the
surface of the delta pad
102 out into the waterbody. The intake 212 of the propulsion device 502 has a
filter to keep out
debris like rocks, weeds, etc. These debris also flow out along with the
excess water back into the
waterbody.
The water that is drawn into the intake 212 is shot out through the nozzle 214
by the action of the
impeller 502, providing thrust to propel the watercraft 104. Compression of
water before it enters
the intake 212, as achieved by the solid surfaces of the tunnel 100, may
improve the efficiency of
the jet drive and also reduce the occurrence of cavitation at the impeller or
propulsion device 502.
Further, the outboard motor 208 is mounted in a manner such that no part of
the motor lies below
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the keel of the watercraft 104. The intake 212 of the jet drive is fed through
the tunnel 100 whose
exit-opening 302 opens on to the extended delta pad 102. The delta pad 102
forms a physical barrier
between the lowest part of the outboard motor 208 and the waterbody. This
arrangement enhances
the safety and stability of the watercraft 104 and also helps protect the
propulsion device 502
located at the lower side of the outboard motor 208. Further, the delta pad
102 ensures that during
operation in shallow waters, the motor/engine 208 and propulsion device 502
are not damaged by
being dragged through the bottom of the waterbody like a riverbed or by being
scraped by rocks or
other debris. As a result, the chances of the watercraft 104 capsizing due to
the propulsion device
502 being struck by rocks or debris is greatly reduced. Further, there is
reduced possibility of the
watercraft 104 getting stuck and stranded in shallow waters. Hence, the safety
of the watercraft is
significantly enhanced. Moreover, this design allows the watercraft 104 to be
operated in shallower
waters than is possible with conventional watercraft since the motor doesn't
extend beyond the
keel of the watercraft 104 resulting in a smaller draft, and the compression
of the water due to the
tunnel design ensures that the propulsion device 502 is fed with water having
sufficient pressure
and flow rate, with reduced cavitation.
FIG. 6 shows a side perspective view of another exemplary embodiment where the
tunnel 100
extends beyond the transom 210 and feeds the intake 212 of the jet drive, but
the delta pad 102 is
not extended to cover the width of the watercraft 104 at the aft end. The
delta pad 102 forms the
lower wall 202 of the tunnel 100 and extends in length to form a channel of
water from which the
intake 212 of the propulsion device 502 is fed. The delta pad 102 is not
extended widthwise. This
embodiment is a simpler design which may be suited to some applications, e.g.,
applications where
the modifications to an existing watercraft need to be kept to a minimum, etc.
FIG. 7 shows an exemplary embodiment with two tunnels 100 feeding water into
intakes 212 of
two propulsion devices 502 with one tunnel 100 located on either side of the
center line of the
watercraft 104. Each tunnel 100 has a corresponding delta pad 102. In this
embodiment, the two
delta pads 102 are connected together in the region beyond the transom 210
such that they form a
single continuous platform behind the transom 210 of the watercraft.
FIG. 8 illustrates a few principal components of a kit that can be utilized to
convert an existing hull
of a watercraft 104 to the tunnel design of the present application according
to an exemplary
embodiment or to incorporate the tunnel 100 while building a watercraft. The
kit includes an upper
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tunnel section 802 that forms the upper wall 204 of the tunnel 100. This
section is a sheet of solid
material that is either pre-bent or flat (to be bent into the required shape
during installation). The
upper tunnel section 802 has fold lines as shown denoting the regions where
the sheet is to be bent
to form the shape of the upper wall 204 of the tunnel.
The upper tunnel section 802 further includes a curved deflector plate 308 at
the end that exits the
transom and feeds the intake 212 of the propulsion device 502. The deflector
plate 308
accommodates a curved wall of the outboard motor 208 as stated previously. The
upper tunnel
section 802 may be formed of sections using a metal like aluminium that is
bent into the required
shape or moulded directly into the required structure using materials like
fiberglass, carbon fiber,
polycarbonates, etc. The kit also includes tunnel sidewall sections 804 that
form sidewalls 304 for
the tunnel. In this embodiment, the sidewalls 304 extend beyond the upper wall
204 of the tunnel
at the end of the tunnel that opens to the intake 212, which is the exit-
opening 302. This allows the
intake 212 to be located adjacent to the deflector plate 308 of the tunnel
while the sidewalls 304,
in conjunction with the delta pad 102, form a channel that holds water to feed
the intake 212. The
sidewalls 304 also provide a solid surface for compression of the water. This
can be seen more
clearly in FIG. 4.
The kit further includes a delta pad section 806 that is to be affixed to the
hull 106 to form the delta
pad 102 as shown in FIG. 1. The delta pad section 806 is installed such that
it begins roughly near
the region of the tunnel 100 where the tunnel height is the highest (for
embodiments, where the
tunnel has a curved wall). The delta pad 102 forms the lower wall 202 of the
tunnel and provides a
solid surface for compression of the water as it falls from the high point in
the tunnel 100 and hits
the delta pad 102 prior to being fed to the propulsion device 502. The delta
pad 102 is also bent
along its length on both sides of the central axis. The delta pad section 806
has fold lines as shown
denoting the regions where the sheet is to be bent while being affixed to the
hull 106 of the
watercraft 104. The angle by which the delta pad 102 bends on both sides of
the axis is the deadrise
of the watercraft, i.e. the deadrise is the angle that the 'wings' of the
delta pad 102 make with the
horizontal. In an exemplary embodiment, a deadrise of approximately 5 is used
for the delta pad
102. A low deadrise helps improve the stability of the watercraft 104 amongst
other benefits.
Generally, the deadrise at the transom is a low value and it transitions to a
sharper angle with a V-
shape at the bow to enable the hull 106 of the watercraft 104 to slice through
water at lower speeds
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and provide a smooth ride. The low deadrise at the transom can be seen in FIG.
3. The watercraft
illustrated in FIGS. 1 and 2 has a hull with a sharp V-shape at the bow which
transitions to a nearly
flat hull at the transom 210 where a delta pad 102 with a low deadrise is
located. This is a modified-
V hull which helps make the ride smoother while preserving speed and 'planing'
(i.e.,
hydroplaning) ability of the watercraft.
The delta pad 102 includes a central flat section between the two bent
sections. The bottom surface
of the central flat section provides a surface that remains in contact with
the waterbody during
planing and may help reduce 'hole shot' of the watercraft. The hole shot is
the time it takes for the
watercraft 104 to achieve planing from the instant at which the throttle of
the engine or motor is
opened. Planing or hydroplaning is a mode of operation for the watercraft
wherein, while the
watercraft is moving faster than a certain speed, the weight of the watercraft
104 is supported
predominantly by hydrodynamic lift rather than by buoyancy due to the volume
of the water
displaced by the watercraft. During planing, the front section or the bow of
the watercraft 104 is
not in contact with the waterbody. Only a small section of the hull 106 of the
watercraft 104 at its
rear section is in contact with or immersed in the waterbody. This greatly
reduces drag and allows
the watercraft 104 to travel at high speeds efficiently. In this embodiment,
the flat section of the
delta pad 102 is the section that is in contact with the waterbody during
planing and facilitates
generation of adequate lift for planing. The low deadrise which makes the hull
106 close to a flat-
bottom hull contributes significantly in transitioning quickly to planing mode
and allowing the
watercraft 104 to skim across the surface of the waterbody to achieve high
performance and speed.
FIG. 9 illustrates the shape of the tunnel 100 according to a few example
embodiments. The figure
shows the side view of the rear section of the watercraft 104 with only the
tunnel 100, motor 208
and a section of the delta pad 102 shown for simplicity. In these embodiments,
the upper wall 204
of the tunnel 100 is curved such that the water experiences compressive forces
predominantly along
the vertical axis. As shown in FIG. 9, the tunnel shape can be customized for
different applications.
In some embodiments, the upper wall 204 of the tunnel has segments that make
sharp angles with
each other whereas in some other embodiments the upper wall 204 has smooth
curves. The lower
wall 202 of the tunnel 100 formed by the delta pad 102 is illustrated in FIG.
9 as a flat surface;
however, the lower wall 202 may also be non-flat in some embodiments.
FIG. 10 illustrates tunnel designs according to a few additional embodiments
wherein the sidewalls
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304 of the tunnel 100 are not parallel to each other or to the center line of
the watercraft 104. These
tunnel shapes are additional ways to further compress the water flowing in the
tunnel 100. FIG. 10
shows top-down views where the sidewalls 204 of the tunnel 100 can be seen to
be curved or non-
parallel. Here, the water experiences compressive forces predominantly along
the horizontal axis.
In some other embodiments, both the upper wall 204 and the side walls 304 may
be curved or non-
parallel to compress the water in both horizontal and vertical axes
simultaneously. The lower wall
202 of the tunnel formed by the delta pad 102 is also shown. FIG. 10
additionally shows a
perspective view for one of the tunnel designs that is also shown in top-down
view. The curvature
of the sidewalls 304 of the tunnel, the entry-opening 206 through which water
enters the tunnel
100, and the lower wall 202 of the tunnel can be seen clearly in this
perspective view.
The entry-opening 206 of the tunnel through which water enters the tunnel 100
from the waterbody
can also have various sizes depending upon the application, size of
watercraft, etc. The location of
the entry-opening 206 and the length of the tunnel 100 may also vary depending
on the application.
The entry-opening 206 may also have a gate that can be adjusted on the fly to
allow the operator
of the watercraft 104 to control the size of the entry-opening 206 during
operation of the watercraft.
This would allow the operator to control the flow rate of water into the
tunnel 100 as well as the
volume of water held in the tunnel which directly impacts the buoyancy of the
watercraft and the
operation of the propulsion device. In some scenarios, the operator of the
watercraft 104 may close
the tunnel gate completely to temporarily disable the operation of the tunnel.
Such a scenario may
arise, for example, when a different propulsion device that is not fed through
the tunnel 100 is
being used to power the watercraft 104 while the regular propulsion device is
being repaired or
serviced, etc.
In some embodiments, the section of the delta pad 102 that forms the lower
wall 202 of the tunnel
may also have a curved shape for additional compression of the water and to
channel the water in
a more controlled manner. In some embodiments, the intake of the propulsion
device 502 may point
sideways or upwards such that instead of the water that is drawn through the
intake 212 being fed
to the propulsion device 502 directly, the water first hits one or more walls
of the intake 212 where
it undergoes further compression and reduction of cavitation and then the
compressed water is fed
to the propulsion device 502.
The solid surfaces that are responsible for compressing the water include the
upper wall 204 of the
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tunnel, the lower wall 202 of the tunnel, the sidewalls 304 of the tunnel, the
delta pad 102 , the
walls of the intake 212 of the propulsion device 502, etc. Curvature of the
walls of the tunnel 100
or a changing width of the tunnel also compresses the water due to collision
of the water molecules
with the solid surface of the walls since the walls are not parallel with the
direction of flow of the
water. The solid surfaces utilized for compression of water may be formed of
metals like aluminium
or materials fiberglass, carbon fiber, wood, foam, rubber, polymers, plastics
etc. depending on
which surface is providing the compression. The solid surfaces may be rigid or
soft, plastic or
elastic.
In some embodiments, the tunnel walls are curved in such a way that the width
or circumference
of the tunnel 100 decreases along the length of the tunnel. The tunnel 100 is
wide at its entry-
opening 206 and narrow at the exit-opening 302 that feeds the intake 212 of
the propulsion device.
As water flows through the narrowing tunnel 100, the pressure of the water
increases, and it is
compressed further. Higher water pressure at the intake 212 may improve the
efficiency of the
propulsion device 502. The width of the tunnel 100 may change either in the
vertical direction or
horizontal direction or both, as depicted in FIGS. 9 and 10.
In another exemplary embodiment, the section of the delta pad 102 that forms
the lower wall 202
of the tunnel 100 may be adjustable or retractable such that the length of the
tunnel 100 and hence
the volume of water held in the tunnel can be adjusted as required.
In some embodiments, more than one tunnel 100 may be used to feed water into
the intake 212 of
a single propulsion device 502 of the watercraft. Usage of multiple tunnels
100 to feed the intake
212 may help further reduce the occurrence of cavitation and increase
compression of the water.
Further, the presence of multiple tunnels may improve the stability of the
watercraft.
The hull design shown in these exemplary embodiments has an advantage of
enabling operation of
the watercraft 104 in very shallow waterbodies that have water depths of just
a few inches. This
facilitates usage of the watercraft in search and rescue missions in shallow
streams, lakes, rivers,
etc. where conventional watercraft cannot operate since they need deeper water
without which they
can get stuck. Other exemplary scenarios include helicopter rescue missions
where the watercraft
can be lowered into water in a flood situation or any other emergency
situations. The tunnel design
shown in the above exemplary embodiments enables the watercraft to operate in
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where the watercraft needs to get through shallow spots without losing
propulsion or getting stuck.
Conventional inboard or outboard jetboats or propeller boats need deeper water
due to lower water
pressure and higher occurrence of cavitation problems in shallow water.
Additionally, the draft of
conventional watercraft is larger due to the propeller or jet extending below
the hull. As a result,
they can easily get stuck in river or lake beds or get damaged by being
dragged through the bed.
Moreover, there is a safety issue with operating conventional watercraft in
shallow waters since
they can develop a leak and even sink due to damage caused by the submerged
propulsion device
being struck by rocks or debris. Further, operating the motor/engine without
sufficient rate of water
flow into the intake can cause the motor/engine to overheat and sustain heavy
damage. The tunnel
design shown above does not face these problems because of the features
discussed previously.
An additional benefit of the tunnel design of the exemplary embodiments shown
in the figures is
that it may help reduce 'listing' of the watercraft. 'Listing' is a phenomenon
where the watercraft
heels (i.e. tilts or leans) to either its starboard or port side due to an
imbalance in the distribution
of weight of the watercraft. The tunnel design of the present invention
reduces listing since it holds
a volume of water in the tunnel 100 which is located in the central region of
the hull 106 of the
watercraft 104. The additional weight of the water present in the tunnel 100
increases the weight
of the central region, thereby reducing the imbalance in the weight
distribution and the associated
listing of the watercraft 104. The water present in the tunnel 100 also adds
to the stability of the
watercraft when in motion, thereby reducing chances of the watercraft
capsizing and improving
the safety of the watercraft.
In some embodiments, the tunnel 100 may include an entry grate or filter at
its entry-opening 206
to prevent weeds, rocks and other debris from entering the tunnel along with
the water from the
waterbody. In some embodiments, the delta pad 102 may have more than one
tilted or angled
section on either side of the central axis. In such a case, the first set of
symmetrical sections make
a small angle with the horizontal which is the deadrise referred to earlier.
The next set of sections
make a larger angle and so on, giving rise to a hull that is multi-segmented
at the aft end with the
segments making progressively larger angles with the horizontal.
Another exemplary advantage of the tunnel design is a reduction in porpoising
of the watercraft.
Porpoising is a phenomenon where instead of operating smoothly in planing
mode, the watercraft
bounces up and down on the water like a porpoise. This makes for an
uncomfortable and inefficient
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ride. A simplified explanation of porpoising is that when the watercraft is in
planing mode of
operation, if the centre of gravity of the watercraft is not aft enough, i.e.
it is too far forward, the
watercraft is unable to sustain planing and the front section or bow falls
back down into the water,
the hydrodynamic lift due to the speed of the watercraft again raises the bow
of the watercraft and
the watercraft again goes into planing, and the cycle repeats. In the
exemplary tunnel design shown
here, the combination of a volume of water being present in the tunnel, the
structure of the delta
pad, and an increase in the overall length of the watercraft together result
in a reduction in
occurrence of porpoising.
Another exemplary advantage in some embodiments is that since the delta pad
102 is extended
beyond the transom 210 of the watercraft and the outboard motor 208 is mounted
on the watercraft
104 such that all parts of the outboard motor 208 including the intake 212 lie
above the delta pad,
the extended delta pad acts as a physical barrier to protect the outboard
motor from damage if the
watercraft were to run aground or in similar scenarios where a conventional
design would result in
damage to the outboard motor. Further, in some embodiments the delta pad 102
or even most of
the hull 106 is reinforced with an additional layer of protective material
like Ultra High Molecular
Weight polyethylene (UHMW), High Density Polyethylene (HDPE) or similar
materials for
enhanced strength and protection. In some embodiments, the delta pad 102
itself may be made out
of such a durable polymer or plastic in combination with a metal or fiberglass
or carbon fiber, etc.
An additional exemplary advantage of some embodiments is that the presence of
an extended delta
pad 102 and extended sidewalls 304 of the tunnel located below the intake 212
of the propulsion
device 502 results in creation of a channel of water that feeds the intake
212. Water that is drawn
through the tunnel 100 flows out along this channel. Most of the water is
drawn into the intake 212
of the propulsion device 502 and the rest flows out to the waterbody. The
presence of compressed
water in the channel at a higher pressure improves efficiency of the
propulsion device 502. Since
the channel that holds a volume of water for the intake 212 is located above
the keel of the
watercraft 104, the propulsion device 502 can continue to operate in very
shallow water since
sufficient water for the propulsion device is, in a sense, scooped up by the
tunnel and fed to the
intake 212 through the channel.
Some watercraft operate with multiple propulsion devices since they require
larger amounts of
power or thrust than can be provided by a single motor or engine. Many of
these use outboard
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motors or engines with conventional hull designs. An exemplary embodiment of
the present
invention has multiple tunnels installed in the hull to support multiple
propulsion devices like
outboard motors or engines. An advantage of this embodiment over conventional
hulls with
multiple motors is that the presence of water-filled tunnels on both sides of
the center line of the
watercraft increases the dynamic stability of the watercraft which becomes
increasingly important
for watercraft operating at high speeds with multiple powerful motors.
Further, since the tunnel
design improves the efficiency of the propulsion device, the watercraft would
need motors or
engines with lower specifications (and hence lower costs and lower weight),
than would be required
when using conventional hull designs.
Although the invention has been described in connection with preferred
embodiments, it should be
understood that various modifications, additions and alterations may be made
to the invention by
one skilled in the art without departing from the spirit and scope of the
invention. For example,
although the above-description has focused on a tunnel installed on a
watercraft with a jet drive
connected to an outboard motor for illustration purposes, the present
invention is equally applicable
to any propulsion system used to power watercraft including but not limited to
jet drives connected
to inboard motors, propellers connected to outboard motors or inboard motors,
sterndrives with a
waterjet, etc. Additionally, in addition to the above described marine
examples, the invention is
applicable outside the marine industry where jet pumps or jet drives are used.
Additionally, the
term motor is used in the description as a generic term to refer to marine
electric motors as well as
marine internal combustion engines, and engines or motors modified for use in
marine applications.
The present invention is also applicable to trolling motors or engines that
are used in conjunction
with bigger motors or engines that propel the watercraft.
All combinations and permutations of the above described features and
embodiments may be
utilized in conjunction with the invention.
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