U.S. patent application number 12/043658 was filed with the patent office on 2009-09-10 for bow lifting body with deadrise.
Invention is credited to Troy Keipper, Steven Loui, Ben Rosenthal, Gary Shimozono.
Application Number | 20090223431 12/043658 |
Document ID | / |
Family ID | 41052289 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090223431 |
Kind Code |
A1 |
Loui; Steven ; et
al. |
September 10, 2009 |
BOW LIFTING BODY WITH DEADRISE
Abstract
A watercraft has a lifting body secured to its bow below the
waterline; the lifting body has deadrise on either side of the
bow.
Inventors: |
Loui; Steven; (Honolulu,
HI) ; Rosenthal; Ben; (Washington, DC) ;
Keipper; Troy; (Honolulu, HI) ; Shimozono; Gary;
(Kapolei, HI) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
41052289 |
Appl. No.: |
12/043658 |
Filed: |
March 6, 2008 |
Current U.S.
Class: |
114/274 |
Current CPC
Class: |
B63B 1/06 20130101; B63B
1/063 20130101; B63B 1/248 20130101; Y02T 70/10 20130101; B63B 1/40
20130101 |
Class at
Publication: |
114/274 |
International
Class: |
B63B 1/24 20060101
B63B001/24 |
Claims
1. A watercraft comprising a hull, including a bow having an outer
surface, and a lifting body attached to said bow below the static
waterline of the hull; said hull having a fore and aft longitudinal
axis, and said lifting body extending laterally away from the outer
surface of the bow and from said longitudinal axis; said lifting
body being buoyant and having a first lifting body portion adjacent
to the bow and extending away from the adjacent outer surface of
the bow and at least a second lifting body portion extending
laterally outwardly from each side of the first lifting body
portion, said second lifting body portions having dead rise with
respect to said first lifting body portion on either side of the
bow of the hull, whereby said lifting body provides buoyant lift at
the bow, hydrodynamic lift at operational speeds and reduction of
vertical acceleration in bow movements.
2. A watercraft as defined in claim 1 wherein said deadrise is
positive.
3. A watercraft as defined in claim 1 wherein said deadrise is
negative.
4. (canceled)
5. (canceled)
6. (canceled)
7. A watercraft as defined in claim 1 wherein said lifting body is
mounted directly on the bow of the hull and produces a surface wave
train as a result of its shape, its proximity to the free surface
of the water and its displacement lift.
8. A watercraft as defined in claim 1 wherein the second lifting
body portions of the lifting body taper towards the lateral edges
of the lifting body.
9. A watercraft as defined in any one of claims 1 to 3, 7 and 8
wherein said first lifting body portion is thicker than said second
lifting body portion.
10. A watercraft as defined in any one of claims 1 to 3, 7 and 8
wherein the lifting body has a thickness to length ratio of between
10 to 33%.
11. A watercraft hull as defined in any of claims 1 to 3, 7 and 8
wherein said first and second lifting body portions have
longitudinal cross-sections extending parallel to the longitudinal
axis of the hull with each such cross-section including
symmetrically cambered and generally parabolically shaped
cross-sectional portions.
12. A watercraft hull as defined in claim 11 wherein the
cross-sections of said first lifting body portion adjacent the bow
has the maximum thickness of the lifting body and the cross-section
of the second lifting body portions being smaller than those of
said first section.
13. A watercraft as defined in claim 10 wherein the lifting body
has a thickness to length ratio of between 10 to 33%.
14. A watercraft hull as defined in any of claims 1 to 3, 7 and 8
wherein said lifting body has a leading edge portion which
conforms, when viewed in plan, to a parabolic form.
15. A watercraft as defined in any one of claims 1 to 3, 7 and 8
including winglets on the outer edges of said lifting body.
16. A watercraft as defined in claim 12 including winglets on the
outer edges of said lifting body.
17. A watercraft as defined in claim 13 including winglets on the
outer edges of said lifting body.
Description
SUMMARY OF THE INVENTION
[0001] The present invention relates to watercraft having a Bow
Lifting Body (BLB) for improved efficiency and seakeeping.
BACKGROUND OF THE INVENTION
[0002] A BLB applied at the bow of a ship can introduce numerous
positive attributes. First, a BLB provides all the positive
attributes of a traditional bulbous bow. Wave cancellation similar
to a traditional bulbous bow is provided by a BLB, in an even
larger speed range. Also, a BLB can be used for ballast or a sonar
dome, similar to traditional bulbous bows.
[0003] Second, lifting bodies have a higher lift to drag ratio
(L/D, efficiency) than that of a hull alone, most noticeably at
high speeds. By adding a component with a higher L/D than that of
the original system in the absence of this new addition, it is
intuitive that the L/D of the entire system increases.
[0004] Bow Lifting Bodies of this type are described in detail in
U.S. Pat. Nos. 7,191,725 and 7,004,093, the disclosures of which
are incorporated by reference.
[0005] These patents disclose the use of a submerged body affixed
to the bow of a ship to reduce overall vessel drag and improve
overall vessel seakeeping behavior. BLB's have several distinct
characteristics which differentiate them from the similarly located
conventional bow bulbs. A BLB has both buoyant and dynamic lift
components whereas the conventional bow bulb has only buoyant lift.
Because the efficiency of a BLB (defined specifically as the ratio
of the body's lift to its drag) can be much greater than that of a
typical ship hull, at high speeds, a portion of the vessel's weight
will be supported by the BLB, thus increasing the vessel's overall
efficiency.
[0006] A typical bow bulb is designed to be effective at a single
design speed. At this speed, the wave generated by the bulb
effectively cancels the wave generated by the ship's hull. This
wave cancellation reduces the overall drag of the craft at this
speed. A BLB, on the other hand, has the ability to cancel the wave
generated by the ship over a much larger range of speeds. Test data
shows wave cancellation over almost the entire speed range for a
specific class of hulls.
[0007] A typical bow bulb has an elliptical or teardrop shaped
cross section. In plan view, therefore, a bow bulb has very little
area to aid in low speed seakeeping. A BLB, on the other hand, has
a large amount of plan area giving it a high degree of low speed
damping, keeping motions low. Finally, a BLB can have active
control surfaces at the extremities or wingtips and edges. This
inclusion of active control allows for improvements in seakeeping
at higher speeds. A bow bulb has no control surfaces or winglets on
which to put them.
[0008] Studies have been conducted showing the effect of deadrise
angle on slamming loads for prismatic shapes. Such studies show
that at higher deadrises (i.e., angle of a surface to the
waterline) slamming loads were decreased. This decrease in slamming
loads is inversely proportional to the deadrise angle, i.e., as the
deadrise increased, the slamming loads were reduced.
[0009] Investigation into the added mass effects, in the frequency
domain, of different shaped bodies has shown that a cupped shape
body will have higher added mass. By increasing added mass over a
wide frequency range, the time-domain motions of the body can be
reduced due to the increase in effective momentum of the body.
Similarly, the drag coefficient of a body in the direction normal
to the cup will be higher, causing a lower tendency to move.
[0010] In general, the effects of anhedral (defined as a wing whose
angle in relation to the groundplane is negative) and dihedral
wings (defined as a wing whose angle in relation to the groundplane
is positive) are well known. The lift decreases with the cosine of
the angle in both instances.
[0011] The effects on lifting body performance due to proximity to
the free surface are known as well. The lift, in general decreases
with increasing proximity to the free surface. Similarly, the
likelihood of cavitation (defined as the point when the pressure on
the lifting body drops below the vapor pressure of the fluid
thereby causing the fluid to boil) and separation increase with
increased proximity to the free surface.
[0012] The behavior of a lifting surface and hull when in close
proximity to each other has not been extensively studied. The
increase in pressure on the lifting body and hull due to the
reduction in cross sectional area between the two bodies is well
known. The overall effect is most likely shape dependent and can
either improve or hurt overall performance.
[0013] It is an object of the present invention to provide a bow
lifting body to improve the overall efficiency of the watercraft or
vessel to which it is attached.
[0014] It is a further object of the present invention to reduce
the slamming loads of a vessel employing a BLB.
[0015] Yet another object of this invention is to decrease low
speed motions of a vessel employing a BLB.
[0016] A still further object of the invention is to reduce the
presence of BLB tip vortices.
SUMMARY OF THE INVENTION
[0017] In accordance with an aspect of the present invention, an
improved BLB is provided which meets these objectives by having
either negative or positive deadrise angle relative to the surface
of the water.
[0018] The addition of deadrise to a BLB attached to the bow of a
watercraft improves upon the low speed motions of a typical BLB as
described in U.S. Pat. No. 6,263,819. In the specific case of
positive deadrise, a BLB according to the invention improves the
overall efficiency, reduces the slamming loads, and increases the
lift on the BLB.
[0019] It has been found that adding deadrise to a BLB attached to
the bow of a vessel can improve on the overall design of said
vessel. The addition of deadrise as described herein increases the
pressure on the hull and BLB due to proximity between the hull and
lifting surface and reduces cavitation.
[0020] In addition to the use of deadrise for bow lifting bodies,
the invention contemplates the use of incremented wing angles or
"winglets" on the BLB's. Incremented wing angles for increased
performance have been used in airplanes for many years. The
advantages of specifically designing the wing angle as a function
of span include: reduction of tip vortices and increased wing area
for a given overall footprint. This concept has been expanded to
allow for large changes in deadrise as well as sweep (defined as
the angle of the wing as seen from above) in incremented segments
as a function of span. It has been shown that by allowing for large
changes in deadrise and sweep, the use of incremented wing angles
produces increases in efficiency and reduction in tip vortices.
[0021] The above, and other objects, features and advantages of
this invention will be apparent those skilled in the art from the
following detailed description of illustrative embodiments of the
invention which is to be read in connection with the accompanying
drawings, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is front view of a watercraft having a BLB as
described in U.S. Pat. No. 7,191,725 with no wing angle;
[0023] FIG. 2 is a front view similar to FIG. 1 of a BLB having
positive deadrise in accordance with this invention;
[0024] FIG. 3 is a front view similar to FIG. 1 of a BLB having
negative deadrise in accordance with this invention;
[0025] FIG. 4 is a plot of the change in lift which occurs due to
change in wing angle from -45.degree. negative deadrise to
45.degree. positive deadrise;
[0026] FIG. 5 is a plot similar to FIG. 4 comparing the change in
lift due to change in deadrise for a watercraft with and without a
strut connecting it to the watercraft;
[0027] FIG. 6 is a perspective view of a watercraft showing
pressure distribution on a BLB and its associated hull for a BLB
with no deadrise;
[0028] FIG. 7 is a view similar to FIG. 6 showing pressure
distribution on a BLB and its associated will for a BLB with
positive deadrise; and
[0029] FIGS. 8a-c are illustrations similar to FIGS. 1-3 showing
the use of incremented deadrise or "winglets" on BLB's with
positive, deadrise, no deadrise, and negative deadrise
respectively.
DETAILED DESCRIPTION
[0030] Referring now to the drawings in detail and initially to
FIG. 1, a conventional BLB 10 in accordance with the disclosure of
U.S. Pat. No. 7,191,725 is illustrated secured to the bow of a hull
12. The BLB has a thicker central portion and tapers towards its
lateral edges 14. FIGS. 2 and 3 show the same BLB but with its
lateral sides bent in either positive or negative deadrise.
Deadrise is the angle a surface of a vessel makes to the horizontal
or to the flat waterplane surface.
[0031] A BLB with deadrise as shown in FIG. 2 or 3 provides all of
the positive effects of a typical BLB. However by including the
proper amount of wing angle, slamming loads are reduced, overall
efficiency is increased, low speed seakeeping is improved, and BLB
lift can be increased.
[0032] The improvements to a vessel's low speed seakeeping due to
the addition of wing angle or deadrise (either positive or
negative) to a BLB is due to the changes in added mass and drag
coefficient consequent to the change in BLB shape. The increase in
entrained water due to the "cup" shaped cross section as compared
to a BLB with no wing angle is clear. This increase in "added mass"
will effectively change the vertical and rotational motions of the
attached vessel. Since the equation for acceleration can be stated
as the ratio of the force applied to the mass of the system (this
mass includes the added mass), any increase in system mass will
reduce the accelerations for a given amount of force. Similarly,
the rotational acceleration is the ratio of the moment applied to
the mass moment of inertia (which includes the added mass component
of the moment of inertia). Therefore, as the added mass increases,
the amount of rotational acceleration for a given amount of moment
will be reduced.
[0033] FIGS. 6 and 7 show perspective views of BLBs with no
deadrise (FIG. 6) and positive deadrise (FIG. 7). These drawing
demonstrate how the deadrise increases the area of reduced pressure
on the BLB thereby increasing lift.
[0034] The improvements to overall vessel efficiency over a wide
speed range due to the inclusion of BLB's at the bow of a vessel is
known. This increase in efficiency comes from two sources: the
cancellation of the bow wave by the BLB-generated wave and the
highly efficient dynamic lift generated by the BLB at speed
effectively unloading the vessel's hull. The wave generated by the
BLB is almost entirely due to the displaced volume of the BLB and
its proximity to the free surface. The actual shape of the BLB has
very little effect on the size and shape of the wave being
generated. For this reason, the inclusion of deadrise (either
positive or negative) will not significantly change the wave
cancellation as seen in a typical BLB. However, the second
component of the improved efficiency (namely, the ability to unload
the hull) will be affected by the inclusion of deadrise (again,
both positive and negative). In the case of negative deadrise
(anhedral), the lift will reduce with the cosine of the wing angle
.beta., as shown in the chart of FIG. 2. Since no other effects on
vessel efficiency will be seen, the overall efficiency of the
vessel will drop. In the case of positive deadrise (dihedral), the
lift will again reduce with the cosine of the wing angle. However,
the proximity of the lifting surfaces to the hull will have a large
effect on the pressures of both the hull and the lifting body.
Simulations have shown that this decrease in pressure on the top
side of the lifting body (and thus lift over the entire lifting
body) far outweighs the reduction in lift due to wing angle (this
is shown in FIG. 7), thereby producing an increase in lift. Since
the efficiency of a system can be defined as the ratio of lift to
drag, the overall efficiency of the system can be said to have
increased.
[0035] The reduction in BLB slamming due to the inclusion of
positive deadrise is due to the effective increase of deadrise at
the bow of the vessel. As shown in FIG. 1, a typical BLB (center)
would have very little or no deadrise in cross-sectional view. As
has been shown in several studies, by increasing the effective
deadrise on a vessel, the slamming loads are reduced. It is clear
that the BLB with dihedral deadrise has a much higher effective
deadrise angle.
[0036] Simulations in two independent, commercial fluid dynamics
codes (USAero and CFX) have shown the proximity of the wings to the
hull when positive deadrise is included effectively increases the
overall lift of the BLB. As noted above, FIGS. 6 and 7 show a
three-dimensional view of the BLB with positive deadrise affixed to
the bow a vessel alongside a BLB with no deadrise affixed to the
bow of the same vessel. As can be seen from the pressure contours,
the area of peak negative pressure on the BLB has increased in the
case with positive deadrise. Lift is defined as the integral of the
pressure. Therefore the deadrise would have increased lift.
[0037] The inclusion of deadrise (either positive or negative)
reduces the overall span of the BLB by the cosine of the deadrise
angle. For practical reasons, the BLB should not exceed the beam of
the boat at the installed longitudinal location. In general, it is
better to have as much wing area as possible. This helps increase
the low-speed damping and increase the high speed efficiency of the
boat. However, if the BLB is made too large, the wingtips will
extend beyond the limits of the boat. By using deadrise, the
effective width of the BLB can be reduced while keeping wing area
large.
[0038] The inclusion of positive deadrise can have a negative
effect on BLB performance if care is not taken. The inclusion of
positive deadrise increases the proximity of the BLB wingtips to
the free surface (the interface between the air and water). This
increase in free surface proximity raises the likelihood of body
cavitation. Cavitation occurs when the water along the body boils
due to drop in pressure. As a surface approaches the free surface,
it can cavitate at a higher pressure. Since the pressure on the BLB
will be dropping due to its proximity to the hull, moving the wing
tips closer to the free surface can exacerbate their problem. For
this reason, in specific cases, it may be desirable to use negative
deadrise in place of positive deadrise. Although the improvements
in efficiency and slamming will be lost, the likelihood of
cavitation will be reduced.
[0039] By including the ability to increment (i.e., bend) the
deadrise and sweep in segments along the span of the BLB, the
overall efficiency of the system can be further improved. FIGS.
8a-c show examples of BLB's with incremented deadrise, i.e.,
deadrise in two different sections of the BLB. One of these
sections on each side of the BLB is a winglet.
[0040] Although the present invention has been described herein in
connection with the illustrative embodiments, it is to be
understood that the invention is not limited to such embodiments
and that various changes and modifications may be effected therein
without departing from the scope or spirit of the invention.
* * * * *