Note: Descriptions are shown in the official language in which they were submitted.
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BARGE DAGGER SKEGS
This invention relates to skegs for barges to
~ stabilize towed barges directionally by deterring yawing.
: Skegs are customarily provided on the raked
counter of the stern overhang of barges to deter yawing
of a barge when towed by a towline trailing a towboat.
Such skegs extend fore and aft over substantially the
entire fore-and-aft extent of the barge stern counter,
and their lower edges are at approximately the same
elevation as the bottom of the barge. Such skegs are
of low aspect ratio, have no leading edge portion spaced
from the stern counter of the barge and are in the form of
flat or cambered plates as distinguished from being
of airfoil cross section. Usually two of such skegs
are provided, arranged symmetrically at opposite sides
of the longitudinal vertical central plane of the barge.
Such conventional skegs are not very efficient
in deterring yaw of a barge which is not self-propelled
but is towed by a towline connected to its bow, and
they do increase the drag of the barge a substantial
amount over the drag of a similar barge having no
skegs.
,` It is a principal object of this invention to
provide skegs for a barge which are more effective than
conventional skegs in producing directional stability
and which reduce drag.
More specifically, it is an object to provide
skegs for a barge which not only will not produce drag,
such as produced by conventional skegs, but which will
reduce the wake and/or the turbulence of the barge wake
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so as actually to reduce the drag normally produced by
the barge hull.
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Another object is to utilize skeg structure
of simple streamlined design having hydrodynamically
desirable characteristics.
The foregoing objects can be accomplished by
a barge comprising a nonpowered, nonsteered hull for
towing by a towline trailing a towboat, said hull
having a substantially flat bottom and a raked stern
counter, and a set of skegs projecting downward from the
aft portion of said stern counter at each side of the
hull longitudinal center line for effecting yaw stability
of said hull, each set including a plurality of skegs
directionally fixed relative to said stern counter, the
lower end of each skeg being higher than the barge
bottom and each skeg having a height greater than its
maximum chord.
Figure 1 is a bottom perspective of the stern
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portion of a barge showing an arrangement of skegs
according to the present invention projecting downward
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from the barge counter.
Figure 2 is a side elevation, Figure 3 is a
stern elevation and Figure 4 is a bottom plan of the
starboard stern portion of a barge equipped with skegs
according to the present invention.
Figure 5 is a detail horizontal section
through a skeg taken on line 5--5 of Figure 2.
Figure 6 is a bottom perspective of the stern
portion of a barge equipped with a modified skeg
- 30 construction according to the present invention.
Figure 7 is a side elevation, Figure 8 is a
rear elevation and Figure 9 is a bottom plan of the
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starboard stern portion of a barge equipped with skeg
construction of the type shown in Figure 6.
Figure 10 is an enlarged fragmentary vertical
section through a portion of the skeg structure taken
along 10--10 of Figure 9.
Two benefits are obtained by utilization of
the present invention which are interrelated, namely,
an increase in effectiveness of the skeg structure to
improve the directional stability of the barge by
deterring yaw and a decrease in the drag of the barge
which reduces the power necessary to propel the barge,
or which results in an increase in speed of the barge
if the same propulsive power is used. Increase in the
effectiveness of the skeg structure to improve directional
stability is obtained by locating the skeg structure
substantially as far aft as possible, by each skeg of
the skeg structure having a high aspect ratio, being
designated a "dagger" skeg by skegs being of airfoil
cross section, by arranging the skeg elements at desirable
angles of incidence, by minimizing tip loss and by
spacing adjacent skeg elements at a sufficient interval
; to minimize flow interference between them. Reduction
in drag is accomplished by utilizing skegs of airfoil
cross section arranged advantageously, by minimizing
tip loss and by spacing adjacent skeg elements at a
sufficient interval to minimize flow interference.
~; Two representative skeg installations according
to the present invention are shown in the drawings, one
being shown in Figures 1 to 5 inclusive and a modification
being shown in Figures 6 to 10 inclusive. The second
form of the invention includes the components shown in
the first form of the invention, and such components
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are numbered correspondingly in such second form. The
skeg structure is applied to the conventional stern
raked counter C of a conventional barge B having a flat
: bottom b. The principle of the invention is applicable
to barges of all sizes but is more beneficial when used
on barges of medium size, 250 feet to 350 feet (76.200
meters to 106.680 meters) in length, or large barges,
350 feet to 450 feet (106.680 meters to 137.160 meters)
in
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length, rather than to small barges, 150 feet to 250 feet
(45.720 meters to 76.200 meters) in length.
The degree of the rake of counter C is not critical
and may be within the range of 10 to 40 to the horizontal,
but it is preferred that the rake be within the range of 15
to 20 to the horizontal. Also, the height of the transom
T of the barge is not critical but preferably is from 20~ to
35% of the total depth of the barge. In the representative
barge shown in the drawings, the rake angle is approximately
15 and the height of the transom is approximately 28% of
the total depth of the barge.
The dagger skegs of the present invention are in
two sets arranged symmetrically at opposite sides of the
longitudinal vertical central plane of the barge. Each set
includes a plurality of dagger skegs, three skegs being
shown in each set illustrated in the drawings. The port set
includes an outboard skeg lp and an inboard skeg 2_, and may
include one or more intermediate skegs 3_. Correspondingly,
the starboard set of dagger skegs includes an outboard skeg
ls and an inboard skeg 2s and may include one or more inter-
mediate skegs 3s. The skegs in each set are arranged in a
row extending athwartships of the barge and preferably the
skegs are of substantially the same height, chord and spanwise
taper.
Each skeg element is preferably of airfoil cross
: section, as shown in Figure 5, a typical suitable cross
section being a Clark Y section or a NASA 22012 section
established by criteria of the National Aeronautics and
Space Adminstration. Each dagger skeg element includes a
root end 4 suitably secured to the aft portion of the barge
counter C. The trailing edge 5 preferably is vertical, and
the leading edge 6 preferably is swept back a moderate
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amount from the root end 4 to the bottom tip 7.
As shown in Figure 5, the airfoil section forms a
cambered side 8 and a side 9 which may be cambered to the
same or a lesser degree, or which may be flat If the
opposite sides of the skeg elements have different degrees
of camber, it is preferred that the outboard skegs l_ and ls
have the greatest difference in camber, that the inboard
skegs 2_ and 2s have the next greatest different in camber,
and that the intermediate skegs 3_ and 3s have the least
difference in camber. It would not be objectionable for all
of the dagger skeg elements to be of symmetrical airfoil
cross sections, and the difference in action of the skegs be
effected by selecting proper angles of incidence for the
skeg elements.
Where the inboard and outboard skeg elements are
of nonsymmetrical cross section, the most highly cambered
side of the outboard skeg elements ls and lp should face
inward and the most highly cambered sides of the inboard
skeg elements 2_ and 2s may face outward or inward. The
cambered inner side of the outboard skeg in each set and the
cambered outer side of the inboard skeg of each set will
then cooperate to provide a venturi passage between the
inboard skeg and the outboard skeg of each set which will
guide the wake of the barge between such skeg elements and
reduce the turbulence in such portion of the wake, thus
correspondingly reducing the drag on the barge. If the
intermediate skeg elements 3~ and 3s are of symmetrical
airfoil cross section, they will not interfere with the
flow. If their sides are cambered unequally, it is preferred
that the side having the greater camber be on the inner side
of the skeg element, as shown in Figure 4, to form the
venturi passage nearer the center of the barge.
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Each dagger skeg element is of high aspect ratio,
as shown in Figure 2. Such aspect ratio should be within
the range of 2 -- 8 to 1 and preferably is within the range
of 2-1/2 -- 4 to 1. The aspect ratio of the dagger skegs
shown in Figure 2 is approximately 2-1/2 to 1. The tip 7 of
the dagger skeg should not project below and preferably
should be slightly above the bottom _ of the barge B, as
shown in Figure 2. The sweptback leading edge 6 of the skeg
is spaced a substantial distance aft of barge bottom b.
Also the fore and aft extent or chord of the root 4 is a
small fraction of the fore and aft extent or run of the
counter C.
The average chord of each dagger skeg element is
selected so that the total area of all of the skeg elements
in each set will be less than the substantially triangular
' area formed by the raked surface of counter C as one side,
the fore and aft extent of the counter C as a second side,
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and the elevation between the bottom of the transom T and
the elevation of the barge bottom b as the third side. Thus
; 20 combined fin areas of all the dagger skegs in each set will
be less than the area of the corresponding single conventional
substantially triangular skeg.
The efficiency of the dagger skegs in providing
directional stability for the barge depends not only on the
total fin area, but also on the location of the skeg elements
and their angles of incidence. To be most effective, the
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; dagger skeg elements should be located as far aft as possible,
as shown in Figures 1 and 2. Also, the outboard skeg elements
- lp and ls should be toed out in the direction of travel of
the barge at an angle 1 of 2 to 10. The inboard skegs 2p
and 2s may be toed in to some extent, such as 2 to 10.
Intermediate skegs 3p and 3s should have 0 angle of incidence,
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or a small angle of incidence in one direction or the other,
depending on the camber of such intermediate skeg elements
and the flow pattern preferred. Also, the angles of incidence
of the port skeg elements and of the starboard skeg elements
need not be identical if a difference in such angles of
incidence will cause the barge to follow a straighter course
by reducing yaw.
Both to reduce the wake of the barge and the
turbulence of the wake and to increase the effectiveness of
the skeg elements in controlling directional stability, the
adjacent skeg elements in a set should not be placed too
close together, nor should the sets of elements at opposite
- sides of the longitudinal vertical central plane of the
barge be placed too close together. It is preferred that
the spacing between adjacent skeg elements be at least
approximately twice the mean chord of the skeg elements, as
shown in Figure 4. While two skeg elements could be used in
each set, or more than three could be used, it is preferred
that there be three skeg elements in each set. If there are
more than three, the aspect ratio of the skeg elements
should be increased by reducing the mean chord of each
element. Consequently, adjacent skeg elements could be
located closer together, but they should not be closer than
1-1/2 times the mean chord to provide the best yaw-deterring
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performance and the greatest reduction in drag.
The individual cantilever dagger skegs shown in
Figures 1 to 4, inclusive, are somewhat vulnerable to being
struck by floating objects over which the barge B may be
towed. The skegs can be unified and strengthened by connecting
the lower portions of the skegs in each set with an elongated
~ bridging member extending athwartships and preferably sub-
-: stantially horizontally. The bridging member 10_ is shown
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in Figure 6 as connecting the tips of the port skegs 1_, 3_
and 2p, and the bridging member lOs is shown as connecting
the tips of the starboard skegs ls, 3s and 2s. Each of the
elongated bridging members is of airfoil cross section and
is shown in Figure 10 as including a trailing edge 5', a
leading edge 6', an upper cambered side 8' and a lower side
9' which either is of lesser camber or is flat.
The cambered upper side 8' of the bridging member
cooperates with the cambered sides of the inboard and outboard
skegs of the set to confine a venturi flow of the wake to a
greater extent than the wake would be confined without such
bridging member. Also, it is preferred that the skeg bridging
members have a negative angle of incidence within the range
of 2 to 10 to provide a forward hydrodynamic reaction
component for reducing or offsetting drag.
Not only does the horizontal bridging member
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reduce turbulence by its cambered upper side promoting
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venturi flow, and reduce drag because of its forward hydro-
dynamic reaction component, but the fact that such bridging
~- 20 member covers the tips of the dagger skegs reduces the
turbulence around such tips and decreases drag. The inter-
connection of the individual skegs by the bridging member
also deters possible tendency of an individual skeg to
vibrate and generally increases the strength of each set of
skegs as a composite structure.
