Note: Descriptions are shown in the official language in which they were submitted.
7g~5~
1 BACKGROUND OF TIE INVENTION
This invention relates to a system for towing
a tow vehicle underwater, and more particularly to
a system for maintaining the tow vehicle at a
eerily stable predetermined distance above the sea
floor.
The increasing demand for petroleum and
petroleum products has given impetus to undersea
research and exploration, with the object of such
exploration being the location of petroleum
deposits. Some of the principal tools in carrying
out such undersea exploration are underwater sonar
or acoustic seabed survey systems, combined sonar
and TV systems, and the like. Such systems are
used for obtaining information relating to horn-
zontal seabed topography and sub-bottom structure
or bathymetric profile as well as actual pictures
of the sea floor. This information is useful, not
only in assisting in the location of offshore oil
deposits, but also in providing a better under-
standing of the oceans generally, their resources,
and the geology of the earth. The closer to the
sea floor the system can be placed, the more
accurate and detailed is the information obtained.
Information about seabed topography and
sub-bottom structure is typically gathered by
towing behind a ship a so-called tow vehicle
containing sonar transducers and other incitory-
mints. The transducers transmit sonar or
acoustical signals toward the sea floor and
receive reflections from the floor and from
sub-floor layers. This information is then trays-
milted to recording devices on the ship where
1'7~37~
l records of the information, for example in the
form of line traces on chart paper, are made. In
gathering such information, it is important that
the tow vacua be maintained at a fairly constant
elevation close to the sea err and that the yaw,
heave and roll of the tow vehicle be minimized.
This becomes especially difficult as the depth of
the water increases since maintenance of the
stability of the tow vehicle is carried out, to
lo the extent possible, by controlling the speed of
the ship and by operation of the winch (letting
out or reeling in the cable). us cable length
increases, such control becomes very difficult. In
particular, the tow vehicle sinks in the water
under its own weight and the weight of the cable,
and then the depth of the vehicle its controlled by
controlling the speed of the ship and the tow
cable winch. If the cable length were very great,
which would be the case of deep water operation,
there would be a significant delay time between
discovering that the tow vehicle should be raised
(for example because an obstacle is being
approached) or lowered (for example because a
valley is being approached), and the actual
raising or lowering of the tow body by increasing
the ship speed (or reeling in the cable) or
reducing the ship speed (or paying out the cable)
respectively. Also, if the cable length is very
great, very small speed changes in the ship cause
the tow vehicle to change depth significantly
thereby making it difficult (and risky to the tow
vehicle) to maintain a stable elevation of the tow
vehicle above the sea floor.
9~7~
1 Because the tow vehicle is connected directly
via the tow cable to the ship, erratic moves of
the ship or cable are transmitted directly to the
tow vehicle, possibly causing it to yaw, heave or
not]. also, since controlling the ship's speed
through the water is the method of maintaining the
tow vehicle above the sea floor, any sudden stops
of the ship may result in the tow vehicle
"crashing" into the sea floor.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a
new and improved ~mderwater tow system by which a
tow vehicle may be towed by a ship.
It is another object of the invention to
provide an ~mderwater tow system whereby a tow
vehicle may be towed at a fairly constant prude-
termined elevation above the sea floor.
It is a further object of the invention to
provide an underwater tow system which maintains
the stability of a tow vehicle and reduces the
yaw, heave and roll.
It is still another object of the invention
to provide an underwater tow system which serves
to reduce the effects of erratic movements of the
ship on the tow vehicle.
It is an additional object of the invention
to provide an underwater tow system in which
stoppage of tune towing ship will not cause the tow
vehicle to drop to the sea floor.
It is also an object of the invention to
provide an underwater tow system which may be
operated substantially unattended over a wide
range of speeds.
Z 7
1 It is another object of the invention to
provide an underwater tow system which includes a
buoyant tow vehicle capable of floating to the
surface of the water in the event the vehicle is
detached from the tow cable.
The above end other objects of the invention
are realized in a specific illustrative embodiment
of an underwater tow system which includes a
buoyant tow vehicle for housing apparatus to be
used underwater, apparatus for coupling the tow
vehicle to a tow cable, and a weight member
attached to the coupling apparatus or the tow
cable. The weight member has a sufficient weight
to pull the tow vehicle downwardly in water until
the weight member contacts the sea floor. With
this configuration, a fairly constant predator-
mined elevation of the tow vehicle above the sea
floor can be maintained by appropriate selection
of the distance between the tow vehicle and the
point of attachment of the weight member to the
coupling means or tow cable, and by maintaining a
fairly constant speed of the ship through the
water. Attachment of the weight member to the
coupling apparatus or tow cable also serves to
isolate the tow vehicle from the effects of
erratic movements of the ship or forward portion
of the tow cable. Of course, any sudden stops by
the ship would not cause the tow vehicle to drop
to the sea floor since the tow vehicle is buoyant.
In accordance with one aspect of the invent
lion, the coupling apparatus includes a shear
element which will release in the event a certain
pulling force is applied to the tow vehicle. The
~79~7~
tow vehicle also includes a signal producing device so that in the event the
sheer element releases and the tow vehicle floats to the surface, the tow
vehicle will produce seagulls to indicate its location so that it can be no-
thieved
One especially advantageous method of using the tow system involves
paying out a substantial length of tow cable so that some of the cable, as well
as the weight member, drag along the sea floor. This relieves the ship's tow
cable winch operator from carefully attending the winch in an attempt to main-
lain only the weight member in contact with the sea floor.
The improvement or combination which is claimed as the invention here-
in is an underwater tow system adapted for being towed by a tow cable behind a
vessel. The system includes a tow vehicle err housing apparatus to be used
underwater, the tow vehicle having positive buoyancy in water, means for couple
in the tow vehicle to the tow cable to allow the vehicle to float upwardly
from the cable, cud weight means attached to the coupling means or the tow
cable, the weight means having a weight sufficient to pull the tow vehicle
downwardly in water until the weight means contacts the water floor. Other
and more particular embodlm3nts of the invention are defined in the claims
appended hereto, which define the monopoly being claimed by the applicant.
BRIEF DESCRIPTION OF THE DRAWINGS
m e above and other objects, features and advantages of the present
invention will become apparent from a consideration of the following detailed
description presented in connection with -the accompanying drawings in which:
FIG. 1 is a side view of an underwater tow system made in accordance
with the present invention, showing the system as it could be utilized under-
water;
- 5 -
1~797~3
FIG. 2 is a side elevation view of the tow vehicle of FIG. 1 showing
the positioning of some of the components in the vehicle;
FIG. 3 is a fragmented, perspective view of the furled assembly
of the ~mdexwater tow system of FIG. l;
FIG. 4 is a cross sectional view of the clamp of FIG. 3 taken along
lines 4--4;
FIG. 5 is a front view of the coupling apparatus for coupling the
chain of FIG. 3 to the
- pa -
l furled assembly; and
FIG. 6 is a side view of the coupling
apparatus for coupling the tow cable to the tow
vehicle.
DETAILED DESCRIPTION
Referring to FIG. l, there is shown an
~mderwater tow system 4 made in accordance with
the present invention and being towed by a surface
vessel 8. The tow system 4 is coupled by way of a
tow cable 12 to a winch 16 on the vessel. The tow
cable 12 includes, in a conventional manner,
electrical conductors for connecting electrical
apparatus on board the ship 8 with underwater
apparatus housed in a tow vehicle 20 of the
underwater tow system.
The underwater tow system 4 includes the tow
vehicle 20 (see FIGS. 1 and 2) formed generally in
the shape of a torpedo and having an elongate
cylindrical body 24 rounded on a front end 28
thereof. The rear of the body 24 tapers inwardly
to accommodate three fins 32 circumferential
spaced about the body. The streamlined shape of
the tow body 24, together with the fins 32, serve
to stabilize movement of the tow vehicle through
the water.
Eyelets 36 are attached to the top of the
body 24 at spaced apart locations to provide
coupling or lifting elements by which the tow
vehicle 20 may be lifted from the water.
Illustrative parameters of the tow vehicle 20
are a body length of about 17 feet, a body
diameter of 3 feet, and a weight of 1500 pounds in
air (when component electrical apparatus is
~2~7~7~
1 included). The tow body 20 is constructed to be
buoyant in water, with a net buoyant force of
about 250 pounds. Buoyancy is achieved by include-
lung within the tow body 24 a plurally of
syntactic Exam cylinders, balls or blocks 42
positioned against the upper wall. of the body as
shown in FIX. 2, and held in place, for example,
by epoxy. Of course, other buoyant material might
flus be utilized provided such material did not
interfere with operation of electrical equipment
contained in the tow vehicle. Syntactic foam has
been found to be suitable since it does not
resonate to thereby create interference with
acoustical equipment which might be utilized on
the tow vehicle.
Also included in the tow vehicle is a convent
tonal pinner 44 which is arranged to auto-
magically commence transmitting an acoustical
signal when power to the pinner is interrupted.
This would occur if, for example, the tow vehicle
were detached from the tow cable. A light beacon
46 is positioned on top of the tow vehicle to emit
light ire the tow vehicle floats to the surface.
That is, the fight beacon is attached to emit
light when the water pressure Ells below some
level indicating that the vehicle is nearing the
surface.
A furled assembly I interconnects the tow
cable I with the tow vehicle 20 and with a chain
weight 48. The chain weight 48 includes a
plurality of links, an end one of which is coupled
to the furled assembly 40. The chain weight is
provided to pull the tow vehicle 20 and tow cable
-- 7 --
~Z~7~7~
1 12 downwardly in the water until the chain
contacts the sea floor. As the ship 8 moves in the
water, the chain weight 48 will drag over the sea
floor and, since the tow vehicle 20 is buoyant,
the tow vehicle Wylie "fly" or move through the
water at a substantially constant predetermined
distance above the sea floor. This distance
depends upon the towing speed and the length of
the cable or coupling between the furled
assembly 40 and the tow vehicle 20. For a tow
vehicle having a buoyant force of about 250
pounds, a weight for the chain 48 advantageously
is about 2000 pounds. This weight, it has been
fumed, is sufficient to dampen small]. erratic
movements by the tow Cobb 12 caused either by sea
currents or by small. speed surges of the vessel 8.
Because of this dampening effect, the tow vehicle
20 remains more stable as it is pulled through the
water. That is, the yaw, heave and roll which
might otherwise occur in the tow vehicle 20 by
-reason of erratic movements of the tow cable 12
are reduced. Also, in the event that the ship 8
comes to a halt, the tow vehicle 20, being
buoyant, will continue to float above the sea
floor and not "crash" into the floor or other sea
floor obstacle.
Although other types of weighting devices
could be used, it has been found that the use of a
chain 48 is advantageous since the total weight
can be readily modified by simply removing or
adding links. Also, slight variations in the speed
of the ship will generally result simply in a few
more (or less) chain links contacting the sea
i7'9
1 floor to still maintain the elevation of the tow
vehicle 20 at a substantially constant height
above the sea floor. Thus there is not a single
speed threshold level at which the weight is
Lyle.. Ed from I.. he sea pharaoh as might be the case
with a single intro weight.
FLOG. 3 shows a more detailed perspective view
of the furled assembly 40 of FIG. 1. This
assembly is swivel ably coupled by an electron
mechanical coupler 54 to the cable 12. The coupler
54 is of conventional design. The assembly 40
includes a saddle 52 composed of a curved channel
56 into which the cable 12 is inserted and a pair
of skirts 60 which extend downwardly on either
side of the cable 12 as shown. An elongate upper
extension of the channel 56 and slcirts 60 is
placed in a clamp 64 for clamping the furled
assembly onto the cable 12. The cable 12 thus runs
through the channel 56, between the skirts 60, and
generally curves with the curvature of the
channel.
The clamp is shown in greater detail in FIG.
4, which is a cross-sectional view thereof taken
along lines 4--4 of FIG. 3. As shown in FIG. 4,
the clamp includes a top plate 68 and a bottom
plate 70 held in a clamping relationship by bolts
72. The channel 56 of the airhead assembly 52
which is held between the clamp includes a
friction pad 74. A channel element 78 is welded to
the plate 70 and includes therein a similar
friction pad 76. These pads are shaped to fit
snugly about the tow cable 12 to hold the tow
- cable in place when the clamp is tightened.
~LZ3L~79t79
l Advantageously, the friction pads 74 and 76 are
made of lead to deform against the cable as the
clamp is tightened. The pads are held in place in
the channel 56 and the channel element 78 by
pressure. The side walls of the two channels 56
and 78 will mate to prevent damage to the cable 12
ion the event the bolts 72 are tightened too tight.
Referring again to FIG. 3 and also to FIG. S,
it will be seen that the furled assembly 52 also
includes a coupling mechanism 80 interconnecting
the skirts 60 to the chain weight 48. The coupling
mechanism 80 includes a first Levis 82, the free
ends of which extends about the skirts 60 to align
openings in the ends of the Levis with openings
lo in the skirt 60 through which a Levis pin 84 is
inserted A cotter pin 86 then secures the Levis
pin 84 in place to thereby secure the cloves 82 on
the skirts 60.
The base of the Levis 82 is swivel ably
attached by way of a bit 88 to the base of a
second Levis 90, as best seen in FIG. 5. A shear
pin 92 extends through aligned openings in the
free ends of the Levis 90 and through a sleeve
94. A shackle 96 is fitted in place about the
sleeve 94 and this shackle is then linked with the
end link of the chain weight 48 to secure the
chain weight onto the furled assembly. The
shear pin 92 is selected so as to break and
release the shackle 96 from the cloves 90 when the
shackle is subjected to some predetermined pulling
force. Thus, if the chain gets caught on the sea
bottom, the shear pin 92 will release the chain to
thus avoid possible damage to the furled
-- 10 --
97~
1 assembly which might otherwise occur if the chain
weight 48 were allowed to continue pulling on the
assembly. The breaking strength owe the shear pin
92 must, of course, be greater than the weight of
the chain 48 so that while being l.. punched on the
water, the chain doesn't cause the shear pin to
break. For a chain weight of about 2000 pounds,
the breaking strength of the shear pin 92 might
illustratively be 4000 pounds.
FIG. 6 shows a side view of a connector
mechanism by which the tow gable 12 is coupled to
the underneath side of the body 24 of the tow
vehicle 20. This connecting apparatus includes a
gripping element 100 suitable for connection to
the end of the tow cable 1.2. An exemplary gripping
element might be the element known as Dyna-Grip
produced by Preformed Line Products, Inc. of
Cleveland, Ohio. The end of the gripping element
loo opposite the end at which the element its
connected to the tow cable 12, is Wormed into a
Levis and includes a Levis pin 102 which is
inserted in aligned openings in the ends of the
Levis to extend through the opening in a tongue
104 inserted in the Levis. The tongue 104 is
attached to a yoke 106 which includes aligned
openings through which a shear pin 108 extends.
The shear pin 108 also extends through another
coupling element 110 which extends within a yoke
112 which is coupled to the underneath side of the
body 24 of the tow vehicle. The shear pin 108 has
an illustratively breaking strength of about
10,000 pounds so that if the tow vehicle gets
caught. on some type of underwater obstruction, the
-- 11
aye
l pin Wylie break and release the tow vehicle to
allow it to float to the surface and be recovered.
Upon release by the shear pin 108, electrical
connectors 116 and 120 (such as the ERR type
waterproof connectors produced by Boston Insulated
Wire Co.) are pulled apart interrupting electrical
power to the pinner 44 and this causes the pinner
(FIG. 2) to emit acoustical. signals which may be
detected on the towing ship to indicate the
lo location of the tow vehicle. In addition the
beacon light 46 begins emitting light signals as
the vehicle reaches the water surface. The post-
toning of the buoyant material 42 maintains the
tow vehicle 20 upright on the surface so that the
beacon light 46 remains out of water. The connect
lion between the tow vehicle and the cable 12
allows pivoting in two degrees.
In use, it may be advantageous simply to pay
out a sufficient amount owe tow cable 12 so that
while towing the tow vehicle, a portion of the
cable itself drags over the sea floor. Allowing a
portion of the tow cable 12 to drag on the sea
floor, as well as the chain weight 48, serves to
further isolate the effects of erratic movement of
the ship 8 from the tow vehicle 20 and to
alleviate the ship winch operator from trying to
maintain only the chain weight 48 in contact with
the sea floor.
It should be understood that the above-
described arrangements are only illustrative of
the principles of the present invention and that
numerous modifications thereof could be devised by
- those skilled in the art without departing from
7 I
1 the spirit and scope of the invention. For
example, weights other than the chain 48 might be
utilized to pull the tow vehicle 20 to the sea
floor. Also, a variety of mechanisms could be
employed to join the tow cable, weight and tow
vocal. The appended claims are untended to cover
all such alternative embodiments and arrangements.
- 13 -
