Underwater cable burial machine having improved cable laying apparatus

The cable laying apparatus, which solves many of the problems heretofore associated with existing cable laying mechanisms for underwater burial machines, uses a pivotally liftable depressor wheel, located within a feed shoe which tracks the groove cut by the plow. There are a pair of arcuate cable guides, one on each side of the depressor wheel, which assist in the guidance of both cables and bodies, without permitting either to bind. When the assembly to which the depressor wheel is attached is raised upward and rearward the guides prevent the cable from escaping while allowing a body to pass through the opening which is formed.

BACKGROUND OF THE INVENTION 
The present invention relates to underwater cable burial machines. In 
particular, the invention relates to an underwater cable burying machine 
having an improved cable laying apparatus which includes a depressor wheel 
for guiding the cable into a groove cut in the seabed by a plow. 
Underwater burial machines are used to bury communications cables in the 
sea bottom in an effort to protect the cables from damage. These machines 
plow a groove in the seabed beneath a body of water, and they 
simultaneously lay a cable into the groove which they have plowed. Burial 
machines use at least one plow blade to cut a groove into the seabed 
immediately in front of a cable laying mechanism. The cable is then placed 
into the groove thus formed in order that it will be somewhat beneath the 
surface of the seabed. After the cable has been laid into the groove, 
water pressure and underwater currents eventually cause the vertical walls 
of the groove to collapse and move sand and soil into the groove, thereby 
covering the cable and assisting in the overall burial operation. 
A cable laying mechanism must ideally track the groove cut by the plow, and 
it must lay a cable into that groove. Periodically, however, i.e., every 
twenty to fifty miles, a device, called a "body", which may contain a 
repeater or other electronic apparatus, is attached to the cable. While 
the cables are relatively thin, i.e., typically about one-half inch in 
diameter, the bodies are typically several inches in diameter, and they 
may be up to about ten inches in diameter. Accordingly, it is important 
for the cable laying mechanism to be adapted to handle both the cable and 
the bodies, and it is important that in being able to handle bodies, the 
cable laying mechanism does not lose its ability to recapture the cable. 
Further, it is important to have a cable laying mechanism which does not 
readily permit the cable to bind following the passage of a body through 
the mechanism. 
In view of the foregoing problems which were not solved by the cable laying 
mechanisms of the prior art, an improved cable laying mechanism which can 
overcome these problems would be desirable. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a new design approach has been 
disclosed which solves many of the problems heretofore associated with 
existing cable laying mechanisms for underwater burial machines. The new 
design uses an efficient configuration of a pivotally liftable depressor 
wheel, located within a cable feed shoe which tracks the groove cut by the 
plow. A pair of arcuate cable guides, one on each side of the depressor 
wheel, assist in the guidance of both cables and bodies, without 
permitting either to bind.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Referring to FIG. 1, a simplified side view of the cable laying apparatus 
10 of the present invention is shown in use on a cable laying machine 12 
in a cable laying operation. The cable laying machine 12 is mounted on a 
sea sled 14 which is being towed along the seabed 16 by a surface vessel 
18. The towing is accomplished by means of a combination towing/umbilical 
cable 20. 
During the towing operation, a communications cable 22 is unspooled from a 
spool 24 on the vessel 18. As the sled 14 is pulled forward, a plow 26 
cuts a groove 28 in the seabed 16, and the communications cable 22 is laid 
into the groove 28 by the cable laying apparatus 10 which is located on 
the rear of a carriage 30 which is fixed to the sled 14 using a four bar 
linkage 32. As will be understood by those skilled in the art, the four 
bar linkage 32 allows the carriage 30 to be moved up and down relative to 
the sled 12. This permits the plow 26 and cable laying apparatus 10, both 
of which are attached to the carriage 30, and both of which are shown to 
extend through the flat bottom of the sled 12, to be moved up and down 
relative to the bottom of the sled 12. The four bar linkage 32 allows the 
plow 26 and the cable laying apparatus 10 to be moved up above the bottom 
of the sled 12 when the sled 12 is recovered onto the deck of the vessel 
18 for transportation or maintenance. In addition, the four bar linkage 32 
can be used to adjust the depth of the groove 28 in the event that that 
becomes necessary due to the makeup of the seabed 16, i.e., if a rock 
layer is encountered below the surface of the seabed 16 at a depth which 
is less than the normal cable laying depth. By way of example, if the 
normal cable laying depth was twelve inches, and a rock layer was 
encountered ten inches below the surface of the seabed 16, then the four 
bar linkage 32 could be adjusted using hydraulic cylinders (not shown) so 
that the plow teeth only extended somewhat less than ten inches below the 
seabed 16, thereby preventing damage to the teeth while allowing the 
burial operation to continue. 
As will be understood by those skilled in the art, the combination 
towing/umbilical cable 20 is used to both tow the sled 12, and to carry 
hydraulic fluid and electrical signals between the vessel 18 and the sled 
12. 
Periodically, i.e., every twenty to fifty miles, there will be a "body" 34 
in the communications cable 22. The body 34 corresponds to a device, such 
as a repeater, or other electronic device, which is in-line with the 
communications cable 22, but which has a diameter which is substantially 
greater than the diameter of the communications cable 22. As used herein, 
the term "body" is meant to include any portion of the cable 22 having a 
diameter substantially wider than the remainder of the cable 22. 
Referring to FIG. 2, a perspective view of the carriage 30, showing the 
cable laying apparatus 10 installed thereon, is shown. In FIG. 3 a 
perspective view of the carriage 30, without the cable laying apparatus 
installed, is shown. The cable laying apparatus 10 is comprised of a 
depressor wheel assembly 36, shown in FIGS. 2, 4 and 7-10, and a feed shoe 
assembly 38, shown in FIGS. 2, 5 and 6. 
With reference to FIG. 3, the carriage assembly 30 is made of welded steel 
construction. At the aft part 35 of the carriage assembly 30, there are a 
pair of rails 37, 39 which are used to mount the feed shoe assembly 38. As 
shown in FIGS. 5 and 6, the feed shoe assembly 38 is comprised of an 
elongated feed shoe 42 which is used to guide the cable into the groove 28 
formed by the plow 26 (See FIG. 1), and a top plate 40, which is the 
support member for the feed shoe 42. The feed shoe 42, which is closed at 
the front, has an elongated U-shaped opening 44 formed therein to receive 
the cable 22. The opening 44 extends through the top and rear of the feed 
shoe 42 (See FIG. 6), and it is adapted to receive the cable 22 and to lay 
it into the groove 28 formed in the seabed 16, as the feed shoe 42 is 
pulled through the groove 28. In the preferred embodiment of the 
invention, the closed front of the feed shoe 42 forms an angle of about 
30.degree. with the seabed (See FIGS. 1 and 6), as this has been found to 
be the optimal angle for minimizing the collection of debris by the feed 
shoe 42. 
Similarly, the top plate 40 has an elongated opening 46, which extends 
through the rear of the top plate 40, and a pair of elongated guide rail 
grooves 48, 50 are formed in the top plate 40. The cable 22 is fed through 
the openings 44, 46, and the elongated guide rail grooves 48, 50 are used 
to guide the depressor wheel assembly 36, when it is pivoted upward and 
out of the feed shoe 42, as will be explained below. 
Referring to FIG. 2, the depressor wheel assembly 36 includes a depressor 
wheel 52 which fits through the opening 46 in the top plate 40 and extends 
into the feed shoe 42 in normal cable laying operations. The depressor 
wheel 52 is mounted on a rotatable depressor wheel assembly 36, shown in 
FIG. 4 to include a depressor wheel axle 54, around which the depressor 
wheel 52 rotates. A pair of depressor wheel support brackets 56, 58, which 
hang from a pivoting wheel assembly support axle 60, are used to support 
the depressor wheel axle 54. The wheel assembly support axle 60 hangs from 
vertical members 31, 33 affixed to the carriage 30 (See FIGS. 1 and 2). 
The wheel assembly support axle 60 attaches the depressor wheel assembly 
36 to the carriage 30, and supports the depressor wheel support brackets 
56, 58, while allowing them to pivot around the axle 60. 
On either side of the depressor wheel 52, there are tusk shaped, arcuate 
cable guides 62, 64. With reference to FIGS. 8 and 9, the outer 
peripheries of the cable guides 62, 64 include elongated V-shaped guide 
rails 63, 65, respectively. The V-shaped guide rails 63, 65 ride in the 
elongated guide rail grooves 48, 50 formed in the top plate 40 (See FIG. 
5). 
Referring primarily to FIG. 8, the forward side of the depressor wheel 
assembly 36 includes a cable guiding bridge assembly 89 made up of a 
formed steel piece having a pair of "flat" portions 90, with a deep 
V-shaped portion 92 joining them together. The bridge assembly 89 
terminates at a plate 94 which is shaped to fit both the flat portions 90, 
and the V-shaped portion 92. The bridge assembly 89 is attached to a 
support brace 87, which joins the depressor wheel support brackets 56, 58. 
The cross-sectional shape of the bridge assembly 89, together with the 
cable guides 62, 64, riding in the guide rail grooves 48, 50 in the top 
plate 40, insures that the cable 22 must pass into the feed shoe assembly 
38. 
A clevis 86, shown in FIG. 8, is attached to the bracket 58. A hydraulic 
cylinder 88, shown in FIG. 2, is attached to the carriage 30. A shaft (not 
shown) extends from the hydraulic cylinder 88 and attaches to the clevis 
86. Accordingly, hydraulic pressure may be used to extend the shaft, 
whereby the depressor wheel assembly 36 will be pivoted upward and 
rearward relative to the sled 12 (around the axle 60) when a body 32 must 
be passed through the wheel assembly 36. This pivoting action removes the 
depressor wheel 52 from the rear of the feed shoe assembly 38, but the 
cable guides 62, 64 will continue to ride on their guide rails 63, 65, 
which remain in the guide rail grooves 48, 50 in the top plate 40. 
Consequently, what was formerly a narrow opening (between the bottom of 
the depressor wheel 52 and the bottom of the feed shoe assembly 38) for 
the cable 22, can be made into a much larger opening (i.e., between the 
top plate 40 and the raised depressor wheel assembly 36) to allow the body 
32 to pass therethrough, yet it still remains a closed opening from which 
the cable 22 cannot escape. After the body 32 has passed through the 
raised depressor wheel assembly 36, the depressor wheel assembly 36 is 
lowered, and the depressor wheel 52, with the aid of the bridge assembly 
89 and the cable guides 62, 64, will recapture the cable 22 in the feed 
shoe 40 for additional cable laying. Cammed surfaces 67, 69 on the cable 
guides 62, 64 (See FIGS. 4 and 8), assist in guiding the cable 22 and the 
body 32. 
With reference to FIGS. 9 and 10, additional features of the present 
invention will be explained. As shown in cross section, the depressor 
wheel 52 has a groove 66 formed in its periphery. The groove 66 has a 
cross-section which is shaped to receive the cable 22. 
The wheel also has a series of magnets 70, 72 (FIG. 10), and 70, 74, 76, 
78, 80, 82, 84 (FIG. 7) installed around its rim. While eight magnets are 
illustrated, in the preferred embodiment of the invention, sixteen equally 
spaced magnets are presently used. The magnets 70-84, each cause a Hall 
effect sensor 68 (FIG. 10), which is attached to bracket mounted on 
support brace 87, to generate an electrical signal as the depressor wheel 
52 turns. As most cable laying operations progress at a speed in the range 
of about one-half to three knots, the combination of the magnets and the 
sensor 68, will supply sufficient data to determine (within about 
one-tenth of a knot) the speed at which the cable laying operation is 
progressing. 
Another feature of the present invention is that the axle 54 includes a 
"METROX" load pin 55, manufactured by M/D Totco of Texas. This device 55, 
which is made of strain gauges, is able to measure the residual cable 
tension, which is the tension to which the cable 22 is subjected due to 
the weight of the cable 22 in the water, and other factors. As the tension 
on a fiber optic cable must be limited to something less than about 4,000 
pounds, the data from sensor 55 allows an operator on board the surface 
vessel 18 to monitor the tension on the cable 22. The particular sensor 55 
which is used in the preferred embodiment of the invention is able to 
measure a tension of up to about 5,400 pounds, i.e. an amount far greater 
than that to which the cable 22 should ever be subjected. 
As will be obvious to those skilled in the art, numerous changes can be 
made to the preferred embodiment of the invention without departing from 
the spirit or scope of the invention described herein.