U.S. patent application number 16/523218 was filed with the patent office on 2020-01-23 for over-the-stern deep digging trenching plow with instrumentation for assessing the protective capabilities of a seabed trench.
This patent application is currently assigned to Oceaneering International, Inc.. The applicant listed for this patent is OCEANEERING INTERNATIONAL, INC.. Invention is credited to Michael W. N. Wilson.
Application Number | 20200024826 16/523218 |
Document ID | / |
Family ID | 56069162 |
Filed Date | 2020-01-23 |
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United States Patent
Application |
20200024826 |
Kind Code |
A1 |
Wilson; Michael W. N. |
January 23, 2020 |
Over-the-Stern Deep Digging Trenching Plow with Instrumentation for
Assessing the Protective Capabilities of a Seabed Trench
Abstract
A seabed trenching plow has a chassis, a sled and a towing
assembly. The towing assembly has a pair of wings extending
laterally from each side of the chassis. The wings are aligned on
an axis transverse to the chassis and adapted for connection to a
towing line. The transverse axis is forward of the center of
gravity of the plow and rearward of the sled, affording an over the
stern releasable and retrievable trenching plow of sufficient
weight and strength to excavate a three meter trench in a single
pass. To assess the protective capabilities of the trench, a
threshold signal indicative of a desired composition of
seabed-trench soil is compared with a real-time data signal
indicative of the actual to produce an alarm signal when the
real-time data signal is not protective-capability compliant with
the threshold signal.
Inventors: |
Wilson; Michael W. N.;
(ABERDEENSHIRE, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OCEANEERING INTERNATIONAL, INC. |
HOUSTON |
TX |
US |
|
|
Assignee: |
Oceaneering International,
Inc.
Houston
TX
|
Family ID: |
56069162 |
Appl. No.: |
16/523218 |
Filed: |
July 26, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15601564 |
May 22, 2017 |
10407868 |
|
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16523218 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E02F 5/027 20130101;
B63B 2027/165 20130101; F16L 1/16 20130101; E02F 5/145 20130101;
H02G 1/10 20130101; E02D 1/00 20130101; E02F 5/006 20130101; E02F
5/106 20130101; E02F 5/14 20130101; E02F 3/907 20130101; B63B 35/00
20130101 |
International
Class: |
E02F 5/02 20060101
E02F005/02; E02F 5/14 20060101 E02F005/14; E02F 3/90 20060101
E02F003/90; E02F 5/10 20060101 E02F005/10; E02D 1/00 20060101
E02D001/00; B63B 35/00 20060101 B63B035/00 |
Claims
1. A trenching plow comprising: a. a chassis comprising a
longitudinal axis, comprising: i. a forward end and a rear end, the
chassis defining a first axis extending from the forward end to the
rear end and a second axis extending transversely to the first
axis; ii. a nose plate; iii. a chassis nose; iv. a horizontal end
portion; and v. an end plate disposed opposite the nose plate with
respect to the longitudinal axis; b. a sled connected to the
forward end of the chassis below the nose at a connection point by
uprights, the second axis further oriented forward of a center of
gravity of the seabed trenching plow and rearward of a connection
point of the uprights to the chassis; c. a plow share mounted
against a bottom of the horizontal end portion of the chassis, the
plow share comprising a tip towards the nose plate; d. a set of
moldboards connected to the chassis; and e. a towing assembly
disposed at a predetermined location intermediate the chassis nose
and the horizontal end portion.
2. The trenching plow of claim 1, wherein a bottom of the chassis
lies in fore and aft horizontal planes with an intermediate plane
angled downwardly fore to aft.
3. The trenching plow of claim 1, wherein: a. the chassis comprises
three elongated vertical plates spaced by transverse vertical
reinforcing plates and extending from a nose plate to an end plate;
and b. the set of moldboards are mounted against outer aft-most
faces of the vertical elongated plates.
4. The trenching plow of claim 3, wherein the chassis further
comprises: a. a convex nose beginning at the top edge of the nose
plate and transitioning into a downwardly angled midsection; and b.
a horizontal end section extending from the downwardly angled
midsection to the top edge of the end plate.
5. The trenching plow of claim 4, further comprising: a. a set of
slid skids; b. a set of chassis nose brackets mounted on the
underside of the nose; c. a set of uprights pivotally pinned
between the sled skids and the chassis nose brackets mounted on the
underside of the nose; and d. a reinforcing strut pivotally pinned
between the uprights and the angled midsection of the chassis.
6. The trenching plow of claim 5, wherein: a. the set of sled
uprights and the reinforcing strut are apertured and pinned to
permit adjustment of a vertical distance between the chassis nose
and the angle of the uprights with respect to vertical distance;
and b. the set of sled uprights are pinned to the chassis nose
brackets on a common axis.
7. The trenching plow of claim 4, wherein the tip extends forward
to approximately a point below the junction of the angled
midsection of the chassis with the horizontal end portion of the
chassis.
8. The trenching plow of claim 1, wherein the tip extends
downwardly from the chassis at a distance of between 1.4 meters to
around three meters below the chassis.
9. The trenching plow of claim 1, wherein the plow share comprises
a weight of between more than 40 tons in air to around 100 tons or
more in air.
10. The trenching plow of claim 1, wherein the moldboards comprise:
a. a proximal section; b. a distal section; and c. a hinge pin
joining the proximal section and the distal section at an
angled-cut end.
11. The trenching plow of claim 10, further comprising a wedges can
be inserted above or below the hinge pin so that a bottom of the
moldboard distal section can be locked in either a horizontal or
upwardly angled condition relative to the bottom of the proximal
sections of the moldboards.
12. The trenching plow of claim 10, wherein the moldboards further
comprise: a. a roller configured to reduce friction when the
moldboards traverse a deck of a vessel; and b. a connecting frame
configured to provide reinforcement between the distal sections of
the moldboards.
13. The trenching plow of claim 6, wherein the towing assembly is
disposed on the downwardly angled midsection of the chassis aft of
the connection point of the sled uprights to the chassis nose.
14. The trenching plow of claim 1, wherein the towing assembly
further comprises wings mounted against outer faces of the outer
vertical elongated plates, each wing comprising a mounting ring
aligned on a common axis to facilitate connection to a tow
line.
15. The trenching plow of claim 14, wherein the trenching plow
comprises a center of gravity, the common axis of the towing
assembly mounting rings configured to fall between the sled upright
connecting axis and the center of gravity.
16. The trenching plow of claim 15, wherein: a. the center of
gravity is located around 15 meters aft of the sled upright
connecting axis; and b. the common axis of the towing assembly
mounting rings is approximately midway between the center of
gravity and the sled upright connecting axis.
17. The trenching plow of claim 15, wherein the towing line
connection assembly is located to position the common axis of the
towing assembly mounting rings between the center of gravity and
the sled upright connecting axis.
Description
RELATIONSHIP TO PRIOR APPLICATIONS
[0001] This application is a continuation application of currently
pending U.S. patent application Ser. No. 15/601,564 which is a
divisional application of U.S. patent application Ser. No.
14/749,032, filed Jun. 24, 2015, now issued as U.S. Pat. No.
9,657,455.
BACKGROUND
[0002] This invention relates generally to seabed plows and more
particularly concerns a deep digging over-the-stern trenching plow
with instrumentation for assessing the protective capabilities of a
seabed trench.
[0003] The present practices and equipment, typically requiring
cranes and associated heavy equipment and structures, used to
release and retrieve a plow from a vessel into the sea and from the
sea onto the vessel typically limit the weight of the plow to a
maximum of approximately 20 tons. The trenching depth and strength
of known plows are compromised accordingly.
[0004] The depth achievable in the first trenching pass of these
known 20 ton trenching plows is at best 1.4 meters. Deeper trenches
can be dug by multiple passes, but the deeper the trench and the
greater the number of passes, the greater the forces applied to the
limited strength plow. Therefore, even when multiple passes of
known trenching plows are run, a trench depth of approximately 2.7
meters is the most that can be expected. But, in many applications,
trenches three meters deep may be insufficient to protect their
buried contents. Consider, for example, the impact forces that
might be applied to a pipeline buried in a trench located in an
iceberg zone.
[0005] On the other hand, there is a plow weighing 200 tons that
requires use of an A-frame or crane for launch and retrieval and
can achieve a first pass depth of 2.0 meters and a maximum total
depth of 2.7 meters. The maximum depth of 2.7 meters is dictated
because the configuration required of the plow for launch and
retrieval by A-frame or crane does not afford a plow of sufficient
strength to withstand the forces that will be incurred in
excavating a trench greater than 3.0 meters in depth, regardless of
the number of passes used for the purpose.
[0006] Assuming that a suitable seabed trench can be excavated, the
capability of the trench to protect pipelines, cables and other
objects laid or buried in a seabed trench is a foremost concern.
For example, the likelihood that damage may be caused by icebergs
and other undersea objects drifting or otherwise moving in the
vicinity of the trench is a function of the composition of the soil
in which the object is laid or buried and the depth at which the
object is laid or buried in the soil.
[0007] Plow tip sensors are presently used to measure the shearing
force applied by the tip of the plow to the seabed. Load cells are
also presently used to measure the total tow force applied to the
trenching plow. It is presently understood that the difference
between the measured shearing and total tow forces will be
generally indicative of the non-tip forces applied to the plow.
Such information is useful to understanding the orientation of and
the forces applied to the plow during the trenching process but
does not afford an assessment of the protective capabilities of a
trench.
[0008] The assessment is complicated because the composition of the
soil may change considerably along the path of the trench and the
depth of the trench along its path may vary somewhat from the depth
expected from a given design and adjustable configuration of the
trenching plow.
[0009] It is, therefore, an object of this invention to provide a
trenching plow capable of digging trenches deeper than can be dug
by known trenching plows. It is also an object of this invention to
provide a method for over-the-stern release and retrieval of a deep
digging trenching plow from a vessel into the sea and from the sea
onto the vessel. It is another object of this invention to provide
a method and instrumentation for assessing, on a real-time basis,
the ability of a trench to protect objects laid or buried in the
trench from damage by the impact of external objects.
SUMMARY OF THE INVENTION
[0010] In accordance with the invention a seabed trenching plow has
a chassis, a sled connected to a forward end of the chassis by
uprights and a towing assembly. The towing assembly has a pair of
wings extending laterally from each side of the chassis. The wings
are aligned on an axis transverse to the chassis and adapted for
connection to a towing line. The transverse axis is forward of the
center of gravity of the plow and rearward of the connection point
of the sled uprights to the chassis.
[0011] The method of releasing the seabed plow from a deck of a
vessel having a stern roller includes the steps of connecting the
plow to a towing line at a point forward of a center of gravity of
the plow and rearward of the sled uprights, causing the plow to
traverse along the deck and over the stern roller and allowing the
plow to rotate by gravitation about the stern roller until the plow
is suspended by the towing line from the vessel aft of the stern
roller.
[0012] The method of retrieving the seabed plow from the deck of
the vessel includes the steps of raising the plow from the seabed
to the stern roller at the end of a towing line connected to the
plow at a point forward of a center of gravity of the plow and
rearward of the sled uprights and pulling the chassis to traverse
against and rotate about the stern roller until the plow is resting
on the deck of the vessel.
[0013] Also in accordance with the invention, a method for
assessing the protective capabilities of a seabed trench includes
the steps of generating a threshold signal indicative of a desired
composition of seabed-trench soil for a specific application,
pulling a trenching plow having a plow share with a soil-analyzing
tip along an intended trench path in the seabed, generating a
real-time data signal in response to the composition of the soil
analyzed by the soil-analyzing tip along the intended trench path
and comparing the real-time data signal to the threshold signal to
produce an alarm signal when the real-time data signal is not
protective-capability compliant with the threshold signal.
[0014] The step of generating the real-time data signal may include
the sub-steps of measuring the force required to pull the
soil-analyzing plow tip through the soil, the sleeve friction of
the soil, the pore pressure of the soil and the total pull force
applied by the pulling mechanism to the plow and combining the
measured data according to an algorithm predetermined to produce a
signal indicative of the composition of the soil being analyzed by
the soil-analyzing plow tip.
[0015] The sub-step of measuring may also include measuring the
depth of the soil-analyzing plow tip.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Other objects and advantages of the invention will become
apparent upon reading the following detailed description and upon
reference to the drawings in which:
[0017] FIG. 1 is a perspective view of an over-the-stern trenching
plow utilizing a towing line assembly according to the
invention;
[0018] FIG. 2 is a side elevation view of the over-the-stern
trenching plow of FIG. 1,
[0019] FIGS. 3A-3H are side elevation views of the over-the-stern
trenching plow of FIG. 1 in sequential transition orientations
during retrieval of the over-the-stern trenching plow from the sea
to the stern deck of a transporting/towing vessel;
[0020] FIG. 4 is a side elevation view of the plow of FIG. 1
equipped with trench soil assessment instrumentation in accordance
with the invention; and
[0021] FIG. 5 is a schematic diagram of the trench soil assessment
instrumentation of FIG. 4.
[0022] While the invention will be described in connection with a
preferred embodiment thereof, it will be understood that it is not
intended to limit the invention to those embodiments or to the
details of the construction or arrangement of parts illustrated in
the accompanying drawings.
DETAILED DESCRIPTION
[0023] Turning first to FIGS. 1 and 2, a trenching plow weighing as
much as 100 tons or more includes a chassis 10, a sled 30, a plow
share 40, moldboards 50 and a towing assembly 70.
[0024] The chassis 10 shown has three elongated vertical plates 11
spaced by transverse vertical reinforcing plates 13 and extending
from a nose plate 15 to an end plate 17. The bottom of the chassis
10 lies in fore and aft horizontal planes 19 and 21 with an
intermediate plane 23 angled downwardly fore to aft. The chassis 10
has a convex nose 25 beginning at the top edge of the nose plate 15
and transitioning into a downwardly angled midsection 27 followed
by a horizontal end section 29 extending to the top edge of the end
plate 17.
[0025] The sled 30 is mounted on the chassis 10 below its nose 25.
Uprights 31 are pivotally pinned between the sled skids 33 and
brackets 35 mounted on the underside of the nose 25 and a
reinforcing strut 37 is pivotally pinned between the uprights 31
and the angled midsection 27 of the chassis 10. The uprights 31 and
reinforcing strut 37 are apertured and pinned to permit adjustment
of the vertical distance between the chassis nose 25 and the angle
of the uprights 31 with respect to vertical. The sled uprights 31
are pinned to the chassis nose brackets 35 on a common axis 39.
[0026] The plow share 40 as shown is mounted in any known manner
against the bottom of the horizontal end portion 29 of the chassis
10, as shown under the aft section 17 of the chassis 10, with the
tip 41 of the plow extending forward to approximately a point below
the junction of the angled midsection 27 of the chassis 10 with the
horizontal end portion 29 of the chassis 10. The plow share 40 is
in shape generally similar to known plow shares. However, its tip
41 is considerably further below its chassis 10 than the tips of
known plow shares, the present plow tip 41 being as much as three
meters below the chassis 10 in comparison to known plow tips which
are no more than 1.4 meters below their chassis. Its weight is
significantly greater than the weight of most known plow shares,
the present plow share 40 weighing as much as 100 tons or more in
air in comparison to known plow shares which weigh no more than 40
tons in air. Its width may be, but is not necessarily, wider than
the width of known plow shares, the present plow share 40 being as
much as nine meters wide in comparison to known plow shares which
are no more than 4.2 meters wide.
[0027] The moldboards 50 are mounted in any known manner against
the outer aft-most faces of the outer vertical elongated plates 11.
The moldboards 50 are generally similar to known moldboards, though
their weight may be, but is not necessarily, significantly greater
than the weight of known moldboards, the present moldboards 50
weighing as much as ten tons in comparison to known moldboards
which weigh no more than two tons. Preferably, each of the
moldboards 50 is divided into proximal and distal sections 51 and
53 joined by hinge pins 55 at angled-cut ends 57. Wedges 59 can be
inserted above or below the hinge pins 55 so that the bottom of the
moldboard distal sections 53 can be locked in either a horizontal
or upwardly angled condition relative to the bottom of the proximal
sections 51 of the moldboards 50. As seen in FIG. 1, the moldboards
50 are preferably provided with rollers 61 so as to reduce friction
when the moldboards 50 traverse the deck of a vessel and a
connecting frame 63 providing reinforcement between the distal
sections 53 of the moldboards 50.
[0028] As shown, a towing assembly 70 is located on the downwardly
angled midsection 27 of the chassis 10 aft of the connection point
of the sled uprights 31 to the chassis nose 25. In the embodiment
shown, the towing assembly 70 includes wings 71 mounted against the
outer faces of the outer vertical elongated plates 11. Each wing 71
carries mounting rings 73 aligned on a common axis 75 to facilitate
connection, perhaps in a clevis fashion, to a tow line (not
shown).
[0029] Looking at FIG. 2, the key parameters of the present
trenching plow are the locations of its center of gravity 81, of
the connecting axis 39 between the sled uprights 31 and the chassis
nose brackets 35 and the common axis 75 of the towing assembly
mounting rings 73. In accordance with the invention, the common
axis 75 of the towing assembly mounting rings 73 must fall between
the sled upright connecting axis 39 and the plow center of gravity
81.
[0030] Preferably, and as shown, the center of gravity 81 of the
present plow, which weighs as much as 100 tons or more, is
approximately 15 meters aft of the sled upright connecting axis 39
and the common axis 75 of the towing assembly mounting rings 73 is
approximately midway between the center of gravity 81 and the sled
upright connecting axis 39. In comparison, known trenching plows
have a center of gravity approximately 5-6 meters aft of the nose
of the plow, about 1/3 to the distance of the present plow, and a
tow line connection point forward of the uprights. Therefore, the
present plow results in a moment as much as 12.5 to 15 times that
of known plows.
[0031] In practice, the towing line connection assembly 70 can be
located to position the common axis 75 of the towing assembly
mounting rings 73 anywhere between the center of gravity 81 and the
sled upright connecting axis 39. However, the closer the common
axis 75 of the mounting rings 73 is to the center of gravity 81 the
better, so long as it is forward of the center of gravity 81.
[0032] The configuration and weight of the chassis 10, sled 30,
plow share 40, moldboards 50 and towing assembly 70 are coordinated
to position the center of gravity 81 of the plow at a location
affording a resulting moment suitable to a given 20 to 100 ton or
more trenching plow application.
[0033] Looking at FIGS. 3A-3H, assume a plow weight of 96 tons and
a center of gravity 81 approximately 15 meters aft of the sled
upright connecting axis 39. The transition of the over-the-stern
trenching plow across the stern roller R of a transporting/towing
vessel V during retrieval from the sea W is sequentially shown from
a point P1 of first contact with the roller R to a point P8 at
which the plow has entirely traversed the roller R and is at rest
on the deck D of the vessel V.
[0034] Beginning with FIG. 3A, the plow has been retrieved at the
end of a winch driven tow line L to the point P1 with the plow
oriented for contact between the roller R and the top surface of
the nose 25. The towline L remains turned on the roller R. In this
orientation, the moment of the plow about the roller R is near
minimal.
[0035] As is seen in FIG. 3B, the plow has been further retrieved
to a point P2 at which the apex of the convex nose 25 is in contact
with the roller R, the towline L remains turned on the roller R and
the center of gravity 81 of the plow has rotated the slightly
astern of its position in FIG. 3A. In this orientation, because of
the convex structure of the nose 25 and the sternward shift of the
center of gravity 81, the moment of the plow about the roller R is
greater but still near minimal.
[0036] As is seen in FIG. 3C, the plow has been further retrieved
to a point P3 at which the common axis 75 of the towing assembly
mounting rings 73 is above the contact point P3 and below the high
point of the roller R, so that the towline L is slightly turned on
the roller R. Also, the contact point P3 has shifted to the
downwardly angled midsection 27 of the chassis 10. The center of
gravity 81 of the plow has rotationally shifted further slightly
sternward but very little net shift of the center of gravity 81 has
occurred because of the angled midsection 27 of the chassis 10.
Therefore, in this orientation, the moment of the plow about the
roller R is substantially the same as in FIG. 3B, which is still
near minimal.
[0037] As is seen in FIG. 3D, the plow has been further retrieved
to a point P4 at the junction of the downwardly angled midsection
27 and the horizontal end section 29 of the chassis 10. The common
axis 75 of the towing assembly mounting rings 73 has shifted above
the roller R. The towline L no longer contacts the roller R and has
levered the chassis 10 at the fulcrum point P4 to shift the center
of gravity 81 of the chassis 10 to approximately 2.334 meters 83
astern of the fulcrum point P4, creating a total moment of 224.1
metric ton-meters.
[0038] As is seen in FIG. 3E, the continued pull of the towline L
has caused the horizontal end section 29 of the chassis 10 to
advance slightly on the roller R and has significantly levered the
chassis 10 at the fulcrum point P5 to further shift the center of
gravity 81 of the chassis 10 to approximately 3.768 meters 85
astern of the fulcrum point P5 creating a total moment of 362
metric ton-meters.
[0039] As is seen in FIG. 3F, further continued pull of the towline
L has caused the horizontal end section 29 of the chassis 10 to
advance more significantly on the roller R, levering the chassis 10
at the fulcrum point P6 to further shift the center of gravity 81
of the chassis 10 to approximately 4.518 meters 87 astern of the
fulcrum point P6, creating a total moment of 433.9 metric
ton-meters, the maximum total moment of the retrieval process.
[0040] As is seen in FIG. 3G, further continued pull of the towline
L has caused the chassis 10 to advance until the center of gravity
81 of the chassis 10 is substantially but not quite directly above
the contact point P7, reducing the total moment of the plow about
the roller R once again to near minimal.
[0041] Finally, looking at FIG. 3H, further continued pull of the
towline L has caused the chassis 10 to advance until the plow is
entirely forward of the stern roller R and the plow is resting on
the deck D of the vessel V.
[0042] The release of the plow from the deck D of the vessel V into
the sea S is essentially the reverse of the retrieval process
illustrated in FIGS. 3A-3H, except that independent winch lines are
used to pull the plow in the opposite direction across the stern
roller R, as by a block-and-tackle assembly, against the tension of
the towing line L.
[0043] Turning now to FIG. 4, in order to assess the protective
capabilities of a seabed trench dug by a trenching plow such as the
plow of FIG. 1, the plow share 40 is equipped with a soil-analyzing
tip 41. The soil-analyzing tip 41 includes load pins 43, a pressure
sensor 45 and a friction sensor 47. The load pins 43 measure the
tip reaction force 83 which is the force required to pull the
soil-analyzing plow tip 41 through the soil. For example, the plow
design may anticipate a tip reaction force 83 up to 650 tons. The
pressure sensor 45 measures the pore pressure 85 of the soil
passing under the plow tip 41. The friction sensor 47 measures the
sleeve friction 87 of the soil passing under the plow tip 41. A
load cell 49 is located on the plow or elsewhere in a position
suitable to measure the total pull force 89 applied to the plow via
the tow line L by its pulling mechanism, such as one or more
vessels or winches.
[0044] For example, the plow design may anticipate that a total
pull force 89 on the plow will be in a range of 200 to 250 tons.
Since the total pull force 89 is measured and the offsetting tip
reaction, sleeve and friction forces 83, 85 87 are also measured,
the forces exerted on the plow share 40 between the plow tip 41 and
the bottom of the chassis 10, a distance in the range of 3 meters,
is calculable.
[0045] Turning to FIG. 5, data transfer units 91 powered by
batteries 93 are cable-connected to the sensors 43, 45 and 47 in
the plow tip 41 and collect data to be received by remote data
receiving units 95 which may, for example, be located on remote
operated vehicles 97 in communication with a vehicle controller 99,
a plow controller 101 and a GPS device 103. The data transfer units
91 may, for example, be SENTOOTH 100.RTM. data transfer units.
[0046] In operation, the method for assessing the protective
capabilities of a seabed trench includes the steps of generating a
threshold signal indicative of a desired composition of
seabed-trench soil for a specific application. The trenching plow,
which has a plow share 40 with a soil-analyzing tip 41, is pulled
along an intended trench path in the seabed. As the plow is pulled
along the intended path, a real-time data signal is generated in
response to the composition of the soil analyzed by the
soil-analyzing tip 41. The data signal is herein identified as
being a real-time signal because the amplitude of the signal is
coordinated to the position of the plow along the length of the
trench. If and when the soil is backfilled into the trench to
further increase the protective capability of the trench, within
reasonable limitations, the backfilled soil will be the soil that
was excavated and analyzed during trenching, so that the data
signal substantially accurately indicates the varying composition
of the soil along the backfilled trench. If the trench is not
backfilled, the data signal will even more closely indicate the
varying composition of the soil defining the trench.
[0047] The real-time data signal is then compared to the threshold
signal to produce an alarm signal when the real-time data signal is
not protective-capability compliant with the threshold signal.
[0048] The step of generating a real-time data signal may include
two sub-steps. The force required to pull the soil-analyzing plow
tip through the soil, the sleeve friction of the soil, the pore
pressure of the soil and the total pull force applied by the
pulling mechanism to the plow are all measured as the plow is
pulled along the intended trench path. The measured data is
combined according to an algorithm predetermined to produce a
signal indicative of the composition of the soil being analyzed by
the soil-analyzing plow tip. The algorithm may be standardized or
unique to a given application so as to weigh the measured data
according to the desired predominance of its importance in a given
protective capability analysis.
[0049] The sub-step of measuring may also include measuring the
depth of the soil-analyzing plow tip for inclusion in the measured
data being combined according to the algorithm so as to enable
accounting for depth variations that may occur along the length of
the trench.
[0050] By way of example, a suitable algorithm might weigh the plow
tip reaction force, the sleeve friction of the soil, the pore
pressure of the soil, the total pull force applied to the plow and
the deviation of the depth of the trench from a predetermined depth
as 70%, 10%, 10%, 5% and 5%, respectively.
[0051] Thus, it is apparent that there has been provided, in
accordance with the invention, an improved over-the-stern trenching
plow and a method of releasing and retrieving the plow from the
vessel into the sea and from the sea onto the vessel and a method
and instrumentation for assessing the protective capabilities of a
seabed trench that fully satisfy the objects, aims and advantages
set forth above. While the invention has been described in
conjunction with a specific embodiment thereof, it is evident that
many alternatives, modifications and variations will be apparent to
those skilled in the art and in light of the foregoing description.
Accordingly, it is intended to embrace all such alternatives,
modifications and variations as fall within the spirit of the
appended claims.
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