U.S. patent application number 10/542710 was filed with the patent office on 2006-07-13 for underwater sediment management.
Invention is credited to John H. Redding.
Application Number | 20060150445 10/542710 |
Document ID | / |
Family ID | 9951741 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060150445 |
Kind Code |
A1 |
Redding; John H. |
July 13, 2006 |
Underwater sediment management
Abstract
The present invention relates to underwater sediment management.
In particular, we will describe dredging and scouring apparatus for
removing sand, silt, clay and like materials from sea or river
beds. There is described an apparatus comprising a body (10) having
a bottom face (13, 14) and comprising an outlet flow path (28) in
which is mounted propeller thrust means (29) to direct, in use, a
swirling jet of water downwards towards an area of sea or river bed
or the like, orientation means (48, 49) to connect said apparatus,
in use, to a support means to orientate said apparatus with respect
to the sea or river bed, and at least one inlet flow path (30)
through which water is supplied, in use, to the propeller thrust
means (29); characterised in that the inlet (30) and outlet (28)
flow paths are provided with respective openings in the bottom face
(13, 14) or the body. In the preferred embodiments, the inlet and
outlet flow paths are parallel, but of opposite directions.
Inventors: |
Redding; John H.;
(Lamberhurst, GB) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Family ID: |
9951741 |
Appl. No.: |
10/542710 |
Filed: |
January 26, 2004 |
PCT Filed: |
January 26, 2004 |
PCT NO: |
PCT/GB04/00309 |
371 Date: |
January 6, 2006 |
Current U.S.
Class: |
37/317 |
Current CPC
Class: |
E02F 5/006 20130101;
E02F 3/9206 20130101 |
Class at
Publication: |
037/317 |
International
Class: |
E02F 3/88 20060101
E02F003/88 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 24, 2003 |
GB |
0301660.7 |
Claims
1. An apparatus comprising a body having a bottom face and
comprising an outlet flow path in which is mounted thrust means to
direct, in use, a wash of water downwards towards an area of sea or
river bed or the like, orientation means to connect said apparatus,
in use, to a support means to orientate said apparatus with respect
to the sea or river bed, and at least one inlet flow path through
which water is supplied, in use, to the thrust means; characterised
in that the inlet flow path and outlet flow path are provided with
respective openings in the bottom face of the body; in that at
least a portion of the outlet flow path comprises a duct; and in
that the thrust means comprises a propeller mounted within the
duct.
2. An apparatus as claimed in claim 1 wherein the inlet and outlet
flow paths are parallel, but of opposite directions.
3. An apparatus as claimed in claim 1 wherein the duct is formed
with an outlet in the undersurface of a central section of the
body.
4. An apparatus as claimed in claim 1 wherein an adjustable flow
regulator is provided adjacent the inlet of the inlet flow
path.
5. A apparatus as claimed in claim 4 wherein the flow regulator
comprises a louvre assembly.
6. An apparatus as claimed in claim 1 wherein the body is in the
form of a wing having an angled face at at least one of the leading
and trailing edges thereof.
Description
[0001] The present invention comprises to an apparatus for carrying
out controlled excavation and movement of loose bed material in
marine, river, lake and similar underwater environments. Modifying
the underwater bed topography, by selective removal of bed material
from one area and deposition in another, comes under the ambit of
sediment management. The present apparatus is designed for sediment
management operations, primarily, in shallow water (1-50 m
water-depth).
[0002] The herein-described apparatus incorporates an embodiment of
a means for dredging, scouring, excavation and cleaning, described
more particularly in PCT/GB2003/005030. In the latter document the
embodiment, namely a ducted-propeller, is described in more detail,
together with various alternative modes of operation and means of
deployment. The herein-described apparatus can be seen as providing
a suspended underwater vehicle deployment means, for bring to bear
the operation of the ducted-propeller.
[0003] As such, the present invention is deployable in a similar
manner to the Wing Dredger described in U.S. Pat. No. 6,125,560, in
terms of deployment from a floating vessel by means of suspension
wires for the purpose of controlling the direction of the propeller
jet(s) relative to the bed. A further similarity exists with the
Wing Dredger in the design of the propeller and the duct, and in
having the propeller mounted at the outlet end of the duct.
However, the present invention differs from the Wing Dredger in
being designed specifically for use in shallow water, in being more
versatile in terms of single- and multiple-jet operation and in
embracing a wholly new and novel approach to propeller jetting.
[0004] This new approach recognises and takes advantage of the fact
that the jet created by the said ducted-propeller, is not simply a
thrust means. Rather, it is a complex swirling flow, which includes
a number of embedded vortical flow elements. The various ways in
which the said swirling jet can be modified and can be used for
excavation and controlled movement of bed material are described,
more particularly, in PCT/GB2003/005030. Suffice it to say, swirl
imbues the jet with certain behavioural characteristics, which when
properly directed can be highly beneficial for a range of sediment
management operations.
[0005] In its broadest sense, the present invention provides an
apparatus comprising a body having a bottom face and comprising an
outlet flow path in which is mounted thrust means to direct, in
use, a wash of water downwards towards an area of sea or river bed
or the like, orientation means to connect said apparatus, in use,
to a support means to orientate said apparatus with respect to the
sea or river bed, and at least one inlet flow path through which
water is supplied, in use, to the thrust means; characterised in
that the inlet and outlet flow paths are provided with respective
openings in the bottom face of the body; in that at least a portion
of the outlet flow path comprises a duct; and in that the thrust
means comprises a propeller mounted within the duct.
[0006] Preferably, the inlet and outlet flow paths are parallel,
but of opposite directions.
[0007] Preferably, the duct is formed with an outlet in the
undersurface of a central section of the body.
[0008] Suitably, an adjustable flow regulator is provided adjacent
the inlet of the inlet flow path. Typically, the flow regulator
comprises a louvre assembly.
[0009] In one particular embodiment, the body is in the form of a
wing having an angled face at at least one of leading and trailing
edges thereof. Such face or faces may be provided by means of an
additional wing profile attachment to the body.
[0010] Suitably, the apparatus is of simple box-like construction,
being made from steel plate, with one ducted propeller unit per
apparatus. The design is preferably such that two or more units can
be easily coupled together in different configurations for multiple
jetting operations. In order to be able to operate in very shallow
water and yet maintain a reasonable distance from the bed, the
apparatus is designed with intakes on the underside that face
downwards. Provided the apparatus is initially filled with water
(primed) it can continue to operate when lifted partway above the
waterline, since water will continue to siphon through the body of
the apparatus and into the propeller duct. Adjustable opening
louvre plates over the intakes provide protection from ingress of
debris and also a means for preventing rotation of the apparatus
(countering the propeller torque) when operating in single-jetting
mode. More importantly, they also provide a means for controlling
the rate of water flow through the propeller duct.
[0011] The propeller is driven by a high-pressure hydraulic motor,
which is located axially within the duct. The use of a hydraulic
motor is an integral part of the overall design of the apparatus,
since it enables a very compact and light-weight construction
(compared to the aforementioned Wing Dredger) and also provides for
variable speed and direction control over propeller rotation. The
apparatus can also be more easily fitted with the means to modify
the behaviour of the jet: to create a straight-sided or wide-angle
jet, as required.
[0012] The above and other aspects of the present invention will
now be described by way of example only and with reference to the
accompanying drawings, in which:
[0013] FIG. 1 shows an oblique underside view of the exterior of an
apparatus in accordance with the present invention.
[0014] FIG. 2 shows an oblique topside view of the exterior of the
apparatus of FIG. 1.
[0015] FIGS. 3 and 4 show sectional views through the apparatus of
FIG. 1. FIG. 3 is a vertical section on the long axis, and FIG. 4
is a horizontal section at mid-level.
[0016] FIGS. 5, 6 and 7 show sectional views through one of the
intakes to illustrate the louvre plates and the mechanism
controlling the degree of opening of these plates. FIG. 5 shows the
louvre plates fully open (against the bar stop), FIG. 6 shows the
louvre plates half open (against the bar stop), and FIG. 7 shows
the louvre plates shut (with no flow through the intakes).
[0017] FIGS. 8 and 9 show, in diagrammatic form, the water-flow
circulation through the apparatus of FIG. 1 depending on the
direction of rotation of the propeller. FIG. 8 shows normal flow
jetting, and FIG. 9 shows reverse flow filling (priming).
[0018] FIGS. 10 to 13 shows various ways in which the apparatus can
be suspended from a vessel and various ways in which multiple units
can be coupled together.
[0019] FIGS. 1 and 2 show an embodiment of the apparatus of the
present invention including a rectangular body or tank 10 of
generally light-weight construction; steel plate being a suitable
construction material. The dimensions of the tank, as shown, are in
the ratio: length 3; width 2; height 1.5. It is envisaged that
these dimensions would be represented by metres, however the
overall size of the tank is not critical to the operation of the
apparatus and may be any convenient size or, indeed, shape
[0020] To provide added stiffness to the construction, as shown in
FIGS. 1 and 2, side plates 12, and top and bottom plates 13 and 14,
are joined by angled plates 15. This has the added benefit that on
the inside of the tank the lower sides slope inwards creating a
partial hopper effect. Material carried in-board in suspension with
the intake flow (see FIG. 8) that might otherwise settle inside the
tank, in the angle between the sides and base, is encouraged to
slip down towards the intake and so be re-suspended by the intake
flow.
[0021] Reference to FIG. 3 shows that the hopper effect is
completed by angled fillets 47 placed along the contact between end
plates 16 and bottom plate 14 and between bottom plate 14 and
central bullhead plate 45.
[0022] Various attachment points are provided on the outside of the
tank, as indicated in FIGS. 1 and 2. There are four corner
attachment points 17 at each end, formed by the projections of end
plates 16, and four centre attachment points 18, which comprise
triangular plates 19 welded to angle plates 15. The position and
orientation of triangular plates 19 correspond internally to
bulkhead plate 45. Smaller triangular fillet plates 20 provide
added lateral stiffness to each of the support points.
[0023] Referring to FIG. 2, it can be seen that two hatch-covers 22
are provided on top of the tank that give access, via associated
openings in top plate 13, to the inside of the tank. These hatch
covers are of conventional construction, but are designed
specifically to provide an air-tight seal to the tank when fully
closed. Also on the top of the tank are two grab rails 23 that run
along the outer long edge of top plate 13. These are formed of
steel pipe and are attached at their two ends and at intermediate
locations in such a way that there is communication between the
inside of the tank and the bore of the pipes. Set onto the top of
the grab rail pipes towards each end, are short, internally
threaded, spigot pipes 24, into which non-return valves (not shown)
can be screwed. The non-return valves are designed to allow egress
(venting) from the tank of air and water, but not ingress. Their
function and operation will be described later.
[0024] Also on the top of the tank and attached to top plate 13 by
means of multiple bolts, is a circular plate 25. Circular plate 25,
when removed, gives access to the inside of the tank for the
purpose of removing the propeller duct unit. The circular opening
in top plate 13 that is covered by circular plate 25 is, therefore,
slightly larger in diameter than the widest lateral dimension of
the propeller duct. Circular plate 25 is fitted with a rubber
gasket designed to effect an air-tight seal.
[0025] Also formed centrally in circular plate 25 are three
circular openings set out in triangular fashion, which provide
penetrations for the three hydraulic hoses that connect to the
motor (two high-pressure power hoses and one low-pressure casing
drain hose). Split flanges 26, formed of rigid plastic, and bolted
to circular plate 25 over each opening, encircle each hose and
provide an air-tight seal where the hoses enter the tank. Split
flanges 26 also serve to secure the hoses at the point of entry to
the tank, thus preventing any risk of chaffing of the hoses against
metal edges. Split flanges 26 can be more clearly seen in FIG.
3.
[0026] Completing the appurtenances on the top of the tank, as
shown in FIG. 2, is a small detachable stool-like structure 27,
consisting of a circular ring supported by means of struts at a
fixed distance above the top plate. The hydraulic hoses pass
through the ring and are loosely supported in such a way that
over-bending, or kink-mg, of the hoses at the point of entry into
the tank is prevented.
[0027] Referring to FIG. 1, the circular outlet 28 of the propeller
duct can be seen to be centrally located on the underside of the
tank. Also the position of the propeller 29, just inboard of the
duct opening, can be clearly seen. It should be noted that there
are no rigid obstructions (vanes, struts or other protrusions) in
way of the propeller jet, within or below the outlet end of the
duct.
[0028] Located either side of the propeller duct outlet 28, are two
water intakes 30. These are rectangular in shape and are of such a
size that one on its own would provide for unhindered flow of water
into the propeller duct, when the propeller is rotating at full
speed. Attached to the bottom plate 14 and extending vertically
over each opening are three thick metal grill plates 31. These are
designed to prevent large items of debris, or obstructions sticking
up from the seabed, from penetrating the intakes. They are also
designed to take the weight of the apparatus when the latter is
placed on-deck or onto a hard-standing surface. If the apparatus
were to be placed on a soft surface, wooden sleepers would be used
to prevent the grill plates from penetrating into the surface.
[0029] FIG. 1 also shows that immediately inboard of the intakes 30
are multiple louvre plates 32, which extend across each intake.
These are designed to prevent ingress of smaller debris that might
otherwise pass between the thick metal grill plates 31. Each louvre
plate has a hinge attachment to the bottom of the tank at either
end, such that each plate is free to rotate about a hinge-line
coincident with the bottom edge of the plate. A detail of this
hinge attachment is shown in FIGS. 5 to 7.
[0030] Referring to FIG. 5 it can be seen that a simple horizontal
bar stop 33, supported at either end on pillars 34, allows
adjustment of the amount of opening of the louvre plates 32. Each
pillar 34 has a series of holes drilled into it to allow the bar to
be secured at different heights above the base of the tank. As
presently designed, adjustment of the amount of louvre plate
opening has to be by hand, requiring man access through the hatch
covers with the apparatus on deck. It is envisaged that in due
course a remotely operated louvre adjustment mechanism will be
adopted.
[0031] When the louvre plates are lying flat (FIG. 7), the intakes
are effectively closed, save for minor leakage at the edges of the
plates. This leakage is useful in that during reverse circulation
flow (see below) it allows any residual sediment that may have
collected in the bottom of the tank to be flushed out When the
louvre plates are pointing nearly vertically upwards (FIG. 5), the
intakes are fully open, allowing unhindered flow to the propeller
duct. When no water is being drawn through the intakes, self-weight
causes the plates to fall shut and adopt the imbricate arrangement
shown in FIG. 7.
[0032] It should be noted that the louvre plates are set in such a
way that they face in opposing directions over each intake. While
this is of little consequence when the plates are fully closed or
fully open, it will be appreciated that with the louvre plates at
intermediate positions (FIG. 6), water entering the intake is
forced to do so at an angle, which will be opposed on the two
sides. Opposed deflection of the intake water flow imparts a
turning moment to the apparatus, which helps to counter any
tendency for rotation in the opposite direction induced by the
propeller. Needless to say, the direction of angling of the louvre
plates has to be coordinated with the direction of rotation of the
propeller.
[0033] Lastly, in referring to FIG. 1, it should be noted that
surrounding the outlet end of the propeller duct is a flange plate
35 directly welded to the bottom plate 14. Flange plate 35 has a
series of tapped holes drilled into it. The purpose of the flange
plate is to allow attachment of a flared nozzle, the function of
which is discussed in PCT/GB2003/005030.
[0034] Reference to FIG. 3 shows the inside of the tank in vertical
section to illustrate the disposition of the propeller duct 36 and
motor 37. The propeller duct 36 can be seen to have a vertical
length approximately 2/3 the height of the tank, and to have a
bellmouth 38 at the top (inlet end) to facilitate the inflow of
water. Motor 37 is axially positioned in the duct with its shaft
(not seen) facing downwards and the high-pressure hydraulic fluid
ports (for attachment of the two high-pressure hoses 38) facing
upwards. A side-tap on the motor (not shown) provides attachment
for the casing drain hose 39 (see FIG. 2).
[0035] Motor 37 is supported axially within the duct by means of
collar 40 to which the motor is secured by a ring of axial bolts,
and the collar is secured to the inside of the duct by means of
angled fin plates 41. The fin plates are vertically set in order to
present a limited surface area to the direction of flow and their
edges are also chamfered to further minimise flow obstruction There
are five supporting fin plates 41, equally spaced; this number
being purposely chosen to provide both a rigid axial support to the
motor and an non-equal or non-multiple of the propeller blade
number (four-bladed propeller): the latter being good engineering
practise in terms of ducted propeller design. The arrangement of
the fin plates can be better seen in horizontal section, in FIG.
4.
[0036] The motor can be seen to taper downward at its front end,
forming a smooth transition with the hub of the propeller 29. The
smooth profile of the motor and propeller hub matches the shape of
the duct, giving a uniform width of annulus between the motor and
the duct.
[0037] The duct, complete with motor, can be detached from the tank
and removed through the top of the tank. The duct has three rings
42 welded around its outer circumference. These are designed,
partly, to maintain the ovality of the duct both during and
following fabrication. The uppermost ring also gives added
stiffness to the duct at the point of fixity of the angled motor
support fin plates, while the lowermost ring also acts as a seating
flange when the duct is installed into the tank. This lowermost
ring has two holes drilled into it that act as stabbing guides for
pegs 43 (indicated by small arrows) that stick up from a landing
flange 44 on the bottom of the tank. The two upper rings also have
holes drilled in them to enable the duct to be rigidly secured on
either side to the central vertical bulkhead plate 45. Angled
brackets 46, in pairs, provide the means for bolting the propeller
duct to the bulkhead plate and can be seen in FIG. 4.
[0038] Also visible in FIG. 3 are the fillets 47, which complete
the hopper-like form of the tank base around each intake, as can be
better seen in FIG. 4. The fillets may be of any suitable material,
such as concrete, and may be removable or cast in situ.
[0039] Lastly, in referring to FIG. 3, it should be noted that
while bulkhead plate 45 only extends inwards as far as the
propeller duct, it stretches the full height of the tank; and thus
effectively divides the tank into two separate compartments below
the top level of the propeller duct. Directly over the top of the
propeller duct, however, there is free communication between the
two halves of the tank.
[0040] The workings of the apparatus will now be briefly described
by reference to FIGS. 8 and 9. In the first instance, it will be
assumed that the apparatus is being operated in sufficient depth of
water that the siphonic action is not required.
[0041] FIG. 8 shows that when the propeller is rotating, such as to
produce a downward jet of water, water is drawn through intakes 30;
circulates through each side of the tank; enters the top of the
propeller duct through bellmouth inlet 38; travels through duct 36
and is forced out through duct outlet 28. The reduction in pressure
inside the tank caused by the rotation of the propeller (acting
like an axial flow pump) causes louvre plates 32 to open as far as
paired bar stops 33 will allow. Water is thus sucked upwards into
the tank at a rate determined by the speed of rotation of the
propeller and the degree of opening of the louvres.
[0042] Since all other points of ingress for water into the tank
are sealed, the louvre plates provide an effective means for
regulating (i.e. reducing) the flow of water through the propeller
duct for any given speed of rotation of the propeller. The main
reason for wanting to reduce the flow of water through the
propeller duct is that the axial velocity of the jet is reduced
compared to its swirl velocity and so the Jet Swirl Number is
increased (see PCT/GB2003/005030 for a more detailed description of
Jet Swirl Number). In propeller design parlance, a decrease in flow
through the propeller disc is referred to as a reduction in
propeller advance coefficient (J). One of the significant effects
of this (as described more particularly in PCT/GB2003/005030) is
that the behaviour of the jet is changed, making it more
susceptible to breakdown.
[0043] When starting the apparatus in very shallow water an initial
priming action may be necessary, which is illustrated in FIG. 9.
The propeller is initially rotated in reverse at slow to moderate
speed. This has the effect of forcing water into the tank through
the propeller duct The louvre plates act as (slightly leaky)
one-way-valves preventing wholesale egress of water through the
intakes. Air and then water are thus forced out of the top of the
tank through the four non-return valves in vent holes 24. Once the
tank has been filled with water and purged of air (indicated by
continuous spouts of water from the holes 24) the motor rotation is
quickly reversed to begin normal jetting operations, as explained
by reference to FIG. 8. This priming action can also be used as an
effective way of cleaning (back-washing) residual sediment from the
bottom of the tank; material being flushed out by the leakage flow
that occurs through the gap between the ends of the louvre plates
and the underside of the tank (see FIG. 7).
[0044] Normal jetting, once established, can continue even with
much of the tank out of the water, because the propeller creates
sufficient suction head for water to siphon into the propeller
duct. The fact that the intakes are placed on the underside of the
tank also means that there is less likelihood of air being sucked
in via a drain-hole vortex. Clearly, for this siphonic action to
work effectively the emergent top of the tank has to be fully
air-tight.
[0045] For most operations, where simple jetting of the bed is
required, the apparatus would be suspended by one or two pairs of
wires from a crane, or A-frame, mounted on a support vessel. FIGS.
10 to 13 show a number of possible support options, together with
various ways in which several single-jet units can be coupled
together to form multiple units. In FIG. 10 a single unit is shown
suspended by two wires 48. Loops of chain 49 with their ends
attached to the upper corner points 17 provide a means for
adjusting the roll and pitch of the apparatus. By shackling the
wires to links on one or other side of the centre point of each
loop, forward, or backward pitch can be introduced. By adjusting
the length of each chain independently, sideways roll can be
effected. In this respect, operation similar to that described in
U.S. Pat. No. 6,125,560 is achieved.
[0046] Single unit operation is intended primarily for pipeline (or
cable) jetting work. For instance, where a pipeline laid on the
seabed is required to be lowered below the bed for the purpose of
increased protection. The ability to tilt the apparatus sideways is
important, since by directing the tilted jet just under the pipe as
the unit traverses along and adjacent to the line of the pipe,
material can be displaced to the far side of the pipe to form a
levee stockpile. The same material can then be used to backfill the
trench by jetting from the opposite side with the jet tilted
towards the stockpile and the trench. Note that a significant
advantage of this jetting equipment over conventional pipeline
ploughing equipment is that there is no mechanical contact with the
pipe.
[0047] In FIG. 11 two units are shown coupled together in-line and
suspended in similar fashion, but with the chains 49 attached to
the four upper centre attachment points 18. Because the separation
of the wires and the attachment arrangement of the chains is
identical to that for the single unit (shown in FIG. 10) a double
unit can be operated from the same vessel in exactly the same way
as a single unit. It is a also a very simple matter to couple two
units together in-line, by means of four high-tensile bolts passing
through the four common corner attachment point holes 17.
[0048] A double in-line unit (or indeed a triple in-line unit, as
shown in FIG. 12) would be used primarily for bulk excavation and
movement of material. This might include pre-sweeping of a corridor
through sandwaves for the purpose of preparing a smoothed profile
for laying a large diameter pipeline, or it might include removal
of material from shoal areas in a navigation channel. Either way,
material has typically to be removed in large quantities to an
agreed level, and in the latter case the excavated material has to
be deposited below the navigation depth. By operating two or more
units in-line the jets act in concert to remove a swathe of
material. Typically, the units would be tilted (pitched) in the
direction of forward travel so that material is displaced in this
direction. No sideways roll would be used, as the objective is to
create a level surface.
[0049] Finally, FIG. 13 shows two units coupled together in saddle
fashion, metal struts 50 being used to cross-connect adjacent upper
and lower attachment points (17 and 18) and achieve the desired
angle of convergence of the jets. A similar means of suspension is
used, as in the other sketches. Such a converging jet arrangement
would be employed, for instance, where increased jetting energy was
required for lowering a pipeline (or possibly exhuming an existing
buried pipeline). The focussing of the two jets means that
excavation energy is concentrated at the point of intersection of
the two jets.
[0050] Advantages of the apparatus for the present invention
include: [0051] 1. An improved ability (compared to U.S. Pat. No.
6,125,560) to operate in shallow water for the purposes of carrying
out underwater jetting excavation and movement of bed material.
Said ability being achieved by means of a short propeller duct,
housed inside an air-tight tank, with the primary water intakes on
the underside of the tank and with the ability to carry out an
initial priming operation wherein the propeller is reversed to
induce filling of the tank. [0052] 2. An improved ability and
greater versatility to operate in single- and multiple-jetting
configurations, by coupling single jetting units together. [0053]
3. An improved ability to control and regulate the velocity of flow
through the propeller duct and at its outlet end for the purpose of
modifying the behaviour of the jet. Said control being-exercised by
adjusting the degree of opening of the louvre plates, which
function like one-way valves. [0054] 4. An ability, stemming from
point 3 and the use of various attachments (as discussed in
PCT/GB2003/005030), to carry out very rapid excavation in a wide
range of loose bed materials, with the attendant directional
movement of the excavated material over long distances (100 m's).
[0055] 5. An ability, also stemming from point 3 and the use of
various attachments (as discussed in PCT/GB2003/005030), to carry
out excavation (albeit at a slower rate) in stiff clay materials
that are otherwise not amenable to excavation by means of
low-pressure water jetting. [0056] 6. An ability, equal with U.S.
Pat. No. 6,125,560 to operate the apparatus from a support vessel
by means of a wire suspension system wherein the attitude of the
apparatus can be adjusted in terms of both pitch and roll. Said
capability being used for the purpose of sideways displacement of
material (such as for pipeline jetting) and for forward
displacement of material (such as for pre-sweeping and sediment
management operations). [0057] 7. An added benefit, further to
point 3, that the said louvre plates also provide a means for
preventing access of debris into the propeller duct. [0058] 8. An
added benefit, further to point 3 and point 7, that the said louvre
plates when half open also provide a means for preventing rotation
of the apparatus by countering the turning moment induced by the
propeller. [0059] 9. The added benefit, further to point 7, wherein
thick grill plates over the intakes protect from ingress of coarse
debris and penetration of seabed obstructions. Said grill plates
also provide a means for supporting the apparatus when not in use.
[0060] 10. A simple body shape that is strong, light-weight and
functional (in terms of forming an air-tight sealed tank), that is,
in effect, self-cleaning by having a hopper-like base form, that
has attachment points strategically placed to enable the body to be
suspended from wires and chains and coupled to like bodies in
different configurations for the purpose of multiple jetting.
[0061] 11. A simple means for installing and removing the propeller
duct, i.e. for maintenance purposes, and to enable said propeller
duct to be used in other propeller jetting embodiments (as
described in PCT/GB2003/005030). [0062] 12. The added benefit,
further to the self-cleaning ability noted in claim 10, of using
the priming action, noted in point 1, as a further means for
cleaning (back-washing) the inside of the tank.
* * * * *