Excavating – Beneath a body of water – Adapted to excavate specific discrete material
Reexamination Certificate
2002-03-14
2004-06-15
Batson, Victor (Department: 3671)
Excavating
Beneath a body of water
Adapted to excavate specific discrete material
C037S321000, C037S323000
Reexamination Certificate
active
06748679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dredging apparatus for extracting bottom-dwelling shellfish such as clams, oysters, mussels, cockles, and crabs from a sea, lake, or riverbed, and for continuously transporting the extracted shellfish to the surface.
More specifically, the invention relates to a hydraulic dredging apparatus that includes a source of pressurized water, at least one water jet arranged to receive water from the pressurized water source and direct it at shellfish-containing sediments, sorting plates for receiving the shellfish-containing sediments excavated by the water jet or jets and separating the shellfish from the sediments, a collection chamber for receiving the separated shellfish, and dual lifting compartments, one of which is connected to the pressurized water source for lifting shellfish from the collection chamber and entraining the shellfish for transport to the surface, and the other of which is arranged to received pressurized air for increasing the transport speed and lifting power while cushioning the shellfish as they are transported to the surface. Unlike previous hydraulic transport mechanisms, the dual-compartment air/water transport arrangement of the invention permits precise control of excavation and transport pressure, without the need for multiple air or water sources and/or manifolds.
2. Description of Related Art
Numerous attempts have been made to devise mechanical harvesters that move or that can be towed along the bottom of a body of water in order to harvest shellfish that live in colonies at the bottom. All of these devices seek to dredge shellfish such as clams, oysters, cockles, mussels, and/or crabs from the bottom of the body of water and either trap the shellfish for retrieval after the device is brought to the surface, or continuously transport the shellfish to the surface as the dredge is being towed along the bottom.
Common problems that the designers of these devices have attempted to solve include problems of efficiency, i.e., the relationship between power or effort expended and the amount of shellfish harvested, problems related to the cost and reliability of the device, which are often a function of complexity, and problems related to environmental damage caused by the device as it is towed across the sea, lake, or riverbed.
The earliest attempts at large-scale shellfish harvesting devices undoubtedly date back to prehistoric times and most likely involved diggers or tongs dragged along the bottom for scooping shellfish into a collection cage or basket that could then be brought to the surface and emptied. More sophisticated but nevertheless fundamentally similar examples of dredges of this type are still being used and are disclosed, for example, in U.S. Pat. Nos. 4,827,635, 4,425,723, and 3,226,854. Such dredges have the advantage of simplicity, but are relatively inefficient because of inherent limitations in the effectiveness of mechanical dredging devices, and the need to repeatedly bring the dredges to the surface to be emptied.
As early as Greek times, high pressure jets of water capable of slicing horizontal layers of sediment were being used to hydraulically harvest shellfish, the loosened or liquified mass of shellfish-containing sediments being sifted to separate the shellfish from the sediments, and the remaining shellfish being collected in a collection cage or basket before being brought to the surface. Such harvesters, which are also still in use, have the advantage of being able to dredge a relatively large area in less time than a purely mechanical harvester, although they still require the collection cage or basket to be periodically brought to the surface for emptying.
In order to avoid the need to periodically bring the dredge to the surface for removal of harvested shellfish, numerous generally unsuccessful attempts have been made to add conveyors that continuously and automatically convey recovered shellfish to the surface, either in connection with a purely mechanical harvester, or in connection with a harvester that uses a hydraulic digging action. These conveyors initially involved purely mechanical conveyance systems in the form of conveyor belts or escalators, but were limited to use in relatively shallow waters since systems of greater length involved intractable problems in handling and complexity. A recent example of a non-hydraulic dredge with a mechanical conveyor is disclosed in U.S. Pat. No. 4,464,851, while examples of hydraulic dredges with mechanical conveyors are disclosed in U.S. Pat. Nos. 2,508,087, 3,462,858, and 3,521,386.
In theory, hydraulic means of conveying extracted shellfish to the surface through pipes or hoses appear to offer greater simplicity and ease-of-handling than purely mechanical conveyance systems, and therefore the possibility of use at greater depths. However, in practice, most of the previously proposed hydraulic conveyance systems have suffered from slow speed, excess energy consumption and, in the case of systems that share water jets for both excavation and transport, difficulties in controlling excavation and transport pressures. For example, the system disclosed in U.S. Pat. No. 3,624,932 requires separate pumps, two corresponding pressurized water lines, and a transport hose to carry out excavation and transport of shellfish to the surface, resulting in relatively high power consumption and an increased possibility of tangling or breakage. The system disclosed in U.S. Pat. No. 3,184,866 utilizes both air and water for excavation as well as transport, and therefore requires even more hydraulic lines including, as illustrated in
FIG. 1
appended hereto, two pressured water lines
49
and
50
with corresponding manifolds
43
and
46
, two pressurized air lines
48
and
41
, and a transport hose
20
to carry the excavated shellfish to the surface. Possibly because of the number of lines required, the system of U.S. Pat. No. 3,184,866 requires both a tow boat and a receiving boat or installation.
More recently, it has been proposed to use the same source of pressurized water for both the excavating jets and transport system of a hydraulic dredging apparatus, thereby eliminating the need for separate hydraulic lines and/or sources. The decrease in water pressure available for transport is compensated for by an improved transport system in which collected shellfish are siphoned rather than pushed or swept out of the collection chamber. Examples of systems in which jets of water are used to hydraulically separate shellfish from sediments, and also to create a siphon or Venturi effect that lifts the separated shellfish into a stream of water and carries them to the surface, are disclosed in British Patent Publication GB1,156,547 and U.S. Pat. No. 6,237,259. The latter system is illustrated in
FIGS. 2 and 3
, appended hereto.
In the system disclosed in U.S. Pat. No. 6,237,259, which was developed by the present inventor, the dredging apparatus includes a sled having a main frame
40
and a digging blade
21
that is inclined forwardly and downwardly relative to the frame so as to extend below the bottom of the frame into the sediments to be dredged. A digging jet pipe
22
is fixed relative to the front surface of the digging blade
21
and is arranged to discharge water under pressure on to the surface of the seabed immediately ahead of the digging blade to fluidize the sediments as they pass onto the blade. The angle of the digging blade
21
is such that a surface section of the seabed cut by the blade travels up the slope of the blade and into the open end or mouth
23
of the frame
40
. Water to the digging jet
22
is supplied by a pump situated on a vessel through a hose
24
connected by suitable fittings to the digging jet. Extending rearwardly from digging blade
21
is a first separating device
25
made up of a plurality of horizontal bars
26
,
27
,
28
arranged in a direction generally parallel to a direction of travel of the apparatus as it is towed by a vessel, for separating shellfish colle
Bacon & Thomas PLLC
Batson Victor
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