AU2012203347A1 - Submersible Raft for Growing and Drying Oysters - Google Patents

Abstract

Abstract of Invention & Method This invention uses the drying method to control the overgrowth of spat on Rock Oysters grown in the intertidal zone, by eliminating the human labour intensive process of removing the oyster baskets from its furniture to the place where it will dry. The invention achieves this by growing the oyster on a reusable raft capable of being either: (a) fully submerged, remaining on the seabed of the intertidal zone (secured in a fashion within the lease area) to facilitate the cultivation process during the natural high tide and remaining on the seabed during low tides; and (b) floated fully above the water surface at both high tide and low tide to facilitate the drying process, without the need to remove the oyster baskets from the raft. The raft remains anchored to the seabed in the intertidal zone by being submerged on the seabed throughout the range of the tide until the oysters require drying and tethered by any appropriate means (J) to a mooring pin (1). When required to initiate the drying process having regard to the cultivation process adopted, the raft is made watertight by sealing the valve holes (F) on the base of the floatation chambers/buoyancy tanks (A) at low tide with a valve (H). The result is that when the tide naturally rises, the raft floats holding the oysters clear of the water and allowing the drying process to occur wherein unwanted spat and other marine growth will desiccate and die; allowing for a cleaner and more marketable oyster. During the drying phase a protective shade cloth (K) is attached and spread over the raft. After sufficient drying, the cover (K) is removed and the watertight integrity breached by removing the valve (H), allowing seawater to engulf the flotation chambers/buoyancy tanks (A) through the valve holes (F)at the next rising tide ensuring the raft remains submerged on the seabed in the intertidal zone to continue the cultivation of the Rock Oyster. 'LAA

Description

EDITORIAL NOTE: The Description has 1 to 6 pages There is 1 page of Claims Complete Patent Specification Submersible Raft for Growing and Drying Oysters The invention is described in the following statement Submersible Raft for Growing and Drying Oysters 1. Prior Art and background Currently it is industry practice to grow single seed (loose and unattached) Rock Oysters in mesh bags and trays on the intertidal flats of estuaries and bays. If left unchecked the overgrowth of juvenile oysters (spat) on the parent or stock oyster will form a clump leaving the oyster generally unmarketable. Controlling the overgrowth is at present achieved in one of two main ways. One method is by dipping the oysters in a vat of hot water (730 C) for several seconds. The other method is by removing the oysters from the seawater for several days; effectively killing the juvenile oysters by desiccation. Both of these processes are labour intensive because they require removal of the oysters from the furniture or apparatus in which they grow (for example longlines and racks) and transport them in order to dip or dry before replacing them on the furniture. In peak season, late February through November, this overgrowth is most prevalent requiring spat control as often as every eight weeks. It can, however, occur all year round. 2. Brief Description of Drawings Figure 1 illustrates a basic structure of the aquaculture furniture ('raft'), comprising at least one or more flotation chambers/buoyancy tanks (A), support beams (B) and the baskets/mesh bags/trays (C) in which the oysters will be cultivated and in the alternate, dried. Furthermore, Figure 1 shows the manner by which the operator will adjust the buoyancy of the raft by use of a valve system (H) and (F). Figure 2 is an elevation of the raft and illustrates the manner by which the raft is deployed at low tide, including the mooring mechanism (1) (J), detailed picture of the valve (H) and the layout of the oyster baskets and sunshade (C) (K).

3. Example 3.1 Flotation Chambers/Buoyancy Tanks A submersible and floatable raft for growing and drying oysters in accordance with this invention requires hollow flotation chambers or buoyancy tanks (A) affixed horizontally to a form a raft like structure which stabilizes the flotation chambers or buoyancy tanks (A) and holds the oyster basket fasteners (E) which carry the oyster baskets (C). The raft floats parallel on the surface of the water or ties on the seabed in the intertidal zone of the seabed. This design comprises two hollow chambers of cylindrical construction affixed horizontally to the raft as shown in Figure 1. The chambers are preferably made from UV stabilised PVC but may be made from any material including metal and fibreglass that can withstand the environmental conditions. Further, a suitable material for the chambers is one that can achieve buoyancy having regard to the size of the float and the weight throughout the growth cycle of the oysters. 3.2 Ports / Valve Holes In order for the raft to be submerged or floated, this design calls for each chamber or buoyancy tank to have open ports or valve holes located at one end of each chamber (H) and a smaller port or breather hole (G) at the opposite end on the highest horizontal surface of the chamber. . The larger of these ports (H) is located at the lowest point of the vertical end cap, at the end where the water enters on a rising tide, of each chamber. The smaller port or breather hole (G), allows air to escape as the water enters through the larger port as described above. The size of these valve holes and breather holes will be determined by the diameter of the chamber and must be sufficient to allow uninterrupted water flow through the chamber when open. This design allows for the larger port to be 50mm in diameter and the smaller port to be 20mm in diameter. The chambers allow seawater to flow in (as the tide rises) and empty out of the chambers at low tide. 3.3 Plugs /Valve Together with the Ports or Holes above, each chamber must be able to be sealed in some fashion in order to float. In this design plugs or valves (H) are inserted into the ports or valve holes (G) at low tide when the chambers are empty of water causing the raft to float when the tide naturally rises again. In order to achieve buoyancy, above the water at any time, this design only requires plugs or valves in the larger ports.. In this design, 55mm circular plugs are made of 19mm thick rubber and are tapered so as to be a push-in fit into the larger port. Each plug has a 6mm hole drilled along its axial centre, Inserted into this hole is a 38mm x 6mm hex-headed threaded stainless steel bolt with a nut and two 30mm diameter stainless steel washers. When assembled the rubber plug is sandwiched between the two washers, the plug is then pressed firmly into the port, the nut is then tightened on the bolt causing the plug to expand in diameter inside the port as it is squashed between the washers. The overall result is a tightly sealed flotation chamber/buoyancy tank (A), resistant to being dislodged when the raft is floating.

3.4 Crossmembers The flotation chambers/buoyancy tanks (A) are held parallel to one another by rigid crossmembers or support beams (B). In this design crossmembers (B) are in pairs on top and beneath the chambers and fastened in the same vertical plane by long bolts or tensioned wires (D). For stability, these beam fasteners (D) in this design run vertically between the cross members and are located either side of the chambers (A) to also prevent any horizontal movement of the chambers. The crossmembers (B) also provide anchor points for placing basket fasteners (E) securing the containers or baskets of oysters (C) in place on the top of raft at all times. This design uses 3 crossmembers (B) (one at each end and one in the middle) and 40 mesh bags (C) positioned along the raft. This design has used baskets, however, six trays approximately 1.5m wide and Im long would also fit evenly along the raft to achieve a similar result The containers are anchored by retainers or basket fasteners (E) in the form of wires, clips or ties. The containers (C) are removable allowing mature oysters to be removed for market and replaced with new stock, otherwise leaving the remainder of the raft structure in place, anchored on the seabed by way of a tether (J) and mooring pin (1). The cross members are preferably made from recycled. UV plastic but may be made from any material including metal, fibreglass and timber that best suits and withstands the environmental conditions whilst allowing the raft to float and be submerged as required. When floated the raft has a cover of shade cloth fitted (K). The cover must be of sufficient size to protect all the oysters on the raft from direct sunlight and is attached at the four corners of the raft and such other intermediate places necessary to secure it.

This design requires a shade cloth 1.5m by 6m of 50-70% light reduction grade. To achieve its protective purpose the shade cloth needs to be at least 50% light reduction grade of shade cloth. 3.5 Anchoring The raft is anchored to the seabed of the intertidal zone throughout the natural tidal cycle by way of a tether (J) attached to a mooring pin (1) so it remains within the perimeter of the oyster lease regardless of whether the raft is submerged or floated. 3.6 Operation For this design, each raft holds three thousand (3000) oysters and as such the raft needs to be 6m in length by 1.5m wide. To achieve buoyancy this requires two chambers, with an approximate combined volume of 600 litres, running the length of the raft beneath the perimeter. The purpose is to achieve stability at all times and be submersible or buoyant as required to control spat growth. The operator of this invention will not require any particular skill set as the invention in itself is designed to simplify and reduce the labour intensive process required by the prior art. Knowledge may be required to understand the methods of growing rock oysters The operation of the invention is, in the best way know to me, provided in this section 3. 4. Aquaculture species The species which are contemplated to be cultivated by the aquaculture assembly is the Pacific Rock Oyster.

Claims (5)

1. a flotation chamber or other buoyancy apparatus secured by crossmembers or beams;

2. baskets for oyster cultivation attached to such raft;

3. a mooring point and tether to secure such raft within an oyster lease area;

4. valve system to allow for flotation and submersion; and

5. a shade cloth to cover the raft for protection from excessive direct sunlight during the drying process; wherein said assembly can either be easily: (a) fully submerged, remaining on the seabed of the intertidal zone (secured in a fashion within the lease area) to facilitate the cultivation process during the natural high tide and remaining on the seabed during low tides; and (b) floated with all oyster baskets fully above the water surface at both the natural high tide and low tide to facilitate the drying process; without the need to unnecessarily remove the oyster baskets from the raft (or their furniture) or transport them to another location to undertake such cultivation and drying processes.