Ocean Farm Technologies Inc. develops and markets innovative technology for aquaculture in exposed open ocean conditions.
Aquapod™ FAQ
Is the Aquapod meant to be submerged all the time or can it be operated as a surface pen?
Doesn't the Aquapod have a high drag coefficient compared to other submersible net pens?
Is the number of separate components and fasteners a problem?
How is the Aquapod deployed and installed at an ocean farm site?
How do your suggested moorings allow for raising and lowering the cages?
How do you do partial and complete harvests out of the Aquapod?
How do you clean the Aquapod mesh?
How resistant is the Aquapod to predators - sharks, seals, and sea lions?
How do you maintain the vertical position of the Aquapod, and how do you raise and lower it?
What are the life cycle costs?
How many fish can you stock in an Aquapod?
Is the Aquapod meant to be submerged all the time or can it be operated as a surface pen?
A better description of the Aquapod is submersible. The species being raised, site conditions, including permit restrictions, currents and wave characteristics will determine the appropriate operating position. All the normal functions of the containment system including feeding, mortality collection, and harvesting are able to be performed while the Aquapod is submerged, so this can be treated as the normal operating position. Some functions, such as net cleaning, can be done subsurface, but are easier done above water. The Aquapod can be easily raised when surface conditions are suitable.
In cases where wave energy is not extreme, the most efficient way to operate the Aquapod is partially surfaced. Feeding, cleaning, and maintenance is facilitated by being surfaced, and when bad weather is expected, it is easy to submerge the pen to get it below the surface energy.
Doesn't the Aquapod have a high drag coefficient compared to other submersible net pens?
Ocean Farm Technologies began drag force testing in November, 2004, with the University of Maine, and these experiments continued with U. Maine in the spring of 2005. In October 2005 The University of New Hampshire conducted a tow test, the results of which have been published and are available at the OFT download site.
The lesser twine surface area of the Aquapod (smooth vinyl compared to synthetic woven netting) will have the effect of lessening the drag on the Aquapod wire mesh netting compared to synthetic woven netting. However drag force is directly related to frontal area, thus the Aquapod has more overall drag than more streamlined structures. This larger frontal area, although it produces more drag, also ensures that there will be more water flowage into and through the containment. Since more water will be passing through Aquapods than other net pens, fish will have cleaner, oxygenated water. In addition to water exchange rate, another useful criterion for fish health is the distance from the fish to the source of clean water. The spherical shape of the Aquapod ensures that the greatest number of fish have access to fresh water.
Drag on a net pen array is an engineering concern that Ocean Farm Technologies is ready to assist farmers with at all stages of site development. Our engineering team can design a mooring for your specific site conditions that is safe, redundant, and economical.
Is the number of separate components and fasteners a problem?
The Aquapod has been designed to be modular, with many separate net panels, each sized to be easily handled, removable and replaceable with minimal effort whether above or below water. Think of it like a brick building: many small components forming a strong structure. Stronger than a brick wall, the Aquapod takes advantage of geodesic geometry to form an incredibly stable structure that is extremely resistant to deformation.
In addition to strength, the modularity of the Aquapod makes this net pen easy to maintain and modify. Individual panels or groups of panels can be removed and replaced while the pen is in the water and stocked with fish. The fasteners used to attach panels are available everywhere, so regular inspection and replacement, which is part of any containment management system, is easy.
How is the Aquapod deployed and installed at an ocean farm site?
OFT has successfully used two methods of deploying the Aquapod. The preferred method is to assemble the entire sphere on a pier with a crane. This is done in lifts, with little or no need to work at any substantial height off the ground, as the 'layers' are a maximum height of 8 feet. Even the A11000 Aquapod can be assembled this way, as our structural engineering is based on a dead weight loading, which greatly exceeds any conceivable current loading. A crane can swing the fully assembled Aquapod from the pier into the water, and with sufficient temporary flotation even a shallow water pier can accommodate the pod. The pod is simply towed to the mooring for installation.
If there is neither crane nor pier the 'off the beach' method of pre-assembly in shallow water and final assembly in deep water is another option. Two hemispheres are pre-assembled into a total of 20 sections (10 sections per hemisphere) which are essentially neutrally buoyant and draw about four feet of water maximum. The 10 sections in each hemisphere are laced together with rope in a specific patented arrangement. Then each hemisphere is towed to deep water, the lacing ropes are tightened, and the sections come together to form a hemisphere. All alignment is taken care of by the lacing system, and fasteners are added later.
How do your suggested moorings allow for raising and lowering the cages?
Site conditions (especially current velocity and water depth) have a significant influence on mooring arrangement, as does site layout whether permit driven or otherwise. There is no one system fits all. The Aquapod is suitable for single point, two point, or four point mooring. Grid systems have advantages, and within a grid system, the Aquapod can be attached to the grid with either four point or two point bridles - the variability of current vector and velocity would be the determining factor.
Vertical positioning in the water column is facilitated by near neutral buoyancy. In practice the simplest way to maintain a specific depth is to keep the pod slightly negatively buoyant, so that it 'hangs' lightly from the mooring bridles. Mechanical raising and lowering have specific advantages to decompression-sensitive species. Cod growers realize the advantages of this system over containments that are pneumatically controlled. For species that are not decompression-sensitive we incorporate specific air chambers for raising and lowering. All these operations can be performed from the surface with no diving.
How do you do partial and complete harvests out of the Aquapod?
In terms of product flesh quality, stress free harvesting is the most critical factor. Harvest ease is what influenced the design of the spherical Aquapod from the beginning. Harvest is accomplished with a minimum of manpower using a fixed funnel net that empties into a fish pump, into which fish are crowded by a semicircular weighted sweep net that pivots on a central axis as the pod is slowly rotated. The fish remain very calm up to the last minutes of harvest. One advantage of this design is that it is very easy to incorporate a grading panel into the sweep net so that smaller fish can escape the harvest sweep and easily get back into the ongrowing section of the pen. Our customers have also developed clever ways to harvest with dip nets and purse nets, working on the surfaced pen.
How do you clean the Aquapod mesh?
Air drying is the easiest and most economical method. With the spherical Aquapod, the entire net surface can be exposed to the sun for air drying in a weekly cycle if only 20% of the net surface area is exposed, leaving 90% of the containment volume underwater. The ability to rotate the Aquapod in practically any orientation makes air drying simple. It's a matter of systematically exposing a small percentage of the surface on a regular basis. The vinyl coated wire mesh and the HDPE struts dry very quickly - much quicker than woven netting - and there is no way that the 'roots' of vegetative growth can get established between fibers as in traditional netting. The key to maintenance is keeping hard growth such as mussels and oysters off, which is easily accomplished by anticipating spat release and timing air drying appropriately.
Periodic pressure washing is often necessary as well. Pressure washing is most effective above water because one can walk on, work on and inspect the pen when surfaced.
How resistant is the Aquapod to predators - sharks, seals, and sea lions?
We have tested the cage extensively with Caribbean reef sharks and nurse sharks, with no predation from these species. Other net pens at the same installation using Spectra (Dyneema) netting, have suffered considerable predation attempts in the same time period, and efforts to prevent shark predation on those cages have failed. We are confident, based on our current experience and knowledge of tiger shark feeding behavior and anatomy that the Aquapod net pens will be 100% effective at tiger shark prevention. Our netting material, Aquamesh® is a commercial product of Riverdale Mills in Northbridge, Massachusetts. A unique product, Aquamesh® is a steel wire mesh product that is galvanized after welding and then PVC coated. Galvanizing after welding sets Aquamesh apart from other products on the market. Its proven durability (over 10 year life cycle) in a variety of marine applications makes it an economical and practical alternative to the conventional use of synthetic-fiber netting.
The anatomy of seals and sea lions is such that they cannot extend their jaw parts as can sharks, making it essentially impossible for these predators to bite through the mesh. There are no corners, no loose netting, and no pockets for these predators to exploit.
How do you maintain the vertical position of the Aquapod, and how do you raise and lower it?
Buoyancy of the Aquapod is essentially neutral, by reason of the unique balance of solid structural materials, therefore requiring very little force to maintain its vertical position in the water column. Unlike pneumatic devices, with hollow air chambers, the buoyancy of the Aquapod does not change with depth, remaining just as neutrally buoyant at 60 meters deep as at the surface. Another advantage of this property is that there is no risk of an air leak or crushing at depth which might cause a catastrophic failure.
Due to this inherent neutral buoyancy, raising of the Aquapod can be accomplished with precision detail mechanically, i.e. using a winch and cable from a surface vessel. This completely eliminates the complex, expensive and failure-prone pneumatic buoyancy puzzle. At specific measured decompression stops, there are ways to maintain position during a pause for decompression. One way to maintain vertical position during the desired decompression stop is with a substantial surface float and a slightly negatively buoyant cage. This would be an option only if surface conditions allow a permanent buoy of this size. The other method would be with a positively buoyant Aquapod, using a pendant weight to control depth.
What are the life cycle costs?
The materials used in Aquapod net pens have very long life expectancy. The reinforced plastic frame is highly UV resistant and has a life expectancy of 40 years. The vinyl coated wire mesh has a life expectancy of 10 years, proven in decades of use in the fishing industry. Corrosion of all metal parts is controlled by the use of sacrificial zinc anodes, which are replaced as needed in a schedule determined by individual site conditions. The result is a fish containment that needs no net replacement and no net removal for cleaning or treatment for ten years.
Operating costs are equally economical. Pen cleaning, inspection, maintenance, harvest, and mortality collection are facilitated by the ease of rotating the Aquapod so that any section of the net is at the surface. Diving costs and risks are greatly reduced compared to other submersible or surface pens.
How many fish can you stock in an Aquapod?
Stocking density depends on site conditions (dissolved oxygen, water temperature and water exchange) species and market size at harvest among other factors. In general, schooling fish such as cod, pompano, moi and amberjack tolerate higher densities than non-schooling fish such as cobia and tuna. Also, smaller net pens have more frequent water exchange, so it is possible to stock smaller pens at a higher density per unit volume.
There are significant site specific issues with water exchange and net pen volume. The Aquapod is an excellent design for water exchange with a broad frontal area, open mesh that is easy to keep clean. Ocean Farm Technologies staff can work with you and your Marine Biologist to determine what stocking density to target for your fish farm.