Note: This updates a previous post.
We are pleased to report the results of our project to develop engineered prototypes for new shellfish aquaculture rafts. We hope that these rafts will lead to increasing the productivity and sustainability of the shellfish industry. Older raft designs in use are mostly constructed from wood and coated Styrofoam (like many older docks). These can degrade with age and in extreme weather conditions may be at risk up resulting in losses of crops and creation of marine debris. In 2006 unusually large storms resulted in large losses of rafts and we have been working with the shellfish industry since to develop new designs. With assistance of the Aquaculture Innovation and Market Access Program we engaged Dynamic Systems Analysis Ltd. in Victoria to help develop new designs through advanced engineering methods and virtual prototyping.
Download the Project Report with plans Note contact us directly for updated plans
Download the Executive Summary and Plans
The necessity of creating better culture raft designs to effectively modernize the shellfish farming industry has been a significant priority to the BC shellfish culture industry. Recently, it has become apparent that much of the industry infrastructure is in need of redesign, upgrades and new investment.
The goal of this project was to respond to industry need and to develop a new shellfish aquaculture raft design using current state-of-the-art materials and techniques. The resulting “open” design will hopefully create high quality rafts for the BC Shellfish Farming industry and improve industry economic profitability and environmental sustainability. Having long-life raft designs that will withstand significant loads from high wind and wave action will reduce industry’s contribution of debris on beaches and subsequently save farmers time and money to replace lost and broken equipment.
The Centre for Shellfish Research conducted an open-source development process with industry, component manufacturers and experts. Two workshops were held, one at the beginning of the project to engage the industry and allow the opportunity for the exchange of ideas and needs to be incorporated into the design. The second industry workshop was held after preliminary designs were complete allowing the opportunity for feedback before final design decisions were made. In addition numerous conversations were conducted with industry members in BC and the US throughout the project.
Expert engineers (Dynamic Systems Analysis) were engaged to work with the project team to assist in developing prototype designs and to provide design recommendations to independent industry efforts. Virtual dynamic systems modeling was employed to simulate how various materials and structures would perform in a dynamic marine environment and greatly accelerated the range of materials and concepts that could be analyzed prior to physical prototyping.
Existing industry standard trimaran and catamaran rafts were modelled to determine weaknesses and safety factors and used as a guideline in new designs. A wide variety of materials were simulated to determine which would be most suitable as potential component materials in terms of both minimum strengths and cost effectiveness.
After testing more than 30 designs virtually, four final designs based on two styles (A & B) were developed for physical prototyping. Final designs use a combination of primary structural beams (steel) and secondary interstitial beams. The supporting structure of the rafts is a combination of galvanized steel 4” steel ‘T’ and ‘I’ beams, assembled with galvanized bolts in order that rafts can be bolted together onsite with simple tools. Standard steel stock comes in 40’ lengths and to maximize the use of steel, the raft dimensions were extended to 27.6’ x 27.6’ (2/3d’s) of a standard beam. Rotomolded dock floats (billets) manufactured by ACE Roto-mold were selected.
Overall, we believe we have been successful in achieving the project objectives. The prototype designs meet the project goals and criteria establish during industry discussions . Both raft styles are approximately 1m x 1m larger than existing designs (8m x 8m), with more capacity (>80 tray droppers and >12,000 lbs floatation).
In summary these designs:
May be able to be moored in a similar fashion to existing designs
- Are as simple as possible with few “custom parts” and structures that could be assembled by farmers with a minimum of tools on-site.
- Have integral structure constructed from non biodegradable materials virtually tested to be capable of withstanding normal to significant weather conditions.
- Isolate the structure of the raft from the components that physically suspend the culture stock so that failure of components suspending stock does not contribute to overall raft failure.
- Have durable components that do not degrade and/or can be maintained or repaired in situ.
- Have commercially available plastic foam filled billets as floatation that will not degrade in the marine environment if damaged.
Prototypes are now being tested and demonstrated at the Deep Bay Field Station in Baynes Sound, BC. Shop drawings of prototypes are available to industry for construction, further testing and continuing advancement.
The video below is a virtual simulation of three of our new prototypes in an extreme weather environment.
This technique has allowed us to “virtually” model and test a variety of construction materials and over 30 designs before settling on the current prototypes.
Continue below for a photoessay on the actual prototypes getting built. We are now going to test the variations of our prototypes at the Deep Bay Field Station research farm and then later release the plans to industry.
Our design is based on “off-the shelf” rotomolded dock floats, and galvanized steel ‘T’ and ‘I’ beams with the idea that they can be bolted together on site (think IKEA 🙂 ) . here we are bolting the connecting assemblies to the floats.
Key in our design is that there are structural beams (steel) and interstitial beams (we are testing 2 sizes of standard wood and plastic wood). The idea here, is that the interstitial beams provide a “weak point” and in the case of extreme weather conditions leading to failure these will break osing only a portion of the crop but not the entire raft. Most traditional rafts use structural beams to deploy product and when they start to fail, the entire structure loses integrity leading to catastrophic failure. This design also allows for a raft to repaired over its lifetime, another challenge with older rafts.
Conducting some “impromptu testing” before launch. This version of the raft has 5 structural beams and 2×4 wood interstitial beams. Further wood and steel rafts will be 2×6 beams which we are happier with.
The very first raft getting launched with little ceremony. It was handy having all the machinery on site to help with this task. The raft goes together fast enough that they could be built at low tide and floated on a rising tide.
Site crew enjoyed watching Brian being set adrift to float out in the bay until the Chetlo could be brought around to tow the raft to the farm.
Details of the plastic wood version. We really like the look of the structural plastic 2×4’s and how they fit snugly within the I-beams. These will add greatly to the lifetime of the raft materials but also add to cost which we have been trying to minimize during design.
Our second launch, high enough to get an underside view, bouncing the rafts up and down and tugging between the machines as they were carried to the shore gave us an opportunity to do some fairly serious and unplanned structural testing. The rafts showed a high degree of flexibility which we liked and looked great.
Version 2 floating and tied off to the Chetlo after a very windy drift down the bay – note the shovel as paddle…. We are hoping that this version will have less “visual profile” on the water as well and contribute to social sustainability.
We will be testing the designs in real world situations, making modifications to the plans, getting industry feedback, developing business case and then releasing the final plans under open license to industry. Contact us if you would like to see the rafts on our farm.