Development of New Raft Technologies for the BC Shellfish Industry

Vancouver Island University Centre for Shellfish Research (VIU SCR)

Table of contents

• Executive Summary
• 1.0 Introduction
• 1.1 Projective objectives
• 1.2 Background
• Key facts about the current designs
• 1.3 Prior work
• 1.4 Partners
• 1.5 Potential Benefits to Industry and Commercialization
• Commercialization potential
• 2.0 Methodology and objectives
• 2.1 Industry involvement
• 2.2 Engagement of experts
• 2.3 Modeling a series of prototypes using computer simulations
• Concept of simulation based design
• Simulation plan
• 2.4 Simulation process
• Step 1: Determine environmental conditions
• Step 2: Model industry standard rafts
• Step 3: Simulations of new and materials
• Step 4: refinements and production of designs
• 2.5 Project communications
• 2.6 Development of prototypes
• 3.0 Outcomes and results
• 3.1 Consultation outcomes
• Operations
• Structure
• Cost
• 3.2 Local and international design review
• 3.3 Summary of design requirements
• 3.4 Simulation results
• Existing wood trimaran raft designs
• Existing wood catamaran raft
• Findings
• 3.5 Final design and prototype development
• 3.6 Comparison of prototype styles
• 3.7 Projected Raft Costs
• 4.0 Discussion
• 4.1 What we like about the prototype designs
• Achieving goals
• Overall Comments
• Relative Cost Comparison
• 4.2 What we don’t like about the prototype design
• 4.3 Future work

Executive Summary

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 the vast majority of 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 modelling 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 Plastics were selected. A summary comparison is shown in the following table.

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.
• Have amortized capital cost per tray dropper of less than $5.00/yr estimated to be the current standard.

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.

1.0 Introduction

1.1 Projective objectives:

The necessity of creating a better raft to effectively modernize the shellfish farming industry has been a significant priority to the BC shellfish culture industry. Recently, it has become very apparent that the vast majority of industry infrastructure is in need of redesign, upgrades and new investment. Having new 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. As a result the BC Shellfish Growers Association (BCSGA) has included testing new raft designs on their working list of industry research and development priorities.

The goal of this project was to respond to the industry need and develop new shellfish aquaculture raft designs using current state-of-the-art materials and techniques. The resulting open source designs can be used to create high quality rafts for the BC shellfish farming industry which will in turn improve industry economic profitability and environmental sustainability. This occurred by bringing much needed engineering support to this issue and engaging industry in a multi-disciplinary collaborative design process. Funding from the Aquaculture Innovation and Market Access Program (AIMAP) has allowed us to design, test and build alternative rafts to the current designs being used by industry.

The specific objectives of this project included:

1. Conduct and facilitate an open-source development process with industry, component manufacturers and experts.
2. Engage expert engineers to work with industry to develop prototype designs and to provide design recommendations to independent industry efforts.
3. Maintain a project communications strategy through information on BCSGA and CSR websites, trade journal articles, industry presentations and press releases.
4. Model a series of prototypes using computer simulations.
5. Model and test in-situ various prototypes at the Deep Bay Field Station under commercial culture situations while making rafts available for demonstration purposes.
6. To develop and test up to four prototype designs for “next generation” shellfish rafts
7. Provide a report for dissemination to industry outlining manufacture detailing, design and capital costs

1.2 Background:

The current state of the art in deepwater shellfish aquaculture is to use 8 metre2 rafts constructed of lumber and either unprotected or coated /covered Styrofoam for the cultivation of shellfish such as oysters and mussels. Generally, these rafts have been built using the expertise and the materials readily available to the farmers. In the last four years with particularly severe wind storms, it has become apparent that more durable rafts are needed as many rafts have broken up and been destroyed resulting in loss of product equipment and environmental/community concerns about debris.

Key facts about the current designs

• Catamaran and Trimaran designs
• Framework and decking- wood; wood and steel
• Dimensions- 24’ x24’, using 2”x6” and 2”x8” lumber to accommodate a two foot square shellfish tray hung at two different depths
• Floats- Styrofoam blocks wrapped in tarpaulin, some use of rotomolded plastic. Flotation costs range from $400 for plain Styrofoam, to $1800 for rotomolded foam
• Useable life of approximately 5 years.
• Approx 80-88 tray stack droppers per raft.
• Design approach: “if it breaks build it bigger”.
• Estimated >1000 over “shelf life” in BC.
• Cost- Large catamaran design costs $6500 + manpower. Smaller trimaran rafts (24’x 24’) cost $1400 - $2000 + construction costs.

During a single storm in December 2006, it was estimated that as many as 100 rafts were severely damaged or lost. In years following, anecdotal reports are that losses continue. This estimate does not take into account the costs of salvage, removal and disposal of ruined equipment or the social and environmental costs of marine debris lost to the marine environment. This has resulted in significant media attention and social issues related to marine debris washing up on local beaches.

Globally shellfish farmers are developing new designs specific to their area and culture methods based on better and more durable materials. This advanced development has so far excluded much of the BC industry. Since winter storms devastated a large number of farms in December 2006, the CSR and the BCSGA have made the development of new more durable technologies a specific research priority and have engaged industry and experts in a collaborative design process that has suffered for lack of resources to develop and test prototypes and then introduce these to the industry at large.

1.3 Prior work

The CSR has worked opportunistically on responding to industry requirements for new raft designs since spring of 2007 when the CSR hosted a one day industry workshop to discuss the issue, bring experts together with industry and engage in a discussion to move the industry forward. This highly successful workshop was funded by the BC Ministry of Agriculture and Lands.

Subsequent to the workshop, the CSR with the UVIC Innovation and Development Corporation (IDC) hosted a working luncheon to discuss the issue. This first workshop included CSR staff, representative of 6 shellfish companies, an engineer from Camosun College, representatives from two commercial float companies and a business specialist from UVIC Innovation and Development Corporation (IDC). Participants in this workshop shared and identified a number of key criteria for moving forward including.

• Issues and common points of failure with current raft designs
• Design considerations for a new raft design?
• What the necessary attributes of a good raft are in terms of operational characteristics, size, flotation, stability, modularity, and service lifetime etc.?
• How much they would be willing to spend for a raft, and what cost benefits would be necessary to justify new raft designs?

1.4 Partners

This project was conducted with the BC Shellfish Growers Association (BCSGA). The shellfish industry has been engaged in preliminary discussions prior to this project and a model for industry involvement was established. Co-leadership on this project with the BCSGA ensured that industries concerns were heard and met during the process.

1.5 Potential Benefits to Industry and Commercialization

Commercialization potential

Industry estimates collaborated with site development information provided by BC Ministry of Agriculture and Lands have indicated that there are in excess of 1000 rafts in British Columbia, the majority of which are estimated to be more than five years old or more, past what would be considered a normal lifespan. Assuming that 100 rafts at a very minimum are replaced per year, the use of new generation rafts would remove approximately 22,000 cubic feet of Styrofoam from risk of loss to the marine environment per year. Construction of another 100 new rafts per year for industry growth would prevent an equivalent amount of Styrofoam from being placed into the marine environment.

Better designs will allow the industry to reduce risk of product and equipment loss due to storm damage. This may be exacerbated by climate change which may result in more severe weather events on the British Columbia coast. New more environmentally sustainable and aesthetically less intrusive designs will also contribute to the shellfish industry achieving more “social license” from coastal communities and thus adding to overall development potential.

Production from an anticipated 1000 new rafts introduced over the next five years would produce wholesale product values of between 12- 18 million dollars annually.

Secondary component fabricator/manufacturers and raft assembly firms will benefit by production of the necessary parts, integrating existing manufacturer’s floats and sell the shellfish rafts as part of their product line, either selling the entire raft or selling the individual components. Over the next five years it is anticipated that over 1000 rafts could enter service with a materials (secondary supplier) opportunity of 5 - 8 million dollars.

Open licensing is expected to promote commercialization. Prototype designs produced through this project are being made publicly available to the BC shellfish industry through the Centre for Shellfish Research and the BCSGA.

2.0 Methodology and objectives

2.1 Industry involvement

A goal of the project was to conduct and facilitate an open- source development process with industry, component manufacturers and experts. Two workshops were held in addition to the pre project workshop, 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.

2.2 Engagement of experts

Expert engineers were engaged to work with the project team to assist in developing prototype designs and to provide design recommendations to independent industry efforts.

Vancouver Island University conducted an open Request for Qualifications among engineering firms and retained Dynamic Systems Analysis of Victoria. Dynamic Systems Analysis, Ltd. (DSA) specializes in risk management in marine environments. DSA primarily focuses on the following industries: renewable energy, submersibles & subsea robotics and ocean engineering: moorings & riser design.DSA is located on the University of Victoria campus in a partnership with the UVIC technology transfer office and the Innovation and Development Corporation.

The core technology used by DSA is an advanced engineering analysis tool called ProteusDS®. This proprietary software was developed by DSA and is used to rapidly construct accurate virtual prototypes of marine assets or operations. The response of the constructed system to ocean wind, waves, and current conditions allows DSA to intelligently assess system performance and prevent catastrophic structural failure.

2.3 Modeling a series of prototypes using computer simulations

Concept of simulation based design

In terms of mechanical engineering, dynamics analysis is the study of forces and their relationship to the motion of bodies. If the nature of loading on a body is understood and a model of the body can be created, dynamic analysis will predict the motion of the body through time. An accurate understanding of the dynamics of a mechanical system is critical to ensure reliable and efficient design.

Computer simulations were utilized by Dynamic Systems Analysis (DSA) to virtually test a wide variety of prototypes developed by the project team. The conceptual theory behind this approach is that to analyze the dynamics of a system, the relationships between the system components must be defined. Traditional analytical techniques and linearized analysis can become too onerous, time consuming, and even impossible. However, the use of nonlinear numerical simulations allows the motions complex mechanical systems of any size to be predicted in a reliable and economical fashion. Examples of the elastic forces calculated and modelling during dynamic analyses are shown in the following diagram.

Simulation plan

The goal of conducting dynamic analyses on virtual prototypes is to remove design weaknesses (optimize) without having to physically construct prototypes. The internal stresses of the raft beams are a function of the dynamic internal forces of the elastic joints in the model. Once the internal stresses exceed the yield strength of the material (incorporating an appropriate safety factor), failure of the object, in this case a culture raft is anticipated.

A standard virtual model of shellfish mooring for raft simulations was developed with mooring properties and schematics based on industry norms. In order to establish internal forces of the raft during environmental forcing, a series of virtual raft models were developed with a series of rigid beam segments with elastic joints. In order to facilitate parametric studies on different materials, geometries, and raft configurations computer scripts were generated in order to quantify the stiffness and inertias of the raft components given fundamental material properties such as density, stiffness, and characteristic dimensions.

Once failure conditions of the raft have been anticipated, materials and raft geometry can be varied to address the design issues. The parametric study was constrained by the allowable materials and geometry dictated by industry feedback, which was determined by the project team staff and took into account numerous “workability” decisions. Raft materials of PVC, wood, steel, and other materials were be incorporated in the simulation model as allowed by constraints.

In summary, this procedure allowed the design team to model elastic virtual rafts, anticipate failures and try many beam shapes & materials.

The specific design process included:

1. Setting the environment (depth, sea state)
2. Establishing safety factors based on the standard industry trimaran raft
3. Simulating to benchmark beam shapes + materials
4. Repeating 3)!......

The: simulation-based design tested the following:

• Shapes: I-beam, pipe/tube, rectangular beams
• Structural materials: aluminum, steel, fiberglass, HDPE, plastic wood, wood
• Rafts styles: trimaran, catamaran, 'frame' catamaran

The following definitions are important in understanding the results of the simulations.

Yield stress- the internal pressure level a structure can sustain at the verge of failure. Yield stress is a known value for many different materials. Steel for example has a significantly higher yield stress over wood.

Safety factor- the ratio of the yield stress over the applied stress of a structure. A safety factor of 1 or lower implies the structure has failed. A design with a larger safety factor will be more tolerant to uncertainties in loading and material imperfections. Safety factors are affected by the material as well as the situation in which it is used. For our usage, a safety factor of 10 is desirable based on the American Bureau of Shipping’s Guide for Building and Classing Floating Production Installations for critical non-field repairable members on offshore structures.

Wing beam- the amount of overhang (unsupported beam length) on the outside of the floats in current designs.

Bending axes- the raft beams can flex in two ways, specified by the primary bending axis (flexing up and down) and the secondary bending axis (flexing side to side). The most important difference between these two bending axes is in their resistance to bending. The resistance to bending about the primary axis increases cubically with beam height, whereas the resistance to bending about the secondary axis increases linearly with beam height. This means that failure is occurring in the secondary bending axis, increasing the beam height will do little to improve the failure and resulting overall safety factor of the raft.

2.4 Simulation process

Step 1: Determine environmental conditions

Weather data from 2 stations in the Strait of Georgia (Stations 46131 and 46146) was used to generalize worst case scenario wind and wave action in the area. From this data it was determined that a 3m, 8 second period wave would be used in initial simulations.

Step 2: Model industry standard rafts

In order to establish a design starting point both Catamaran (2 rows of floats) and Trimaran (3 rows of floats) versions of rafts used in the shellfish industry were simulated by DSA. Existing industry standard trimaran and new wood based catamaran raft designs were modeled to determine weaknesses and safety factors to use as a guideline in new designs.

For each variant, a series of materials were examined with simulated wave propagations hitting the side of the rafts (beam waves) and at an angle of 45 degrees (Beam head waves). Predicted safety factors, the axis of failure and the safety factor of what we termed to be wing beams, the section that hangs out over the beam were calculated.

Step 3: Simulations of new and materials

Simulations and calculations of safety factors were conducted of new components tested with beam-head waves with 2m, 6 second period for rafts of different sizes and made of different materials. The results of these extensive simulations are summarized in Appendix 2.

Step 4: refinements and production of designs

Based on calculations on materials and dimensions, further refinements were made in concept. It was decided to increase the size of the raft from the industry standard of 24’x24’ which is determined by the maximum available size of dimension 2x6” lumber, to 27’x27’. This was based on maximizing recovery from standard steel stock sizes which come in 40’ lengths by using 2/3’s of a standard 40’ length. This also allows the remaining 1/3d’s to be spliced together to create 27’ lengths and maximize material recovery. Having made this assumption, various materials were then simulated to determine which would be most suitable as a frame material. During this design iteration, materials were examined to determine both minimum strengths and cost effectiveness.

2.5 Project communications

This project provided updates to industry through the BCSGA website and print newsletter Tidelines. The CSR developed a PBWiki site during which materials and news of the project was maintained. Many producers, manufacturers and interested parties have requested access to this site. Presentations have were made about the project at conferences such as the Aquaculture Association of Canada Annual meeting in Nanaimo in May 2009, the Pacific Coast Shellfish Growers Association annual meeting in Portland, Washington in September 2009 and at the 2009 and 2010 BCSGA meetings. The project received print coverage in Northern Aquaculture Magazine and the University of Victoria produced a print article on DSA and their role in the project. Additional print media arose from the announcement of funding at VIU by local Member of Parliament, Dr. James Lunney.

Video simulations of raft designs were placed on YOUTUBE at:
http://www.youtube.com/watch?v=NDcAeFNSCdU

A summary article of the project was included on the Deep Bay project blog at:
http://viudeepbay.com/2010/02/17/development-of-new-shellfish- raft-technologies/

This final report has been added to the Deep Bay project blog at:
http://viudeepbay.com/2010/10/13/new-raft-technology-project-final- report/

2.6 Development of prototypes

After narrowing down designs through virtual modelling, shop drawings were produced for two separate styles of prototype rafts. A Request For Proposals was issued for construction of raft components by the purchasing office of Vancouver Island University. A contract for prototypes was awarded to Advanced Integration Technologies Canada – Fabrication in Abbotsford (http://www.aint.com).

3.0 Outcomes and results

3.1 Consultation outcomes

Design considerations raised at workshops which guided further design included the following:

Operations

• Some farmers move their rafts around regularly, others do not. Rafts must be capable of being moored in semi- permanent or easy to release moorings
• Linkage- Rafts are generally chained together with a spacing between the rafts of 4’-20’, larger rafts having more space between them. This is not ideal.
• Modularity- Would be ideal, as it would allow growers to build a new fleet of rafts that work together over a period of years. New designs must be able to be incorporated into existing farm layouts and resemble the existing dimensions as much as possible. Note: This had a significant impact on overall design.
• Ladders and walkways must be able to be mounted on the raft for safety. Most pre-existing industry rafts have wood walkways integral on the structure of rafts, but crews must still work across exposed 2x6 beams which present issues for worker safety. Overboard ladders are typically not built into raft designs but are commercially available. This led to a discussion of whether every raft should have walkways and working platforms built into the raft or should these be separate from the raft design?

Structure

• Raft structure must be constructed out of materials that will not degrade in weather –This had significant effect on design
• Raft design must match the weather conditions. Existing designs when new, generally meet weather requirements and this was used as a baseline for design
• Loading- When fully loaded a single stack of trays can weigh up to 300 lbs in air (100 lbs in water).
• As a raft moves up and down during ocean swells, significant shock loading from the suspended trays occurs, effectively increasing the weight that must be sustained by the structure
• Floatation- A 24’ industry standard beam raft would require 12,000 lbs of floatation to support the trays of a standard mature crop.
• Floatation must be sufficient enough not to cause the break-up of the raft if floats are lost
• Redundancy- A rafting/anchoring system that will not break up as soon as one problem occurs. Note: Existing designs share structural integrity across the entire raft and when a single beam breaks the entire structure weakens often resulting in cascading failures.
• Materials- must be readily available and repairable or replaceable on site by workers

Cost

• Cost- must be cost effective. Existing rafts are “inexpensive” to build but have a relatively short operational lifespan (~5 years) although are often used for longer periods. Cost effectiveness must be determined as a component of life cycle.

3.2  Local and international design review

Local BC designs were reviewed from the original catamaran rafts constructed on Cortes Island by Redonda Seafarms and descendant modifications of this design. Trimaran wood and foam rafts designed by Odyssey Shellfish using wood and wrapped Styrofoam and a recent catamaran raft designed by Odyssey Shellfish Ltd. using a wood structure with steel connections/rotomolded plastic floats and a combination steel and wood raft design used by Taylor Shellfish in Okeover Inlet.

A comprehensive review of other international raft designs was conducted including (Maine, Puget Sound, Scotland and Spain). This included a field trip to Puget Sound to examine and discuss the pros and cons of an aluminum raft developed by Taylor Shellfish Ltd.

It was noted from the design review that most other jurisdictions where shellfish culture is more established as an industry, are trending to steel structures and molded plastic floats (Figure 7). This generally replicates the growth of the finfish industry which moved from wood cages to more weather resistant galvanized steel structures.

3.3 Summary of design requirements

As a result of the industry consultations and existing design review the following design criteria were established:

• Must approximate the existing footprint (24’ x 24’), capacity (>80 tray droppers and >12,000 lbs flotation).
• Be able to be moored in a similar fashion to existing designs
• A simple design including: as few “custom parts” as possible, structures that could be assembled by farmers with a minimum of tools on-site.
• Have integral structure constructed from a non biodegradable material (i.e. not wood) and 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.
• Separate the work platform from the overall raft design in favour of more comprehensive and modular “work- safe” structures similar to standard construction scaffolding that can be moved from raft to raft.

3.4 Simulation results

The simulation was enhanced by first conducting engineering analyses of the existing wood raft designs being used by industry including trimaran and catamaran designs using 2”x6” wood and newer designs utilizing 2”x10” lumber.

The team also tested the hypothesis of keeping existing designs but substituting wood lumber with non-degradable materials such as plastic wood.

Existing wood trimaran raft designs

It was determined from the Trimaran raft simulations that:

• Increasing wood height from 2x6 to 2x10 doubles the safety factor (3.8 to 7.9) when encountering beam waves. The failure axis continues to be the primary axis, so the design has been improved by adding beam height.
• Beam-head waves (45°) cause devastating secondary bending.
• Increasing the height from 2x6 to 2x10 does not significantly increase beam strength in secondary bending (2.5 to 3.8).
• There is little difference in safety factors between the plastic wood and hemlock.

Existing wood catamaran raft

It was determined from the Catamaran raft simulations that:

• Because of the large unsupported masses hanging off the wing beams, the wing beam safety factor is very similar to the internal safety factor for either material (plastic wood or hemlock)

Findings

• Plastic wood and hemlock have very similar safety factors in the simulations
• Plastic wood is less stiff (more pliable) than wood and simulations show significantly larger beam curvatures. Using fibreglass reinforced plastic wood is not expected to improve safety factors because any imperfections in the bonding will compromise the strength of the beams and will likely fail from fatigue (cyclical) loading
• To increase the safety factor of a trimaran raft under beam-head waves (45°), it would be necessary to increase the width, as an increase in height does not significantly affect the failure on the secondary axis where the damage is predicted to occur under simulation.
• Under the same beam sizes, the catamaran raft safety factor was significantly less than that of the trimaran. This difference is due to the larger unsupported span of the catamaran raft.

Computer simulations of the existing wood trimaran and catamaran rafts provided details on structural weaknesses and provided a reference point for relative safety factors. Because of the extreme weather conditions that were used (3m waves with 8 second period), future simulations were based on 2m, 6 second period waves, still extreme waves for the majority of the industry’s locations, but a more likely scenario.

3.5 Final design and prototype development

After testing more than 30 designs virtually, four final designs based on two styles were developed for physical prototyping and shop drawings to aid construction were produced.

Key to the final design is that there are 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. Relatively simple fabrication of the steel was required involving only the drilling of holes and welding of small tabs prior to galvanizing the assemblies (Appendix 3).

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’ (2/3’s) of a standard beam. The remaining 1/3’s were then spliced together to make new full (27.6’) beams. This resulted in an expansion of the capacity of the raft while still resulting in a raft that has approximately the same size as a standard raft.

Rotomolded dock floats (billets) manufactured by ACE Roto- Mold and sold by locally Barr Plastics were selected. Six billets (8’x3’x2’) met the requirement for flotation. These were arranged in two groups of three floats to produce a catamaran raft. As no structural advantage was observed in producing a “wing” style raft, the billets were located at the outside of the raft primary cross beams.

The “T” beams are bolted directly to the plastic billets, these then are used to support the primary steel cross members which are bolted perpendicular to the T beams. Two styles of raft were designed, one using 5 primary I beams and the other with 6 primary beams.

Tabs welded on the vertical surface of the I beams support secondary “interstitial beams” which extend between the primary beams and are nested within the I-beams strcuture. Two types of interstitial beams are being constructed for testing, standard wood lumber and plastic wood.

The design intent of the interstitial beam is that the secondary beams provide a designed "weak point". In the case of extreme weather conditions leading to failure, these will break losing only a portion of the crop but not the entire raft. As mentioned previously, most traditional rafts use structural beams to deploy product and when they start to fail, the entire structure loses integrity often leading to catastrophic failure. The new designs also allow for a raft to be repaired over its lifetime, another challenge with prior raft designs.

3.6 Comparison of prototype styles

Four shellfish raft prototypes have been constructed and deployed at the Deep Bay Field Station, 2 of each version (Raft A and B). A summary comparison has been made. This analysis includes the potential number of drop lines using just interstitial beams (min) and from the perimeter T beams as well (max). Calculated maximum float submergence for the range of anticipated loading was calculated.

3.7 Projected Raft Costs

The component costs of the rafts will be variable on the costs of steel (variable with construction industry) and oil (which affects plastic costs) over time and the number of units purchased at in any order. We also found significant differences in the price of fabrication when bids for our request for tender were received with bids for a single raft ranging from approximately $4,000 to $10,700 per raft. Based on our results we estimate that the prototype designs will cost the following to build (not including HST).

4.0 Discussion

4.1 What we like about the prototype designs

Achieving goals

Overall, we believe we have been successful in achieving the project objectives. The prototype designs meet the project goals of:

• Both raft styles are approximately 1mx1m larger than existing designs (8mx8m), with more capacity (>80 tray droppers and >12,000 lbs).
• May be able to be moored in a similar fashion to existing designs
• The design is 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 a non biodegradable materials virtually tested to be capable of withstanding normal to significant weather conditions.
• The designs 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. We expect the lifespan of this raft to be more than 3-4x the current wood based designs.
• Have commercially available plastic foam filled billets as floatation that will not degrade in the marine environment if damaged.

Overall Comments

The virtual design process proved to be highly effective to work through a range of options without having to build and test and allowed us to analyze existing designs and use them as benchmarks. This greatly informed the design process.

Overall the design meets our intent of remaining as consistent as possible with existing sizes while increasing the size slightly to maximize the use of materials. We believe that the combination of steel structural beams and “weaker” interstitial beams provides a good compromise between required structural strength (expensive) and keeping costs to a minimum (replaceable wood interstitial beams).

Any such design exercise such as this is a series of compromises. Cost as expressed by the industry consultations was repeatedly raised by the most critical factor that would prohibit industry uptake. The design process therefore resulted in the design that utilized the minimum amount of materials that would still result in the required strengths and rejected more elaborate designs or more expensive materials that would have significantly increased safety factors.

As discussed previously, the prototype designs differ from most existing designs in that we have chosen to separate the work platform from the overall raft design. This will require that separate work platforms are either affixed on a permanent or temporary basis to the rafts. We decided that the addition of walkways into the structure of the raft would significantly add to individual cost and engineering of the rafts and perhaps were not the best design solution.

During the project we noted that this design approach was consistent with the approach taken with other advanced international designs. We also noted that worker safety issues have not received much significance in prior raft designs. Like salmon pens which now have railings and other safety features, we believe that this will be an emerging issue in the advancement of the industry. Integral walkways in most cases did not meet emerging worker safety requirements and may contribute to poaching and theft, as unattended rafts may be more easily accessed.

As a result, the final design approach rejected integral walkways in favour of modular “work-safe” work platforms that can be moved from raft to raft. Future work will explore the adaptation of standard scaffolding style components used in the construction industry and their adaptation to raft work platforms that can be moved from raft to raft as required.

Relative Cost Comparison

It is difficult to do a definitive cost comparison analysis as a variety of values have been provided for existing designs and component values change dependent on volume of order, costs of commodities (steel, plastic, wood etc.) and other factors.

Costs must also be amortized over the anticipated lifespan which is both open to debate within industry and variable dependant on site factors and maintenance schedules. In order to to estimate amortized costs we have assumes life spans of 5 years for a standard 2x6 industry raft, 10 years for new 2x10 raft and 15 years for our design. Presumably each of these designs might have longer life spans and these values are conservative.

A rough calculation on the estimated capital costs for two existing and our two new raft designs is provided in the table below. This estimates that the standard design has an amortized annual cost of approximately $400/year, new wood based rafts 650/year and our new designs less than $500/year. More interesting is the comparison of cost per tray dropper per year with the CSR Raft B – having the lowest cost of $4.30 per dropper per year as compared to $5.00 for the existing traditional raft design. Although individual variables in the comparison are debateable, this comparison indicates that the new raft designs are cost effective in comparison to industry norms when amortized over their anticipated life spans.

4.2 What we don’t like about the prototype design

The following observations have been made to date during the testing process.

• Engineering specifications indicate that 2x4 standard lumber is suitable for the secondary interstitial beams. It is our opinion that 2x6 material with the ends notched to fit within the inner portion of the I beam is more suitable as it provides a significant increase in strength with little increase in cost.
• We believe that the tabs which hold the interstitial beams may be improved by having a larger connection to the wood and that bolts may be more appropriate than screws. Alternately placing short pieces of 2x4 within the I-beam between the secondary beams can be used to “lock” the secondary beams into place.
• Plastic lumber provided the strength and the durability required. However we noted that it added substantially to the cost (>$1500/raft). We also noted that the 2x4 plastic lumber is much more pliable and is prone to excessive bending (wobbling) in the secondary axis although
• To date both raft styles have performed equally well in testing. Our personal preference is for the five beam version as it only uses one length of interstitial beam and has less steel. This raft does have reduced overall ut as the tray stacks have greater separation there maybe improved flow rates to culture stock.
• We have noted that the addition of integral vessel tie-up cleats to the T-beams would assist when working with the rafts. We recommend adding this to future rafts as an option.

4.3 Future work

Our future work will be to continue testing of the rafts over long term and demonstrate these to industry. Feedback received from testing and from industry comments will be used to inform future iterations of these prototypes and the adoption of these designs into standard industry use.

As discussed previously, developing a modular “work-safe” platform that can be easily moved from raft to raft will facilitate the use of these designs. Our future work will investigate options for platforms that are guided by standard construction industry scaffolding technologies which meet worker safety standards.

Acknowledgements: This project was made possible by the Aquaculture Innovation and Market Access Program of Fisheries and Oceans Canada and we are extremely grateful for the support. The Innovation and Development Corporation at UVIC facilitated and support early portions of the work. This project was conducted with the BC Shellfish Growers Association in conjunction with ex R&D Manager Dave McCallum. We received significant input from individual BC Shellfish Growers as well as manufacturers and product suppliers, all of whom made this project a success.