Tidal and Wave Energy Device Engineering

Understanding Tidal and Wave Energy: A Maritime Perspective

The Bay of Fundy, home to the highest tides in the world, represents one of the most significant untapped renewable energy resources on the planet. With tidal ranges reaching up to 16 metres and an estimated 160 billion tonnes of water flowing in and out twice daily, the potential for tidal energy extraction in Atlantic Canada is extraordinary. For engineering firms operating in Nova Scotia and the broader Maritime region, the development of tidal and wave energy devices presents both tremendous opportunities and unique technical challenges.

Tidal and wave energy conversion represents the cutting edge of marine renewable energy technology. Unlike wind and solar power, tidal energy offers predictable, consistent generation patterns that can be forecasted years in advance. Wave energy, while more variable, provides access to the enormous kinetic energy stored in ocean swells—energy that travels thousands of kilometres across open water before reaching our shores. Together, these technologies form a critical component of Canada's transition toward sustainable energy systems.

Fundamental Engineering Principles of Tidal Energy Devices

Tidal energy devices operate on well-established hydrodynamic principles, converting the kinetic energy of moving water into electrical power. The power available from a tidal stream is proportional to the cube of the water velocity, meaning that even small increases in current speed yield substantial gains in energy output. This relationship is expressed through the equation P = ½ρAV³, where P represents power, ρ is water density (approximately 1,025 kg/m³ for seawater), A is the swept area of the turbine, and V is the current velocity.

Horizontal Axis Tidal Turbines

Horizontal axis tidal turbines (HATTs) remain the most mature technology in the tidal energy sector. These devices function similarly to underwater wind turbines, with rotor diameters typically ranging from 10 to 25 metres for utility-scale installations. Modern HATTs achieve capacity factors between 25% and 35%, significantly higher than many other renewable technologies due to the predictable nature of tidal flows.

Engineering considerations for HATTs include:

• Blade design optimization for maximum energy capture while minimising cavitation risk at tip speeds exceeding 10 m/s

• Nacelle sealing systems capable of withstanding pressures up to 5 bar at typical deployment depths of 25-50 metres

• Yaw mechanisms that allow the turbine to align with bidirectional tidal flows, or fixed designs with symmetrical blade profiles

• Foundation engineering for seabed conditions ranging from bedrock to unconsolidated sediments

• Corrosion protection systems designed for 20-25 year operational lifespans in aggressive marine environments

Vertical Axis and Cross-Flow Turbines

Vertical axis tidal turbines (VATTs) offer distinct advantages in certain deployment scenarios. These devices accept flow from any direction without requiring orientation mechanisms, making them particularly suitable for locations with complex, multi-directional current patterns. Cross-flow turbines, including Darrieus and Gorlov helical designs, typically operate at lower tip-speed ratios (2.5-4.0) compared to horizontal axis machines, reducing the risk of marine life interaction.

The engineering trade-offs with vertical axis designs include lower peak efficiency (typically 35-40% compared to 45-50% for optimised HATTs) but improved performance in turbulent flow conditions common in real-world deployment sites. For projects in the Minas Passage or other Bay of Fundy locations where current velocities can exceed 5 m/s, structural loading considerations become paramount regardless of turbine orientation.

Wave Energy Converter Technologies and Design Considerations

Wave energy converters (WECs) harvest energy from ocean surface waves through various mechanisms, each presenting unique engineering challenges. The theoretical wave energy resource along Nova Scotia's Atlantic coastline averages 30-40 kW per metre of wave front, with seasonal variations ranging from 15 kW/m in summer to over 60 kW/m during winter storm conditions.

Point Absorbers and Oscillating Bodies

Point absorber WECs utilise the relative motion between a floating buoy and a fixed or semi-submerged reference point to drive power take-off systems. These devices must be tuned to resonate with predominant wave frequencies, typically in the 0.05-0.15 Hz range for North Atlantic conditions. Engineering considerations include:

• Hydrodynamic modelling using boundary element methods and computational fluid dynamics to optimise hull geometry

• Power take-off systems including hydraulic, direct-drive linear generators, and mechanical rack-and-pinion arrangements

• Mooring system design accommodating wave orbital motions while maintaining station-keeping in currents up to 2 m/s

• Survival mode engineering for extreme wave heights exceeding 15 metres during North Atlantic storms

Oscillating Water Column Devices

Oscillating water column (OWC) devices convert wave energy through the compression and expansion of air trapped above a water column within a partially submerged chamber. As waves enter and exit the chamber, bidirectional airflow drives Wells turbines or other self-rectifying air turbines. OWC systems offer the advantage of placing all moving electrical components above the waterline, simplifying maintenance access and reducing marine growth concerns.

For shoreline or breakwater-integrated OWC installations, civil engineering integration becomes critical. Chamber dimensions must be optimised for local wave climate conditions, with typical chamber widths of 6-12 metres and water column depths of 5-10 metres below mean sea level. The resonant frequency of the water column can be adjusted through chamber geometry, allowing designers to target the peak energy period of the local wave spectrum.

Structural Engineering for Extreme Marine Environments

Marine energy devices operating in Atlantic Canadian waters must withstand some of the harshest conditions found anywhere in the world. Design standards typically require survival capability in 50-year return period conditions, which in the Bay of Fundy region translate to significant wave heights of 8-12 metres and peak current velocities exceeding 6 m/s during spring tides.

Material Selection and Corrosion Engineering

Material selection for tidal and wave energy devices requires careful consideration of strength-to-weight ratios, fatigue resistance, and corrosion performance. Common choices include:

• Duplex stainless steels (e.g., UNS S32205) offering excellent corrosion resistance with yield strengths of 450-550 MPa

• Glass-reinforced polymers for turbine blades, providing fatigue resistance and eliminating galvanic corrosion concerns

• High-strength low-alloy steels with cathodic protection systems for primary structural components

• Copper-nickel alloys (90/10 or 70/30) for seawater-exposed heat exchangers and piping systems

Cathodic protection system design must account for current densities of 100-150 mA/m² for bare steel in flowing seawater, with anode consumption rates carefully calculated to achieve the target 20-25 year design life. Combined coating and cathodic protection strategies can reduce current demand by 80-90%, significantly decreasing anode mass requirements.

Fatigue Analysis and Structural Dynamics

Fatigue loading represents the dominant structural design consideration for tidal turbines, with blade root connections and main shaft bearings experiencing millions of load cycles annually. Turbines operating in 2.5 m/s average current will complete approximately 1.5 million rotations per year at typical rotational speeds of 10-15 RPM. Combined with wave-induced loading and turbulence effects, cumulative fatigue damage must be carefully analysed using spectral methods and rainflow counting techniques.

Foundation design for seabed-mounted devices requires comprehensive geotechnical investigation. In the Bay of Fundy region, seabed conditions vary from exposed bedrock requiring drilled and grouted anchors to thick glacial till deposits suitable for gravity base or suction caisson foundations. Scour protection design must account for bed shear stresses that can exceed 50 N/m² during peak tidal flows.

Electrical Systems and Grid Integration

Connecting marine energy devices to the electrical grid presents unique engineering challenges related to power quality, subsea cable routing, and the variable nature of tidal and wave resources. Tidal energy offers the advantage of highly predictable generation patterns, allowing grid operators to forecast output months in advance with accuracy exceeding 95%.

Power Conversion and Conditioning

Modern tidal turbines typically employ permanent magnet synchronous generators with full power conversion through back-to-back voltage source converters. This configuration allows variable-speed operation to maximise energy capture while providing precise control over reactive power output and fault current contribution. Generator ratings for utility-scale tidal turbines range from 500 kW to 2 MW, with ongoing development of larger machines up to 3 MW.

Wave energy converters often require more complex power conditioning systems due to the irregular, oscillatory nature of wave forces. Power take-off systems may produce output with significant harmonic content and rapid power fluctuations. Energy storage integration—whether through hydraulic accumulators, flywheels, or battery systems—can smooth output and improve power quality to meet grid code requirements.

Subsea Cable Engineering

Subsea export cables must be designed to withstand mechanical loading from currents, waves, and potential anchor strikes while providing reliable electrical performance for the project lifetime. Cable burial to depths of 1-2 metres provides protection in sandy or muddy substrates, while rock placement or cast-iron shell protection may be required where burial is impractical.

For tidal energy installations in high-current environments, cable routing must avoid areas of active sediment transport while minimising exposure to scour. Dynamic cable sections at device connections require careful fatigue analysis, with bend stiffeners and buoyancy modules designed to limit curvature and tension within acceptable limits throughout the operational envelope.

Environmental Engineering and Regulatory Compliance

Marine energy projects in Canadian waters must satisfy rigorous environmental assessment requirements under the Impact Assessment Act and obtain authorizations under the Fisheries Act, the Species at Risk Act, and various provincial regulations. Engineering design decisions directly influence environmental performance and regulatory outcomes.

Marine Life Interaction Mitigation

Turbine blade design must consider potential interaction with marine mammals, fish, and diving seabirds. Blade tip speeds below 12 m/s generally reduce strike risk, while leading-edge geometry can be optimised to deflect rather than impact approaching organisms. Acoustic deterrent systems and real-time monitoring using sonar or optical systems may be integrated into turbine control strategies, allowing shutdown when protected species are detected within defined exclusion zones.

Electromagnetic field emissions from subsea cables can potentially affect electrosensitive species such as sharks, skates, and rays. Cable armouring with magnetic steel provides inherent shielding, while cable burial further attenuates field strength at the seabed surface. Engineering analysis should demonstrate field levels below the 25 μT threshold typically associated with behavioural responses in sensitive species.

Sediment Transport and Benthic Habitat

Large-scale tidal energy extraction has the theoretical potential to modify local hydrodynamics and sediment transport patterns. Engineering studies must include numerical modelling of far-field effects, particularly for array deployments exceeding 10-20 MW of installed capacity. In the Bay of Fundy context, maintaining the natural tidal regime is essential for preserving the intertidal mudflat ecosystems that support internationally significant shorebird populations.

Partner with Sangster Engineering Ltd. for Your Marine Energy Projects

The development of tidal and wave energy technologies represents a transformative opportunity for Atlantic Canada, leveraging our world-class marine energy resources to contribute to national climate goals while building regional industrial capacity. Successfully delivering these complex projects requires engineering expertise spanning hydrodynamics, structural analysis, electrical systems, and environmental science.

Sangster Engineering Ltd. brings decades of professional engineering experience to marine energy projects throughout Nova Scotia and the Maritime provinces. Our team understands the unique challenges of working in Atlantic Canadian waters—from the extreme tidal ranges of the Bay of Fundy to the powerful wave climate of our Atlantic coastline. We provide comprehensive engineering services including feasibility studies, detailed design, regulatory support, and construction oversight for tidal and wave energy installations of all scales.

Whether you are developing a demonstration-scale device, planning a commercial array, or seeking to supply components to the growing marine energy sector, Sangster Engineering Ltd. offers the technical expertise and local knowledge essential for project success. Contact our Amherst office today to discuss how we can support your tidal and wave energy engineering requirements and help bring sustainable marine energy to Atlantic Canada.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.