In an era where fuel efficiency, cost reduction, and environmental regulations drive shipping industry decisions, the Mewis Duct has emerged as one of the most practical solutions for improving vessel performance. This energy-saving device has proven to deliver fuel savings of 3-8%, making it an attractive investment for shipowners.
What is a Mewis Duct?
The Mewis Duct, developed by Becker Marine Systems, is a pre-swirl stator and duct system that enhances the flow of water to the propeller, reducing energy losses and improving thrust efficiency. It consists of:
A duct (ring-shaped structure) that reduces wake losses and straightens water flow.
Stator blades inside the duct that generate a pre-swirl effect, optimizing water flow before it reaches the propeller.
The duct works by increasing the efficiency of water inflow, ensuring that the propeller operates under optimal conditions, leading to fuel savings, emission reductions, and enhanced propeller performance.
Ship Types That Benefit the Most from a Mewis Duct
While the Mewis Duct is a valuable efficiency upgrade, it is not suitable for all ships. It works best on vessels with full hull forms, operating at moderate to low speeds, where hydrodynamic efficiency gains are maximized. Below is a breakdown of ship types that benefit the most:
- Bulk Carriers
Bulk carriers, particularly Capesize, Panamax, and Handymax vessels, experience significant propulsion efficiency gains due to their large, full-form hulls.
These ships often operate at speeds of 10-14 knots, making them ideal candidates for Mewis Duct installation.
The fuel savings result in a faster return on investment (ROI) for shipowners, especially for long-haul operations.
- Tankers (Crude Oil, Product, Chemical, and LNG Carriers)
VLCCs, Aframax, and Suezmax tankers benefit greatly from the Mewis Duct because of their high displacement and relatively slow speeds (10-13 knots).
LNG and LPG carriers also see efficiency gains, as they operate at relatively lower speeds with high power demands.
The duct reduces wake turbulence, improving propulsion and decreasing fuel consumption.
- Container Ships (Mid-Sized and Large Vessels)
While ultra-large container vessels (ULCVs) over 18,000 TEU may not always require a Mewis Duct due to their hull shape and speed, mid-sized container ships (2,000-12,000 TEU) can achieve 3-5% fuel savings with proper installation.
Container ships operating at eco-speeds (14-18 knots) see notable improvements in efficiency.
The Mewis Duct also reduces vibrations, contributing to better long-term operational reliability.
- General Cargo Ships and Multi-Purpose Vessels
These ships operate at low to moderate speeds, typically between 9-13 knots, making them ideal for Mewis Duct implementation.
They benefit from better propulsion efficiency, lower maintenance costs, and reduced fuel consumption.
- Other Vessel Types
Ro-Ro and Car Carriers: These ships can benefit from the Mewis Duct, particularly if they operate at speeds below 15 knots.
Heavy Lift and Project Cargo Vessels: Given their high displacement and low-speed operations, they also experience efficiency improvements.
Vessels That Do Not Benefit
High-speed vessels (e.g., ferries, cruise ships, naval ships) operating above 20 knots.
Smaller vessels with light hull forms, where the hydrodynamic benefits are minimal.
Materials Used for Mewis Duct Construction
The Mewis Duct is primarily constructed from:
High-Strength Steel: Commonly used due to its structural integrity and resistance to impact loads.
Composite Materials (FRP – Fiber Reinforced Polymer): Used in certain applications to reduce weight and prevent corrosion.
Marine-Grade Aluminum: Less common but used in cases where weight reduction is a key factor.
Protective Coatings: Special anti-corrosion coatings are applied to steel ducts for longevity in seawater.
A Comprehensive Guide to Installing a Mewis Duct in a Shipyard
The installation of a Mewis Duct is a meticulous process that requires careful planning, precision engineering, and thorough post-installation testing to ensure optimal performance. As this energy-saving device directly impacts a vessel’s propulsion efficiency, the installation must follow a structured approach that minimizes operational disruptions while maximizing performance gains.
The installation process can be broken down into three major phases: Pre-Installation (Assessment and Planning), Installation at the Shipyard, and Post-Installation (Testing & Commissioning). Each phase is essential to achieving the desired efficiency improvements and ensuring the longevity of the Mewis Duct system.
Pre-Installation (Assessment and Planning)
Before proceeding with a Mewis Duct installation, shipowners and engineers must evaluate its feasibility. This phase includes:
- Hydrodynamic Analysis: Computational Fluid Dynamics (CFD) simulations assess the vessel’s wake flow and propulsion efficiency to determine if a Mewis Duct will provide measurable benefits.
- Structural Assessment: The stern structure and propeller clearance are analyzed to confirm compatibility and identify any necessary modifications.
- Custom Fabrication: The duct is manufactured according to the ship’s specific dimensions, ensuring proper fitment and hydrodynamic optimization.
Once these steps confirm that the Mewis Duct will enhance propulsion efficiency, the vessel is scheduled for dry-docking, and installation begins.
Installation Phase at the Shipyard
Once the planning is complete and the custom-fabricated Mewis Duct is ready, the vessel enters the shipyard for installation. This phase requires highly skilled technicians and specialized equipment to ensure that the duct is correctly positioned and securely attached.
Dry-Docking the Vessel
To allow for full access to the stern and propulsion system, the vessel is dry-docked. This process involves placing the ship on a stable platform, draining the surrounding water, and securing it in place for safe working conditions. Dry-docking is essential as it provides the shipyard team with the unobstructed access necessary for precise installation work.
Stern Preparation
Before the Mewis Duct can be installed, the area surrounding the propeller must be thoroughly prepared:
- The hull surface is cleaned and treated to remove any fouling or residue that could affect adhesion.
- Alignment guides and markings are placed to ensure accurate positioning.
- In some cases, minor modifications to the stern structure are required to properly accommodate the new duct.
- Positioning and Welding
Installing the Mewis Duct is a highly precise operation. Advanced laser alignment systems are used to ensure the duct is positioned correctly relative to the propeller. This step is critical because even small deviations can impact hydrodynamic efficiency.
- Once aligned, the duct is temporarily secured using tack welding to hold it in place.
- After confirming the correct placement, full-scale welding is performed, attaching the duct permanently to the hull.
- The weld seams undergo rigorous inspections to ensure structural integrity and watertight sealing.
- Structural Reinforcement
Given the significant hydrodynamic forces acting on the Mewis Duct, additional reinforcements may be required. This involves:
- Adding brackets or stiffeners to distribute loads evenly.
- Conducting stress tests to ensure that the duct can withstand operational pressures.
- Inspecting for any potential weak points that could lead to premature wear or failure.
- Application of Protective Coatings
Once welding and reinforcement are complete, the duct is coated with:
- Anti-corrosion paint to prevent rust and degradation.
- Anti-fouling coatings to minimize marine growth, which could otherwise reduce efficiency over time.
These coatings extend the lifespan of the Mewis Duct, ensuring long-term performance with minimal maintenance.
- Propeller Optimization (If Required)
In some cases, a Mewis Duct installation may require modifications to the propeller. Adjustments such as reducing propeller pitch or fine-tuning the blade design can further enhance efficiency and reduce cavitation. Shipowners and engineers assess whether such modifications are necessary during the installation process.
Post-Installation Phase: Testing and Commissioning
Once installation is complete, the final phase involves comprehensive testing and performance verification to ensure that the Mewis Duct delivers the expected fuel savings and efficiency improvements.
Final Alignment and Inspection
Before the vessel returns to service, a detailed structural and visual inspection is conducted to confirm:
- Proper duct positioning and secure attachment.
- The integrity of weld seams and reinforcements.
- The effectiveness of protective coatings and anti-fouling layers.
- Sea Trials: Performance Evaluation
CARELL’s Expertise in Mewis Duct Installations
The Mewis Duct is a proven, cost-effective technology that significantly improves propulsion efficiency, reduces fuel consumption, and lowers emissions. Its application is particularly advantageous for bulk carriers, tankers, container ships, and general cargo vessels, where fuel efficiency and operational cost savings are paramount.
With proper installation in a qualified shipyard, shipowners can expect a return on investment in as little as one year, making it a strategic upgrade for vessels aiming to enhance performance while meeting environmental regulations.
At CARELL, we have successfully completed multiple Mewis Duct installations with full satisfaction from both shipowners and manufacturers’ representatives. Our expertise in ship retrofits, combined with state-of-the-art engineering solutions and precision installation, ensures that each project delivers maximum efficiency gains with minimal downtime.
If you are considering a Mewis Duct installation for your fleet, trust CARELL‘s extensive experience in energy-saving retrofits. Contact us today to discuss how we can help optimize your vessel’s performance and reduce operational costs with a tailor-made installation plan.
