What are the best practices for reducing hull resistance and drag?

1 Hydrodynamic principles

Hull resistance is the force that opposes the motion of a vessel through water, and consists of frictional, wave, form, and appendage resistance. Drag is the component of hull resistance that acts parallel to the water flow. To reduce hull resistance and drag, you need to understand how the shape, size, and surface of the hull affect the flow of water around it. Streamlining, lifting, and foiling are hydrodynamic principles that can help you optimize the hull design. Streamlining means reducing the cross-sectional area and wetted surface of the hull, as well as avoiding sharp edges and corners for minimizing turbulence and separation of water flow. Lifting involves creating a positive pressure difference between the upper and lower sides of the hull to generate a lift force that partially offsets the weight of the vessel and reduces wave resistance. Foiling uses hydrofoils or wings that lift the hull above the water surface to eliminate wave resistance and reduce frictional resistance.

2 Hull design

The hull design is a vital factor in determining the hull resistance and drag of a vessel. Depending on the type, purpose, and speed of the vessel, different hull shapes and configurations can be more or less suitable for reducing hull resistance and drag. Some of the design aspects that can influence the hydrodynamic performance are the length-to-beam ratio, displacement-to-length ratio, and bulbous bow. A higher length-to-beam ratio usually reduces wave resistance and increases speed potential, but it can also raise frictional resistance and decrease stability and maneuverability. On the other hand, a lower displacement-to-length ratio means a lighter and slimmer hull, which reduces form and frictional resistance but may also diminish payload capacity and seakeeping ability. Additionally, a bulbous bow modifies the wave pattern to reduce wave resistance at high speeds, but it can also increase frictional resistance and decrease performance at low speeds or in rough seas.

3 Hull maintenance

The hull maintenance is a significant factor that affects the hull resistance and drag of a vessel. Over time, the hull surface can become deteriorated due to corrosion, fouling, or damage, leading to increased roughness and friction. To prevent this, you need to inspect, clean, and repair the hull regularly, as well as apply protective coatings and antifouling systems. Hull cleaning, coating, and modification are all practices that can help reduce hull resistance and drag. Hull cleaning involves removing dirt, debris, or marine growth from the hull surface with mechanical, chemical, or biological methods. It can reduce frictional resistance and improve fuel efficiency and speed of the vessel; however, it may also damage the hull coating or harm the environment if not done properly. Hull coating involves applying a layer of paint or material to the hull surface in order to protect it from corrosion, fouling, or abrasion. It can reduce roughness and friction of the hull while enhancing its appearance and durability; however, it may also increase weight and cost of the vessel and require frequent reapplication or removal. Lastly, hull modification means adding or removing features or devices to the hull surface in order to improve its hydrodynamic performance. It can include installing fins, flaps, spoilers, or propeller nozzles to reduce drag or increase thrust of the vessel; however it may also alter stability, maneuverability or noise of the vessel and require additional maintenance or testing.