What are the different types of resistance that affects a ship's movement at sea??

Summary

This video explores the different types of resistance faced by ships while moving through water. It covers five key types: frictional resistance, pressure (form) resistance, wave resistance, added resistance in waves, and air resistance. The script highlights how vessel shape, like a bulbous bow, can reduce resistance, improving efficiency. Special mention is made of non-stick silicon-based paints that help maintain hull efficiency over time. The video concludes by emphasizing the importance of understanding these resistance factors to enhance ship performance, particularly for large and fast vessels.

Takeaways

• 😀 The power required to move a ship through water depends on propulsive efficiency and total resistance, which includes factors like displacement, shape, and speed.
• 😀 Resistance faced by a vessel is categorized into five types: frictional resistance, pressure resistance, wave resistance, added resistance in waves, and air resistance.
• 😀 Frictional resistance occurs due to the friction between the ship's hull and the water, which is affected by the roughness of the hull and increases over time.
• 😀 Pressure or form resistance happens when the ship's momentum pushes water aside at the bow, causing increased pressure, which leads to resistance.
• 😀 Wave resistance is the result of wave systems along the hull that are caused by pressure differences. A bulbous bow can reduce this resistance by neutralizing wave systems.
• 😀 The use of a bulbous bow generates a secondary wave system that counteracts the ship's own wave system, reducing wave resistance.
• 😀 Added resistance in waves occurs due to the ship's motion during rough seas, storms, or swells, which adds to the overall resistance encountered.
• 😀 Air resistance is influenced by the portion of the ship above the waterline and varies based on the draft, wind, and wave direction.
• 😀 Non-stick, silicon-based hull paints help maintain constant frictional resistance by preventing fouling and can be applied to the propeller to improve efficiency.
• 😀 The application of anti-fouling paint helps maintain speed and efficiency over the ship's lifetime, although it is an expensive system best suited for large, fast ships.

Q & A

What determines the power required to move a ship through water?

The power required to move a ship through water depends on the propulsive efficiency and the total resistance the ship faces, which is influenced by the ship's displacement (weight), shape, and speed.

What is frictional resistance and how does it occur?

Frictional resistance is caused by the friction between the water and the ship's hull. It occurs as water in the boundary layer is accelerated by the ship's speed and dragged by molecular friction. Over time, the hull roughens, increasing this resistance.

What happens to the frictional resistance as the ship ages?

As the ship ages, the roughness of its hull typically increases due to factors like paint layers, corrosion, and damage, resulting in a gradual increase in frictional resistance and a decrease in speed and efficiency.

Can the frictional resistance be kept constant over a ship's lifetime?

Yes, frictional resistance can be kept constant with the use of non-stick, silicon-based hull paints, which prevent fouling and maintain a smooth surface. This helps sustain the ship's efficiency and fuel consumption over time.

What is pressure (form) resistance and how does it occur?

Pressure or form resistance occurs when the ship pushes water aside at the bow, causing an increase in pressure at the front. Afterward, there is a drop in pressure as the water is released, contributing to the resistance.

How does a bulbous bow reduce form resistance?

A bulbous bow helps reduce form resistance by improving the ship's underwater body shape, minimizing pressure increases near the bow and smoothing out the flow of water, which reduces drag.

What is wave resistance and how is it affected by the bulbous bow?

Wave resistance is caused by wave systems along the hull created by pressure differences. A bulbous bow reduces wave resistance by generating its own wave system that interferes with and neutralizes the ship's existing wave system, reducing drag.

What is added resistance in waves and when does it occur?

Added resistance in waves occurs when the ship encounters rough seas, stormy weather, or swells. The motion of pitching, heaving, and rolling in such conditions increases the resistance faced by the vessel.

How does air resistance affect the movement of ships?

Air resistance, also known as wind resistance, is influenced by the ship's shape and draft above the waterline. It can affect the ship's movement, with varying resistance depending on the direction of the wind and the ship's vertical position in the water.

What is the purpose of non-stick hull paint, and is it cost-effective?

Non-stick hull paint is designed to prevent fouling and maintain a smooth surface, thereby reducing frictional resistance. However, it is an expensive system and is most beneficial for large, fast ships, as the investment pays off primarily with these types of vessels.