Hull (watercraft) facts for kids

A hull is the main body of a ship or boat. It's super important because it helps the vessel float and not sink! Think of it as the shell that holds everything together and keeps the water out.

What a Hull Looks Like

Almost all boats and ships have a special shape. This shape helps them stay steady and move easily through the water.

• The front part, called the bow, is usually narrow and pointy.
• The middle part, called the midships, gets wider smoothly.
• The back part, called the stern, usually narrows down again.

Some hulls might have a keel. This is a fin-like part at the bottom. A keel can help a boat stay upright, steer better, or even help a sailboat move forward. Boats also have parts like a rudder or fins to help steer and keep them stable.

How Ships Float: Archimedes' Secret

Have you ever wondered why a giant ship floats, but a small rock sinks? It's all thanks to a smart Greek scientist named Archimedes. He figured out the science of "hydrostatics," which is about how liquids and pressure work.

Archimedes' Principle Explained

Archimedes' Principle says that water pushes up on an object that is in it. This push is called the buoyant force.

• When you put an object in water, it sinks until it pushes aside, or "displaces," an amount of water that weighs the same as the object itself.
• So, a ship doesn't really just sit on top of the water. It sinks a little bit until the water it pushes away weighs exactly the same as the ship.
• Because the ship's weight is spread out over a large area, it can displace a lot of water without sinking too deep. This is why ships and even submarines can float!

Think of it like this: your weight pulls you down, but the water's buoyant force pushes you up. These two forces work against each other. NASA even uses this idea! Astronauts train for space by working on spaceship parts underwater. This helps them feel what it's like to be weightless.

Important Hull Words

Here are some common terms used when talking about a hull:

• Bow: This is the very front part of the hull.
• Stern: This is the very back part of the hull.
• Portside: This is the left side of the boat when you are facing the bow (the front).
• Starboard: This is the right side of the boat when you are facing the bow.
• Waterline: Imagine a line around the hull where the water surface touches it when the boat is still. That's the waterline.
• Midships: This is the exact middle point of the hull along its length, at the waterline.
• Baseline: This is an imaginary line at the very bottom of the hull. It's used as a starting point to measure how tall different parts of the boat are.

Hull Measurements

"LWL & LOA"

Hulls have different measurements that describe their size and shape. These are important for how a boat will perform.

Main Measurements

These are the basic sizes of a hull:

• Length Overall (LOA): This is the total length of the boat from its very front to its very back.
• Length on the Waterline (LWL): This is the length of the boat measured only at the waterline.
• Beam (B): This is how wide the hull is at its widest point.
• Depth (D): This is the vertical distance from the top of the keel (bottom) to the underside of the main deck.
• Draft (d or T): This is how deep the hull goes into the water, measured from the bottom of the hull to the waterline.
• Freeboard (FB): This is the distance from the waterline up to the main deck. It tells you how much of the hull is above the water.

Shape-Related Measurements

These measurements are calculated based on the hull's shape and its main dimensions:

• Volume (V): This is the amount of water the hull pushes aside when it's in the water.
• Displacement (Δ): This is the weight of the water that the hull pushes aside. According to Archimedes' Principle, this weight is equal to the weight of the boat itself when it's floating!

Related pages

• ship
• submarine

Images for kids

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  Hull form lines, lengthwise and in cross-section

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  Ship above the water with the entire hull visible

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  Royal Navy World War II MTB planing at speed on calm water showing its hard chine hull with most of the forepart of the boat out of the water.

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  Principal hull measurements