1. Boat Hull Design

2. Boat Hull Design Buoyancy & Displacement
Archimedes Principle states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object.
Buoyancy
The force that a liquid uses to support a floating or submerged object
Displacement
The weight or volume of water pushed out by an object in the water

3. Boat Hull Design Buoyancy & Displacement
Fluids exert an upwards force on objects immersed within them
Gravity exerts a downwards force on objects
If density of object is greater than fluid, it sinks

4. Boat Hull Design Stability
Stability - a stable vessel must be able to stay upright under all reasonable conditions. There are three conditions of stability: stable, unstable and neutral. The force of gravity gives unstable objects a tendency to move to a stable position.
Center of Gravity - the focus point in an object of gravitational pull. Hull center should always be low to improve stability. Ballast is usually added to a hull to lower the center of gravity.

5. Boat Hull Design Stability

6. Boat Hull Design Boat Classes
Hover Craft
Displacement
Planing
Hydroplane

7. Boat Hull Design Displacement Boats
A displacement boat is designed to glide through the water smoothly with a minimum of power Generally, these boats are very stable and ride smoothly.

8. Boat Hull Design Planing Boats
Planing boats are designed to rise up on top of the water. They can go very fast, but need more power to get up on top of the water. The heavier the boat, the more power required to get it "on plane."

9. Boat Hull Design Displacement vs. Planing Boats
The displacement boat has smooth lines and curves that gently move water out of its way, both sideways and down. Because the water moves gradually, there is less resistance against the boat.
The planing boat moves quickly and the water can't get out of its way, it resists the boat so much that the boat stays on top of the water. If the planing boat slows down, as it sometimes must do, it sinks into the water just as a displacement boat does. Since a planing boat is not designed to glide through the water, the ride can sometimes be bumpy and unstable.

10. Boat Hull Design Parts & Terms
Hull: The body of the boat not including the motor or sails or "extra stuff."
Beam: The width of the boat from the port side to the starboard side at the widest point.

11. Boat Hull Design Types of Hulls
Flat bottom boat These boats are generally less expensive to build and have a shallow draft (the part of the boat that's under the water).

12. Boat Hull Design Types of Hulls
Flat bottom boat cont..
They can get up on plane easily but unless the water is very calm they tend to give a rough ride because of the flat bottom pounding on each wave. They also tend to be less stable and require careful balancing of cargo and crew.

13. Boat Hull Design Types of Hulls
Vee bottom boat - The vee bottom tends to have a sharper entry into the water which provides for a smoother ride in rough water. They do, however, require more power to achieve the same speed.

14. Boat Hull Design Types of Hulls
Vee bottom boats cont.
This design offers a good ride in rough water as the pointed bow slices forward and the "V"-shaped bottom softens the up- and-down movement of the boat. The degree of the angle of the "V" is called "deadrise." As the "V" shape extends to the back of the boat, it usually flattens out until it all but disappears at the transom. Some "V"-bottom boats have a flat surface at the very bottom called a "pad." This pad allows a little more planing surface and at the sacrifice of a little softness in the ride, but this addition increases top speed.

15. Boat Hull Design Deadrise
The angle the bottom of the boat makes with the horizontal line across the bottom of the boat.
If the angle is less than 20 degrees, the fairly flat bottom boat will go fast in calm water.
If the angle is more than 20 degrees, this “steep deadrise” hull work best in rough waters.

16. Boat Hull Design Types of Hulls
Tunnel Hulls Tunnel boats have been designed to trap a cushion of air beneath the hull to reduce drag on the outside hulls. Many race boats are constructed with tunnel hulls and are sometimes called "hydroplanes."

17. Boat Hull Design Types of Hulls
Multi-Hull Catamarans, trimarans, pontoon boats and some house boats use a multi-hull design. The wide stance provides greater stability. Each of the hulls may carry any of the above bottom designs.

18. Boat Hull Design Types of Hulls
Keel: is the part of the boat that goes down from the bottom of the hull. It keeps the boat from slipping sideways through the water.
Centerboard: a board that goes down the center of the boat to keep it from tipping (heeling).
Full Keel: is when the keel is more a part of the hull. It is filled with ballast and keeps the boat stable .
Skeg: a straight, shallow,keel that helps keep the boat going straight.

19. Boat Hull Design Bow Shapes
Modified Clipper used on powerboats, used as a spray deflector.
Plumb very old design used on sail & power boats.
Short Overhang used on light sail boats
Long Overhand used on heavy cruiser-racer boats.
Knuckle similar to Long Overhand, but the tip is cut for weight.

20. Boat Hull Design Underwater Contours
The part of the boat where
the bottom meets the side
is called the
TURN OF THE BILGE.
The varying shapes give the hull different characteristics ranging from promoting stability to deflecting spray from the boat