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Initial stability or primary stability is the resistance of a
boat A boat is a watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles A vehicle (from la, vehiculum) is a machine A machine is any physical system with ordered structural and functional properties. It m ...

boat
to small changes in the difference between the vertical forces applied on its two sides. It is determined by the angle of tilting on each side of the boat as its center of gravity (CG) moves sideways as a result of the passengers or cargo moving laterally, or as a response to an external force (e.g. wave). The wider the boat and the further its volume is distributed away from its center line (CL), the greater the initial stability. Wide mono-hull small boats such as the
jon boat A jon boat (or johnboat) is a flat-bottomed boat constructed of aluminum, fiberglass, or wood with one, two, or three bench seats. They are suitable for fishing , hunting and just cruising around. The nearly flat hull (watercraft), hull of a jon ...
have a great deal of initial stability and allow the occupants to stand upright to engage in
fishing Fishing is the activity of trying to catch fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ...

fishing
activities, and so do narrower small boats such as W-kayaks that feature a twin hull. Very narrow mono-hull boats such as
canoes A canoe is a lightweight narrow watercraft, water vessel, typically pointed at both ends and open on top, propelled by one or more seated or kneeling paddlers facing the direction of travel and using a single-bladed paddle. In British English, ...

canoes
and
kayaks A kayak is a small, narrow which is typically propelled by means of a double-bladed paddle. The word kayak originates from the word ' (). The traditional kayak has a covered deck and one or more cockpits, each seating one . The cockpit is som ...

kayaks
have little initial stability, but twin-hull W-kayaks are considerably more stable due to the fact that their buoyancy is distributed at a greater distance from their center line and therefore acts more effectively to reduce tilting. For purposes of stability, it is advantageous to keep the
centre of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force ma ...
as low as possible in small boats, so occupants are generally seated. Flatwater
rowing shells In watercraft, a racing shell (also referred to as just a ''fine boat'' (UK) or just ''shell'') is an extremely narrow, and often comparatively long, rowing boat specifically designed for Rowing (sport), racing or exercise. It is outfitted with lon ...
, which have length to
beam Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized group ...
ratios of up to 30:1 are inherently unstable and must be actively balanced by the athletes. After approximately 10 degrees of lateral tilt hull shape gains importance and
secondary stability A kayak is a small, narrow watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles used in water, including boats, ship A ship is a large watercraft that travels the world's oceans and other sufficiently d ...
becomes the dominant consideration in boat stability.


Other types of ship stability

*
Secondary stability A kayak is a small, narrow watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles used in water, including boats, ship A ship is a large watercraft that travels the world's oceans and other sufficiently d ...
* Tertiary stability: For kayak rolling, tertiary stability, or the stability of an upside-down kayak, is also important (lower tertiary stability makes rolling up easier)


See also

*
Ship stability ''Ship stability'' is an area of naval architecture and ship design that deals with how a ship behaves at sea, both in still water and in waves, whether intact or damaged. Stability calculations focus on centers of gravity, centers of buoyancy, t ...

Ship stability
* Kayak#Types of stability Classical mechanics Boats {{water-transport-stub