Initial stability
Encyclopedia
Initial stability is the resistance of a boat
to a small amount of lateral tilting from its equilibrium position
. It is determined by the difference in the volume of water displaced
on each side of the boat as it tilts and is relatively independent of hull
shape for small angles of tilt.
The wider the boat, the greater the difference in water volume displaced during lateral tilting and the greater the initial stability.
Wide boats such as the jonsboat have a great deal of initial stability and allow the occupants to stand upright to engage in fishing
activities.
Very narrow boats such as canoe
s and kayak
s have little initial stability. It is essential to keep the centre of gravity as low as possible in such craft so occupants generally sit down at all times. Flatwater rowing shells, which have length to beam
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 becomes the dominant consideration in boat stability.
Boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...
to a small amount of lateral tilting from its equilibrium position
Mechanical equilibrium
A standard definition of static equilibrium is:This is a strict definition, and often the term "static equilibrium" is used in a more relaxed manner interchangeably with "mechanical equilibrium", as defined next....
. It is determined by the difference in the volume of water displaced
Displacement (fluid)
In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, as in the illustration, and from this the volume of the immersed object can be deduced .An object that sinks...
on each side of the boat as it tilts and is relatively independent of hull
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
shape for small angles of tilt.
The wider the boat, the greater the difference in water volume displaced during lateral tilting and the greater the initial stability.
Wide boats such as the jonsboat have a great deal of initial stability and allow the occupants to stand upright to engage in fishing
Fishing
Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....
activities.
Very narrow boats such as canoe
Canoe
A canoe or Canadian canoe is a small narrow boat, typically human-powered, though it may also be powered by sails or small electric or gas motors. Canoes are usually pointed at both bow and stern and are normally open on top, but can be decked over A canoe (North American English) or Canadian...
s and kayak
Kayak
A kayak is a small, relatively narrow, human-powered boat primarily designed to be manually propelled by means of a double blade paddle.The traditional kayak has a covered deck and one or more cockpits, each seating one paddler...
s have little initial stability. It is essential to keep the centre of gravity as low as possible in such craft so occupants generally sit down at all times. Flatwater rowing shells, which have length to beam
Beam (nautical)
The beam of a ship is its width at the widest point. Generally speaking, the wider the beam of a ship , the more initial stability it has, at expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position...
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 becomes the dominant consideration in boat stability.