Please enable JavaScript.
Coggle requires JavaScript to display documents.
Lecture 6 – Ship hydrostatics - Coggle Diagram
Lecture 6 – Ship hydrostatics
Hydrostatics
Hydrostatics is a branch of physics that deals with the characteristics of fluids at rest
Why do ships float?
Archimedes principle
Ship transverse stability basics
Weight (w) acts downward through the center of gravity
Buoyancy forces act upward as one force through underwater geometric center
Metacenter (M) lies at the intersection of the vector of buoyancy and the centerline for 5º - 10º heeling angle
The centers of buoyancy (B) and gravity (G) strive at all times to remain vertically aligned.
metacentric height (GM)
and should be positive for stable ships
Stable condition
The ship returns to its upright condition after
removing the external load.
KM –KG = GM (+)
GZ righting lever
Neutral condition
The ship will have angle of loll after removing
the external load.
KM –KG = 0 and GM = 0
GZ = 0
Unstable condition
The ship will continue to heel further after
removing the external load.
KM –KG = GM (-)
GZ is a capsizing lever
The inclining experiment
Weight of the empty ship must be accurate
The ship must be free to roll
Sea must be calm with no wind
No disturbance waves
The test must be conducted on both starboard and port side with consistent outcome to ensure accuracy.
Ship Geometry
Volumes, dimensions of cargo holds
Seakeeping, i.e safety in waves
Resistance, i.e. hull performance and energy efficiency
Aesthetics
Numerical integration
Integration is nowadays carried out using computers
Numerical estimations do not always represent reality
Useful for any geometry
If evenly spaced ordinates
Rectangle rule (Piecewise constant estimation of curve)
Trapezoidal rule (Piecewise linear estimation of curve)
Simpson I rule
Simpson II rule
Hydrostatic curves
A series of graphs that give values such as the center of buoyancy, displacement, moment causing unit trim, and center of flotation
Bonjean curves
They are used for the purpose of obtaining, for any given waterline the areas of the immersed portion of each transverse section throughout the ship's length
Ship transverse stability for a ship subject to external load
Stable if she returns to her upright condition
Neutral if she develops large angle of loll
Unstable if she continues to capsize