EXAM 1 Flashcards
Defn: The distance from the center of buoyancy (B) to the transverse metacenter (M)
Metacentric Radius (BM)
Defn: The plane defined by the intersection of the ship’s hull with the surface of the water. The enclosed area of the hull at the waterline in square feet.
Waterplane OR Area of the Waterplane (AWP)
Formula: Metacentric radius (BM)
BM = Moment of Inertia / Volume
BM = I / V
A vessel with G below M is said to have what kind of stability?
Positive stability
How is GM found aboard a ship?
By referencing the stability booklet
Defn: A line perpendicular to the keel, passing through the intersection of the stem and the summer load line.
Forward Perpendicular (FP)
A ship with G above M is said to have what kind of stability?
Negative stability
Defn: The point at which all the vertically downward forces of weight are considered to be concentrated; The center of mass of the vessel.
Center of gravity
Defn: The weight that must be loaded to increase (or discharge to decrease) the mean draft by one inch.
Tons per Inch Immersion
Formula: Quarter Mean Draft
M/M/M = Avg Fwd + Avg Aft + (6)Avg Mid
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Defn: The intersection of a vertical line through B with a line drawn through the keel (K) and the center of gravity (G). The point to which G may rise and the vessel will still have positive stability.
Metacenter (M)
Defn: The height of the center of gravity above the keel
KG
Defn: Transverse stability of a vessel for small angles of inclination (up to 10 degrees)
Initial stability
A ship that has no righting tendency (GZ = 0) i.e. if heeled over from a wave will remain at that angle until it is acted upon by another wave from an opposite side, that vessel is said to have __________ stability.
Neutral stability
Formula: Volume (V)
V = Displ. x 35 ft-t
OR
V = Length x Breadth x Depth = L x B x D
Defn: The vertical distance between G and M. Used as a measure of initial stability, denoted as GM.
Metacentric height (GM)
Defn: The midway point between the forward perpendicular and the after perpendicular.
Midships Point
Formula: Righting Moment (RM) What are its units?
= Displacement / Righting Arm RM = w / d Foot-tons
What is the term used for a ship with a smaller GM?
‘tender’
A vessel where G and M are at the same height has what kind of stability?
Neutral stability
Formula: Area of the Waterplane (AWP)
AWP = L x B x p
OR
AWP = TPI x 420
Formula: Waterplane Coefficient (p)
p = Area of the Waterplane = AWP
Length x Breadth L x B
Formula: GG’
GG’ = w x d
final displ
Then:
KG = initial KG +/- GG’
Formula: Area of the Waterplane (AWP)
AWP = Tons Per Inch Immersion (TPI) x 420
Defn: A line perpendicular to the keel, passing through the rudder post.
After Perpendicular (AP)
Defn: The point at which all the vertically upward forces of buoyancy are considered to be concentrated; The geometric center of volume of the immersed portion of the vessel.
Center of buoyancy
Formula: Height of the Metacenter (KM)
KM = KB + BM
Defn: The condition where the fore-aft mean draft is greater than the midships draft.
Hogging
Defn: The true measure of a vessel’s stability for small angles of inclination up to 10 degrees.
Righting Moment (RM)
If a ship will heel over until it reaches the angle where KG equals KM, at which point it will stop and rest at that angle of heel it is said to have _________ stability.
Negative stability
Formula: Metacentriz Height (GM)
GM = GZ
sin ø
Formula: GZ (Righting Arm)
GZ = GM sin ø
Defn: The vertical distance of the metacenter with the keel of the vessel. Varies with Draft and with Angle of Inclination Supplied by the shipbuilder in the ship’s stability booklet
Height of the Metacenter (KM)
What is the term used for a ship with a larger GM?
‘stiff’
Formula: Center of Buoyancy (KB)
KB = Draft x .53 (Merchant ship)
KB = Draft x .50 (Barge)
Defn: The ability of a vessel to right itself after being acted upon by an outside force The tendency or ability of a ship to right itself when heeled to one or the other side.
Stability
If GZ is said to be an ‘upsetting arm’ then a vessel has what kind of stability?
Negative stability
A ship that when heeled over by external forces will attempt to right itself is said to have ________ ________.
Positive stability
Defn: The condition where the midships draft is greater than the fore-aft mean draft.
Sagging
Formula: Theory of Moments
KG = total moments
total final displ
Formula: Moment of Inertia (I)
- Barge
- Merchant ship
I = (L x B3) (Barge)
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I = L x B3 x K (Merchant ship)
Defn: The length of a horizontal line drawn from G to the line BM. Always perpendicular to BM. Found in the cross curves or statical stability curves.
Righting Arm (GZ)