Vessel Stability and Construction Flashcards
6 cards from real SVOP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Vessel Stability and Construction flashcards as text
What is 'metacentric height' (GM) and why is it important?
Answer: The vertical distance between the centre of gravity (G) and the metacentre (M) — a larger GM indicates greater initial stability and a stiffer, faster-righting vessel
GM is the distance between the centre of gravity (G) and the metacentre (M), the theoretical pivot point of the vessel's buoyancy when heeled slightly. A positive GM (M above G) means the vessel is stable; a larger GM means it rights itself faster and more powerfully — but too large a GM causes violent rolling.
How does adding weight high in a vessel affect its stability?
Answer: It raises the centre of gravity (G), reducing GM and making the vessel more tender and susceptible to capsize
Adding weight high in the vessel raises G (the centre of gravity). Since GM = KM − KG, raising G increases KG, reducing GM. A reduced GM means less initial stability, more tender rolling, and reduced ability to withstand heeling forces.
What is 'angle of vanishing stability' (AVS)?
Answer: The heel angle at which the righting lever (GZ) returns to zero and the vessel will capsize rather than right itself if heeled beyond that point
The Angle of Vanishing Stability (AVS) is the heel angle beyond which the righting moment becomes zero and then negative — if heeled past this point by any cause, the vessel will capsize. A higher AVS indicates better resistance to capsize in extreme conditions.
What is 'free surface effect' and how does it affect vessel stability?
Answer: Liquid in a partially filled tank that sloshes to the heeled side, effectively raising the centre of gravity and reducing GM
Free surface effect occurs when liquid in a partially filled tank shifts to the low side when the vessel heels. This acts as if the vessel's G has risen — the GM correction (GGm) reduces effective GM, making the vessel less stable.
What is 'reserve buoyancy' and why is it important for small commercial vessels?
Answer: The watertight volume of the hull above the waterline that can provide additional buoyancy if the vessel takes on water — essential for maintaining afloat and recovering from swamping
Reserve buoyancy is the buoyant volume above the current waterline — the enclosed, watertight hull above the waterline that would resist sinking if lower compartments were flooded. High freeboard = more reserve buoyancy = greater survival margin if flooded or swamped.
What does a vessel's 'Stability Letter' or 'Stability Booklet' contain and why must it be aboard?
Answer: Official Transport Canada-approved loading and stability information specifying maximum loads, weight distribution limits, passenger capacities, and loading instructions for each service condition
A Stability Letter (for small commercial vessels) or Stability Booklet (larger vessels) is issued following a Transport Canada stability assessment and provides approved loading conditions showing that the vessel is stable and safe. Operators must follow it to ensure stability at sea.