Stability

Question 1

Buoyancy

Answer 1

• Upthrust,An upward force exerted by a fluid that opposes the weight of an object.
• Center of Buoyancy & center of gravity must be close to one another for stability

Question 2

Listing

Answer 2

• The degree that a ship leans or tilts to stbd or port,with no external force acting upon it
• It is caused by the off-centerline distribution of weight aboard due to uneven loading or flooding

Question 3

Loll

(Unstable in the upright postion)

Answer 3

Caused by either free surface or excessive top weight or a
combination of both. This will cause the vessel to flop over to either side and the period of roll will be irregular.

(Different from list in that the vessel is not induced to heel to one side or the other by the distribution of weight, it is merely incapable of maintaining upright postion)

Question 4

FSE is..

Free surface effect

Answer 4

Produced by a fluid moving through a compartment like water on a tray.Even a small level of water can affect stability (by moving center of gravity) if it’s spread across a large enough area.
The momentum of the water as its sloshes from side to side can capsize the ship

Question 5

How to reduce FSE

Answer 5

• Put water overboard
• Build dwarf bulheads to break up the surface area of water
• Drain water to lower compartment

Question 6

Stability is..

Answer 6

The ability of the ship to return to the upright postion after external force is applied to it

Question 7

What is list?

Answer 7

• Caused by the addition of an off center weight ,that will cause ship to heel towards the added weight.
• It is a stable condition
  A vessel is said to be listed when it is
  inclined by forces within the vessel,
  e.g. movement of weight within the
  vessel

Question 8

Types of eductors & how they work

Answer 8

1. Fixed eductors,Fitted IMS low in ship where flooding is likely
2. Portable eductors
   Use HPSW through a venturi to create suction to remove water
   3.Salvage eductors

Question 9

What is the venturi effect?

Answer 9

Velocity increases pressure decreases
Occurs when a fluid is that is flowing through a pipe is forced through a narrow section,the narrow flow of water creates a vacuum that draws the water up.

Question 10

Ballast

Answer 10

Weight added lower down in ship,ensures center of gravity is lower increasing stability

Question 11

Free Surface Effect

Answer 11

When a ship has a partly full tank (slack tank) adversely effecting stability.
as the ship leans side to side the liquid will respond and move the ships center of mass to the side.slowing its return to vertical
the momentum becomes more & more extreme until the ship capsizes

Question 12

Effect of flooding low in ship

Answer 12

• Weight of water low in the ship will increase stability but FSE will reduce it.
• The FSE is the same whether it is high or low in the ship.

Question 13

Effect of flooding high up in ship

Answer 13

• Weight of water high in the ship and the FSE will have a combined effect of reducing stability.
• The FSE is the same whether it is high or low in the ship.

Question 14

Types of floods

Answer 14

• Slow flood-ingress of water into a compartment which can be controlled by pumping, after intial leakstopping.
• Free flood-Ingress of water in a compartment that cannot be controlled & where inital leakstopping has failed
• Free surface*