Stability

Question 1

Stable equilibrium?

Answer 1

G below M- Positive GM

Question 2

Neutral equilibrium?

Answer 2

G and M same height

Question 3

Unstable equilibrium?

Answer 3

G above M - Negative GM

Question 4

What is a stiff vessel?

Answer 4

Large GM
Larger righting lever
Difficult to incline initially
Returns to upright quickly
Uncomfortable for crew
Undue stress on vessel and cargo
Racking stress

Question 5

What is a tender vessel?

Answer 5

Small GM
Easy to incline initially
Smaller righting lever
More comfortable for crew and passengers
DANGERS OF SYNCHRONOUS ROLLING
Chance of Dangerous Gv through fuel consumption

Question 6

Stiff vs Tender vessel?

Answer 6

Stiff comes upright more aggressively while tender has a smoother roll

Question 7

Free surface effect?

Answer 7

Freedom of movement of liquid within a body i.e a tank.

Creates a free surface moment which will counteract our righting moment

Will cause a virtual rise of G and reduce GM

We can calculate free surface correction and take it away from our solid GM and it will give us actual GM

Question 8

How to reduce free surface effect?

Answer 8

FiIll or empty tanks or use long skinny tanks

Watertight integrity (Scuppers, freeing ports, fairleads, vent covers, hawse pipe covers etc)

Question 9

Preparations for drydock? (9)

Answer 9

1. Discuss docking plan with the yard
2. Remove or reduce free surface effect as much as possible
3. Stability calculations for the rise of G when the vessel takes the block to ensure enough GM
4. Consult dock authorities on draught of vessel and trim required
5. Sound all tanks to be aware of quantities
6. Make sure doors and hatches are shut
7. Lock up ship’s lavatories
8. Rig up enough fenders
9. Man mooring stations

Question 10

What is a dry dock plan?

Answer 10

Underwater profile of vessel , shows recommended positions for blocks.

Question 11

How do we prepare for bad weather?

Answer 11

Watertight integrity

Ensure doors & hatches are closed,
W/T closed,
Hawse pipe & vent covers on,
unnecessary sea valves closed

Vessel security

Scuppers & freeing ports are clear,
extra lashings and stowed correctly
reduce free surface effect
fill ballast tank if possible,
check emergency comms

Crew safety

Reduce access to deck,
rig lifelines and safety harnesses, modify watch routine,
prepare food in advance

Question 12

Storm shutters & deadlights

Answer 12

Storm shutters goes on the outside of a window and deadlight on the inside, eg over your porthole

Question 13

What is GT?

Answer 13

Internal volume of ship

Question 14

What is NT?

Answer 14

Earning capacity of the ship (spaces available for cargo, crew quarters, engine room)

Question 15

What is reserve buoyancy?

Answer 15

Volume from waterline to freeboard

Question 16

What happens to G when you add a weight?

Answer 16

G moves towards the added weight

Question 17

What is fresh water allowance?

Answer 17

The amount of decrease of draught when moving from saltwater to freshwater

Question 18

What is list?

Answer 18

Vessel tilting to one side due to uneven weight distribution

Question 19

What is angle of loll?

Answer 19

State of a ship that is unstable when upright and therefore takes on an angle of heel to either port or starboard.

Question 20

What is the metacenter?

Answer 20

Point of intersection between force line through B, and centre line at a small angle

Question 21

What brings a vessel back over?

Answer 21

Righting lever (GZ) will create a righting moment that brings vessel back over

The bigger the GM, the bigger the GZ, the bigger the righting moment

Question 22

How do I correct an angle of loll?

Answer 22

Move weight from the high-side to below where it is lolled which will create an angle of list instead