Master (Yachts less than 500gt)
Stability (Master Yachts)

Duration

The course must take place over five days or 30 hours of formal instruction.

Content

The course will consist of five sections:

• Basic principles
• List and related problems
• Curves of statical stability
• Loll and related problems
• Dry docking and longitudinal stability

Assessmnt

Assessment will be by written 2.5 hour examination. The pass mark will be 60%.

Basic Principles

1.  Understands basic principles of hydrostatics and related terms

a)  Calculates the displacement of a box shaped vessel for a given draught and relative density
b)  Calculates the draught and freeboard for a box shaped vessel given the displacement and relative density

2.  Appreciates fineness of hull form and resistance to forward motion

a)  Defines block coefficient and appreciates its influence with regard to resistance to forward motion
b)  Calculates the displacement of a vessel given the length, breadth, draught, relative density and block coefficient
c)  Outlines how fluid flow causes resistance to forward motion with regards to skin friction, and wave making only.
d)  Has a basic understanding of planning
e)  Outlines the hull forms required for semi-displacement and planning craft
f)  Explains the principles of squat
g)  Explains the principles of ship to ship interaction
h)  Explains the principles of ship to shore interaction

3.  Understands the concept of statical stability

a) Draws a sketch of a vessel in stable equilibrium to show the positions of G and B when heeled to an angle up to deck edge immersion
b) Explains, with reference to the sketch in 3a, how the forces through G and B create a righting lever and righting moment and how the magnitude of GZ is influenced by      the vessel’s beam

4.  Understands the concept of initial stability

a) Defines the transverse metacentre (M) and initial metacentric height (GM)
b) States that KM is influenced by the (beam)3
c) Shows that the vessel will have a restoring moment if G is below M and an upsetting moment if G is above M
d) Appreciates the magnitude of GM with regards to safety, stiff and tender motion

5.  Solves problems involving loading, discharging and shifting weights

a)  Demonstrates the effect on the C of G when loading, discharging and transferring weights

b)  Calculates, by taking moments about the keel, the final position of KG when loading and discharging weights and obtains GM

List and Related Problems

1.  Understands list

a) Draws a diagram to show that the force lines through G & B lie in the same vertical line when at an angle of list and that the ship oscillates about this equilibrium angle
b) Draws a diagram of an upright vessel with G off the centreline to show that an angle of list can be assessed as tanθ= GG1/GM
c) States that an angle of list is influenced by the magnitude of GM
d) Calculates an angle of list using tanθ= GG1/GM.  (Data sheet giving Natural Function Of Angles  0o to 6o to be supplied.)
e) Explains how to correct list by adding, removing and transferring weights.

2.  Understands the inclining experiment

a) States the reasons for conducting an inclining experiment
b) Gives elementary explanation of the procedures involved in conducting an inclining experiment
c) Prepares a check list of precautions to be observed before and during an inclining experiment in order to ensure an accurate result

3.  Recognises the effect of slack tanks on the centre of gravity

a) Understands that a slack tank causes a reduction in GZ and explains that this can be considered as a free surface correction resulting in an increased KG and virtual loss of GM
b) States that the Virtual GM = Solid GM minus Free Surface Correction
c) States that Free Surface Correction:

d) Obtains Free Surface Moment from stability data book and calculates correction and virtual GM

Curves of Statical Stability

1.  Understands curves of statical stability

a)  Uses GM to obtain the slope of the curve at the origin of the GZ curve
b)  Sketches a GZ curve for a vessel in stable equilibrium and identifies the following information given on the curve:

i. range of positive stability
ii. maximum GZ and angle at which it occurs
iii. angle of vanishing stability
iv. approximate angle of deck edge immersion
v. dynamical stability

c)  Sketches a curve for a vessel in stable equilibrium given initial GM, maximum GZ and angle at which it occurs, range and the angle of vanishing stability
d)  Distinguishes between curves for stiff and tender vessels
e)  Explains how a change in KG (with reference to comparison between departure and arrival conditions) affects the shape and main features of the curve
f)  Explains how a change in freeboard affects the shape and main features of the GZ curve
g)  States the criteria for minimum stability identified in the code with regards to GM, maximum GZ and angle at which it occurs
h)  Defines and describes dynamical stability
i)  States that a simplified stability curve or table of maximum KG’s can be provided to ensure that the minimum stability criteria are met
j)  Uses simplified stability information in conjunction with simple loading/discharging problems including an allowance for free surface effect
k)  Explains the effect of a steady and gusting beam wind on a motor and sailing vessel and how the respective angles of heel can be assessed from the GZ curve using      a constant wind-heeling lever

Loll and Related Topics

1.  Demonstrates an understanding of loll

a)  States that when GM is negative an upsetting moment is created and, provided the negative GM is not too large, the vessel will attain stable equilibrium at an angle of loll
b) Compares the dangers that can arise to a vessel when lying at an angle of loll in still water and at sea
c) States that loll is corrected by achieving a positive GM and that this must be achieved under a controlled manner
d) States that loll can be corrected by removing weights from the high side first and adding to the low side first and explains the danger of reversing the procedures
e) Explains procedure and the response of the vessel if loll is corrected by filling a sub divided centreline tank
f) Distinguishes between list and loll

2   Recognises the danger of slack tanks with tender vessels

a) Explains the factors affecting free surface effect with reference to FSM, RD, displacement, position of tank in vessel, depth of liquid in the tank and the effect of longitudinal subdivision

Dry-docking and Longitudinal Stability

1.  Understands dry-docking, slipping and lifting

a) Explains the use of a docking plan
b) Explains the preparation of the yacht and dry dock prior to dry-docking
c) Explains the need for an acceptable trim and adequate GM with reference to the buoyancy lost at the waterline being transferred to the point of contact at the keel and that the rise in KG (loss of GM) can be considered as a weight removed from the keel
d) Explains the importance of aligning the support structure and lifting equipment with the vessel’s main strength members

2.  Understands the stability data supplied to yachts

a)  Demonstrates an awareness of the contents of the stability data supplied to yachts

3.  Understands terms used in longitudinal stability

a)  Defines forward perpendicular, after perpendicular, length between perpendiculars, and length overall

b)  Defines trim, change of trim, longitudinal centre of floatation and MCTC