Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Simplified Stability Information

The purpose of this guide is to provide assistance with determination of ship stability based on the use of the "Simplified Stability Information for MV Twosuch" booklet as used in examination for Master Class 4

A worked example will be used to show the student the processes involved in determination of a safe stability condition. The student must be deemed competent in the compilation and calculation of ship stability in order to complete this course. A copy of : "Simplified Stability Information for MV Twosuch" will be required by the student available from the bookshop. An outline of the booklet structure follows on the next page.

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Simplified Stability Booklet

M.V. TWOSUCH

The booklet used for examination is an extract from a Ship's Stability Information booklet.

The booklet is broken down into 9 sections:

Items in blue type are covered in this document.

• 1. Information and General

• 2. General Data

• 3. Tank Location

• 4. Summary of Spaces

• 5. Tank Data

• 6. Calculation of KG and LCG for any condition of loading

• 7. Guidance notes for the calculation of KG and LCG for any condition of loading

• 8. Curve of limiting KG

• 9. Curve of limiting LCG

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

The purpose of the Displacement table is to determine final KG and LCG so that these values can be plotted on diagrams and from these diagrams the state of stability can be determined. Each time the vessel varies the weights on board, the stability condition will change.

The Displacement Table is completed for the state of the vessel at the time the calculation is required.

A number of conditions are provided within the stability booklet to give examples of specific conditions that may be encountered during a voyage.

These are found on pages 13 - 19 of the stability booklet. It is important to note that they are examples only.

Page 12 has a blank table ready for you to enter the actual condition or planned condition of the vessel .

TANKS

• Take Sounding

• Find VCG/LCG

Displacement Table

• Enter Data:

• Mass, KG, LCG, FSN

Calculate

• Vertical Moment

• Longitudinal Moment

Displacement Table - Concept Steps to follow

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

An example of the table is provided on page 26 and the method of calculation is shown on page 27 of the stability book. If tanks are full, data can be taken from Section 4, page 6, SUMMARY OF SPACES. If tanks are partially filled, data can be taken from Section 5, pages 7-11, TANK DATA The information required is: • the weight of liquid in the tank in tonnes • the vertical centre of gravity of the liquid in metres • the longitudinal centre of gravity of the tank in relation to

amidships in metres (" +" if forward of amidships " -" if aft of amidships) • The Free Surface Number (FSN) as taken from the TANK

DATA located at the top of the table (only required if the tank is slack or likely to become slack)

Displacement Table - Operation

TANKS

•Take Sounding

•Find Capacity,VCG&LCG

Displacement Table

•Enter Data:

•Mass, KG, LCG, FSN

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Calculate

• Vertical Moment

• Longitudinal Moment

Displacement Table - Operation

Moments are weights multiplied by a distance from a specific point. For Vertical moments of liquids within a tank, the weight (mass) of the liquid is multiplied by the distance of the vertical centre of gravity of the liquid above the keel (as found in the tank tables) As an example, Condition 2 page 12 has : ITEM MASS KG VERTICAL MOMENT Fresh Water 8.9 2.06 = (8.9 x 2.06) = 18.33 t-m The Longitudinal Moments are found in a similar way. This time we are concerned with the distance from amidships ( + if forward, - if aft) ITEM MASS LCG LONG MOMENT Fresh Water 8.9 +5.05 = (8.9 x 5.05) = + 44.95 t-m

Moments Liquid Items

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Displacement Table - Operation

In addition to liquids, there are other items that will change their weight and therefore vertical and longitudinal moments. In Condition 2 these are : • Crew and Effects • Stores • Provisions

Details on how these items vary and how specific values are applied to the Displacement Table are listed starting on page 22, Section 7 of the stability book. Other variables are : • Brine Tank • Catch • Cod End on page 22 onwards

Calculate

• Vertical Moment

• Longitudinal Moment

Non Liquid Items

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Displacement Table - Operation

The process to complete the table is: • Add all the Mass (Weights) • Add all the Vertical moments • Add all the Longitudinal moments • Add all the Free Surface Numbers (FSN) Note : the sign is important with longitudinal moments, the resultant moment will either be + or - The total vertical and longitudinal moments and FSN values are entered into the row titled Deadweight in the Displacement Table. There is a row titled Lightship with values already entered. (some values are shown in the side panel) Add the Deadweight and Lightship values to get Displacement values

ITEM Mass Vert Longt

Deadweight

Lightship 148.46 516.61 -96.00

Displacement

Total mass (weight) goes here

Add Deadweight values to the Lightship values to get the Displacement values

Total vertical moment goes here

Total longitudinal moment goes here

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Displacement Table - Operation

The final steps to determine KG and LCG: • Divide the total vertical moment by the new displacement.

The figure obtained is the KG. • Divide the total longitudinal moment by the new

displacement. The figure obtained is the LCG. • Divide the total free surface numbers (FSN) by the new

displacement. The figure obtained is added to the KG to get the KG fluid.

These calculations are explained on page 25 of the stability book. Note that if the LCG is a negative number the LCG is aft of amidships. Using the figures obtained, plot the KG fluid with the new displacement value on the Curve of Limiting KG in Section 8. Using the figures obtained, plot the LCG with the new displacement value on the Curve of Limiting LCG in Section 9.

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Curve of limiting KG

Curve of limiting LCG

Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Curve of Limiting KG

The values used in the diagram are taken from the worked example on page 27 of the TWOSUCH booklet.

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Curve of Limiting LCG

The values used in the diagram are taken from the worked example on page 27 of the TWOSUCH booklet.

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Enter with position of LCF

Enter with displacement

The intersection falls betweenthe yellow lines. The vesselhas a safe trim.

Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Vertical Longitudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port

FW Stbd

FO fwd Port

FO fwd Stbd

DB fwd Stbd

DB fwd Port

DB aft Stbd

DB aft Port

ER wings Stbd

ER wings Port

Lube Oil

Crew and Effects

Stores

Provisions

Brine Tank

Cod end Load

Catch

Winch Load

Warp load

Deadweight

Lightship

Displacement

This page including the table can be printed out and used as a blank pro-forma. Tables will be given over the next few pages with different sounding values and different stores and provision values. Determine the weights from the soundings and then the associated KG and LCG and FSN values. Determine the total Weights, Vertical moments, Longitudinal moments and FSN values.

Worked Example – Blank Sheet

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Worked Example - Calculating Moments To obtain the vertical moment of FW Port, first determine the weight of liquid in the tank from the tank tables and then multiply this weight by the KG as found from the tank tables.

Vertical Longitudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port Full 4.4 2.06 9.06

Vertical Longitudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port Full 4.4 5.05 22.2

Vertical Longitudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port Full 0.65

To obtain the longitudinal moment of FW Port, use the weight of liquid in the tank and multiply this weight by the LCG as found from the tank tables. Finally obtain the FSN and enter into the FSN column.

For explanation purposes the individual calculations have been shown on three separate lines. In practice the calculations would be done on one line

x =

x =

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Vertical Longitudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port Full

FW Stbd 1.4

FO fwd Port Full

FO fwd Stbd Full

DB fwd Stbd Full

DB fwd Port Full

DB aft Stbd 0.6

DB aft Port Full

ER wings Stbd Full

ER wings Port Full

Lube Oil Full

Crew and Effects 1.5 4 6

Stores 5 3

Provisions 10 2 7

Brine Tank Full

Cod end Load

Catch

Winch Load

Warp load

Deadweight

Lightship 148.46 516.61 -96

Displacement

Worked Example - Soundings Determine the weights from the soundings and then find the associated KG and LCG and FSN values from the tank tables Assume all tanks containing liquids will be slack at some time. Determine the total Weights, Vertical moments, Longitudinal moments and FSN values. To obtain the vertical moment multiply weight by KG. To obtain the longitudinal moment multiply weight by LCG and use the appropriate sign. + if forward of amidships - if aft of amidships

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Vertical Longtudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port F 4.4 2.06 9.06 5.05 22.22 0.65

FW Stbd 1.4 1.7 1.35 2.30 4.85 8.25 0.65

FO fwd Port F 4.5 1.78 8.01 3.45 15.53 2.2

FO fwd Stbd F 4.5 1.78 8.01 3.45 15.53 2.2

DB fwd Stbd F 6.55 1.17 7.66 1.25 8.19 4.14

DB fwd Port F 6.55 1.17 7.66 1.25 8.19 4.14

DB aft Stbd 0.6 3.8 0.97 3.69 -1.78 -6.76 4.72

DB aft Port F 6.4 1.2 7.68 -1.78 -11.39 4.72

ER wings Stbd F 6.3 2.4 15.12 -4.83 -30.43 0.44

ER wings Port F 6.3 2.4 15.12 -4.83 -30.43 0.44

Lube Oi l F 0.55 2.5 1.38 -7.9 -4.35 0.18

Crew and Effects 1.5 4 6.00 6 9.00

Stores 5 3 15.00 0 0.00

Provis ions 10 2 20.00 7 70.00

Brine Tank F 3 4.4 13.20 -5.5 -16.50

Cod end Load 0.00 0.00

Catch 0.00 0.00

Winch Load 0.00 0.00

Warp load 0.00 0.00

Deadweight 71.05 139.89 57.03 24.48

Lightship 148.46 516.61 -96.00

Displacement 219.51 656.497 -38.969

Worked Example - KG

After the table has been completed the next step is determination of KG. KG is found by dividing the Vertical Moments

by the Displacement … 𝐾𝐺 =656.5

219.5= 2.99𝑚

To account for the Free Surface Effect the total FSN is divided by the Displacement

FSE= FSN÷ 𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 … FSE= 24.5

219.5= 0.11𝑚

KGf is KG + FSE … 𝐾𝐺𝑓 = 2.99 + 0.11 = 3.10𝑚

The Curve of Limiting KG is now entered with the Displacement 219.5t on the bottom of the graph And the KGf 3.10 on the side of the graph. The intersection of these values falls below the Curve so the vessel is considered safe for KGf

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Worked Example - LCG

The next step is determination of LCG. LCG is found by dividing the Longitudinal Moments by the Displacement …

𝐿𝐶𝐺 =38.969

219.5= − 0.17𝑚

The Curve of Limiting LCG is now entered with the Displacement 219.5 t on the bottom of the graph and the LCG = - 0.17m on the side of the graph. The intersection of these values lies between the curves. The vessel is considered safe for LCG.

The vessel has complied with both KG and LCG limits. The vessel is considered safe from a stability standpoint.

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Vertical Longtudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port F 0.65

FW Stbd 0.20

FO fwd Port F

FO fwd Stbd 0.60

DB fwd Stbd MT

DB fwd Port MT

DB aft Stbd MT

DB aft Port F

ER wings Stbd 1.40

ER wings Port F

Lube Oi l HALF

Crew and Effects 1.50 4.00 6 6.00 9.00

Stores 5.00 3.00 15 0.00

Provis ions 3.00 2.00 6 7.00 21.00

Brine Tank F 3.00 4.40 13.2 -5.50 -16.50

Cod end Load 0.50 11.40 5.7 -5.50 -2.75

Catch F 24.00 2.60 62.4 0.50 12.00

Winch Load 0.00 0 0.00

Warp load 0.00 0 0.00

Deadweight

Lightship 148.46 516.61 -96.10

Displacement

Example 2

Given the information in this Displacement Table, determine the KGf and LCG of the vessel and from this information determine if the vessel is in a safe stability condition. Assume all fuel and freshwater tanks are slack. The term MT is shorthand for Empty.

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Vertical Longtudinal

Item Sounding Weight KG Moment LCG Moment FSN

FW Port F 4.40 2.06 9.064 5.05 22.22 0.65

FW Stbd 0.20 0.10 0.65 0.065 4.70 0.47 0.65

FO fwd Port F 4.50 1.78 8.01 3.45 15.53 2.2

FO fwd Stbd 0.60 0.60 0.51 0.306 3.45 2.07 2.2

DB fwd Stbd MT 0 0.00

DB fwd Port MT 0 0.00

DB aft Stbd MT 0 0.00

DB aft Port F 6.40 1.20 7.68 -1.78 -11.39 4.72

ER wings Stbd 1.40 4.50 2.29 10.305 -4.77 -21.47 0.44

ER wings Port F 6.30 2.40 15.12 -4.83 -30.43 0.44

Lube Oi l HALF 0.28 2.50 0.7 -7.90 -2.21 0.18

Crew and Effects 1.50 4.00 6 6.00 9.00

Stores 5.00 3.00 15 0.00

Provis ions 3.00 2.00 6 7.00 21.00

Brine Tank F 3.00 4.40 13.2 -5.50 -16.50

Cod end Load 0.50 11.40 5.7 -5.50 -2.75

Catch F 24.00 2.60 62.4 0.50 12.00

Winch Load 0 0.00

Warp load 0 0.00

Deadweight 64.08 159.55 -2.46 11.48

Lightship 148.46 516.61 -96.10

Displacement 212.54 676.16 -98.56 11.48

Example 2

This is the completed table From this the following KGf and LCG information is derived.

KG 3.18m FSN 0.05m KGf 3.24 LCG -0.46m

The intersection of KGf and Displacement place the value below the Limiting Curve therefore the vessel is safe from a KG standpoint. The intersection of LCG and Displacement place the value between the Limiting Curves therefore the vessel is safe from a LCG perspective.

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Basic Stability–Guide 3… Simplified Stability Booklet - M.V. TWOSUCH

Introduction Displacement Table Limiting KG Limiting LCG Examples

Congratulations

You have now completed the E-Learning course in Basic Stability.

Guide 2 covered these additional topics...

• Loadline, Fresh Water Allowance

• Dock Water Allowance

• Draft, Mean Draft, Trim

• Displacement and Block Coefficient

• Hydrostatic Tables, TPC

• Movement of G in the transverse plane

• Movement of G in the longitudinal plane

• Free Surface and Loll

Home Page

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Guide 1 covered the following topics...

• Terms and Abbreviations

• Density and Specific Gravity

• Laws of Flotation

• Centre of Gravity and shift of centre of gravity