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Introduction Hydrostatic Properties Calculation Process Conclusion
Preliminary Hydrostatic CalculationsNAME 338: Ship Design Project and Presentation
Zobair Ibn Awal, PhD
Bangladesh University of Engineering and Technology (BUET)Dhaka 1000, Bangladesh
May 14, 2018
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Introduction
I It is customary in the design of a ship to calculate and plot ascurves a number of hydrostatic properties of the vessel’s format a series of drafts.
I Such curves are useful in loading and stability studies duringthe design phase.
I Large scale plots of these curves for a newly built ship are thenmade for the assistance of the vessel’s operating personnel.
I Such curves are known as the vessel’s curves of form, orsynonymously, hydrostatic curves.
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Hydrostatic Curves/Curves of Form
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Some Concepts
I Calculation of hydrostatic properties of ship’s hull requireapplication of methods of integration.
I The calculation takes three forms:
1. Integration of plane areas to find quantities which are onlyarea related.
2. Integration to find volumes and related quantities.3. Integration which are accomplished for area but for which the
answer required also makes use of a volume.
I A formalized tabular method of performing and recording thecalculations make use of a displacement sheet.
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What are the Hydrostatic Properties?
1. Displacement, ∆
2. Longitudinal Center of Buoyance, LCB
3. Longitudinal Center of Flotation, LCF
4. Tons per unit immersion, TPI or TPC or TPcm
5. Waterplane area coefficient, Cwp
6. Longitudinal Metacentric Height, BML
7. Transverse Metacentric Height, BM
8. Moment to change Trim 1 cm, MCT1cm
9. Height of Center of Buoyancy, KB
10. Block Coefficient, CB
11. Midship Section Coefficient, CM
12. Prismatic Coefficient, CP
13. Wetted Surface Area, S
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What are the necessary inputs?
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What is the sequence of Calculation?
I 1. Calculate, plot Bonjean curves (see Section 6 of PNA).
I 2. Read Bonjean curves at desired drafts; integratelongitudinally to calculate, then plot at each draft:displacement, LCB; extend displacement curve to zero draft.
I 3. Read waterline half-breadths at each draft desired,calculate waterplane area, calculate, plot LCF , TPcm, Cwp;calculate IT about ships centerline, calculate IL abouttransverse axis through LCF at each draft.
I 4. Using displacement from (2) and IT and IL from (3),calculate, plot BML; calculate all at each draft.
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What is the sequence of Calculation? (Contd.)
I 5. Integrate displacement curve vertically to calculate KB at aseries of drafts; plot KB.
I 6. Calculate plot KM from KB and BM, (4) and (5), at eachdraft.
I 7. Calculate GML using assumed KG , KB from (5), BML
from (4); using ship length between draft marks, calculate,plot MCT1cm at each draft.
I 8. Using TPcm, LCF (3), and ship length between draftmarks, calculate coming plot increase in displ. for 1 cm trimby stern at each draft.
I 9. Read displacement from curve (2), calculate, plot CB ;calculate, plot CM from midship Bonjean curve; calculate, plotCP from CM and CB at each draft.
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What is the sequence of Calculation? (Contd.)
I 10. Read waterline half breadths at appropriate stations anddrafts, calculate wetted surface over main body of ship at eachdraft using differential surface area method (see Section 7).
I 11. Girth stations at ends of ship, approximate wetted surfaceof ends; calculate, plot wetted surface of complete ship byadding wetted surface of main body from (10) at each draft.
I 12. Using water-plane areas from (3), integrate vertically toget displacement and KB, check results obtained in (2) and(5).
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Examples: Bonjean Curve
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Examples: Bonjean Curve
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Examples: Bonjean Curve
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Examples: Waterplane Characteristics
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Examples: Waterplane Characteristics
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Examples: Displacement and LCB
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Examples: Displacement and LCB
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Examples: Displacement and KB
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Examples: Displacement and KB
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Examples: Summary
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Reference
Lewis, EV, 1988. Principles of naval architecture, Volume 1:Stability and Strength, Jersey: SNAME.
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Thank you!
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