This document describes software developed to optimize ship scantling values through an automated process. The software takes minimum and maximum scantling values as input, generates combinations of values, evaluates each combination's strength and cost, and identifies the best combination that meets strength requirements at the lowest material cost. It was tested on a sample 174m ship and found combinations that saved over 16 million rupees by choosing optimized scantling values. The software uses branch and bound and backtracking algorithms and could potentially be expanded to optimize designs for entire ships.

1. Development of Software for Scantling
Optimization of Ship
By
Abhishek Mondal
12NA30002
Department of Ocean Engineering & Naval Architecture
IIT Kharagpur
Under the guidance of
Prof. R. Datta

2. Contents
• Introduction
• Ship Design
• Motivation
• Objective
• Test Case
• Calculation
• Software Demonstration
• Results
• Analysis
• Software Development
• Conclusion
• Future Scope
• References

3. INTRODUCTION
• The strength & cost of a ship are always a topic of key interest
to Naval Architects and Ship Builders
• However those two factors exist in opposite poles
• Too strong & heavy ships are slow and expensive
• Weak ship hulls suffer from minor hull damage and in some
extreme cases catastrophic failure and sinking.

4. SHIP DESIGN
These issues are considered during various initial design stages
of ship design like
Preliminary Design
• Principal Dimensions ( L,B,T ) & Hull Form ( CB , CWP , CM , CP)
General Arrangement Design
• Interior of ship like bulkheads, ballast tanks, decks etc.
Structural Design
• Scantling values like plate thickness, stiffener dimensions etc.

5. MOTIVATION
• Stresses developed at the various locations of a ship can be
easily evaluated from the known values of load case.
• A large number of combinations of the scantling values can be
obtained using the empirical formulae given in the rulebooks.
• But which one is the better one of those in terms of both
strength & economy ??
• This is where the motivation to develop this software lies.

6. OBJECTIVE
• This software takes the input of minimum and maximum
scantling values.
• Eventually it generates a lot number of combinations of
scantlings and evaluate the output parameters.
• Thus the main objective of this software i.e to come up with
the best combination of scantlings by optimizing material
procurement cost that also simultaneously meet the strength
constraints can be fulfilled.

7. TEST CASE
• Ship parameters for the test case are:
• Length : 174 m (Lpp)
• Breadth : 22.9 m
• Draft : 10.45 m (LWL)
• Depth : 14.4 m
• Design Speed : 15 knots ( ~ 28 kmph)
• Displacement : 33910 tonne
• Length of Midship Region : 50 m

8. TEST CASE
• Midship section of the ship:

9. CALCULATION
• From the given load condition, it was found that the maximum
bending moment at the midship is 925581 Tonne.m
• Bending stress is given as : (M*y)/INA = M/Z
where Z is the section modulus
• Scantlings are obtained using empirical formulae from the
rulebook
• Scantlings, Bending Moment & Principal Dimension of the ship
are taken as the input to the software

10. SOFTWARE DEMONSTRATION
• Inputs of the plate thickness

11. SOFTWARE DEMONSTRATION
• Inputs for number of stiffeners

12. SOFTWARE DEMONSTRATION
• Inputs of girders and principle dimensions of the ship

13. SOFTWARE DEMONSTRATION
• Cost input & Options for Optimization

14. SOFTWARE DEMONSTRATION
• Output Window : Cost & Scantling Details

15. RESULTS
• Outer Bottom
• Inner Bottom
Distance between LWL & Outer bottom (H0) 10.45
Design pressure (MPa) 0.12317131
stiffener spacing, s (mm) 900
span of stiffeners (m) 3.6
Depth 'd' of the centre girder (mm) 1800
stress for longitudinal (MPa) 160
Thickness of outer bottom 17.3840676
Section Modulus 'Z' of the bottom longitudinal 823.092259
Distance between LWL & Inner bottom (Hi) 8.65
Design pressure (MPa) 0.10758339
Allowable stress (MPa) 160
Thickness of inner bottom 21.985
'Z' of the inner bottom longitudinals 884.832002

16. RESULTS
• Bilge
• Deck
Distance between LWL & Bilge (Hb) 8.73
Design pressure (MPa) 0.10827619
Allowable stress 120
Thickness of bilge 16.2990804
Distance between LWL & Deck height (Hd) 3.95
Design pressure (MPa) 0.021614787
Frame spacing, s [mm] 900
Thickness of deck plate (mm) 11.376
section modulus 'Z' of deck longitudinal 192.5877546
section modulus 'Z' of deck girders 150.1026894

17. RESULTS
• Side Shell
Stress, [N/mm2] 120
Height above LWL (Hsu) 2
Height below LWL (Hsl) 3.25
Design Pressure Above LWL (MPa) 0.027075
Design Pressure Below LWL (MPa) 0.06082
Spacing of stiffeners, s (mm) 900
Span of stiffeners 3.6
Thickness of the side shell 14.352
'Z' of side longitudinals 180.9273

18. ANALYSIS
• Clearly there are many combinations of scantling values are
possible for similar value of stress at deck
Scantlings Combination 1 Combination 2 Combination 3
Material Cost 522,079,809 537,880,648 531,914,648
Outer Bottom Plate thickness 0.17m 0.18m 0.18m
Inner Bottom Plate thickness 0.23m 0.24m 0.24m
keel Plate thickness 0.23m 0.23m 0.23m
Bottom Side Tank thickness 0.18m 0.19m 0.19m
Top Side Tank thickness 0.12m 0.12m 0.12m
Deck Plate thickness 0.12m 0.12m 0.12m
Side Shell Plate thickness 0.16m 0.16m 0.16m
Bilge Plate thickness 0.15m 0.16m 0.16m
Center Girder thickness 0.18m 0.19m 0.19m
Side Girder thickness 0.16m 0.16m 0.16m
Hatch Side Girder thickness 0.13m 0.14m 0.14m
Number of Outer Bottom Longitudinal 16 16 16
Number of Inner Bottom Longitudinal 10 10 8
Number of Deck Longitudinal 10 8 10
Number of Bottom Side Tank Longitudinal 10 10 10
Number of Side Shell Plate Longitudinal 10 10 10
Number of Top Side Longitudinal 10 10 10
Number of Bilge Plate Longitudinal 8 8 8

19. ANALYSIS
• The Software generates 1000 such possible combinations
which has marginally different stress and scantlings.
• But if we consider combination 1 & 2 we find that there is a
possibility of saving a huge sum of 16 million rupees by
choosing right combination of scantling values which satisfy all
the local and global strength constraints.

20. SOFTWARE DEVELOPMENT
• This software is developed on Java Platform using the Java
Swing Toolkit.
• It is based on Back Tracking & Branch and Bound Algorithms

21. SOFTWARE DEVELOPMENT
• Cost Function
• This software divides the whole of the mid-ship into
different panels and performs the cost analysis of each
panel.
• Summation of material cost of each panel gives the total
material cost of mid-ship.
• Total Cost = Cost of plates + Cost of stiffeners
= Cp*T*L*B*ρ + Cs*ρ*L*N*A*(1+Cf)

22. CONCLUSION
• The software seems to be very effective when proper set of
scantlings are required to choose from a large number of
available combinations.
• It helps in saving a lot of material procurement cost.
• In our test case a ship of 174 m length was experimented to
find the optimized scantling values of the ship. However it
works well with any type ship of any given dimension.

23. FUTURE SCOPE OF WORK
• This software module is designed for mid ship portion of the
ship. This can be extended for the entire ship to obtain a
perfect cost optimization in future.
• This software module can be upgraded to a higher level where
empirical formulae can be built in the software itself so that
there’s no need of manual scantling inputs.

24. REFERENCES
• Rules and Regulations for the Construction and Classification of High
Speed Crafts and Light Crafts, 2010- Indian Register of Shipping
• Thomos H.Cormen, Charles E.Leiserson, Ronald L.Rivest and Clifford
Stein Introduction to Algorithms. third edition, MIT Press, 2009
• Jens Clausen Jesper Larsson Träff, Implementation of parallel branch-
and-bound algorithms – experiences with the graph partitioning
problem. DIKU, Department of Computer Science, University of
Copenhagen, Universitetsparken 1, DK-2100 Copenhagen O,
Denmark
• LBR-5 Structural optimization Software Manuel

25. THANK YOU