1. Design stages and design spiral
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
NAME 217: Theoretical Ship Design
Design stages and design spiral

2. Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design process
The life of a ship may be divided into two distinct parts:
The period of Construction
The period of Operation.
The owner is most concerned with the second period but the Naval Architect is more concerned with the first.
The first period can be further divided into two stages:
Design
Build.
Naval Architects are concerned in both stages but the Designer is most involved in the first stage.

3. Design process (contd.)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design process (contd.)
The actual design process is not a single activity but for most ships consists of three or four distinct phases:
Basic Design ( Concept Design
( Feasibility Design
Contract Design Contract Design
Detailed Design Detailed Design
The three or four phases are conveniently illustrated in the Design Spiral as an iterative process working from owner's requirements to a detailed design.

4. Design Spiral: Buxton (1972)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design
Spiral:
Buxton
(1972)

5. Design Spiral: Rawson & Tupper (1994)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design
Spiral:
Rawson
& Tupper
(1994)

6. Design Spiral: Taggart (1980)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design
Spiral:
Taggart
(1980)

7. Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design spiral (contd.)
Taggart shows the process starting at the outside of the spiral, where many concept designs may exist, and converging in to the single, final, detailed design.
Rawson & Tupper and Buxton show the process starting at the centre of the spiral where very little information is known and proceeding outwards to represent the ever increasing amount of information generated by the design process.
In either representation it is clear that a series of characteristics of the ship are guessed, estimated, calculated, checked, revised etc. on a number of occasions throughout the design process in the light of the increased knowledge the designer(s) have about the ship.

8. Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design spiral (contd.)
The analogy of the Design Spiral can be extended to demonstrate the passage of time as the design progresses.
If a time axis is constructed at the centre of one of the figures perpendicular to the plane of the paper then as time passes between successive activities so the spiral is traced out on the surface of a cone.
This class deals essentially with only the basic (or preliminary) design process which is considered to be completed when the characteristics of the ship which will satisfy the requirements given by the owner have been determined.

9. Detailed Definition of Phases of Ship Design
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Detailed Definition of Phases of Ship Design
Before looking at the specific features of preliminary design, it is expedient to reexamine the fundamental requirements for every ship. Every ship designer, no matter how logical and realistic they may be, needs to get back to first principles every so often in the search to make nature serve. The following simple requirements for every ship:
i) To float on or in water
ii) To move itself or to be moved with handiness in any manner desired
iii) To transport passengers or cargo or any other useful load, from one place to another
iv) To steer and to turn in all kinds of waters
v) To be safe, strong and comfortable in waves
vi) To travel or to be towed swiftly and economically, under control at all times
vii) To remain afloat and upright when not too severely damaged.

10. Basic or Preliminary Design
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Basic or Preliminary Design
Basic or preliminary design is the process of finding the set of principal characteristics of a ship which satisfies the requirements in the ship owner's proposal document.
Several preliminary designs may be worked up, each satisfying the requirements but differing in characteristics not specifically set out in the proposal such as type of propelling machinery.
Basic design includes both Concept design and Feasibility design

11. Basic or Preliminary Design (contd.)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Basic or Preliminary Design (contd.)
Basic design includes the selection of ship dimensions, hull form, power (amount and type), preliminary arrangement of hull and machinery, and main structure. The correct selection will ensure the attainment of the owner's requirements such as deadweight, cargo capacity, speed and endurance as well as good stability (both intact and damaged), seakeeping and manoeuvrability.
In addition there must be checks of, and the opportunity to modify, cargo handling capability, crew accommodation, hotel services, freeboard and tonnage measurement. All of this must be done while remembering that the ship is but part of a transportation, industrial or service system which is expected to be profitable.

12. Basic or Preliminary Design: Concept design
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Basic or Preliminary Design: Concept design
In Concept design the aim is to explore both a basic design and systematic variations of it in order to find the effect of a small change in Length, Beam etc.
With the objective of finding the most effective or most economic solution.
Much of the background data used will be in the form of curves and formulae which allow simple methods to be used in the evaluation of the effects of variation.
A design variation which would not be economic in service or would not be profitable to build would be discarded while further variations might be applied to a design which survived this stage.

13. Basic or Preliminary Design: Feasibility design
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Basic or Preliminary Design: Feasibility design
In Feasibility design (Preliminary design for Taggart) the most successful concept design is developed further to ensure that it can be turned into a real ship.
The effect of choosing "real" engines, "real" plate thicknesses will inevitably induce minor but significant changes to layout, weights and dimensions.
The completion of this phase should provide a precise definition of a vessel that will meet the owner's requirements and hence the basis for the development of the plans and specifications necessary for the agreement of a contract.

14. Design process Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design process

15. Design process Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design process

16. Design process Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design process

17. Design process Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Design process

18. Prime parameters of ship design
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Prime parameters of ship design
There are only three prime parameters by which the first
estimate of size of a ship may be made. They are
volume
mass
linear dimension
One of these will dominate the choice of size of ship to carry the required pay load.

19. Prime parameters of ship design (contd.)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Prime parameters of ship design (contd.)
Volume-limited ships or capacity carriers are those
which when full are not down to their minimum
freeboard.
Mass-limited ship is one where there will be unused
volume when the mass required is carried.
Dimensionally-limited ships are those minimum
dimensions are determined by the dimensions
of their pay load

20. Volume-limited Frigate Cargo ship
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Volume-limited
Volumes are given over to various functions
Frigate
Cargo ship
Most destroyers and frigates devote about 20 percent of their enclosed
volume to armament and about 5 percent to tankage.
Cargo ships of some 20,000 Mtons. Deadweight would normally except to
devote at least 50 percent of their volume to cargo and 25 percent to
machinery.

21. Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Mass-limited
Whether or not volume is more dominant than mass, an early estimate
of displacement Is necessary. Typical values of the deadweight ratio or
more correctly deadmass ratio are:
Historical data may be used to give the estimates of each weight group
of various merchant ships.

22. Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Mass-limited (contd.)

23. Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Mass-limited (contd.)
Percentage of deep displacement mass given over to various functions for a frigate
Relative costs of elements of
frigate

24. Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Linear dimensions
Limitations to linear dimensions occur through such needs as
Crossing the bar over a harbor or dock entrance
Passing under a bridge
Docking in a dock of a particular length
Operating in shallow waters
Berthing at a confined quay
Movement down a canal
Unloading beneath gantry cranes

25. Linear dimensions (contd.)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Linear dimensions (contd.)
Frigate weather deck

26. Linear dimensions (contd.)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Linear dimensions (contd.)
Container stack
Container ships are similarly constrained by the linear dimensions of
their payload. The additions of standard container dimensions do give
designers of such ships choices in beam and Depth close to steps as
shown in figure imposed by their internal stowage's.

27. Computer Aided Ship Design process
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Computer Aided Ship Design process

28. Computer Aided Ship Design process (contd.)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Computer Aided Ship Design process (contd.)

29. Computer Aided Ship Design process (contd.)
Department of Naval Architecture & Marine Engineering
Bangladesh University of Engineering & Technology, Dhaka-1000
Computer Aided Ship Design process (contd.)