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

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.

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.

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

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

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

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.

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.

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.

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

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.

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.

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.

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

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

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

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

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.

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

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.

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.

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

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

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

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

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.

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

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.)

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.)