Developing The Design

Design development is not a smooth 'one-way' progression. As a simple example, the power required of the main propulsion system cannot be finally decided until the shape and displacement of the ship are known, but these depend upon the size and weight of that propulsion system. The development of the design must be an iterative process. Intelligent guesses, often based on a previous design, known as the type ship, are needed in the early stages to ensure the first solutions are not too wide of the mark.

The type ship is one which is carrying out most of the functions asked of the new ship and which is judged to be close to the size needed. From this base the designer can get a first approximation to the principal dimensions of the new ship. Allowance would be made for different capacities, perhaps higher speed, a smaller crew and so on. A feel for the size of the ship will be obtained from the weight or volume of cargo to be carried. The type ship will then give a guide to the ratio of the dimensions but these can be modified to give the form coefficients desired to give the desired propulsive efficiency, seakeep-ing and manoeuvring characteristics. The values of ratios such as length to beam or draught must be checked as being within the usually accepted limits. Absolute dimensions must be compared with limiting values for ports and waterways the ship is to use.


From the principal dimensions first assessments of draughts, stability, power, etc. can be made. Each of these will lead to a better picture of the design. It is an iterative process which has been likened to a spiral because each ship feature must be considered more than once and at the end of each cycle the designer should have approached the final design more closely. However, the use of the term spiral implies a steady progression which ignores the step functions that occur such as when a larger machinery set has to be fitted or an extra bulkhead added, or some significant design change is deliberately introduced to meet some new regulation. A better analogy is a network which shows the many inter-dependencies present in the design. This network would really be a combination of a large number of inter-active loops.

Not all design features will be considered during every cycle of the design process. Initial stability would be considered early on, large angle stability would follow later but damaged stability would not be dealt with until the internal layout of the design was better defined. The first estimate of power, and hence machinery required, would be likely to be changed. There would be corresponding changes in structural weight and so the design develops. Some of the initial assessments, for instance that of the longitudinal bending moment, can be made by using approximate formulae. When the design is reasonably defined more advanced computer programs can be employed.

How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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