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No. 5077
Anonymous
22nd September 2014
Monday 10:37 pm
5077
>>5076
The term you're looking for is "naval architecture".
Ships are traditionally constructed from the ground-up. First the keel is laid, which acts as the backbone of the boat. Then ribs or bulkheads are added, creating a framework which can be clad and decked.
The process of drawing out a ship's lines is done by cutting the vessel into numerous imaginary sections in three planes - vertically across the width (the body plan), vertically along the length (the sheer plan) and horizontally along the length (the waterline plan). Drawing lines the traditional way is as much art as science. Small fishing boats and ferries were often designed by sailors themselves, using traditional designs that were handed down by word-of-mouth.
Drawing lines was traditionally done by eye, based on known characteristics of various hull forms - a hull with a deep and round belly is stable but slow, long tapering lines make a boat fast but limits cargo capacity and so on. As our understanding of hydrodynamics improved, we learned more theoretically rigorous ways of designing a hull form; Computer simulation and CAD is now the norm amongst commercial and racing architects, but many designers of pleasure craft still do things with pencil and paper.
Bulkheads can be cut directly from the body plan; Lofting involves tabulations of measurements from all three plans. The main difficulty involved in lofting comes from the complexity of the mathematics required to describe space curves (curved planes in three dimensions). A diverse range of lofting techniques evolved to allow parts to be accurately drawn and cut using simpler methods; Nonetheless, a skilled loftsman may still need several weeks to loft a round hull.
Lofting a smooth hull precisely is enormously difficult, so many boats designed to be constructed by amateurs are designed with a multi-chined hull, built with hard edges and simple curves. Popular modern examples include the Mirror and Optimist dinghies and many yachts designed by Steve Roberts; Traditional examples include scows and junks.
Modern boat builders can take advantage of newer materials (plywood, fibreglass, epoxy) and modern methods (stitch-and-glue construction) to build excellent boats simply and quickly. It is now completely feasible to build a good dinghy in a few weekends, or a small ocean-going yacht in a year or two of evenings and weekends. Some very simple designs like the Puddleduck Racer can be built in less than five days and for just a couple of hundred pounds fully rigged. Architects like John Welsford specialise in designing tough, adventurous yachts that can be built by inexperienced amateurs; His Fafnir and Swaggie designs are masterful examples of economy. Traditional clinker or carvel construction is vastly more laborious and tends to produce heavier and less efficient hulls.
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