Page 26 - Ship Construction.DJ Eyres 6Ed

Ch03-H8070.fm Page 15 Wednesday, October 18, 2006 6:52 AM

3
Development of Ship Types

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A breakdown into broad working groups of the various craft which the
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
shipbuilder might be concerned with are shown in Figure 3.1. This covers a
wide range and reflects the adaptability of the shipbuilding industry. It is
obviously not possible to cover the construction of all those types in a single
volume. The development of the vessels with which the text is primarily
concerned, namely dry cargo ships (including container ships and dry bulk
carriers), tankers (oil, liquid gas and chemical) and passenger ships follows.

Dry Cargo Ships
ึ
If the development of the dry cargo ship from the time of introduction of
steam propulsion is considered the pattern of change is similar to that
shown in Figure 3.2. The first steam ships followed in most respects the design
of the sailing ship having a flush deck with the machinery openings pro-
tected only by low coamings and glass skylights. At quite an early stage it
was decided to protect the machinery openings with an enclosed bridge
structure. Erections forming a forecastle and poop were also introduced at
the forward and after respectively for protection. This resulted in what is
popularly known as the ‘three island type’. A number of designs at that time
also combined bridge and poop, and a few combined bridge and forecastle,
so that a single well was formed.
Another form of erection introduced was the raised quarter deck. Raised
quarter decks were often associated with smaller deadweight carrying
vessels, e.g. colliers. With the machinery space aft which is proportionately
large in a small vessel there is a tendency for the vessel to trim by the bow
when fully loaded. By fitting a raised quarter deck in way of the after holds
this tendency was eliminated. A raised quarter deck does not have the full
height of a tween deck, above the upper deck.
Further departures from the ‘three island type’ were brought about by
the carriage of cargo and cattle on deck, and the designs included a light
covering built over the wells for the protection of these cargoes. This
resulted in the awning or spar deck type of ship, the temporary enclosed
spaces being exempt from tonnage measurement since they were not per-
manently closed spaces. These awning or spar deck structures eventually