Page 167 - Ship Construction.DJ Eyres 6Ed

Ch15-H8070.fm Page 156 Wednesday, October 18, 2006 6:56 AM
156 Ship Construction
of the motion. Masks are often constructed of horizontal pieces of wood
with spaces left between each piece to increase the resistance.
One or two shipyards are forced to provide arrangements for slewing the
vessel once it has left the ways, as the river into which the ships are launched
is very narrow in relation to the ship’s length. Chain drags, weights, or
anchors may be placed in the water to one side of the building berth for
this purpose. These are then made fast to the stern of the ship with drag
--- ใช้เพื่อการศึกษาเท่านั้น---
lines of a predetermined length. Once the vessel is clear of the ways the
slack of the lines is taken up and the stern swings so that the ship is pointing
up river.
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี

Side Launches

Side launching is often used where the width of water available is consider-
ably restricted. There are in fact some advantages to this method, for example
the absence of keel declivity, and the relatively simple cradle and short
ground ways which do not extend into the water. However it means that a
large area of waterfront is taken up by a single building berth, and the ship
is only reasonably accessible from one side during construction.
ึ
The ground ways are arranged transversely, i.e. at right angles to the line
of keel. Sliding ways also can be placed transversely with the packing above
them forming the cradle, but they are generally arranged longitudinally. In
this case where they are parallel to the keel the sliding ways are in groups
covering two or three ground ways. Packing again forms the cradle with tie
pieces between the groups of sliding ways.
One of the features of side launching is the drop where the ground ways
are not extended into the water; consequently large angles of heel occur
when the vessel strikes the water. As a result it is necessary to carry out
careful stability calculations and close any openings before side launching
a vessel. It is true of course that stability calculations are also required for
a conventional end launch.

Building Docks

Perhaps the greatest advantage of the building dock is the relative simplicity of
the task of getting the vessel waterborne (see Chapter 11). When it is con-
venient the dock may be flooded and the vessel floated out. Calculations
are needed to check the stability and loads exerted by the blocks during
flooding, the whole problem being similar to that of un-docking a vessel
which has been dry-docked for survey or other reasons.
In some shipyards conventional berths are fitted at their river end
with what is virtually a pair of dock gates. This can be of advantage when