Page 165 - Ship Construction.DJ Eyres 6Ed

Ch15-H8070.fm Page 154 Wednesday, October 18, 2006 6:56 AM
154 Ship Construction
1. Four days before launch a start is made on ramming up the launch
blocks, i.e. driving in the wedges (Figure 15.2) to raise ship off the build-
ing blocks. This is done by a dozen or so men using a long ramming
pole, a gang working either side of the ship.
2. Two days before the launch a start is made on removing the shores.
3. On the morning of the launch everything is removed up to the high water
mark and tumbler shores are put in aft. These are inclined shores which
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fall away as the ship starts to move.
4. Every second keel block is then removed, and the vessel is allowed to
settle.
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
5. An evently distributed number of keel blocks are then taken out so
that only about twenty keel blocks are left supporting the ship.
6. Half an hour before the launch the last remaining keel blocks are
removed.
7. The bilge blocks are then removed.
8. The full ship’s weight comes on the triggers at the time planned for the
launch.
9. Release of triggers on launch by sponsor.

If the vessel fails to start under the action of gravity, the initial movement
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may be aided by hydraulic starting rams which are provided at the head of
the cradle.

ARRESTING ARRANGEMENTS In many cases the extent of the water
into which the ship is launched is restricted. It is then necessary to provide
means of arresting the motion of the ship once it is in the water. There are a
number of methods available for doing this, one or more being employed at
most ship launches.
The commonest arrangement is to use chain drags which are generally
arranged symmetrically on either side of the ship. Each chain drag is laid
in the form of a horseshoe with its rounded portion away from the water,
so that as the ship moves down the ways the forward portion of the drag is
pulled through the remainder of the pile. This prevents any excessive
shock load in the chain which would occur if the pile of chain were to be
suddenly accelerated to the speed of the ship. The wire rope drag lines
are attached to temporary pads on the side of the ship, and supported by
rope tricing lines as they are led slightly forward and then aft along the
ship’s sides. Each drag line is then led forward and shackled to the chain
drag (see Figure 15.4). As the ship is released and moves aft the tricing
lines are broken in turn, the work done absorbing some of the ship’s
energy.
To further increase the resistance to motion of the ship wooden masks
may be fitted at the stern of the ship. The mask is made as large as possible
but located low down to present a flat surface to the water in the direction