uEYDOCKING  AND  PAINTING	615
wood by cutting a small hole the size of a pinhead. The mollusc
then bores its way into the wood, develops in length to a few inches,
and lines its burrow with a shelly substance which it secretes.
The wood in time soon becomes riddled with holes and crumbles
away.
DRYDOCKING.
(Se^e also page 339.)
A Graving Dock is one with a cofferdam gate. The gate is
opened, the ship floated in, the gate is then closed, the water pumped
out, and the ship is left resting on keel blocks and steadied upright
by side shores and bilge shores.
A Floating Dock has no ends, but has a double bottom and
high side tanks. The tanks are flooded with water until the bottom
of the structure sinks below the level of the vessel's keel. The vessel
is floated in, and steadied into position, the tanks are then pumped
out, and the dock rises under the vessel and lifts her up.
A Slipway is a cradle on an inclined railway track extending
into the water. The cradle is run down the trackway under the
vessel, which she approaches bow on, rides on the cradle, and is
hauled up the slip by means of winches and wire purchases.
In Dry Dock.—Examine all underwater valves, sea cocks,
injection and ejection pipes, and particularly rudder pintles, gudgeons
and bearings for clearances and renewals. Take a note of any in-
dented plates if they are*not to be renewed, remembering that they
are indicated by letters A9 B, C9 etc., from the keel upwards and
numbered 1, 2, 3, etc., from aft forward. Propeller nut and boss
should be examined for corrosion, and zinc plates, if any, renewed.
Look for evidence of leakage at riveted joints in way of peak tanks,
and bulkheads due to panting, and encircle the rivets with a
chalk mark as they will either have to be caulked or renewed.
When any rivets have been knocked out for the purpose of
draining water ballast tanks it will obviously be necessary to make
sure that the holes have been reriveted.
When repairs and painting have been completed notify the chief
engineer when water is to be run into the dock, so that he may ensure
that all underwater openings will be closed.	k	,