PLATING

449

bulb section used for beams; E is a built beam section introduced when
a wood deck is laid over the beams, or wherever an extra strong beam
is required; F is a heavy section introduced where great strength is
required, a centre keelson, for example, and in the way of engine and

D E
Fig. 36 —Wood Deck Butts.
boiler spaces; G is a semi-box beam formed by riveting a plate to two
adjacent beams, thus binding them together and merging both beams
into a single girder. See also page 597.
Planking.—Figure 36 illustrates beam sections showing also how the
ends of deck planks are butted and bolted to the beams. A hole is bored
through the plank to take a galvanised screw bolt which passes through
a hole in the flange of the beam and is screwed up by means of a nut
on the underside of the beam. The head of the bolt is sunk into the
plank with a thread of oakum round its neck, well coated with white
lead and screwed up by a nut on the underside of the beam. A "dowel"
of wood, also coated with white lead, fills up the enlarged hole over the
top of bolt and the planking is then planed off smooth.
It will be noticed that the planks fit closely at the lower edge and are
slightly apart at the top edge. This is purposely done so that the
oakum may be driven tightly into the wedge-shaped butts and seams
without being forced right through. The seams and butts of deck
planking are "payed," that is, filled with pitch or marine glue. In the
figure, A is a built beam; B is a rolled section with a plate resting on it
ao that the under side of the planking has to be scored out to fit over the