488 NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE
also cut at the engine and boiler spaces. Eefer to the deck plan of
Caledonian Monarch and note the gaps made by the hatches in the upper
deck which, of course, are repeated in the lower deck.
The Hatch Openings not only weaken the vessel structurally but
ako afiect her seaworthiness unless every precaution is taken to restore
the lost strength by means of additional girders either permanent,
portable or both, and by brackets, hatch coamings, covers and
tarpaulins to resist the inroad of heavy seas breaking on board.
Half Beams are those that are cut to provide the hatch openings.
They are fitted to every frame, their inner ends being secured to the
lower edge of the hatch coaming by angle lug pieces, one flange of which
is riveted to the coaming and the other to the beam.
The Coamings of upper deck cargo hatches should have a minimum
height above the deck of 2 feet and be stiffened all round the upper
edge with angle bars and half round sections. The lower edge extends
a little below the bottom of the beam and is usually rounded ofl (as
shown in Figure 48) to take away the sharp edge.
The inner ends of the cut beams are supported by pillars spaced
not more than four frame spaces apart, but should this arrangement of
pillaring be departed from the coaming must then be bracketed to the
deck when it is over 15 feet long. The deck plating is doubled at the
hatch corners. Rounded corners are more graceful in appearance and
stronger than square ones, as the coaming plate is then continuous all
round the hatchway instead of being joined by an angle bar. An angle
bar connects the deck plating to the side of the coaming and ensures a
watertight fit.
Portable Hatchway Beams are fitted inside the coaming to form a
framework for the wooden hatch covers to rest upon and also to restore
some of the lost transverse strength due to cutting the beams. The
athwartship beams are spaced so that the unsupported length of hatch
cover does not exceed 4 J feet, with a slight modification in the case .of
hatchways in spaces fitted exclusively for the accommodation of pass-
engers and light goods. The portable web beams are stiffened at their
upper and lower edges with double angle bars. All hatchway fore and
afters are supported at their ends on a 3-inch ledge formed by steel
' carriers fitted to the coamings and to the ends of the portable webs.
The wooden hatch covers are solid and at least 2| inches thick; the
angles on which they rest are at least 2J inches wide.
The Cleats to take the battens and tarpaulins are spaced not more
than 2 feet apart and the end cleats are placed not more than 6 inches