Single pull macgregor type hatch cover.pdf - Cochin University of ...

leakage can cause cargo damage and, if over a prolonged period, damage to the
ship’s internal structure. Long-term structural decline can lead to structural
collapse and total loss.
1.2 EARLY HATCH COVERS
The upper deck hatches of early steamships, in common with those of sailing
ships, were small by present standards: four meters by two would not have been
untypical hatchway dimensions, even for ocean going vessels in the mid-19 th
century. Deck openings were bounded by vertical coamings and spanned by
wooden boards usually laid athwart ships: water tightness was maintained by
tarpaulins spread over the boards and secured by wedges and cleats at the
coamings, an arrangement which had then been in use for centuries. Web beams
were sometimes placed across the largest hatchways but it was not until 1879 that
their use became mandatory for all vessels classed with Lloyd’s Register of
Shipping having hatchways more than 12 feet long. Coamings were required to be
of iron constructions. No minimum height was specified and it was not until forty
years later that they appeared in Lloyd’s Rules. Hatch boards were made of solid
woods 63 mm thick and of such an overall size that they could be handled
manually. Since they were laid transversely across the hatchway it was necessary
to use ‘fore and afters’ to reduce their unsupported span. These were the heavy
baulks of timber placed longitudinally across the hatchway, on the top of the
transverse iron beams and supported at each end by brackets attached to the
coamings. The hatch boards, in turn, were placed across the fore and after which
were so spaced that the unsupported span of the boards did not exceed the
maximum allowed.
After the turn of the 20 th century, the practice of arranging hatch boards
longitudinally began to be adopted. There were sound reasons for this change. A
typical cargo ship hatch,7.5m(25 ft) long and 5 m(16 ft) wide, with athwart ship
hatch boards, would have been fitted with two transverse web beams and three
fore afters which, because of their overall length would each have been made up
in three pieces, one for every beam space as shown in figure 1.1. With
longitudinal hatch boards the same hatch would have required no more than four
transverse beams space 1.5 m apart each of lighter construction than the two webs
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