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

Longitudinal deformation of the top of the coaming is due to the hogging or
sagging of the vessel. It depends on hatchway length and may be as much as 7-8 mm
at each end. Longitudinal deformation is compensated for by fitting at the ends of the
hatch cover with wide gaskets whose rubber absorbs the relative movement of the
compression bars as the sip works. Hatch end cleats must allow such movements,
which would otherwise be taken up at the cross joint with attendant risk of leakage.
Steel to steel contact is must. The purpose of this is to prevent the over compression
of the gaskets. However, it gives rise to a frictional force whose magnitude depends
on the pressure of the cover on the coaming bar and their relative movement.
Transverse deformation is caused mainly due to the vessel’s changes in draft
as cargo is worked, but also by hogging and sagging. Deformation of as much as 15-
25 mm over the width of long hatchways is possible. Relative movement between the
cover and the coaming is allowed for in a similar way to longitudinal deformation, by
providing the cover with wide gaskets, and by ensuring that the wheels on one side of
the hatch cover panels are free to move laterally as shown in fig 3.4
Figure 3.4 Hydrostatic pressure
Source: Cargo Access Equipment for Merchant Ships.
Torsional deformation is caused by the combination of non symmetrical
loading of the vessel and hydrodynamic forces when the ship heads diagonally into
waves. It can rack the midships hatchway diagonal of a large container ship by as
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