In a previous post I indicated an improved closure method for restraining particulates within a freight container. To finally, hopefully, quantify the cargo behaviour it is necessary to consider the effects of full intermodal activity. Ships will undoubtedly present constant motions which might eventually flatten the container contents. Accepting that worst case scenario simplifies the calculation of the dunnage required to maintain effective sealing of the contents against spillage when opening the doors.

There are 2 sizes for standard containers, 20 ft & 40 ft. Imperial units are chosen by design. Containers originated in 1930’s Britain where the standard was 30 ft & pounds feet prevailed throughout the Empire. Despite the 20 & 40 ft names normal engineering MKS units apply. Respective floor areas are 14.134 & 28.621 m2 & payloads are 28.32 & 26.73 tonnes therefore maximum heights to be restrained for material with SG=1.0 are 2.00 & 0.93m. So coal can never fill a 20 footer to capacity whereas cement will struggle to fill a 40 footer, obviously, but the commercial & practical limitations need to interact effectively. A correctly restrained load is not for debate when the dunnage is correctly placed. Conditions such as negative surcharge or sloping floor have been sensibly ignored. All available containment methods e.g. liners, plywood panels, sequentially opened doors or letterboxes will release some spillage.

The closure method described earlier will minimise that spillage. Users are given freedom to decide the vertical pitch of planks according to their width & mindful of the customer’s acceptance of spillage release.

Consignors should ensure that their loading regime complies with their consignees transport facilities regarding weight transfer during transit. Such effects are very small but police attitudes also differ. ■