Photo of the month – April 2002

Cargo securing for ro-ro maritime transport:

Two 30 metric ton steel billets are loaded on a roll trailer. The trailer is then loaded onto a ro-ro ship which is to cross the Atlantic. The steel billets have been secured by being placed on lumber beams and „lashed down“ with three long-link chains each.

Cargo securing for an Atlantic crossing must be designed to withstand lateral acceleration of 0.8 g. The coefficient of friction of the lumber beams can be assumed to be µ = 0.3 , which means that securing must additionally be provided for 0.5 times the weight of the cargo (15 metric tons per billet). The following should be noted:

1. At sea, tie-down lashing, especially for such large masses, is not an appropriate way to secure cargo as prestressed lashings can slacken due to extended exposure to the stresses of rough seas.
   
   
2. Long-link chains are possibly unsuitable for tie-down lashing as they can catch or jam on the edges of the cargo and so be unable to transfer the prestressing onto the opposite side.
   
   
3. Prestressing of 50,000 daN per steel billet would have to be applied in order to ensure proper securing of the cargo on the roll trailer.
   
   
4. Such cargos may be secured on the roll trailer effectively and economically by two loop lashings on each side.
   
   
5. It should be noted that the roll trailer itself must be secured as cargo on the ship.

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