English to Italian Tech/Engineering Ships, Sailing, Maritime containers

I suspect that in this case spreader simply means "crane":
"Container means any ISO Container 20’, 40’ 45’ 48’ or 53’ in length including but not limited to, high cubes, pallet-wide, flat racks, platforms, reefer and tank Containers, conforming with the safety requirements of CSC plate (Convention for Safe Containers), and which is normally handled by means of a Container spreader."
Wikipedia's definition of a spreader is:

"The spreader is a device used for lifting containers and unitized cargo.

The spreader used for containers has a locking mechanism at each corner that attaches the four corners of the container. A spreader can be used on a container crane, a straddle carrier and at any other machinery to lift containers."