Which splice is considered not rated for efficiency?

The back splice is not rated for efficiency primarily because it is designed to terminate a rope or line, rather than to join two lengths of rope together for strength. The back splice involves twisting the strands of the rope back upon themselves and securing them, which provides a tidy and finished end to the rope. However, this type of splice does not enhance the load-bearing capacity of the rope when compared to the original strength of the rope itself.

In contrast, other types of splices, such as short splices or long splices, are specifically intended to join two pieces of rope or line together in a way that maintains or even improves the overall strength of the connection, thus being rated for efficiency. The eye splice also creates a loop at the end of the rope and maintains the original strength of the material, making it efficient for lifting or anchoring purposes.

The distinction lies in the purpose and strength capacity of the different splice types, where the back splice primarily serves as a finishing technique rather than an efficient load-bearing joint.