Countries which have not ratified the collision convention 1910 (USA and others), the collision is not considered to be a peril, unlike Hague-Visby rules which consider collision to be a peril.
By this clause, cargo owner can claim his full damage caused by the non carrying vessel. The non carrying vessel than claims his portion from the owners of the cargo carrying ship (which is equivalent to the percentage of blame for the collision).
Now the carrier of the cargo claims his portion (which he paid to the non carrying ship) from the cargo owner, i.e, cargo owner indemnifies the ship carrying cargo.
However, the validity of the claim was said to be invalid when tested in court. But still it is sometimes included into the charter party.