Packed containers' gross mass is verified prior to stowage aboard ship. The shipper is responsible for the verification of the gross mass of a container carrying cargo.
The shipper is also responsible for ensuring that the verified gross mass is communicated in the shipping documents sufficiently in advance to be used by the Vessel Master or his representative and the terminal representative in the preparation of the ship stowage plan.
In the absence of the shipper providing the verified gross mass of the packed container, the container should not be loaded on to the ship unless the master or his representative and the terminal representative have obtained the verified gross mass through other means.
For more details to see full text of regulation, as to below:
a. SOLAS official guidelines
SOLAS_CHAPTER_VI_Regulation_2_Paragraphs_4-6.pdf
b. MSC.1 Circ.1475
(Guidelines regarding Verified Gross Mass of a Container Carrying Cargo -Secretariat.pdf)