"船级规定" can be translated into English as "classification society rules" or "ship classification regulations".
"Classification society rules" is a more common and specific term in the maritime industry, referring to the regulations and standards set by classification societies for the design, construction, and maintenance of ships.
"Ship classification regulations" is a more straightforward translation that also conveys the meaning accurately, though it may be slightly less commonly used in professional contexts compared to the first option.
In most professional maritime settings, "classification society rules" would be the preferred and more widely recognized term.