English to French Tech/Engineering Ships, Sailing, Maritime ship construction, naval construction

Type of document: procurement contract for refit
Country and dialect: Canada, Canadian English into Canadian French
Target audience: technical professional audience, contractors
Context: list of drawings and documents in appendix

I don't quite understand what main bottom is. Maybe the bottom deck, but I'm not sure.

I don't have access to the said plan, unfortunately.

Other drawings in the list, for exemple: General arrangement, piping, plan views and transv section.

Thanks!