What are the legal requirements for loans on bottomry?

In the context of bottomry, the correct answer focuses on the legal documentation required to ensure that the loan is valid and enforceable. For loans on bottomry, it is essential that they are recorded in the vessel's registry certificate and the commercial registry. This requirement serves multiple purposes: it provides public notice of the loan, establishes the priority of the lender's claim in the event of a default, and protects both the borrower and lender by formally documenting the loan's terms and conditions.

By recording the loan in the appropriate registries, all parties involved in maritime commerce can ascertain the financial obligations associated with a vessel. This transparency is crucial in maritime law, as it helps to prevent disputes over ownership and financial responsibility. The other choices, while they may reflect certain practices in other types of loans or contracts, do not directly address the specific legal formalities that pertain to loans on bottomry. Thus, the requirement for documentation in the vessel's registry and commercial registry stands out as the essential legal requirement for loans on bottomry.