For the source text click/tap here: Bava Metzia 69
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One may increase the rent for his land (although he intends to lend money to the renter), and he need not be concerned that this is interest.
What is the case? If one rents a field from his fellow for ten kor annually, and proposes, “Loan me two hundred zuz to improve the land, and I will pay you twelve kor annually,” it is permitted (for it is not a loan; rather, the renter is merely an agent of the landowner to improve the field). But an increased rental may not be offered for a store or a ship (if the money will be used for merchandise for the store or the ship; it would only be permitted if it would be used for the store or the ship itself).
And the men of pitch [benei kufera], i.e., sailors, are accustomed to paying rent at the time of pulling and paying for damage at the time of breakage.
"Men of Pitch” בְּנֵי כוּפְרָא allows us to explore the history of shipbuilding and the use of resins like pine tar.