First I want to remind everyone of a seagoing adage that is applicable to this discussion and that is "different ships, different long splices." As those of you who have been studying maritime history for a while know, a long splice is a method of permanently joining two pieces of line (a splice) while only minimally increasing the line's circumference so the line can pass through the swallow of a block. The point of the saying "different ships, different long splices" refers to each ship and captain having a different way of doing things, often the same thing.
Carl--your caution is dead-on, and also applies to plans. We have to use them but with care. Thanks for corroborating what I strongly suspected about correspondence. I would love to know about some specific collections in which you've found this sort of thing. --Phillip
I am currently working on a dissertation about the operational aspects of 18th-century maritime smuggling among the West Indies and the North American colonies. Although vessel technology is not my primary focus, it is an element of my work. I have found merchant correspondence to be helpful with this. Occasionally, these archives will include correspondence from captains back to the office, but even where it is one-sided, merchants' correspondence often includes references to materials and measurements. This is particularly true in contracts with shipwrights/suppliers.
Insurance records are another useful resource for this data. Depositions taken in the wake of marine casualties often include technical details, particularly where gear failure was considered part of the cause.