NavList:

I am bilingual: I speak both British and American.  I have not encountered, in contemporary English, the term “wrinkles” as used by Lecky for many years.  It is and was an idiomatic usage, and has the meaning Frank has described.

Although Lecky says in his Preface to the First Edition that “Every sailor knows what is meant by a ‘Wrinkle’…”, the usage was sufficiently informal that it does not appear in the sample of contemporary 19^th century dictionaries, British and American, that I have reviewed.  As always with English idioms it is fun to consider the origins of the idiom.

The literal meaning of a wrinkle, being a crease or a fold, was extended to two common idiomatic meanings.  The more common is to describe a process or mechanical item which is not yet working perfectly, perhaps in the prototype stage, as having a few wrinkles.  In other words, the process or operation is not yet smooth, and the “wrinkles need to be ironed out”.  This usage is still very common in the UK, Australia, New Zealand and probably elsewhere.

The second was to describe an older person as a “wrinkle” (because as we age we develop wrinkles on our skin).  Although this usage has (I think) disappeared it was common when I was a child, and I think also know to my father, grandfather and probably great grandfather (which is far enough back to cross with Lecky’s period).

The extension of the idea of age is that of experience.  Bringing experience to a problem can solve it, where the tyro (another archaic term found in navigation texts of the era) is otherwise stuck.  So experience can iron out the wrinkles: a combination of two idioms.

Shortening that further, when experience gives rise to a technique, trick, or way of working a problem, this became known as a “wrinkle”.

That is, I believe, the path to Lecky’s usage.  As I understood it as a child, a wrinkle is a trick or solution arrived at by one who is experienced.

Isn’t English fun?