How did "doblar" come to mean "turn"?

Question

Inspired by this question on Italian SE

In Italian, French and English (and probably other languages) there are words cognate to Spanish doblar, which mean "to round (a cape, an isle etc.)" in the narrow nautical sense: "to double Cape Horn", doppiare il Capo di Buona Speranza etc.

The Treccani dictionary states that at least in Italian, it's a calque from Spanish:

2, è un calco dello spagn. doblar

I don't speak Spanish, so I might be wrong, but my understanding is that, unlike the other languages, doblar in Spanish means "to change the direction of movement" in the general sense, and not just in this narrow nautical sense.

Etymological dictionaries do state that it came from Latin duplus ("double"), but don't expand on the semantic development of this word: how exacly the meaning shifted from "to double" to "to turn". At least I could not find anything. DRAE only mentions Del lat. duplāre, de duplus 'doble'., same for Wiktionary.

So how exactly did doblar came to mean "to turn" in Spanish?

Answer 1

It seems clear that the original meaning is "to duplicate".

Entry #4 in the DLE may give a hint on its evolution. It can be translated as "to fold". By folding paper (papyrus?) or tissue you duplicate the number of layers.

In order to do that you need to bend it, which takes us to Entry #6.

And when, instead of bending paper, you bend your trajectory, you get the meanings #10 and #11.

Just a hypothesis.

Answer 2

Doblar has several meanings and, according to its etymology, they all fall within the origin of the word.

DOBLAR

El verbo doblar (aumentar en dos, torcer algo encorvándolo, volver una cosa sobre otra) viene del latín duplare, compuesta con duplus (doble) y la terminación -are usada para formar verbos.

La palabra duplus nos dio: doble, doblete, doblez, etc. Se relaciona con dos raíces indoeuropeas.

• La primera es dwo (dos) que daría diploma y dipluro.
• La segunda es pel-5 (doblar, plegar), que parece ser una variante de plek (plegar, trenzar).

_{Source etimologiasdechile.net}

Edit

I think the relationship between to fold and to turn may be related to the etymology described in the first part of the answer.

The root plek has the same origin as plicāre which means doblar and is the origin of llegar (to arrive). Therefore, putting both meanings together, it is not difficult to interpret the mixture between to arrive and to turn that results in doblar as to turn.

_{See from plicare to llegar}

plicāre (Latin)
Inflection of plicō (present active infinitive)
Inflection of plicō (second-person singular present passive imperative)
Inflection of plicō (second-person singular present passive indicative)

plico (Latin)
From Proto-Indo-European *pleḱ-‎ ("to plait, to weave") (with i from the compounded forms). Cognate with Latin plectō.
(transitive) I fold, bend or flex; I roll up
(transitive) I arrive (this meaning comes from sailors, for whom the folding of a ship’s sails meant arrival on land)