You are not alone in having not seen the word used in this way.

'Mèche' here is as in 'mèche de gouvernail' or 'rudder stock', the bar or rod on a ship extending from topsides to the rudder beneath water level, and controlling it.

There is probably no need to translate it since it is but an optional term for 'bras' or 'tige'. I doubt many French readers understand 'mèche' here, and certainly few English readers would understand the relevance of 'stock'.

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Note added at 41 mins (2022-01-21 01:04:06 GMT)
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Were a word to be used for it, ideally you would know the shape, dimensions, purpose, etc. of this 'mèche'. 'Bras' and 'tige' are relatively generic, 'mèche' implies something more specific, but the specifics are lacking. Is it long, short, thick, narrow, square, or round? Does it support something? Or does it rotate (like a rudder stock or a drill bit), say, to control something? Etc.

mèche Substantiv, feminin
plus rare : drill bit n, bit n, lock n, wisp n, tow n, tendril n
https://www.linguee.fr/francais-anglais/search?source=auto&q...

mèche nf (foret) bit, drill bit n
Une mèche de 8 devrait suffire pour ces chevilles.
An 8 mm bit should be enough for those dowels.
https://www.wordreference.com/fren/mèche

Definition: axe de rotation du safran (partie du gouvernail), placé derrière la coque ou traversant parfois celle-ci dans une jaumière
Term: mèche de gouvernail
Term: mèche
Definition: that part of a rudder which acts as a vertical shaft through which the turning force of the steering gear is transmitted to the rudder body
Term: rudderstock
https://iate.europa.eu/entry/result/1593317/fr-en

Definition: outil de coupe en acier, utilisé pour le perçage. Il existe plusieurs types de forets: foret hélicoïdal, foret à canon, foret à centrer. Le foret hélicoïdal est le plus utilisé
Term: foret
Term: drill
https://iate.europa.eu/entry/result/1211975/fr-en

mèche / wick | ~ (text) / slub, coarse o. rough roving | ~ (outil) / bore bit| … ~ de gouvernail (nav) /rudder post o. spindle
(Brandstetter, Dictionnaire Gènèral de la Technique Industrielle)

All mechanical parts have one property in common: they are rod-shaped.
I therefore propose to translate as follows: 'a vertical arm, or spindle, or vertical rod.'
The term "spindle" may be replaced by 'axle', 'stem', 'pole', 'shaft', esp. 'crankshaft' or similar, depending on its form and function.

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Note added at 1 day 11 hrs (2022-01-22 12:11:12 GMT)
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Au vu des nombreux dispositifs mentionnés dans le texte et qui nous sont inconnus, il est utile de faire des recherches dans les articles suivants :

Un ballon dirigeable est un aéronef léger, plus précisément un aérostat, renfermant des dispositifs destinés à assurer la sustentation ainsi que des systèmes de propulsion lui conférant une certaine manœuvrabilité.
https://fr.wikipedia.org/wiki/Ballon_dirigeable

An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power.[1] Aerostats gain their lift from a lifting gas that is less dense than the surrounding air.
:
In 1910, Torres y Quevedo proposed the idea of attaching an airships nose to a mooring mast and allowing the airship to weathervane with changes of wind direction.
https://en.wikipedia.org/wiki/Airship

Un zeppelin est un aérostat de type dirigeable rigide, de fabrication allemande ; dans la langue usuelle, le mot « zeppelin » peut désigner, par extension, n’importe quel type de ballon dirigeable.
https://en.wikipedia.org/wiki/Zeppelin

A Zeppelin is a type of rigid airship named after the German inventor Count Ferdinand von Zeppelin (German pronunciation: [ˈt͡sɛpəliːn]) who pioneered rigid airship development at the beginning of the 20th century.
:
The Art Deco spire of the Empire State Building was originally designed to serve as a mooring mast for Zeppelins and other airships,
https://en.wikipedia.org/wiki/Zeppelin

Un mât d'amarrage ou d'ancrage est une tour destinée à immobiliser l'avant d'un ballon dirigeable sur un aérodrome, ou une étendue d'eau. Pendant un court séjour, il peut supporter les câbles électriques et les canalisations d'eau potable assurant le fonctionnement de l'appareil.
https://fr.wikipedia.org/wiki/Mât_d'amarrage