Could be - on the other hand, if it is dialectical it would open up all sorts of punny possibilities - eg 'fine wood pinnaling covered every bulkhead of the stately galleon'
It's the little holes made by Gribbles. Often seen in wooden boat surveys... "Little pinnals all over 'er there were"...
Also used to describe the eyesight of one who has imbibed as in.... "Eyes like little pinnals in the snow"....
A long shot.
Wooden dowels used to connect heavier timbers are called trennels [ from tree-nails?].
These were sometimes called pins. This is apparently where Pin Mill gets it's name, where such pins were milled.
Could pinnals be a variation on that theme? [pin nails]
I've never heard the expression, this is pure conjecture.
Dan
A dictionary gives the follwing :-
pin·na(pn)
n. pl. pin·nae (pn) or pin·nas
1. Botany A leaflet or primary division of a pinnately compound leaf.
2. Zoology A feather, wing, fin, or similar appendage.
3. Anatomy See auricle.
[Latin, feather; see pet- in Indo-European roots.]
pinnal adj.
With that in mind, I wonder if a pinnal might be the wing or feather like sping projection that stops the rudder jumping of the pintal???
Could be a bit of Bristolian 'He came round the cornel and nearly knocked me ovel. I fair near fell off me pinnals.' Course, it doesn't get you any nearer a meaning.