Danielle....
100 years ago, builders used
Iron nails in boat construction, and today
Galvanized bolts are used in temporary hull repair work
We understand that your
Steel nails would only be cosmetic as the planking is glued to the frames and these joints were supported by clamps during the curing of the glue
In todays full size wooden boat building of this type and form of build, bronze bolts are used as the main element of holding the planks to the frames, and secondary bronze nails are used to assist the structure
The nail evidence you see in the full sized vessel is a result not of corrosion but a mechanical occurrence .......the timber planking even though protected externally and internally on and within the vessel by a painting system, has a moisture content [~~8 to 10%?]...so this timber will expand and contract with variations in temperature
So the head of the bronze bolt or nail remains stable and stationary, however the wood surrounding the fasteners can move, hence the circular cracking [the diameter] of the nail or bolt head size you see in the paint work
I must agree here with Ian......if corrosion commenced on your 1.5 mm diameter steel pin nails.....with moisture even from the atmosphere would initially blister the paint work and the with the presence of oxygen ......continue to corrode down in the diameter of the nails......in a few years the hull surface would be visually catastrophically damaged
Why not go back to some trawler builder friends and get their thoughts of steel nails in wooden hulled vessels
I am sure you vessel will have many brackets and plates that you could manufacture from steel plate or shim and you could prematurely rust these for effect...without affect
Derek