I have a question about metallurgy and iron scantling.
If a ship has no attribute points on iron scantling, does metallurgy have no affect?
Obviously 2.5% of zero is zero.
But does each ship have a base amount of iron scantling that can be improved by metallurgy?

As far as I have read and understood what's written about this, the answer is "NO, metallurgy has no effect on a ship with 0 points in Iron Scatling".

So, if you don't use iron scatling on your ships, researching metallurgy is not really meaningful.