Currently, material consumption depends only on ship's tier. For a given ship it's always the same amount of goods per repaired percent.
The speed of repairs (that is, the percentage repaired overnight) increases with skill and decreases with the damage taken.
I'm speaking only of normal daily repairs here, perks are handled separately.
That sounds pretty much right. I'm just wondering how useful planks are right now. Sailcloth is good, no doubt about that, but planks seem a bit too ineffective to do much good. The amount i typically have with me can fix about 8%, which together with ammunition and provisions keeps my ship loaded by about half. That still gives me a pretty decent speed. Maybe it's realistic to only carry enough wood to fix minor damage, but from a gameplay perspective you'd have to really cripple your speed to do any good with your planks. Maybe it should stay the way it is, i dunno, but i'm lately starting to consider not bringing planks at all. Perhaps i should bring a merchant ship in tow loaded with planks instead, like a medic. (which, now that i think about it, does not actually sound like such a bad idea)